Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

5. MOSFET Transistors & Circuits - I

S. S. Dan and S. R. Zinka

Department of Electrical & Electronics EngineeringBITS Pilani, Hyderbad Campus

March 2, 2016

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Outline

1 Semiconductors

2 MOSFET Operation

3 MOSFET as a Circuit Element

4 The MOSFET as an Amplifier & a Switch

5 Biasing in MOS Amplifiers

6 Summary

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Outline

1 Semiconductors

2 MOSFET Operation

3 MOSFET as a Circuit Element

4 The MOSFET as an Amplifier & a Switch

5 Biasing in MOS Amplifiers

6 Summary

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Dielectrics / Insulators

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Dielectrics / Insulators

444

44

444

Atoms

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Conductors

444

44

444

+

+++

++

+++

−

−−

−

−

−

−

−

−

−

−−

−

−

−

−

−

−−

−−

−

−

−

−−

−−

−

−

−

−

−−

− Cations

Free electrons

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Semiconductors

444

44

444

Valenceelectrons

Covalentbond

Silicon atoms

4+

4+4+4+

4+4+

4+4+4+

−

−− −

−

−− −

−

−− −

−

−− −

−

−− −

−

−− −

−

−− −

−

−− −

−

−− −

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Semiconductors at Room Temperature

444

44

444

Valenceelectrons

Freeelectron

Covalentbond

Silicon atoms

Hole

Brokencovalent

bond

4+

4+4+4+

4+4+

4+4+4+

−

−− −

−

−− −

−

−− −

−

−− −

−

−− −

−

−

− −

−

−− −

−

−− −

−

−− −

+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

n type Semiconductors

Covalentbonds

Valenceelectrons

Silicon atoms

444

44

444

5+

4+4+4+

4+4+

4+4+4+

−

−− −

−

−− −

−

−− −

−

−− −

−

−− −

−

−

− −

−

−− −

−

−− −

−

−− −

+

Free electrondonated by

impurity atom

Pentavalentimprurity atom

(donor)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

p type Semiconductors

Covalentbonds

Valenceelectrons

Silicon atoms

444

44

444

3+

4+4+4+

4+4+

4+4+4+

−

−− −

−

−− −

−

−− −

−− −

−

−− −

−

−− −

−

−− −

−

−− −

+

Trivalentimprurity atom

(acceptor)

−

−− −

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PN Junction

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PN Junction

x

carr

ier

conce

ntr

ati

on

[log

sca

le]

p-doped n-doped

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PN Junction

x

carr

ier

conce

ntr

ati

on

[log

sca

le]

p-doped n-doped

"Diffusion force" on electrons"Diffusion force" on holes

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PN Junction

x

carr

ier

conce

ntr

ati

on

[log

sca

le]

p-doped n-doped

spacecharge region neutral regionneutral region

"Diffusion force" on electrons"Diffusion force" on holes

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PN Junction

x

carr

ier

conce

ntr

ati

on

[log

sca

le]

p-doped n-doped

spacecharge region neutral regionneutral region

E-field

"Diffusion force" on electrons"Diffusion force" on holes

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PN Junction

x

carr

ier

conce

ntr

ati

on

[log

sca

le]

p-doped n-doped

spacecharge region neutral regionneutral region

E-field

"Diffusion force" on electrons"Diffusion force" on holes

E-field force on electronsE-field force on holes

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Outline

1 Semiconductors

2 MOSFET Operation

3 MOSFET as a Circuit Element

4 The MOSFET as an Amplifier & a Switch

5 Biasing in MOS Amplifiers

6 Summary

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Why MOSFETs ?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Why MOSFETs ?

• MOSFET has become by far the most widely used electronic device,especially in the design of integrated circuits

• Compared to BJTs, MOSFETs can be made quite small and theirmanufacturing process is relatively simple

• Operating MOSFETs requires comparatively little power

• One can implement digital and analog functions utilizing MOSFETsalmost exclusively (i.e., with very few or no resistors)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Why MOSFETs ?

• MOSFET has become by far the most widely used electronic device,especially in the design of integrated circuits

• Compared to BJTs, MOSFETs can be made quite small and theirmanufacturing process is relatively simple

• Operating MOSFETs requires comparatively little power

• One can implement digital and analog functions utilizing MOSFETsalmost exclusively (i.e., with very few or no resistors)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Why MOSFETs ?

• MOSFET has become by far the most widely used electronic device,especially in the design of integrated circuits

• Compared to BJTs, MOSFETs can be made quite small and theirmanufacturing process is relatively simple

• Operating MOSFETs requires comparatively little power

• One can implement digital and analog functions utilizing MOSFETsalmost exclusively (i.e., with very few or no resistors)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Why MOSFETs ?

• MOSFET has become by far the most widely used electronic device,especially in the design of integrated circuits

• Compared to BJTs, MOSFETs can be made quite small and theirmanufacturing process is relatively simple

• Operating MOSFETs requires comparatively little power

• One can implement digital and analog functions utilizing MOSFETsalmost exclusively (i.e., with very few or no resistors)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Device Structure (NMOS)

S

G

D

B

Sourceregion

Drain region

(a)

W

n+

Oxide (SiO2)

Metal

L

n+

p-type substrate(Body)

Channelregion

n+

L

Metal

Channelregion

Oxide (SiO2)(thickness = tox)

p-type substrate(Body)

n+

Source (S) Gate (G) Drain (D)

Bod y (B)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Device Structure (NMOS)

S

G

D

B

Sourceregion

Drain region

(a)

W

n+

Oxide (SiO2)

Metal

L

n+

p-type substrate(Body)

Channelregion

n+

L

Metal

Channelregion

Oxide (SiO2)(thickness = tox)

p-type substrate(Body)

n+

Source (S) Gate (G) Drain (D)

Bod y (B)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

A Few Points About MOSFET

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

A Few Points About MOSFET

• Since SiO2 is an excellent electrical insulator. So, another name for theMOSFET is the insulated-gate FET (IGFET).

• Modern MOSFETs are fabricated using a process known as silicon-gatetechnology, in which a certain type of silicon, called polysilicon, is used(instead of metal) to form the gate electrode.

• Observe that the substrate forms pn junctions with the source and drainregions. In normal operation these pn junctions are kept reverse-biasedat all times.

• MOSFET is a symmetrical device; thus its source and drain can beinterchanged with no change in device characteristics.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

A Few Points About MOSFET

• Since SiO2 is an excellent electrical insulator. So, another name for theMOSFET is the insulated-gate FET (IGFET).

• Modern MOSFETs are fabricated using a process known as silicon-gatetechnology, in which a certain type of silicon, called polysilicon, is used(instead of metal) to form the gate electrode.

• Observe that the substrate forms pn junctions with the source and drainregions. In normal operation these pn junctions are kept reverse-biasedat all times.

• MOSFET is a symmetrical device; thus its source and drain can beinterchanged with no change in device characteristics.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

A Few Points About MOSFET

• Since SiO2 is an excellent electrical insulator. So, another name for theMOSFET is the insulated-gate FET (IGFET).

• Modern MOSFETs are fabricated using a process known as silicon-gatetechnology, in which a certain type of silicon, called polysilicon, is used(instead of metal) to form the gate electrode.

• Observe that the substrate forms pn junctions with the source and drainregions. In normal operation these pn junctions are kept reverse-biasedat all times.

• MOSFET is a symmetrical device; thus its source and drain can beinterchanged with no change in device characteristics.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

A Few Points About MOSFET

• Since SiO2 is an excellent electrical insulator. So, another name for theMOSFET is the insulated-gate FET (IGFET).

• Modern MOSFETs are fabricated using a process known as silicon-gatetechnology, in which a certain type of silicon, called polysilicon, is used(instead of metal) to form the gate electrode.

• Observe that the substrate forms pn junctions with the source and drainregions. In normal operation these pn junctions are kept reverse-biasedat all times.

• MOSFET is a symmetrical device; thus its source and drain can beinterchanged with no change in device characteristics.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Inversion Layer

Oxide (SiO2)

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-

----------- ------------ ------------ ------------ ----- - - - - - -

-- - -

- - -- - -

--- -- - - - - - - - - -

--

Threshold voltage, Vt, which is required to form the inversion layer, typicallylies in the range of 0.3 V to 1.0 V

The excess of vGS over Vt is termed the effective voltage or the overdrivevoltage (vOV)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Inversion Layer

Oxide (SiO2)

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-

----------- ------------ ------------ ------------ ----- - - - - - -

-- - -

- - -- - -

--- -- - - - - - - - - -

--

Threshold voltage, Vt, which is required to form the inversion layer, typicallylies in the range of 0.3 V to 1.0 V

The excess of vGS over Vt is termed the effective voltage or the overdrivevoltage (vOV)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Inversion Layer

Oxide (SiO2)

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-

----------- ------------ ------------ ------------ ----- - - - - - -

-- - -

- - -- - -

--- -- - - - - - - - - -

--

Threshold voltage, Vt, which is required to form the inversion layer, typicallylies in the range of 0.3 V to 1.0 V

The excess of vGS over Vt is termed the effective voltage or the overdrivevoltage (vOV)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Inversion Layer

Oxide (SiO2)

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-

----------- ------------ ------------ ------------ ----- - - - - - -

-- - -

- - -- - -

--- -- - - - - - - - - -

--

Threshold voltage, Vt, which is required to form the inversion layer, typicallylies in the range of 0.3 V to 1.0 V

The excess of vGS over Vt is termed the effective voltage or the overdrivevoltage (vOV)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Oxide Capacitance

We can express the magnitude of the electron charge in the channel by

|Q| = Cox (WL) vOV (1)

where Cox, called the oxide capacitance, is the capacitance of the parallel-platecapacitor per unit gate area.

Oxide capacitance Cox is given by

Cox =εox

tox. (2)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Oxide Capacitance

We can express the magnitude of the electron charge in the channel by

|Q| = Cox (WL) vOV (1)

where Cox, called the oxide capacitance, is the capacitance of the parallel-platecapacitor per unit gate area.

Oxide capacitance Cox is given by

Cox =εox

tox. (2)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Oxide Capacitance

We can express the magnitude of the electron charge in the channel by

|Q| = Cox (WL) vOV (1)

where Cox, called the oxide capacitance, is the capacitance of the parallel-platecapacitor per unit gate area.

Oxide capacitance Cox is given by

Cox =εox

tox. (2)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Charge per unit channel length (ρL) and electric field strength (E) across thelength of the channel are as given below:

ρL =|Q|L

= CoxWvOV (3)

E =vDS

L(4)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDSGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Charge per unit channel length (ρL) and electric field strength (E) across thelength of the channel are as given below:

ρL =|Q|L

= CoxWvOV (3)

E =vDS

L(4)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDSGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Charge per unit channel length (ρL) and electric field strength (E) across thelength of the channel are as given below:

ρL =|Q|L

= CoxWvOV (3)

E =vDS

L(4)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDSGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Charge per unit channel length (ρL) and electric field strength (E) across thelength of the channel are as given below:

ρL =|Q|L

= CoxWvOV (3)

E =vDS

L(4)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDSGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Charge per unit channel length (ρL) and electric field strength (E) across thelength of the channel are as given below:

ρL =|Q|L

= CoxWvOV (3)

E =vDS

L(4)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’d

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Electric field causes the channel electrons to drift toward the drain with a ve-locity given by

velocity = µnE = µnvDS

L. (5)

So, current iD is given as

iD = ρL × velocity =

[(µnCox)

(WL

)vOV

]vDS. (6)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’dGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Electric field causes the channel electrons to drift toward the drain with a ve-locity given by

velocity = µnE = µnvDS

L. (5)

So, current iD is given as

iD = ρL × velocity =

[(µnCox)

(WL

)vOV

]vDS. (6)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’dGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Electric field causes the channel electrons to drift toward the drain with a ve-locity given by

velocity = µnE = µnvDS

L. (5)

So, current iD is given as

iD = ρL × velocity =

[(µnCox)

(WL

)vOV

]vDS. (6)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’dGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Electric field causes the channel electrons to drift toward the drain with a ve-locity given by

velocity = µnE = µnvDS

L. (5)

So, current iD is given as

iD = ρL × velocity =

[(µnCox)

(WL

)vOV

]vDS. (6)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’dGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Electric field causes the channel electrons to drift toward the drain with a ve-locity given by

velocity = µnE = µnvDS

L. (5)

So, current iD is given as

iD = ρL × velocity =

[(µnCox)

(WL

)vOV

]vDS. (6)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’dGate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

Electric field causes the channel electrons to drift toward the drain with a ve-locity given by

velocity = µnE = µnvDS

L. (5)

So, current iD is given as

iD = ρL × velocity =

[(µnCox)

(WL

)vOV

]vDS. (6)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’d

vGS Vt

vGS= Vt+vOV1vGS

iD

0

Slope gDS = kn vOV

vGS= Vt+vOV2

vGS= Vt+vOV3

vDS

---

iD = (µnCox)

(WL

)vOVvDS = k′n

(WL

)vOVvDS = knvOVvDS = gDSvDS�

�k′n = µnCox is known as the process transconductance parameter.

kn = k′n (W/L) is known as the MOSFET transconductance parameter.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’d

vGS Vt

vGS= Vt+vOV1vGS

iD

0

Slope gDS = kn vOV

vGS= Vt+vOV2

vGS= Vt+vOV3

vDS

---

iD = (µnCox)

(WL

)vOVvDS = k′n

(WL

)vOVvDS = knvOVvDS = gDSvDS

�

�k′n = µnCox is known as the process transconductance parameter.

kn = k′n (W/L) is known as the MOSFET transconductance parameter.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’d

vGS Vt

vGS= Vt+vOV1vGS

iD

0

Slope gDS = kn vOV

vGS= Vt+vOV2

vGS= Vt+vOV3

vDS

---

iD = (µnCox)

(WL

)vOVvDS = k′n

(WL

)vOVvDS = knvOVvDS = gDSvDS�

�k′n = µnCox is known as the process transconductance parameter.

kn = k′n (W/L) is known as the MOSFET transconductance parameter.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS ... Cont’d

vGS Vt

vGS= Vt+vOV1vGS

iD

0

Slope gDS = kn vOV

vGS= Vt+vOV2

vGS= Vt+vOV3

vDS

---

iD = (µnCox)

(WL

)vOVvDS = k′n

(WL

)vOVvDS = knvOVvDS = gDSvDS�

�k′n = µnCox is known as the process transconductance parameter.

kn = k′n (W/L) is known as the MOSFET transconductance parameter.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS+

-

iS=iD iD

iD

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d

Source xL

vGD

vDSvOV(vOV

vGS

Voltage

Vt

Average = 1 vDSVoltage dropalong the channel

2

21 vDS)-

0 DrainL2

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS+

-

iS=iD iD

vCox = vGS −Vt − v (x)

dQ (x) = −CoxWdx (vGS −Vt − v (x))

ISD = ρ (x) v (x) =dQ (x)

dxdxdt

= −CoxW (vGS −Vt − v (x))dxdt

= −IDS = −ID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS+

-

iS=iD iD

vCox = vGS −Vt − v (x)

dQ (x) = −CoxWdx (vGS −Vt − v (x))

ISD = ρ (x) v (x) =dQ (x)

dxdxdt

= −CoxW (vGS −Vt − v (x))dxdt

= −IDS = −ID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS+

-

iS=iD iD

vCox = vGS −Vt − v (x)

dQ (x) = −CoxWdx (vGS −Vt − v (x))

ISD = ρ (x) v (x) =dQ (x)

dxdxdt

= −CoxW (vGS −Vt − v (x))dxdt

= −IDS = −ID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS+

-

iS=iD iD

vCox = vGS −Vt − v (x)

dQ (x) = −CoxWdx (vGS −Vt − v (x))

ISD = ρ (x) v (x) =dQ (x)

dxdxdt

= −CoxW (vGS −Vt − v (x))dxdt

= −IDS = −ID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS+

-

iS=iD iD

vCox = vGS −Vt − v (x)

dQ (x) = −CoxWdx (vGS −Vt − v (x))

ISD = ρ (x) v (x) =dQ (x)

dxdxdt

= −CoxW (vGS −Vt − v (x))dxdt

= −IDS = −ID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***From the definition of mobility,

dxdt

=

− µnE (x) = µndv (x)

dx.

So,

ID = CoxW (vGS −Vt − v (x)) µndv (x)

dx⇒ ID dx = µnCoxW (vGS −Vt − v (x)) dv (x) .

Taking the integral on both sides, the left relative to dx, the right relative to dv(x) gives∫ L

0IDdx =

∫ vDS

0µnCoxW (vGS −Vt − v (x)) dv (x)

⇒ IDL = µnCoxW[(vGS −Vt) v (x)− v2 (x)

2

]vDS

0

⇒ ID = µnCoxWL

[(vGS −Vt) vDS −

v2DS2

]= kn

[vOV −

vDS

2

]vDS. (7)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***From the definition of mobility,

dxdt

= − µnE (x) = µndv (x)

dx.

So,

ID = CoxW (vGS −Vt − v (x)) µndv (x)

dx⇒ ID dx = µnCoxW (vGS −Vt − v (x)) dv (x) .

Taking the integral on both sides, the left relative to dx, the right relative to dv(x) gives∫ L

0IDdx =

∫ vDS

0µnCoxW (vGS −Vt − v (x)) dv (x)

⇒ IDL = µnCoxW[(vGS −Vt) v (x)− v2 (x)

2

]vDS

0

⇒ ID = µnCoxWL

[(vGS −Vt) vDS −

v2DS2

]= kn

[vOV −

vDS

2

]vDS. (7)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***From the definition of mobility,

dxdt

= − µnE (x) = µndv (x)

dx.

So,

ID = CoxW (vGS −Vt − v (x)) µndv (x)

dx

⇒ ID dx = µnCoxW (vGS −Vt − v (x)) dv (x) .

Taking the integral on both sides, the left relative to dx, the right relative to dv(x) gives∫ L

0IDdx =

∫ vDS

0µnCoxW (vGS −Vt − v (x)) dv (x)

⇒ IDL = µnCoxW[(vGS −Vt) v (x)− v2 (x)

2

]vDS

0

⇒ ID = µnCoxWL

[(vGS −Vt) vDS −

v2DS2

]= kn

[vOV −

vDS

2

]vDS. (7)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***From the definition of mobility,

dxdt

= − µnE (x) = µndv (x)

dx.

So,

ID = CoxW (vGS −Vt − v (x)) µndv (x)

dx⇒ ID dx = µnCoxW (vGS −Vt − v (x)) dv (x) .

Taking the integral on both sides, the left relative to dx, the right relative to dv(x) gives∫ L

0IDdx =

∫ vDS

0µnCoxW (vGS −Vt − v (x)) dv (x)

⇒ IDL = µnCoxW[(vGS −Vt) v (x)− v2 (x)

2

]vDS

0

⇒ ID = µnCoxWL

[(vGS −Vt) vDS −

v2DS2

]= kn

[vOV −

vDS

2

]vDS. (7)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***From the definition of mobility,

dxdt

= − µnE (x) = µndv (x)

dx.

So,

ID = CoxW (vGS −Vt − v (x)) µndv (x)

dx⇒ ID dx = µnCoxW (vGS −Vt − v (x)) dv (x) .

Taking the integral on both sides, the left relative to dx, the right relative to dv(x) gives∫ L

0IDdx =

∫ vDS

0µnCoxW (vGS −Vt − v (x)) dv (x)

⇒ IDL = µnCoxW[(vGS −Vt) v (x)− v2 (x)

2

]vDS

0

⇒ ID = µnCoxWL

[(vGS −Vt) vDS −

v2DS2

]= kn

[vOV −

vDS

2

]vDS. (7)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***From the definition of mobility,

dxdt

= − µnE (x) = µndv (x)

dx.

So,

ID = CoxW (vGS −Vt − v (x)) µndv (x)

dx⇒ ID dx = µnCoxW (vGS −Vt − v (x)) dv (x) .

Taking the integral on both sides, the left relative to dx, the right relative to dv(x) gives∫ L

0IDdx =

∫ vDS

0µnCoxW (vGS −Vt − v (x)) dv (x)

⇒ IDL = µnCoxW[(vGS −Vt) v (x)− v2 (x)

2

]vDS

0

⇒ ID = µnCoxWL

[(vGS −Vt) vDS −

v2DS2

]= kn

[vOV −

vDS

2

]vDS. (7)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS ... Cont’d ***From the definition of mobility,

dxdt

= − µnE (x) = µndv (x)

dx.

So,

ID = CoxW (vGS −Vt − v (x)) µndv (x)

dx⇒ ID dx = µnCoxW (vGS −Vt − v (x)) dv (x) .

Taking the integral on both sides, the left relative to dx, the right relative to dv(x) gives∫ L

0IDdx =

∫ vDS

0µnCoxW (vGS −Vt − v (x)) dv (x)

⇒ IDL = µnCoxW[(vGS −Vt) v (x)− v2 (x)

2

]vDS

0

⇒ ID = µnCoxWL

[(vGS −Vt) vDS −

v2DS2

]= kn

[vOV −

vDS

2

]vDS. (7)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Pinch-off

Source xVoltage drop

along the channel(a)

L2

Drain

Drain

0 L

vGD = Vt

vDS = vOVvOV

Voltage

Vt

Average = 1 vOV2

21 vOV

SourceChannel

vGS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Pinch-off

Source xVoltage drop

along the channel(a)

L2

Drain

Drain

0 L

vGD = Vt

vDS = vOVvOV

Voltage

Vt

Average = 1 vOV2

21 vOV

SourceChannel

vGS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Pinch-off Doesn’t Mean Channel Blockage

Oxide (SiO2)

Gate electrode

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-

--------------------- - - - - - -

- - - ------ - -

- - - - - - - - - ---------------------- -

- -

--

-- - - -

--- - - -

-

vDS+

-

iD

Current continues to flow through the pinched-off channel, and the electrons thatreach the drain end of the channel are accelerated through the depletion region that

exists there and into the drain terminal.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Pinch-off Doesn’t Mean Channel Blockage

Oxide (SiO2)

Gate electrode

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-

--------------------- - - - - - -

- - - ------ - -

- - - - - - - - - ---------------------- -

- -

--

-- - - -

--- - - -

-

vDS+

-

iD

Current continues to flow through the pinched-off channel, and the electrons thatreach the drain end of the channel are accelerated through the depletion region that

exists there and into the drain terminal.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Pinch-off Doesn’t Mean Channel Blockage

Oxide (SiO2)

Gate electrode

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-

--------------------- - - - - - -

- - - ------ - -

- - - - - - - - - ---------------------- -

- -

--

-- - - -

--- - - -

-

vDS+

-

iD

Current continues to flow through the pinched-off channel, and the electrons thatreach the drain end of the channel are accelerated through the depletion region that

exists there and into the drain terminal.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

What Happens to the Extra vDS

Any increase in vDS above vOV appears as a voltage drop across the depletion region.Thus, both the current through the channel and the voltage drop across it remain

constant in saturation.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

What Happens to the Extra vDS

Any increase in vDS above vOV appears as a voltage drop across the depletion region.Thus, both the current through the channel and the voltage drop across it remain

constant in saturation.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

What Happens to the Extra vDS

Any increase in vDS above vOV appears as a voltage drop across the depletion region.Thus, both the current through the channel and the voltage drop across it remain

constant in saturation.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Saturation Current

When vDS = vGS −Vt = vOV ,

ID = IDsat = kn

(vOV −

vDS2

)vDS

=12

kn (vGS −Vt)2

=12

knv2OV . (8)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Saturation Current

When vDS = vGS −Vt = vOV ,

ID = IDsat = kn

(vOV −

vDS2

)vDS

=12

kn (vGS −Vt)2

=12

knv2OV . (8)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Saturation Current

When vDS = vGS −Vt = vOV ,

ID = IDsat = kn

(vOV −

vDS2

)vDS

=12

kn (vGS −Vt)2

=12

knv2OV . (8)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Saturation Current

When vDS = vGS −Vt = vOV ,

ID = IDsat = kn

(vOV −

vDS2

)vDS

=12

kn (vGS −Vt)2

=12

knv2OV . (8)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS

iD

0 vDS......�� ��Where is cut-off region located in the above graph?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS

iD

0

Almost a straight linewith slope proportionalto OV

vDS

v

......�� ��Where is cut-off region located in the above graph?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS

iD

vDS sat =0

Curve bends becausethe channel resistanceincreases with vDS

Almost a straight linewith slope proportionalto OV

vDSvOV

v

......�� ��Where is cut-off region located in the above graph?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS

iD

vDS sat =

vGS = +Vt

0

Curve bends becausethe channel resistanceincreases with vDS

Almost a straight linewith slope proportionalto OV vOV

Current saturates because thechannel is pinched off at thedrain end, and vDS no longeraffects the channel.

vDSvOV

v

......�� ��Where is cut-off region located in the above graph?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS

iD

vDS sat =

vGS = +Vt

0

Triode Saturation

Curve bends becausethe channel resistanceincreases with vDS

Almost a straight linewith slope proportionalto OV vOV

Current saturates because thechannel is pinched off at thedrain end, and vDS no longeraffects the channel.

vDSvOV

v

......�� ��Where is cut-off region located in the above graph?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Modes of Operation

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Modes of Operation

vGS

vDS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Modes of Operation

vGS

vDS

VtnC

ut-o

ff

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Modes of Operation

vGS

vDS

Vtn

vDS = vGS - VtCut

-off

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Modes of Operation

vGS

vDS

VtnC

ut-o

ffTriode

vDS = vGS - Vt

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Modes of Operation

TriodevGS

vDS

Vtn

vDS = vGS - Vt

Saturation

Cut

-off

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS versus VGS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS versus VGS

vGS = Vt+vOV3

vGS = Vt+vOV2

vGS = Vt+vOV1vDSvGS Vt (Cutoff)

vGS = Vt+vOV4

0

knvO2V1

knvO2V2

knvO2V3

knvO2V4

iD

12

12

12

12

......

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS versus VGS

vGS = Vt+vOV3

vGS = Vt+vOV2

vGS = Vt+vOV1vDSvGS Vt (Cutoff)

vGS = Vt+vOV4

vOV10 vOV2 vOV3 vOV4

knvO2V1

knvO2V2

knvO2V3

knvO2V4

iD

12

12

12

12

......

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS versus VGS

vGS = Vt+vOV3

vGS = Vt+vOV2

vGS = Vt+vOV1vDSvGS Vt (Cutoff)

vGS = Vt+vOV4

vOV10 vOV2 vOV3 vOV4

knvO2V1

knvO2V2

knvO2V3

knvO2V4

iD

12

12

12

12

......

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS versus VGS

vDS = vOViD= knvDS1

22

vGS = Vt+vOV3

vGS = Vt+vOV2

vGS = Vt+vOV1vDSvGS Vt (Cutoff)

vGS = Vt+vOV4

vOV10 vOV2 vOV3 vOV4

knvO2V1

knvO2V2

knvO2V3

knvO2V4

iD

12

12

12

12

......

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS versus VGS

vDS vOVSaturation region

vDS vOVTrioderegion

vDS = vOViD= knvDS1

22

vGS = Vt+vOV3

vGS = Vt+vOV2

vGS = Vt+vOV1

vDSvGS Vt (Cutoff)

vGS = Vt+vOV4

vOV10 vOV2 vOV3 vOV4

knvO2V1

knvO2V2

knvO2V3

knvO2V4

iD

12

12

12

12

......

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Is ID really independent of vDS in the saturation region?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Length Modulation ... Contd

DrainSource

LL - L

Channel

vOV- vDS- vOV- ++

L ......

From (8)

IDsat =12

µnCoxW

L− ∆L(vGS −Vt)

2

=12

µnCoxWL

11− ∆L/L

(vGS −Vt)2

≈ 12

µnCoxWL

(1 +

∆LL

)(vGS −Vt)

2

=12

knv2OV (1 + λvDS), (9)

where λ is a process-technology parameter which related to MOSFET parameters by theequation ∆L

L = λvDS.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Length Modulation ... Contd

DrainSource

LL - L

Channel

vOV- vDS- vOV- ++

L ......

From (8)

IDsat =12

µnCoxW

L− ∆L(vGS −Vt)

2

=12

µnCoxWL

11− ∆L/L

(vGS −Vt)2

≈ 12

µnCoxWL

(1 +

∆LL

)(vGS −Vt)

2

=12

knv2OV (1 + λvDS), (9)

where λ is a process-technology parameter which related to MOSFET parameters by theequation ∆L

L = λvDS.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Length Modulation ... Contd

DrainSource

LL - L

Channel

vOV- vDS- vOV- ++

L ......

From (8)

IDsat =

12

µnCoxW

L− ∆L(vGS −Vt)

2

=12

µnCoxWL

11− ∆L/L

(vGS −Vt)2

≈ 12

µnCoxWL

(1 +

∆LL

)(vGS −Vt)

2

=12

knv2OV (1 + λvDS), (9)

where λ is a process-technology parameter which related to MOSFET parameters by theequation ∆L

L = λvDS.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Length Modulation ... Contd

DrainSource

LL - L

Channel

vOV- vDS- vOV- ++

L ......

From (8)

IDsat =12

µnCoxW

L− ∆L(vGS −Vt)

2

=12

µnCoxWL

11− ∆L/L

(vGS −Vt)2

≈ 12

µnCoxWL

(1 +

∆LL

)(vGS −Vt)

2

=12

knv2OV (1 + λvDS), (9)

where λ is a process-technology parameter which related to MOSFET parameters by theequation ∆L

L = λvDS.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Length Modulation ... Contd

DrainSource

LL - L

Channel

vOV- vDS- vOV- ++

L ......

From (8)

IDsat =12

µnCoxW

L− ∆L(vGS −Vt)

2

=12

µnCoxWL

11− ∆L/L

(vGS −Vt)2

≈ 12

µnCoxWL

(1 +

∆LL

)(vGS −Vt)

2

=12

knv2OV (1 + λvDS), (9)

where λ is a process-technology parameter which related to MOSFET parameters by theequation ∆L

L = λvDS.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Length Modulation ... Contd

DrainSource

LL - L

Channel

vOV- vDS- vOV- ++

L ......

From (8)

IDsat =12

µnCoxW

L− ∆L(vGS −Vt)

2

=12

µnCoxWL

11− ∆L/L

(vGS −Vt)2

≈ 12

µnCoxWL

(1 +

∆LL

)(vGS −Vt)

2

=12

knv2OV (1 + λvDS), (9)

where λ is a process-technology parameter which related to MOSFET parameters by theequation ∆L

L = λvDS.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Length Modulation ... Contd

DrainSource

LL - L

Channel

vOV- vDS- vOV- ++

L ......

From (8)

IDsat =12

µnCoxW

L− ∆L(vGS −Vt)

2

=12

µnCoxWL

11− ∆L/L

(vGS −Vt)2

≈ 12

µnCoxWL

(1 +

∆LL

)(vGS −Vt)

2

=12

knv2OV (1 + λvDS), (9)

where λ is a process-technology parameter which related to MOSFET parameters by theequation ∆L

L = λvDS.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Channel Length Modulation ... Contd

DrainSource

LL - L

Channel

vOV- vDS- vOV- ++

L ......

From (8)

IDsat =12

µnCoxW

L− ∆L(vGS −Vt)

2

=12

µnCoxWL

11− ∆L/L

(vGS −Vt)2

≈ 12

µnCoxWL

(1 +

∆LL

)(vGS −Vt)

2

=12

knv2OV (1 + λvDS), (9)

where λ is a process-technology parameter which related to MOSFET parameters by theequation ∆L

L = λvDS.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Realistic ID – VDS– VGS Curve

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Realistic ID – VDS– VGS Curve

Triode Saturation

0

VOV

vDS

iD

......

IDsat =12

knv2OV (1 + λvDS)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Realistic ID – VDS– VGS Curve

Triode Saturation

0

VOV

vDS-VA = 1/

iD

- ......

IDsat =12

knv2OV (1 + λvDS)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Before proceeding further, let’s see a few other MOSFET types ...

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PMOS

DG

B

S

S

n-type substrate

p+ p+

D

+

G

B

n-type substrate

induced p channel

p+ p+

iDiG=0iD

+vGS vDS-

iD

-

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PMOS

DG

B

S

S

n-type substrate

p+ p+

D

+

G

B

n-type substrate

induced p channel

p+ p+

iDiG=0iD

+vGS vDS-

iD

-

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

CMOS

GD

n+n+

PMOS

S

SiO2Thick SiO2 (isolation)

G

Polysilicon

SGateoxide

NMOS

D

p-type body

n well

p+ p+

SiO2

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

CMOS

GD

n+n+

PMOS

S

SiO2Thick SiO2 (isolation)

G

Polysilicon

SGateoxide

NMOS

D

p-type body

n well

p+ p+

SiO2

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Outline

1 Semiconductors

2 MOSFET Operation

3 MOSFET as a Circuit Element

4 The MOSFET as an Amplifier & a Switch

5 Biasing in MOS Amplifiers

6 Summary

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

NMOS Circuit Symbol

B

D

S

G B

D

S

G

D

S

G

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

NMOS Circuit Symbol

B

D

S

G B

D

S

G

D

S

G

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PMOS Circuit Symbol

B

S

D

G

S

G B

D

S

D

G

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

PMOS Circuit Symbol

B

S

D

G

S

G B

D

S

D

G

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID−VDS Characteristics

vDS vOVSaturation region

vDS vOVTrioderegion

vDS = vOViD= knvDS1

22

vGS = Vt+vOV3

vGS = Vt+vOV2

vGS = Vt+vOV1

vDSvGS Vt (Cutoff)

vGS = Vt+vOV4

vOV10 vOV2 vOV3 vOV4

knvO2V1

knvO2V2

knvO2V3

knvO2V4

iD

12

12

12

12

......

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID−VDS Characteristics

vDS vOVSaturation region

vDS vOVTrioderegion

vDS = vOViD= knvDS1

22

vGS = Vt+vOV3

vGS = Vt+vOV2

vGS = Vt+vOV1

vDSvGS Vt (Cutoff)

vGS = Vt+vOV4

vOV10 vOV2 vOV3 vOV4

knvO2V1

knvO2V2

knvO2V3

knvO2V4

iD

12

12

12

12

......

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID−VGS Characteristics

vDS vGS –Vtn

vGS

vOV

Vtn

iD

0

0 ......

In saturation region MOSFET operates as a constant current source where the value ofthe current is determined by vGS according to the following equation:

IDsat =12

knv2OV =

12

kn (vGS −Vt)2 .

So, in effect MOSFET in saturation region operates as a voltage controlled current source(VCCS).

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID−VGS Characteristics

vDS vGS –Vtn

vGS

vOV

Vtn

iD

0

0 ......

In saturation region MOSFET operates as a constant current source where the value ofthe current is determined by vGS according to the following equation:

IDsat =12

knv2OV =

12

kn (vGS −Vt)2 .

So, in effect MOSFET in saturation region operates as a voltage controlled current source(VCCS).

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID−VGS Characteristics

vDS vGS –Vtn

vGS

vOV

Vtn

iD

0

0 ......

In saturation region MOSFET operates as a constant current source where the value ofthe current is determined by vGS according to the following equation:

IDsat =12

knv2OV =

12

kn (vGS −Vt)2 .

So, in effect MOSFET in saturation region operates as a voltage controlled current source(VCCS).

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID−VGS Characteristics

vDS vGS –Vtn

vGS

vOV

Vtn

iD

0

0 ......

In saturation region MOSFET operates as a constant current source where the value ofthe current is determined by vGS according to the following equation:

IDsat =12

knv2OV =

12

kn (vGS −Vt)2 .

So, in effect MOSFET in saturation region operates as a voltage controlled current source(VCCS).

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Large-signal Equivalent Circuit Model (Saturation)

G

S

D

vDS

+

vGS

+

vGS VtnvDS VtnvGS

kn12

vOV2

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Large-signal Equivalent Circuit Model (Saturation)

G

S

D

vDS

+

vGS

+

vGS VtnvDS VtnvGS

kn12

vOV2

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Including Channel Length Modulation

G

S

D

vDS

+

vGS

+

vGS VtnvDS VtnvGS

kn12

vOV2 (1+λvDS)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Including Channel Length Modulation

G

S

D

vDS

+

vGS

+

vGS VtnvDS VtnvGS

kn12

vOV2 (1+λvDS)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Let’s solve a few problems ...

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Outline

1 Semiconductors

2 MOSFET Operation

3 MOSFET as a Circuit Element

4 The MOSFET as an Amplifier & a Switch

5 Biasing in MOS Amplifiers

6 Summary

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Stripped Down Version of CS Amplifier

VDD

RD

+

iD

vO=vDSvGS–

+

-

vDS = VDD−iDRD (10)

��

�

The output voltage is taken between the drain and ground, rather than simply acrossRD. Why?

What is the significance of negative sign in (10)?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Stripped Down Version of CS Amplifier

VDD

RD

+

iD

vO=vDSvGS–

+

-

vDS = VDD−iDRD (10)��

�

The output voltage is taken between the drain and ground, rather than simply acrossRD. Why?

What is the significance of negative sign in (10)?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Stripped Down Version of CS Amplifier

VDD

RD

+

iD

vO=vDSvGS–

+

-

vDS = VDD−iDRD (10)

��

�

The output voltage is taken between the drain and ground, rather than simply acrossRD. Why?

What is the significance of negative sign in (10)?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Stripped Down Version of CS Amplifier

VDD

RD

+

iD

vO=vDSvGS–

+

-

vDS = VDD−iDRD (10)��

�

The output voltage is taken between the drain and ground, rather than simply acrossRD. Why?

What is the significance of negative sign in (10)?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Voltage Transfer Characteristic (VTC)

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

Since iD = 12 knv2

OV in saturation region, expression for segment AB is given by

vDS = VDD −12

kn (vGS −Vt)2 RD. (11)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Voltage Transfer Characteristic (VTC)

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

Since iD = 12 knv2

OV in saturation region, expression for segment AB is given by

vDS = VDD −12

kn (vGS −Vt)2 RD. (11)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Voltage Transfer Characteristic (VTC)

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

Since iD = 12 knv2

OV in saturation region, expression for segment AB is given by

vDS = VDD −12

kn (vGS −Vt)2 RD. (11)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Voltage Transfer Characteristic (VTC) ... Contd

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

When vGS > vDS + Vt, the transistor enters into triode region. So, from (11), vGS corre-sponding to the point B is given by solving the equation

VGS|B = VDD −12

knRD (VGS|B −Vt)2 + Vt. (12)

From the above equation,

VGS|B = Vt +

√2knRDVDD + 1− 1

knRD. (13)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Voltage Transfer Characteristic (VTC) ... Contd

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

When vGS > vDS + Vt, the transistor enters into triode region. So, from (11), vGS corre-sponding to the point B is given by solving the equation

VGS|B = VDD −12

knRD (VGS|B −Vt)2 + Vt. (12)

From the above equation,

VGS|B = Vt +

√2knRDVDD + 1− 1

knRD. (13)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Voltage Transfer Characteristic (VTC) ... Contd

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

When vGS > vDS + Vt, the transistor enters into triode region.

So, from (11), vGS corre-sponding to the point B is given by solving the equation

VGS|B = VDD −12

knRD (VGS|B −Vt)2 + Vt. (12)

From the above equation,

VGS|B = Vt +

√2knRDVDD + 1− 1

knRD. (13)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Voltage Transfer Characteristic (VTC) ... Contd

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

When vGS > vDS + Vt, the transistor enters into triode region. So, from (11), vGS corre-sponding to the point B is given by solving the equation

VGS|B = VDD −12

knRD (VGS|B −Vt)2 + Vt. (12)

From the above equation,

VGS|B = Vt +

√2knRDVDD + 1− 1

knRD. (13)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Voltage Transfer Characteristic (VTC) ... Contd

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

When vGS > vDS + Vt, the transistor enters into triode region. So, from (11), vGS corre-sponding to the point B is given by solving the equation

VGS|B = VDD −12

knRD (VGS|B −Vt)2 + Vt. (12)

From the above equation,

VGS|B = Vt +

√2knRDVDD + 1− 1

knRD. (13)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Biasing the MOSFET to Obtain Linear Amplification

VDD

RDID

VDSVGS

––

++

C

Vt0 VGS

VDS

vDS

VDD vGS

VDD

Q

A

B

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Biasing the MOSFET to Obtain Linear Amplification

VDD

RDID

VDSVGS

––

++

C

Vt0 VGS

VDS

vDS

VDD vGS

VDD

Q

A

B

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Biasing the MOSFET to Obtain Linear Amplification ...

iD

vDS

RD

VDD

vgs+

vGS

VGS

+-

vGS

vDS

VDDVGS

VDS

VDD

Vt

A

Q

B

C

Slope at Q = voltage gain

Time

Time

vds

vgs

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Biasing the MOSFET to Obtain Linear Amplification ...

iD

vDS

RD

VDD

vgs+

vGS

VGS

+-

vGS

vDS

VDDVGS

VDS

VDD

Vt

A

Q

B

C

Slope at Q = voltage gain

Time

Time

vds

vgs

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Biasing the MOSFET to Obtain Linear Amplification ...

iD

vDS

RD

VDD

vgs+

vGS

VGS

+-

vGS

vDS

VDDVGS

VDS

VDD

Vt

A

Q

B

C

Slope at Q = voltage gain

Time

Time

vds

vgs

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Small-Signal Voltage Gain

In saturation region,

vDS = VDD −12

kn (vGS −Vt)2 RD.

So, small signal voltage gain is given by

Av =dvOUT

dvIN=

dvDS

dvGS

∣∣∣∣vGS=VGS

= −kn (VGS −Vt)RD = − knVOVRD︸ ︷︷ ︸ = − gm︸︷︷︸RD. (14)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Small-Signal Voltage Gain

In saturation region,

vDS = VDD −12

kn (vGS −Vt)2 RD.

So, small signal voltage gain is given by

Av =dvOUT

dvIN=

dvDS

dvGS

∣∣∣∣vGS=VGS

= −kn (VGS −Vt)RD = − knVOVRD︸ ︷︷ ︸ = − gm︸︷︷︸RD. (14)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

The Small-Signal Voltage Gain

In saturation region,

vDS = VDD −12

kn (vGS −Vt)2 RD.

So, small signal voltage gain is given by

Av =dvOUT

dvIN=

dvDS

dvGS

∣∣∣∣vGS=VGS

= −kn (VGS −Vt)RD = − knVOVRD︸ ︷︷ ︸ = − gm︸︷︷︸RD. (14)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Maximum Achievable Small-Signal Voltage Gain

Since ID = 12 knV2

OV , the above equation can be re-written as

Av = − IDRD

VOV/2. (15)

Since IDRD can approach but never exceed the power supply voltage VDD,

|Av|max =VDD

VOV/2. (16)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Maximum Achievable Small-Signal Voltage Gain

Since ID = 12 knV2

OV , the above equation can be re-written as

Av = − IDRD

VOV/2. (15)

Since IDRD can approach but never exceed the power supply voltage VDD,

|Av|max =VDD

VOV/2. (16)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Maximum Achievable Small-Signal Voltage Gain

Since ID = 12 knV2

OV , the above equation can be re-written as

Av = − IDRD

VOV/2. (15)

Since IDRD can approach but never exceed the power supply voltage VDD,

|Av|max =VDD

VOV/2. (16)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Gain vs VGS & Gain vs RD

C

Vt0 VGS

VDS

vDS

VDD vGS

VDD

Q

A

B

C

Vt0

vDS

VDD vGS

VDD

As RD valueincreases

Av = −kn (VGS −Vt)RD

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Gain vs VGS & Gain vs RD

C

Vt0 VGS

VDS

vDS

VDD vGS

VDD

Q

A

B

C

Vt0

vDS

VDD vGS

VDD

As RD valueincreases

Av = −kn (VGS −Vt)RD

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Gain vs VGS & Gain vs RD

C

Vt0 VGS

VDS

vDS

VDD vGS

VDD

Q

A

B

C

Vt0

vDS

VDD vGS

VDD

As RD valueincreases

Av = −kn (VGS −Vt)RD

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Gain vs VGS & Gain vs RD

C

Vt0 VGS

VDS

vDS

VDD vGS

VDD

Q

A

B

C

Vt0

vDS

VDD vGS

VDD

As RD valueincreases

Av = −kn (VGS −Vt)RD

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Circuit Representation of CS Amplifier

+

−

vgsgmvgs

RD

+

−

vds

iD

vDS

RD

VDD

vgs+

vGS

VGS

+-

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Circuit Representation of CS Amplifier

+

−

vgsgmvgs

RD

+

−

vds

iD

vDS

RD

VDD

vgs+

vGS

VGS

+-

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Physical Significance of gm

vDS vGS –Vtn

vGS

vOV

Vtn

iD

0

0Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

QQ

slope = gm

gm =diD

dvGS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Physical Significance of gm

vDS vGS –Vtn

vGS

vOV

Vtn

iD

0

0Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

QQ

slope = gm

gm =diD

dvGS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Physical Significance of gm

vDS vGS –Vtn

vGS

vOV

Vtn

iD

0

0Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

QQ

slope = gm

gm =diD

dvGS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Instead of VTC, we can also use the concept of load-line to understand theoperation of a CS amplifier.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Understanding VTC using Load Line

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Understanding VTC using Load Line

iD

vDS

+

vGS

vDS0

iD vGS= VDD

vGS= ...

vGS= VGS B

vGS= ...

vGS= VGS

vGS=…

Triode Saturation

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Understanding VTC using Load Line

iD

vDS

RD

VDD

+

vGS

vDS0

iD

ID

VDD

Load-lineslope= -1/RD

vGS= VDD

vGS= ...

vGS= VGS B

vGS= ...

vGS= VGS

vGS=…

Triode Saturation

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Understanding VTC using Load Line

iD

vDS

RD

VDD

+

vGS

VGS

vDS0

iD

ID

VDDVDS

Load-lineslope= -1/RD

vGS= VDD

vGS= ...

vGS= VGS B

vGS= ...

vGS= VGS

vGS=…

Triode Saturation

Q

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Understanding VTC using Load Line

iD

vDS

RD

VDD

vgs+

vGS

VGS

+-

vDS0

iD

ID

VDDVDSVDS B= VGS B - VtVDS C

C

B

Q

A

Load-lineslope= -1/RD

vGS= VDD

vGS= ...

vGS= VGS B

vGS= ...

vGS= VGS

vGS=…

Triode Saturation

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Understanding VTC using Load Line

vDS0

iD

ID

VDDVDSVDS B= VGS B - VtVDS C

C

B

Q

A

Load-lineslope= -1/RD

vGS= VDD

vGS= ...

vGS= VGS B

vGS= ...

vGS= VGS

vGS=…

Triode Saturation

Vt0 VGS B

=VGS B–Vt

VDS B

vDS

VDD

VDD vGS

Saturation

B

Cut-off

Triode

A

C

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Points A, Q, and C – from Application Point of View

VDD

RD0

vDS = VDD

vGS≤Vt

rDS

VDD

RD

vGS = VDD

vDS = VDSC

�� ��What is the value of closure resistance rDS?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Locating the Bias Point Q - using Load Line

VDD

Q1

vGS= ...

vDS

iD

Q2

0

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Separating the DC Analysis and the Signal Analysis

vGS

(gmRD ) V

0

vDSmax

VDS

min vGSmax - Vt

vDS

0

vGS

VGS

V

t

t

(VGS - Vt)V2 2

VDD

vDS

<<

<

<

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Outline

1 Semiconductors

2 MOSFET Operation

3 MOSFET as a Circuit Element

4 The MOSFET as an Amplifier & a Switch

5 Biasing in MOS Amplifiers

6 Summary

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Bias & Bias Stabilization

What is the difference between biasing and bias stabilization?

Maintaining a stable ID is known as bias stabilization. Why?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Bias & Bias Stabilization

What is the difference between biasing and bias stabilization?

Maintaining a stable ID is known as bias stabilization. Why?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Bias & Bias Stabilization

What is the difference between biasing and bias stabilization?

Maintaining a stable ID is known as bias stabilization. Why?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Bias Stabilization

VDD

RD

+

iD

vO=vDSvGS–

+

-

We have seen that the small signal voltage gain for a CS amplifier is given by

Av =dvDS

dvGS

∣∣∣∣vGS=VGS

= − knVOV︸ ︷︷ ︸RD = − gm︸︷︷︸RD. (17)

Since ID = 12 knV2

OV , re-arranging the above equation gives

Av = − IDRD

VOV/2. (18)�

�Since RD is constant and VOV do not vary much, it is important to maintain stable and

predictable value of IDto stabilize the gain.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Bias StabilizationVDD

RD

+

iD

vO=vDSvGS–

+

-

We have seen that the small signal voltage gain for a CS amplifier is given by

Av =dvDS

dvGS

∣∣∣∣vGS=VGS

= − knVOV︸ ︷︷ ︸RD = − gm︸︷︷︸RD. (17)

Since ID = 12 knV2

OV , re-arranging the above equation gives

Av = − IDRD

VOV/2. (18)�

�Since RD is constant and VOV do not vary much, it is important to maintain stable and

predictable value of IDto stabilize the gain.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Bias StabilizationVDD

RD

+

iD

vO=vDSvGS–

+

-

We have seen that the small signal voltage gain for a CS amplifier is given by

Av =dvDS

dvGS

∣∣∣∣vGS=VGS

= − knVOV︸ ︷︷ ︸RD = − gm︸︷︷︸RD. (17)

Since ID = 12 knV2

OV , re-arranging the above equation gives

Av = − IDRD

VOV/2. (18)�

�Since RD is constant and VOV do not vary much, it is important to maintain stable and

predictable value of IDto stabilize the gain.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Bias StabilizationVDD

RD

+

iD

vO=vDSvGS–

+

-

We have seen that the small signal voltage gain for a CS amplifier is given by

Av =dvDS

dvGS

∣∣∣∣vGS=VGS

= − knVOV︸ ︷︷ ︸RD = − gm︸︷︷︸RD. (17)

Since ID = 12 knV2

OV , re-arranging the above equation gives

Av = − IDRD

VOV/2. (18)

�

�Since RD is constant and VOV do not vary much, it is important to maintain stable and

predictable value of IDto stabilize the gain.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Bias StabilizationVDD

RD

+

iD

vO=vDSvGS–

+

-

We have seen that the small signal voltage gain for a CS amplifier is given by

Av =dvDS

dvGS

∣∣∣∣vGS=VGS

= − knVOV︸ ︷︷ ︸RD = − gm︸︷︷︸RD. (17)

Since ID = 12 knV2

OV , re-arranging the above equation gives

Av = − IDRD

VOV/2. (18)�

�Since RD is constant and VOV do not vary much, it is important to maintain stable and

predictable value of IDto stabilize the gain.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Various Biasing Techniques

1 Biasing by fixing VGS

2 Biasing by fixing VG and connecting a resistance in the source

3 Biasing using a drain-to-gate feedback resistor

4 Biasing using a constant-current Source

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Various Biasing Techniques

1 Biasing by fixing VGS

2 Biasing by fixing VG and connecting a resistance in the source

3 Biasing using a drain-to-gate feedback resistor

4 Biasing using a constant-current Source

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

VG

+VGS

ID

ID+

ID =12

kn (VGS −Vt)2

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

VG

+VGS

ID

ID+

ID =12

kn (VGS −Vt)2

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

VG

+VGS

ID

ID+

ID =12

kn (VGS −Vt)2

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

iD

vGS0

VG

+VGS

ID

ID+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

iD

vGSVGS

ID1

0

VG

+VGS

ID

ID+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

iD

vGSVGS

ID1

0

ID2

Device 2

Device 1

VG

+VGS

ID

ID+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

iD

vGSVGS

ID1

0

ID2

Device 2

Device 1

VG

+VGS

ID

ID+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

.

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source

+ +

VG

VGS

RS

ID

ID

Slope= 1 RS

iD

0 VG vGS

VG = VGS + RSID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source

+ +

VG

VGS

RS

ID

ID

Slope= 1 RS

iD

ID1

0 VGS1 VG vGS

VG = VGS + RSID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source

+ +

VG

VGS

RS

ID

ID

Slope = 1 RS

Device 2

iD

ID2

ID1

VGS20 VGS1 VG vGS

Device 1

VG = VGS + RSID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source ... Cont’d

VGS

0

RG1

RG2

VG

RD

RS

ID

VDD

ID

ID

VDD

RD

VSS

ID

0

RS

VGSRG+

+

�

�What is the purpose of the combination of RG1 and RG2?

What is the purpose of the resistor RG?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source ... Cont’d

VGS

0

RG1

RG2

VG

RD

RS

ID

VDD

ID

ID

VDD

RD

VSS

ID

0

RS

VGSRG+

+

�

�What is the purpose of the combination of RG1 and RG2?

What is the purpose of the resistor RG?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source ... Cont’d

VGS

0

RG1

RG2

VG

RD

RS

ID

VDD

ID

RD

VDD

RSRG2

CC1

RG1

vsig

Rsig

+

+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source ... Cont’d

VGS

0

RG1

RG2

VG

RD

RS

ID

VDD

ID

RD

VDD

RSRG2

CC1

RG1

vsig

Rsig

+

+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

3 Biasing Using a Drain-to-Gate Feedback Resistor

RD

RG

VDD

ID

ID0

VDSVGS

+

+

VGS = VDS = VDD − RDID

⇒ VDD= VGS + RDID (19)

�� ��What is the purpose of the resistor RG?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

3 Biasing Using a Drain-to-Gate Feedback Resistor

RD

RG

VDD

ID

ID0

VDSVGS

+

+

VGS = VDS = VDD − RDID

⇒ VDD= VGS + RDID (19)�� ��What is the purpose of the resistor RG?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

3 Biasing Using a Drain-to-Gate Feedback Resistor

RD

RG

VDD

ID

ID0

VDSVGS

+

+

VGS = VDS = VDD − RDID

⇒ VDD= VGS + RDID (19)

�� ��What is the purpose of the resistor RG?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

3 Biasing Using a Drain-to-Gate Feedback Resistor

RD

RG

VDD

ID

ID0

VDSVGS

+

+

VGS = VDS = VDD − RDID

⇒ VDD= VGS + RDID (19)�� ��What is the purpose of the resistor RG?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

4 Biasing Using a Constant-Current Source

I

I I=D

RD

RG

DD

VSS

VGS

Q2Q1

R

0

To source oftransistor Q

ID1ID2

IREF

+

I = ID2 = ID1(W/L)2(W/L)1

= IREF(W/L)2(W/L)1

(20)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

4 Biasing Using a Constant-Current Source

I

I I=D

RD

RG

DD

VSS

VGS

Q2Q1

R

0

To source oftransistor Q

ID1ID2

IREF

+

I = ID2 = ID1(W/L)2(W/L)1

= IREF(W/L)2(W/L)1

(20)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

4 Biasing Using a Constant-Current Source

I

I I=D

RD

RG

DD

VSS

VGS

Q2Q1

R

0

To source oftransistor Q

ID1ID2

IREF

+

I = ID2 = ID1(W/L)2(W/L)1

= IREF(W/L)2(W/L)1

(20)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

4 Biasing Using a Constant-Current Source

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

4 Biasing Using a Constant-Current Source

I I=D

RD

RG

DD

VSS

VGS

Q2 Q1

R

0

ID1ID2

IREF

+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

4 Biasing Using a Constant-Current Source

I I=D

RD

RG

DD

VSS

VGS

Q2 Q1

R

0

ID1ID2

IREF

+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Outline

1 Semiconductors

2 MOSFET Operation

3 MOSFET as a Circuit Element

4 The MOSFET as an Amplifier & a Switch

5 Biasing in MOS Amplifiers

6 Summary

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying a Small vDS

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS

+

-

iS=iD iD

iD

ρL =|Q|L

= CoxWvOV

E =vDS

L

velocity = µnE = µnvDS

L

iD = ρL×velocity = (µnCox)

(WL

)vOVvDS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Applying Large vDS

Gate electrode

Inducedn-type

channel

Depletion region

n+

p-type substrate

n+

S G D

vGS

B

+

-vDS+

-

iS=iD iD

vCox = vGS −Vt − v (x)

dQ (x) = −CoxWdx [vGS −Vt − v (x)]

ID = kn

[vOV −

vDS2

]vDS

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Modes of Operation

P+ N+ N+

P substrate

Gate DrainSource

depletion region

VGS VTH

P+ N+ N+

P substratepinched-off channel

Saturation mode at point of pinch-off

VGS VTH

Gate DrainSource

P+ N+ N+

P substrate

Saturation mode

VGS VTH

Gate DrainSource

P+ N+ N+

P substrate

Gate DrainSource

(inversion layer)

depletion region

Linear operating region (ohmic mode)

VGS VTH Channell

VGS VTH-VDS

VGS VTH-VDSVGS VTH-VDS =

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Modes of Operation

TriodevGS

vDS

Vtn

vDS = vGS - Vt

Saturation

Cut

-off

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS

iD

vDS sat =

vGS = +Vt

0

Triode Saturation

Curve bends becausethe channel resistanceincreases with vDS

Almost a straight linewith slope proportionalto OV vOV

Current saturates because thechannel is pinched off at thedrain end, and vDS no longeraffects the channel.

vDSvOV

v

......�� ��Where is cut-off region located in the above graph?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

ID versus VDS versus VGS

vDS vOVSaturation region

vDS vOVTrioderegion

vDS = vOViD= knvDS1

22

vGS = Vt+vOV3

vGS = Vt+vOV2

vGS = Vt+vOV1

vDSvGS Vt (Cutoff)

vGS = Vt+vOV4

vOV10 vOV2 vOV3 vOV4

knvO2V1

knvO2V2

knvO2V3

knvO2V4

iD

12

12

12

12

......

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

Realistic ID – VDS– VGS Curve (due to Channel LengthModulation)

Triode Saturation

0

VOV

vDS-VA = 1/

iD

- ......

IDsat =12

knv2OV (1 + λvDS)

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET Basic Formulas

NMOS:

• vOV = vGS −Vt

• ID =(µnCox

WL) (

vOV − vDS2

)vDS = kn

(vOV − vDS

2

)vDS

• ID ≈ knvOVvDS (for small vDS)

• IDsat =12 knv2

OV (when vDS = vGS −Vt = vOV)

• IDsat =12 knv2

OV (1 + λvDS) (with channel length modulation)

PMOS:

One can use the above set of equations for PMOS by replacing the device parameters asshown below:

Vtn →∣∣Vtp

∣∣ & λn →∣∣λp∣∣

vGS → vSG & vDS → vSD

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

MOSFET as an Amplifier & a Switch

iD

vDS

RD

VDD

vgs+

vGS

VGS

+-

C

Vt0 VGS

VDS

vDS

VDD vGS

VDD

Q

A

B

vDS = VDD − iDRD

Av =dvDS

dvGS

∣∣∣∣vGS=VGS

= −kn (VGS −Vt)RD = −knVOVRD = −gmRD = −(

ID

VOV/2

)RD

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

1 Biasing by Fixing VGS

iD

vGSVGS

ID1

0

ID2

Device 2

Device 1

VG

+VGS

ID

ID+

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

2 Biasing by Fixing VG and Connecting a Resistance inthe Source

+ +

VG

VGS

RS

ID

ID

Slope = 1 RS

Device 2

iD

ID2

ID1

VGS20 VGS1 VG vGS

Device 1

VG = VGS + RSID

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

3 Biasing Using a Drain-to-Gate Feedback Resistor

RD

RG

VDD

ID

ID0

VDSVGS

+

+

VGS = VDS = VDD − RDID

⇒ VDD= VGS + RDID�� ��What is the purpose of the resistor RG?

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus

Semiconductors MOSFET Operation MOSFET as a Circuit Element The MOSFET as an Amplifier & a Switch Biasing in MOS Amplifiers Summary

4 Biasing Using a Constant-Current Source

I

I I=D

RD

RG

DD

VSS

VGS

Q2Q1

R

0

To source oftransistor Q

ID1ID2

IREF

+

I = ID2 = ID1(W/L)2(W/L)1

= IREF(W/L)2(W/L)1

5. MOSFET Transistors & Circuits - I ECE/EEE/INSTR F244, Dept. of EEE, BITS Pilani Hyderabad Campus