Question

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

• A. $\frac{2}{3}A_{v}$
• B. $A_{v}$
• C. $\frac{3}{2}A_{v}$
• D. $\frac{A_{v}}{2}$

Answer 1

Answer: (A)

$A_{v}=\beta \frac{R_{out}}{R_{in}}=25 \frac{R_{out}}{R_{in}}$

$\because\quad G_{m}=\frac{\beta}{R_{in}}\Rightarrow R_{in} =\frac{\beta}{G_{m}}=\frac{25}{0.33}$

$\therefore \quad A_{v}=25 \frac{R_{out}}{25}\times0.03$

Now, $A_{v}^{'}=20 \frac{R_{out}}{20}\times0.02$

$A_{v}^{'}=\frac{2}{3} A_{v}$