lecture21-140624.pdf

Lecture 21 – Output Amplifiers (6/24/14) Page 21-1

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

LECTURE 21 – OUTPUT AMPLIFIERS

LECTURE ORGANIZATION

Outline

• Introduction

• Class A Amplifiers

• Push-Pull Amplifiers

Lecture 21 – Output Amplifiers (6/24/14) Page 21-2

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

INTRODUCTION

General Considerations of Output Amplifiers

f

f

V

V

v

i

i

t

i

t

i

i

Lecture 21 – Output Amplifiers (6/24/14) Page 21-3

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

Output Current Requirements for an Output Amplifier

Consider the current requirements placed by the load on the output amplifier:

Result:

|i

| > C

·SR

Fortunately, the maximum current for the resistor and capacitor do not occur at the same

time.

Output

Amplifier

+

v

Lecture 21 – Output Amplifiers (6/24/14) Page 21-4

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

Output Resistance Requirements for an Output Amplifier

In order to avoid attenuation of the amplifier voltage signal, the output resistance of the

amplifier must be less than the load resistance.

To avoid attenuation of the amplifier voltage signal, R

.

Lecture 21 – Output Amplifiers (6/24/14) Page 21-5

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

Separation of the Amplifier Bias from the Load Resistance

Unfortunately, when a low load resistance is connected to the output of an amplifier, the

bias conditions can be changed.