Question

Given that β=200, input frequency is f = 20Mhz and short circuit current gain is A = 100. What is the unity gain frequency?

(a) 2308 Mhz

(b) 2000 Mhz

(c) 2508 Mhz

(d) 3000 Mhz

I have been asked this question by my college professor while I was bunking the class.

My doubt stems from High Frequency Response in division Transistor Frequency Response of Analog Circuits

Answer 1

Right choice is (a) 2308 Mhz

To explain: A = \(\frac{β}{\sqrt{1+(20Mhz/fβ)^2}}\)

1 + (20/f)^2 = 4

20/f = 1.732

fβ = 11.54 Mhz

Unity gain frequency = βfβ = 200 x 11.54Mhz = 2308 Mhz.