If an npn transistor (with C = 0.3 pF) has a unity gain

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If an npn transistor (with C = 0.3 pF) has a unity gain cut-off frequency f_T of 400 MHz at a d.c. bias current I_c = 1 mA, then value of its C is approximately (V_T = 26 mV)

1. 15
2. 30
3. 50
4. 96

Correct Option: A

Given : C = 0.3 pF

∴ g_m =	\|I_C\|(mA)	=	1	A/V
	26 mV		26

⇒ C =	g_m	=	1 / 26	= 15 pF
	2π f_T		2π × 4 × 10⁸