# Why does op-amps gain decrease at high frequency...

by PianoDentist
Tags: decrease, frequency, gain, opamps
 P: 951 Actually I asked this question my professor not so long ago. You see op amps can be internally frequency compensated and not internally frequency compensated. The one that ARE internally compensated have a capacitor inside. Now why they are compensated, and what are they compensating for? Normally op amps go beyond 1MHz frequency, but after this, they are not very stable. Meaning, it can go into oscillation very easily. This can lead into a thing called "ringing". You might want to google that. But if you put that small capacitor inside, you cut off frequencies over 1MHz, effectively. Which makes it a low pass filter in a sense. But even if you don't have that capacitor, your frequencies will go down after a certain frequency, because of parasitic capacities. [between two transistors, diodes, etc. you get the idea :D] All in all, frequencies go down because of capacitors, capacitors are low-pass filters, because their reactance: $X_c =\frac{1}{\omega C}$ $\omega -> \infty$ $X_c -> 0$.