simulation of a superheterodyne receiver using pspice - School of ...

The BJT used in the IF amplifier is the same as that used in RF amplifier and will use
the same formulae for its dc conditions.
β
DC
(i.e. dc current gain of the transistor) using current values from Pspice:
β
DC
=
I
I
C
B
3.23mA
= = 20.1
160.42uA
This is a much smaller value than the corresponding value in the RF amplifier, but it
is still an acceptable value.
α
DC
=
I
I
C
E
3.23mA
= = 0.995
3.247mA
This is the same as the RF amplifier.
V
V
I
B
E
E
R2
50k
= VDD
= 20V
R1
+ R2
80k
+ 50k
= V −V
= (7.7 − 0.7) V = 7V
B
V
=
R
E
E
BE
7V
= = 3.5mA
2kΩ
= 7.7V
Pspice gives values for the base and emitter voltages as 7.167V and 6.494V
respectively and emitter current as 3.247mA.
The internal resistance of the transistor:
25mV
r ' e = = 7. 14Ω
I E
The load resistance:
−6
L 210X10
R = =
= kΩ
L −
CR 582X10
X 20
18
12
S
L1
VO
RL
Voltage gain: A = = =
C1Rs
V
= 2521
V r'
e r'
e
IN
The voltage gain expressed in dBs: 20log(2521) = 68dB.
Power gain = current gain X voltage gain = 20.1 X 2521 = 50672.
Input Impedance of the transistor:
VB
7.167V
RIN = = = 420kΩ
I 17.08uA
B
R
Total
IN IN
7
= R1
R2
R = 80k
50k
420k
= 28. kΩ
Ref. [6] Appendix B
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