Question

How does the physical characteristic of semiconductor account for the increase in frequency of op-amps?

(a) Transistor values

(b) Junction capacitance

(c) Dopant concentration

(d) None of the mentioned

This question was addressed to me by my college director while I was bunking the class.

My question comes from High Frequency Op-Amp Equivalent Circuit topic in section Operational Amplifier Applications of Linear Integrated Circuits

Answer 1

The accurate choice is (b) Junction capacitance

Grasp the essence with: Op-amps are composed of BJTs and FETs which contain junction capacitors. These junction capacitors are very small and take finite values at higher frequency. So, when the reactances of these capacitors decrease, the frequency increases.