Question 8.8: The input impedance of an amplifier without feedback is 1 KΩ...
The input impedance of an amplifier without feedback is 1 KΩ. The open-loop voltage gain of the amplifier is 20,000. Calculate the value of input impedance when negative feedback is used.
β=\frac{R_{1}} {R_{1}+R_{2}} =\frac{500}{500+5,000}=\frac{500}{5,500}=0.09
Z_ {i} = ( 1+Aβ)Z = (1+20,000×0.09 ) ×1 × 10^{3}
= 1,801 × 1 × 10^{3} = 1,801 KΩ
It is seen that the input impedance has increased from 1 KΩ to 1,801 KΩ.
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