1

Small-Signal Analysis of the 741We can analyze the small-signal voltage gain of the 741 op-amp by dividing it into its basic circuits and using results previously obtained

in the DC analysis.

2

The Input Stage

Ω==

+=

Ω===

=

M 2.1 200,NFor )1(4

k 63.2µA 5.9mV 25

4

idRerNidR

ITVer

eriv

ei

ββ

3

The load circuit of the input stage

erivoi

mG

eioi

21

2α

α

==

=

4

Finding Ro5 and Ro6

Ω==Ω=Ω=

=====+=

M 7.6// M 2.18 ;M 10.5

A 9.5 V; 50 ;kΩ 63.2

)//(1[

164

064

ooo

o

AAo

eE

Emoo

RRRRR

IV/IVrrR

rRgrR

µ

π

5

Example: Determine the small-signal differential voltage gain of the 741 op-amp input stage. Assume transistor gain of β = 200 and Early

voltages of VA = 50 V.

6

mA/V 365.0026.00095.06

6

k 5470095.0

026.0200

66

M 4.07)(201)(18.63292

kΩ 3290158.0

026.0200

1616

kΩ 6.18)]1.0)(201(63.9//[50

kΩ 63.954.0

026.0200

1717

]8)1(17//[9

)1(162

]6//2(61[61

)2//1//4()2//1//4(

===

Ω=×

==

Ω=+=

=×

==

=+=

=×

==

++=++=

+=

=−=

TVCI

mg

CITVr

iRCITVr

ERCITVr

RrRERERriRrRmgoractR

iRacRorTVCQI

iRacRormgdA

βπ

βπ

βπ

βπ

βππ

7

636)07.4//18.7//26.5)(026.05.9(

MΩ 26.50095.050

44

M 7.1847)]0.365(1//55.26[11

MΩ 26.50095.050

66

−=−=

===

Ω=+=

===

dA

CIAVor

actRCIAVor

8

The Gain (Second) Stage)])(1//()[1( 81717916162 RrRrR eei ++++= ββ

BoBo

oBoo

rRRRR

1313

17132 kΩ 81)//(=

==

9

The Output Stage

2023samin

14satmax

EBEBtCEEEo

BECECo

VVVVvVVCVv

+++−=−−=

10

11

Circuit for Finding the Output Resistance Rout

12

Gain, Frequency Response, and Slew Rate of the 741

V/V 243147

))(//( 3221211

22

22

=+

−−

=

o

outL

Lvoomom

o

o

i

o

i

i

i

o

ARR

RGRGRRG

vv

vv

vv

vv

13

Frequency Response

Hz 1.42

1M 5.2)MΩ 4//MΩ 7.6()2//1(

)21(

==

Ω===

+=

tRinCpf

iRoRtRACCinC

π

14

A Simple Model of the 741

CCmGt

CCjmGjA

CsCmG

siVsoVsA

1;1)(

1)()(

)(

==

==

ωω

ω

15

Slew Rate

CCISR

tCCItov

2

2)(

=

=