Question

For given feedback amplifier, identify type of feedback, feedback ratio $\beta$ and voltage gain with feedback $A_{vf}$



Feedback $\beta$ $A_{vf}$
(a) Voltage series $\frac{19}{20}$ $-20$

(b) Current series $\frac{19}{20}$ $\frac{400}{21}$

(c) Voltage series $\frac{1}{20}$ $\frac{400}{21}$

((d) Current series $\frac{1}{20}$ $-20$

• A. a
• B. d
• C. b
• D. c

Answer 1

The correct option is D c

Given feedback is voltage series
Voltage gain without feedback
$\frac{V_0}{V_i}=\frac{2}{5\times {10}^{-3}}=400$
$V_f$ (feedback voltage) =voltage across $1k\Omega )$
$=V_0\left(\frac{1}{1+19}\right)=\frac{V_0}{20}$
$\beta =\frac{V_f}{V_0}=\frac{1}{20}$
$V_c+V_f-V_s=0$
$V_c=V_s-V_f$
$V_0=A{V}_s-A{V}_f$
$V_0=A{V}_s-A\beta V_0$
$\frac{V_0}{V_s}=\frac{A}{1+A\beta }$
$=\frac{400}{1+400\times \frac{1}{20}}=\frac{400}{21}$