Question

In a common emitter $(CE)$ amplifier having a voltage gain $A_v$, the transistor used has transconductance $0.03mho$ 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)

$A_v=\beta \frac{R_{out}}{R_{in}}=25\frac{R_{out}}{R_{in}}$

$\because G_m=\frac{\beta }{R_{in}}\Rightarrow R_{in}=\frac{\beta }{G_m}=\frac{25}{0.33}$

$\therefore A_v=25\frac{R_{out}}{25}\times 0.03$

Now, $A_v^{{}^{\prime }}=20\frac{R_{out}}{20}\times 0.02$

$A_v^{{}^{\prime }}=\frac{2}{3}{A}_v$