The gain of an amplifier falls from 100 to 40 when negative feedback i

1.	The gain of an amplifier falls from 100 to 40 when negative feedback is applied. If the input voltage is 1V, calculate (i) feedback factor (ii) Feedback voltage.
Answer» A = 100 A_f= 40 V_in = 1V A_f = \(\frac{A}{1+A\beta}\) 40 = \(\frac{100}{1+100\beta}\) 1 + 100β = \(\frac{100}{40}\) = 2.5 A = \(\frac{V_o}{V_{in}}\) 100β = 2.5 - 1 = 1.5 100 = \(\frac{V_o}{1}\) β = \(\frac{1.5}{100}\) = 0.015 V_o = 100V β = \(\frac{V_f}{V_o}\) V_f= βV_o = 0.015 x 100 = 1.5 V V_in = V_s - V_f 1 = V_s - 1.5 V_s = 2.5 Volt

The gain of an amplifier falls from 100 to 40 when negative feedback is applied. If the input voltage is 1V, calculate (i) feedback factor (ii) Feedback voltage.

Answer»

A = 100

A_f= 40

V_in = 1V

A_f = \(\frac{A}{1+A\beta}\)

40 = \(\frac{100}{1+100\beta}\)

1 + 100β = \(\frac{100}{40}\) = 2.5

A = \(\frac{V_o}{V_{in}}\)

100β = 2.5 - 1 = 1.5

100 = \(\frac{V_o}{1}\)

β = \(\frac{1.5}{100}\) = 0.015

V_o = 100V

β = \(\frac{V_f}{V_o}\)

V_f= βV_o

= 0.015 x 100

= 1.5 V

V_in = V_s - V_f

1 = V_s - 1.5

V_s = 2.5 Volt