BJT – Analysis of Bias

Yong Heui Cho @ Mokwon University

Some of slides are referred to:[1] A. S. Sedra & K. C. Smith, Microelectronic Circuits.

2

Electronic Circuits

8. BJT – Operational Principle

9. BJT – Model

10. BJT – Analysis of Bias

11. Analysis of CE Amplifier

3

CE Amplifier• CE (Common Emitter)• Input: Base, Output: Collector• Common: Emitter

4

CB Amplifier• CB (Common Base)• Input: Emitter, Output: Collector• Common: Base

5

CC Amplifier• CC (Common Collector)• Emitter Follower• Input: Base, Output: Emitter• Common: Collector

6

ComparisonType CE CB CCinput Base Emitter Base

output Collector Collector Emittercommon Emitter Base CollectorV gain large large noneI gain large none large

application first stage amplifier

high fre-quency am-

plifierbuffer

7

Bias Point• Quiescent point• Active mode

8

CE Amplifier• 4 R and 1 TR

9

Active Condition• Collector Current (IC) = about mA• CE Voltage (VCE) = VCC/2

10

Analysis of Bias (I)• Thevenin equivalent circuit

CCBB

BBB V

RRRV

21

2

21

2111 //

BB

BBBBB RR

RRRRR

VBB

RB

11

Analysis of Bias (II)• B-E loop: collector current (IC)

VBB

RB

VCC

RC

RE

BEBBE

EEBEBBBB

IRRVRIVRIV

)1(

BCBE IIII )1(

EB

BEBBB RR

VVI)1(

E

BEBB

EB

BEBBC

RVV

RRVVI

)1()(

12

Analysis of Bias (III)• C-E loop: CE voltage (VCE)

VBB

RB

VCC

RC

RE

BCBE IIII )1(

EECECCCC RIVRIV

)( ECCCC

EECCCCCE

RRIVRIRIVV

13

Selection of R

kRR BB 10, 21

BE RR

LC RR