EX$9-2($optional$)$

In circuit A$,$ transistor $Q_1$ works as a common emitter amplifier and transistor $Q_2$ works as a common base amplifier.

$($a$)$ Draw the $AC$ equivalent circuit. Here, use circuit B as the equivalent circuit of the transistors which can be obtained by ignoring $(1-)r_c.$ You may also assume that the impedances of the capacitors are zero for AC$.$

$($b$)$ Find approximate values for $A_v=\frac{v_o}{v_i}$ when $r_b,r_e$ and $$ of the transistor are $400,26$ and $99,$ respectively.

$$IICuIL