Discussion 1BTransistors

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About Me(Super) Senior CS & Math Double Major4th time TAing this class, taught 16A for a year

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Discussion 1B: Transistors

Transistors are electrical devices that switch or amplify electrical signals and power.

Common Terminology

What is a transistor?

MOS: Metal-Oxide SemiconductorFET: Field-Effect Transistor

BJT: Bipolar Junction Transistor

CMOS TransistorsC stands for “Complementary”

NMOS NMOS : PM OS pmos :Drain : Higher

source : HigherSource : Lower Notice

→ Drain '. Lowerthe bubble

in the PNOS

N stands for N - Type P stands for P - Type"

Type " refers to the semiconductor material that makes these transistors.( out of scope)

Why do we care about transistors?Some call it the greatest invention of the 20th century!

We can build logic gates out of CMOS Transistors

You can build a CPU with logic gates and a clock (61C Logisim Project)

A clock can be made out of transistors. (Ring oscillator)

We can amplify signals using transistors. (Op-Amps are a lie)

•

a.

a

•

←Not Gate

Digital clock

whyDo-17-177 type✓

takes some time

to switch frominput-outputT → F

Breakdown of a Transistor ParasitictankNMOS switch Model Resistor - Switch Model Capac

' RC Model

D NMOS . DD G

Vtn'

- threshold 6 . ( I closed when I ¥ Closed when. ←

Closed b f v f-I } I , when o

Vos 7- Vthcµ=

Vbs ZV

Gs Node ! / Vos ZUM { RN I { RN

voltages T Internal -Vos = Vo - Vs S

Resistance S S

Switch Model Resistor - Switch Model RC Model

PMOS S Ss ss ← opposite G & Uso ? Htpl G ↳ VSGZ Ntp ) -

G -fly of NMOS O

pmos has o l l

l a negative Cp = } RpD D threshold { RP I * Uso > Ntpl

Vsb = Us - Vo potential p ylD

Utp : PM 's switch Model Resistor- Switchthreshold RC ModelUses Analyze Logical Analyze Power

behavior of consumption Analyze the timetransistor delay of each

Normally pnos is ON when Vbs S Vtp transistorUsb Z lvtpl

CMOS InverterVpp The CMOS Inverter is a NOT Gate o-1>0-0

T we define OV as a logical False and Vpp -_5V as

of[ a logical True . Suppose Vtn=lVtpl= VDI✓ out"

tie "

* ou

T OV

Assume Vin -_ True -_ VppNew Circuit ( Assume switch model)

UDD Usb = Us - VG '

Upp- .

S= Upp - Vpp Gwin . T

Vin -6014 = o o i rD

. to rout -- OVAsk : Is o > Ntpl ? -

Ub -- Vin - Upp - Iµ. : switch isg- Upp o D

Vs = Vpp Up -- tout off / open oVbs = Vpp 7 Vtn=

# s =p ✓ Ex : Ven > Up,

Vin = Upp or Vin -- T : Vin = 0 or Vin = F/

Circuit uns ! Circuit Upp-

-

( PMOS is off'

' f PMO ) is ON

' ↳ UoutKohout '

f NMOS is on': L

Nmos is off= i

,I

✓out is connected to ground so i

'

'

V' out is connected to Upp sobout = OV :' bout = VDDl

ll

l

ll

l

l

l

l

l

l

l.

3. Single Transistor Inverter

up , switch ModelVos zum OC Vtnl VDD

- f → ¥R " } Ci ) what is Vast when Vin = OV

•nobout

I . Label 6. D. S 2.

Calculate Vbs 3.Switch is on/off ?

Vinay} . D : bout Vbs -_ Vo -Vs Vos = O L VenVin 44 = Vin - O so switch is off/ open

=S O = O Voort

Vo - Vin, Us -

- O,Vo -- tout yep T

4. Resulting circuit : by R , Ito bout

y Voet - Vpb since in ,'- O

=

Lii ) what is Vouet when Vin = Ubb ?I . Label 6

,D,S 2

. Calculate Vos

p Vouet Vos = Vo - Us 3- Switch on/off ?

Vin 44 = Vpp - O Vos - Vpp > VtnSo = Vpp so switch is out closed

Vb = Vpp,Us - O

,Vp -- Vout E

4. Resulting circuit : { Ri Vout= 0 since rout is

1-Vout

connected to ground .

=

Part 2 : Using resistor - switch model +4 → In Vos ZUM

Ven { RN OL Utu L Vbb=

R , VPDCi ) what is Vouet when Vin -- O ? - in , -_ 0

vi. +tf ""t - punt Vos = Vo - Vs ip , } Rt sinceVino- I } = o - o = O L Vtn to Vat nothing is

NOT Gate°

.S

NMOS is off ( open { RN connectedOV bout = UDD

Cii ) what is Vout when Vin = Vpn ?✓ DD

p G= Vin-

- Vas Vos = Vpb > Utu -

by } s -- OVNmos is out closed {Io wut

s D= VoutRµ= to RI tf RN

Voltage Dividers : you = RI Upp = ÷, HPDRct RN t

'

Doesn't reachtrue O

.

Using this inverter. designers should label Ivpp as False

or create some threshold H if VL H, then Vis False

Here Ha to Voy will suffice.

Ciii ) How much power does this circuit consume when Vin -_ o ?

✓DDRemember P = IV - in} p ,when Vin = OVto ← open

circuit

since i -- o,p=o .

Ii '- o

Civ ) How much power does this circuit consume when Vin - Von ?

emi v i = VI V= Vpp since

} Rt RctRNpower is consumed across

- vout both resistors.

tf RN p= Vast=-

R ,t RN

Vin -

- OV Vin -- UppUpp Vpb

( V) compare to CMOS Inverter : -

CMOS inverter consumes zero powerFRP { RPw -

This is why CMOS is desirable over-Vmt

single NMOS transistor. } RN } RN= =

P=o p=o since Vouet - o

Summary (Main Takeaways )

I.

Two Transistors CPMOS and NMOS ),they behave like

switches

-4 -4Nmos PMOS

2.We can build Logic gates out of Transistors

✓DD Upp VDD

VinVout In circuits -

--

-Do- → vinofldhov.at ORuin.iq#Ru..+0RVin-tdhovout44 IR=

=

3.

CMOS Inverter is desirable over single NMOSIPMOS since

CMOS consumes zero power when no load is attached .

4. Looking Forward : Transistors always have delay due to parasitic

capacitance .