Electronic Circuit Analysis

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Electronic Circuit Analysis
Consider the circuit shown in Fig. 6.3.
R'
L
Expression for input power Psis, '
b
Fig. 6.3
P s = Ib 2 (RS' + hie)
Expression for output power Po is,
.'. Power Gain
Po = Ic 2 .R L'
I 2R '
C L
Ib 2 (Rs' + hie)
hf/R L '
= ----"=---=-
Rs' + hIe
Considering only the BJT, expression for power gain
hf/R L
A p(8JT) = h. = hre' ~ R L'
Ie
Maximum power is transferred to the base-emitter circuit of BJT, when impedance matching is
done as,
Rs' = hIe
:. Matched input Power Gain
2 ' h fe RL
Ap (Matched input) = 2h.
Ie
- b gm·RL'
Ap- fe' 2
To maintain output voltage and power levels stable, the circuit must be designed accordingly.
6.4 Tuned Class B and Class C Amplifiers
The efficiency of the output circuit of an amplifier increases as the operation is shifted from class A
to B and then to C.
In class C amplifiers, efficiency approaches 100%.