BJT - Analysis of Bias

1. 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. 2
Electronic Circuits
8. BJT – Operational Principle
9. BJT – Model
10. BJT – Analysis of Bias
11. Analysis of CE Amplifier

3. 3
CE Amplifier
• CE (Common Emitter)
• Input: Base, Output: Collector
• Common: Emitter

4. 4
CB Amplifier
• CB (Common Base)
• Input: Emitter, Output: Collector
• Common: Base

5. 5
CC Amplifier
• CC (Common Collector)
• Emitter Follower
• Input: Base, Output: Emitter
• Common: Collector

6. 6
Comparison
Type CE CB CC
input Base Emitter Base
output Collector Collector Emitter
common Emitter Base Collector
V gain large large none
I gain large none large
application
first stage
amplifier
high frequency
amplifier
buffer

7. 7
Bias Point
• Quiescent point
• Active mode

8. 8
CE Amplifier
• 4 R and 1 TR

9. 9
Active Condition
• Collector Current (IC) = about mA
• CE Voltage (VCE) = VCC/2

10. 10
Analysis of Bias (I)
• Thevenin equivalent circuit
CC
BB
B
BB V
RR
R
V
21
2



VBB
RB

11. 11
Analysis of Bias (II)
• B-E loop: collector current (IC)
VBB
RB
VCC
RC
RE
  BEBBE
EEBEBBBB
IRRV
RIVRIV
)1( 



BCBE IIII )1(  
EB
BEBB
B
RR
VV
I
)1( 



E
BEBB
EB
BEBB
C
R
VV
RR
VV
I





)1(
)(



12. 12
Analysis of Bias (III)
• C-E loop: CE voltage (VCE)
VBB
RB
VCC
RC
RE
BCBE IIII )1(  
EECECCCC RIVRIV 
)( ECCCC
EECCCCCE
RRIV
RIRIVV




13. 13
Selection of R
 kRR BB 10, 21
BE RR 
LC RR 


