Chapter 5: BJT AC Analysis - Islamic University of Gazasite.iugaza.edu.ps/ahdrouss/files/2010/02/Revision-class.pdf · Common-Emitter Collector Feedback Configuration • This is

Chapter 5: BJT AC Analysis

http://www.pdfonline.com/easypdf/?gad=CLjUiqcCEgjbNejkqKEugRjG27j-AyCw_-AP

Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.

Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky

BJT Transistor Modeling

• A model is an equivalent circuit that represents the AC characteristics of the transistor.

• A model uses circuit elements that approximate the behavior of the transistor.

• There are two models commonly used in small signal AC analysis of a transistor:

– re model– Hybrid equivalent model




Common-Base Configuration

Input impedance:

Output impedance:

Voltage gain:

Current gain:

ec II e

e I

mV26r

ei rZ

oZ

e

L

e

LV r

R

r

RA

1Ai




Common-Emitter Configuration

bbe III 1

This image cannot currently be displayed.

The diode re model can be replaced by the resistor re.

more…

ee I

mV26r




Common-Emitter Configuration


Input impedance:

Output impedance:

Voltage gain:

Current gain:

ei rZ

oo rZ

e

LV r

RA

oriA




Common-Collector Configuration


Input impedance:

Output impedance:

Voltage gain:

Current gain:

ei rZ )1(

Eeo RrZ ||

eE

EV rR

RA

1 iA




Common-Emitter Fixed-Bias Configuration

AC equivalent

re model




Common-Emitter Fixed-Bias Calculations

Co 10Rre

Cv

e

oC

i

ov

r

RA

r

)r||(R

V

VA

eBCo r10R,10Rri

eBCo

oB

i

oi

A

)r)(RR(r

rR

I

IA

C

ivi R

ZAA

Current gain from voltage gain:

Input impedance:

Output impedance:

Voltage gain: Current gain:

eE r10Rei

eBi

rZ

r||RZ

Co

O

R10rCo

Co

RZ

r||RZ




Common-Emitter Voltage-Divider Bias

re model requires you to determine , re, and ro.




Common-Emitter Voltage-Divider Bias Calculations


Input impedance:

Output impedance:

Voltage gain:

Current gain:

ei

21

r||RZ

R||RR

Co 10RrCo

oCo

RZ

r||RZ

Co 10Rre

C

i

ov

e

oC

i

ov

r

R

V

VA

r

r||R

V

VA

eCo

Co

r10R,10Rri

oi

10Rrei

oi

eCo

o

i

oi

I

IA

rR

R

I

IA

)rR)(R(r

rR

I

IA

C

ivi R

ZAA




Common-Emitter Emitter-Bias Configuration




Impedance Calculations

Eb

Eeb

Eeb

bBi

RZ

)R(rZ

1)R(rZ

Z||RZ

Input impedance:

Output impedance:Co RZ




Gain Calculations


Voltage gain:

Current gain:

Eb

Eeb

RZE

C

i

ov

)R(rZEe

C

i

ov

b

C

i

ov

R

R

V

VA

Rr

R

V

VA

Z

R

V

VA

bB

B

i

oi ZR

R

I

IA

C

ivi R

ZAA




Emitter-Follower Configuration

• This is also known as the common-collector configuration.• The input is applied to the base and the output is taken from the

emitter.• There is no phase shift between input and output.




Impedance Calculations

Input impedance:

Output impedance:

eE rReo

eEo

rZ

r||RZ

Eb

Eeb

Eeb

bBi

RZ

)R(rZ

1)R(rZ

Z||RZ




Gain Calculations


Voltage gain:

Current gain:

EeEeE RrR,rRi

ov

eE

E

i

ov

1V

VA

rR

R

V

VA

bB

Bi ZR

RA

E

ivi R

ZAA




Common-Base Configuration

• The input is applied to the emitter.

• The output is taken from the collector.

• Low input impedance.• High output impedance.• Current gain less than unity.• Very high voltage gain.• No phase shift between input

and output.




Calculations

eEi r||RZ

Co RZ

e

C

e

C

i

ov r

R

r

R

V

VA

1I

IA

i

oi

Input impedance:

Output impedance:

Voltage gain:

Current gain:




Common-Emitter Collector Feedback Configuration

• This is a variation of the common-emitter fixed-bias configuration• Input is applied to the base• Output is taken from the collector• There is a 180 phase shift between input and output




Calculations

F

C

ei

R

R1

rZ

FCo R||RZ

e

C

i

ov r

R

V

VA

C

F

i

oi

CF

F

i

oi

R

R

I

IA

RR

R

I

IA

Input impedance:

Output impedance:

Voltage gain:

Current gain:




Collector DC Feedback Configuration

• This is a variation of the common-emitter, fixed-bias configuration

• The input is applied to the base• The output is taken from the

collector• There is a 180 phase shift

between input and output




Calculations

F

C

ei

R

R1

rZ

FCo R||RZ

e

C

i

ov r

R

V

VA

C

F

i

oi

CF

F

i

oi

R

R

I

IA

RR

R

I

IA

Input impedance:

Output impedance:

Voltage gain: Current gain:


Documents

Chapter 5: BJT AC Analysis - Islamic University of Gazasite.iugaza.edu.ps/ahdrouss/files/2010/02/Revision-class.pdf · Common-Emitter Collector Feedback Configuration • This is