Question

In the amplifier circuit shown below,

The value of the voltage gain $|\frac{V_0}{V_s}|$ is equal to _____.
(Assume $V_T=25mV$ and $\beta$ is very large )

• A. 150

Answer 1

The correct option is A 150
As $\beta$ is very large, $I_E=I_C=0.5mA$

$g_m=\frac{I_C}{V_T}=\frac{0.5}{25}=20mA/V$

Drawing small signal model, we get


Now, $V_s=-V_{in}$

$V_0=g_m{V}_s{R}_c$

$A_v=|\frac{V_0}{V_s}|=g_m{R}_c$
= 20 $\times {10}^{-3}\times 7.5\times {10}^3$ = 150