Example-2 (Capacitor-Coupled CB Design)

Design a CB amplifier using an npn transistor as shown in fig. 3 with β = 100, V_CC= 24 V, R_load= 2KΩ, R_E = 400Ω V_BE = 0.7V. Design this amplifier for a voltage gain of 20.

Fig. 3

Solution:

Since there are fewer equations than there are unknowns, we need an additional constraint, so we set

R_C = R_load = 2 K Ω

Then we have,

R_ac = 1.40 K Ω and R_dc =2.40 KΩ

For maximum swing, we set I_CQ to

We now find that

The current gain is given by

and input impedance is given by

We use the bias equation to find the parameters of the input bias circuitry.

The bias resistors are then given by

The maximum peak-to-peak undistorted output voltage is

V_out(peak-peak) = 1.8 | I_CQ | (R_load || R_C) = 11.3 V

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