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

junctions. In the Pspice library Q2N2222 refers to an NPN transistor. The dc bias
voltage forward biases the base emitter junction and reverse biases the base collector
junction.
The ratio of dc collector current, I , to dc base current, I , is called the dc beta,
C
B
β
DC
, which is the dc current gain of the transistor (typical values range from 20 to
200 or higher). Taking current values from Pspice:
β
DC
=
I
I
C
B
6.037mA
= = 198.5
30.42uA
The ratio of I to dc emitter current, I , is the dc alpha,
less than 1).
C
E
α
DC
(this value is always
α
DC
=
I
I
C
E
6.037mA
= = 0.995
6.068mA
Other important dc conditions include:
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
= = 7mA
1kΩ
= 7.7V
Pspice gives values for the base and emitter voltages as 6.756V and 6.068V
respectively and emitter current as 6.068mA.
The internal resistance of the transistor:
25mV
r ' e = = 3. 6Ω
I E
L1
VO
RL
Voltage gain: A = = =
C1Rs
V
= 25
V r'
e r'
e
IN
Where the load resistance is the dynamic impedance of the tuned LC circuit. The
voltage gain expressed in dBs: 20log(25) = 28dB.
Power gain = current gain X voltage gain = 198.5 X 25 = 3970.
Input Impedance of the transistor:
VB
7.7V
RIN = = = 253kΩ
I 30.42uA
B
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