Lecture 12 Bipolar Junction Transistor...
Transcript of Lecture 12 Bipolar Junction Transistor...
Lecture 12
Bipolar Junction Transistor (BJT)
BJT 1-1 Wednesday 15/11/2017
Outline
Continue BJT analysis with small AC signal
Common-Emitter configuration
• Analysis using various biasing circuits
BJT 1-2
Common-Emitter Configuration
BJT 1-3
bbe III 1
The diode re model can be replaced by the resistor re.
e
eI
mV 26r
Can you deduce the input impedance ?
Common-Emitter Configuration
BJT 1-4
Input impedance:
Output impedance:
Voltage gain:
Current gain:
e
B
ii rZIV
o o
o L
Z r
Z R
e
LV
r
RA VV
i
o
oi rA o C
i B
I II I
RL
Vo
Vi
At load:
Common-Emitter Fixed-Bias Configuration
BJT 1-5
• The input is applied to the base
• The output is from the
collector
• High input impedance
• Low output impedance
• High voltage and current gain
• Phase shift between input and
output is 180
Common-Emitter Fixed-Bias Configuration
BJT 1-6
AC equivalent circuit
re model-based BJT circuit
Common-Emitter Fixed-Bias Calculations
BJT 1-7
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
iv
i
iR
ZA
ZA
VRV
II
i
Co
i
o
Current gain from voltage gain:
Input impedance:
Output impedance:
Voltage gain: Current gain:
B e
i B e
i e R 10 r
Z R || r
Z r
Co
O
R10rCo
Co
RZ
r||RZ
Common-Emitter Voltage-Divider Bias Configuration
BJT 1-8
AC equivalent circuit using the re model
Common-Emitter Voltage-Divider Bias Calculations
BJT 1-9
Current gain from voltage gain:
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
BJT 1-10
AC equivalent circuit using the re model
Common-Emitter Emitter-Bias Calculations
BJT 1-11
Eb
Eeb
Eeb
bBi
RZ
)R(rZ
1)R(rZ
Z||RZ
Input impedance:
Output impedance:
Co RZ
Voltage 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
Current gain:
bB
B
i
oi
ZR
R
I
IA
Current gain from voltage gain:
C
ivi
R
ZAA
Example
BJT 1-12
For the CE Emitter-Bias Configuration circuit: (a) Determine re and the internal small-signal transistor output resistance (b) Find Zi and Zo. (c) Calculate Av and Ai.
Solution
BJT 1-13
Emitter-Follower Configuration
BJT 1-14
• 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.
Emitter-Follower Configuration Calculations
BJT 1-15
Input impedance:
Output impedance:
Current gain from voltage gain:
Voltage gain:
Current gain:
i B b
b e E
b e E
b E
Z R ||Z
Z r ( 1)R
Z (r R )
Z R
eE rReo
eEo
rZ
r||RZ
EeEeE RrR ,rRi
ov
eE
E
i
ov
1V
VA
rR
R
V
VA
bB
Bi
ZR
RA
ii v
e
ZA A
r
BJT 1-16
Lecture Summary
Covered material Continue BJT analysis with AC signal
Common-Emitter and common-collector configurations • Analysis using various biasing circuits
Material to be covered next lecture
Effect of source/load impedance on current and voltage gain
Introduction to cascaded systems Introduction to FET transistors