Question

In a common emitter (CE) amplifier having a voltage gain $G$, the transistor used has transconductance $0.03{\Omega }^{-1}$ and current gain $25.$ If the above transistor is replaced with another one with transconductance $0.02{\Omega }^{-1}$ and current gain $20$, the voltage gain will be-

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

Answer 1

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

Voltage gain $A_v=\frac{\Delta V_C}{\Delta V_B}=\frac{R_L\Delta I_c}{\Delta V_B}=g_m{R}_L$

$\frac{A_{v_1}}{A_{v_2}}=\frac{g_{m_1}}{g_{m_2}}\Rightarrow \frac{G}{A_{v_2}}=\frac{0.03}{0.02}$

$\Rightarrow A_{v_2}=\frac{2}{3}G$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(B\right)$ is the correct answer.