A common source FET amplifier has Cgs = 50 pF and Cgd =

A common source FET amplifier has C_gs = 50 pF and C_gd = 5 pF. The value of source resistance R_S for high 3 dB frequency of 100 kHz will be—

Given, C_gs = 50 pF, C_gd = 5 pF, f_T = 100 KHZ, R_S =?

We know that, f_T =	1
	2 π(C_gd + C_gs) R_S

or R_S =	1
	2 π(C_gd + C_gs) f_T

or R_S =	1
	2 × 3·14 (50 + 5) × 10^–12 × 100 × 10³

or R_S = 28·89 kΩ
Hence alternative (C) is the best option.