Question

In a common emitter (CE) amplifier having a voltage gain $G$, the transistor used has transconductance $0.03mho$ and current gain $25$. If the above transistor is replaced with another one with transconductance $0.02mho$ and current gain $20$, the voltage gain will be

• A. $\frac{2}{3}G$
• B. $1.5G$
• C. $\frac{1}{3}G$
• D. $\frac{5}{4}G$

Answer 1

The correct option is A $\frac{2}{3}G$

$A_v=\beta \frac{R_L}{R_i}$ $(g_m=\frac{\Delta I_C}{\Delta V_B}=\frac{\Delta I_C}{\Delta I_B{R}_i})$

$G=\left(\frac{\beta }{R_i}\right)R_L$ $(g_m=\frac{\beta }{R_i})$

$=g_m{R}_L\Rightarrow G\propto g_m$

$\frac{G_2}{G_1}=\frac{g_{m_2}}{g_{m_1}}\Rightarrow G_2=\frac{0.02}{0.03}\times G$

$=\frac{2}{3}G$