lecture22-150128.pdf

Lecture 22 – Compensation of Op Amps (6/24/14) Page 22-1

CMOS Analog Circuit Design © P.E. Allen - 2016

LECTURE 22 – INTRODUCTION TO OP AMPS

LECTURE OUTLINE

Outline

• Op Amps

• Categorization of Op Amps

• Compensation of Op Amps

Pages 261-286

Lecture 22 – Compensation of Op Amps (6/24/14) Page 22-2

CMOS Analog Circuit Design © P.E. Allen - 2016

OP AMPS

What is an Op Amp?

The op amp (operational amplifier) is a high gain, dc coupled amplifier designed to

be used with negative feedback to precisely define a closed loop transfer function.

The basic requirements for an op amp:

• Sufficiently large gain (the accuracy of the signal processing determines this)

• High speed/frequency

Lecture 22 – Compensation of Op Amps (6/24/14) Page 22-3

CMOS Analog Circuit Design © P.E. Allen - 2016

Why Op Amps?

The op amp is designed to be used with single-loop, negative feedback to accomplish

precision signal processing as illustrated below.

The voltage gain,

V

V

(s)

=

V

out

(s)

V

in

(s)

≈

Lecture 22 – Compensation of Op Amps (6/24/14) Page 22-4

CMOS Analog Circuit Design © P.E. Allen - 2016

OP AMP CHARACTERIZATION

Linear and Static Characterization of the CMOS Op Amp

A model for a nonideal op amp that includes some of the linear, static nonidealities:

where

R

id

= differential input resistance

C

id

= differential input capacitance

R

icm

= common mode input resistance

R

= common mode input capacitance

n

Lecture 22 – Compensation of Op Amps (6/24/14) Page 22-5

CMOS Analog Circuit Design © P.E. Allen - 2016

Linear and Dynamic Characteristics of the Op Amp

Differential and common-mode frequency response:

V

out

(s)[V

(s)] ± A

c

(s)

V

(s)+V

(s)

2

s

p

3

- 1 ···

v0

2

)(s -p

2

)(s -p

3

)···

where p

, p

, p

,··· are the poles of the differential-frequency response (ignoring zeros).