March 3, 20051

EE 359 Electronic Circuits

Multistage AmplifiersMultistage Amplifiers

Two Stage CMOS OpAMP

Bipolar OpAmp

SPICE

March 3, 20052

EE 359 Electronic Circuits

HW #5

• 7.10, 7.21, 7.71, 7.88

Due Tuesday

March 3, 20053

EE 359 Electronic Circuits

Why Multistage?

• Practical transistor amplifiers consist of a number of stages connected in cascade.

• First stage typically high input impedance, & CMMR

• Middle stages amplification

• Last stage, low output impedance

March 3, 20054

EE 359 Electronic Circuits

Two stage CMOS

Q8,Q5:current mirrors

March 3, 20055

EE 359 Electronic Circuits

Differential Input

013

313 ||||

1

2rr

g

vgv O

m

idmg

Usually the leakage resistances are much larger than 1/g_m3

3

13 2 m

midg g

gvv

March 3, 20056

EE 359 Electronic Circuits

Differential Gain

March 3, 20057

EE 359 Electronic Circuits

Differential Input

22

2

23

41

234

idm

id

m

mmo

idmgmo

vg

v

g

ggi

vgvgi

March 3, 20058

EE 359 Electronic Circuits

• vG2=0, vG1=vid

2/2

1

||

0

04020

omd

momid

d

ArgA

rrgRGv

vA

March 3, 20059

EE 359 Electronic Circuits

Equivalent Circuit MOSFET Opamp

March 3, 200510

EE 359 Electronic Circuits

Bias Circuit for Opamp

• Bias current independent of Supply Voltage and MOSFET threshold volage

• Q_12, Q_13 deliberately mismatched, Q_12 4x wider

March 3, 200511

EE 359 Electronic Circuits

Bipolar Opamp

March 3, 200512

EE 359 Electronic CircuitsBipolar Opamp

March 3, 200513

EE 359 Electronic Circuits

Small Signal Analysis

• Input and output Impedances

March 3, 200514

EE 359 Electronic Circuits

Gain of Second Stage

March 3, 200515

EE 359 Electronic Circuits

Last stage

March 3, 200516

EE 359 Electronic Circuits

Small Signal Model

March 3, 200517

EE 359 Electronic CircuitsFrequency Response

March 3, 200518

EE 359 Electronic Circuits Spice Simulation

March 3, 200519

EE 359 Electronic Circuits

Opamp Transfer Function

March 3, 200520

EE 359 Electronic Circuits

Differential Gain

March 3, 200521

EE 359 Electronic Circuits

Frequency Response• Adjust frequency resonse by adding resistor in Q4

March 3, 200522

EE 359 Electronic Circuits

Common Mode Rejection Ratio