Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith1

Single-Stage Integrated-Circuit Amplifiers

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Outline• Comparison between the MOS and the BJT• From discrete circuit to integrated circuit

- Philosophy, Biasing, …etc.• Frequency response• The Common-Source and Common-Emitter amplifier

with active loads • The Common-Gate and Common-Base amplifier

with active load• The Source and Emitter Follower• The CS and CE amplifier with source degeneration• Current mirrors with improved performance• Cascode amplifier and transistor pairings

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

6-1 Comparison between the MOS and the BJTDC characteristics

• Transconductor (iD - vGS v.s. iC - vBE )

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

• Channel-length modulation (iD - vDS ) v.s. Early effect (iC – vCE)

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Low-frequency operation

• Transconductance

Doxnm IL

WCg ⎟⎠⎞

⎜⎝⎛= )(2 µ

T

Cm V

Ig =

• Input resistance

• Output resistance

• Intrinsic gain

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

High-frequency operation

225.1

32 and For

)(2

LVf

WLCCCC

CCgf

OVT

oxgsgdgs

gdgs

mT

πµ

π

≅

≅>>

+=

222

and For )(2

WVf

CCCCCC

gf

TT

de

mT

πµ

π

πµπ

µπ

≅

≅>>

+=

• Cutoff frequency

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

• Technology speed figure of merit v.s. Time:

• Estimated frequency performance based on scaling

Trends in IC technology

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

DC range of operation 2-3 decades of ID ∝ (VGS –VT )2

>5 decades of IC ∝ eVBE

Noise (thermal about the same) More 1/fLess 1/f

Small-signal output resistance ( ro ) Smaller for short channel

Slightly larger

Switch implementation GoodPoor

Capacitor implementation Reasonably goodVoltage dependent

MOSBJT

Cutoff frequency ( fT ) 50GHz100GHz

Comparison

From analogue or digital point of view?

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

6-2 From Discrete- to Integrated- circuitComponents

(The pictures are copied from http://140.114.23.141/htdocs/course/922_EE226002/Introduction.pdf , S.H. Hsu)

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Hardware products

(The pictures are copied from http://140.114.23.141/htdocs/course/922_EE226002/Introduction.pdf , S.H. Hsu)

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Design topologies

• Active load to replace R

R=?

• Current biasing

• Direct-coupled

Differential architecture to decouple DC signals (Ch7)

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

IC Biasing – current mirror (amplifier)

• Io / IREF =

• Minimum Vo =

• Effect of ro :

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Current steering

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

• Io / IREF =

• Minimum Vo =

• Effect of ro :β

11 ++

= mm

II

REF

O

BJT current mirror

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

6-3 Frequency response• In analysing the frequency response of circuits,capacitors 1/sC inductors sL

T(s)Vi(s) Vo(s)

01

1

01

1)(bsbs

asasasT nn

n

mm

mm

++++++

= −−

−−

L

L

Zeros :Poles :)())((

)())(()(21

21

n

mm PsPsPs

ZsZsZsasT−−−−−−

=L

L

Substituting s=jw into T(s) The gain and phase response v.s. w

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Bode plot

0

1)(ps

sT+

=a pole

a zero0)( zssT +=

|)(| sT )(sT∠

How about positive-valued poles/zeros?

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Example

)10/1)(10/1(10)( 52 ss

ssT++

=

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Example- continued

)10/1)(10/1(10)( 52 ss

ssT++

=

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

High-frequency response

• Frequency response of a direct-coupled amplifier

)/1()/1)(/1()/1()/1)(/1()(

21

21

n

nH pspsps

zszszssF++++++

=L

L

We are mostly interested in 3-dB frequency, fH (or f3dB)

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Methods to derive fH

• If a dominant pole exists1/1

1)(P

H wssF

+≅

• If not, use the cond. |F(wH)| = ½ to derive

⎟⎟⎠

⎞⎜⎜⎝

⎛+++−⎟⎟

⎠

⎞⎜⎜⎝

⎛+++≅ 22

22

122

22

1

1111111ZnZZPnPP

H wwwwwww LL

• Open-circuit time constants

∑≅

iioi

H RCw 1

Rio : resistance seen by Ci when all other Cs are open-circuit and all sources equal zeros

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Example 6.6

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Miller’s theorem – one useful technique for analysing freq response

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Example 6.7

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

6-4 Common-Source and Common-Emitter amplifers with acitive loads

===

o

vo

i

RAR

Common-source amplifier

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Common-source amplifier with active load

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

• Large-signal characteristics

• Small-signal characteristics (in region III)

===

out

v

in

RAR

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

• High-frequency response

(i) Analysis by Miller’s Theorem

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

(ii) Analysis by Open-circuit time constants

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

(iii) Exact analysis

Single-stage IC Amplifiers

Hsin Chen, 2005

Electronics II

c.f.: Microelectronic Circuits, 5th ed., Sedra/Smith

Formulas for Common-Emitter amplifier with active load