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Common emitter amplifier equivalent circuit
We define resistance RB as parallel combination of R1 and R2 so RB = [1/(1/R1 +1/R2)]
Similarly, RL’ as parallel combination of RC and RL, so RL’ = [1/(1/RL +1/RC)]
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Small signal equivalent circuit 2
Voltage gain Av0:
The input voltage is given as:
The voltage gain is then given as:
For large RE1 we can have:
Thus for
The voltage gain will be independent of the transistor parameters
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Small signal equivalent circuit 3
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Small signal equivalent circuit example
DC equiv. circuit
Now from Eqs. 4.47 and 4.53
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Small signal equivalent circuit example contd.
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