Why is the roll-off gain of the op amp 6db/double frequency?

乱世煮酒论天下

Why is the roll-off gain of the op amp 6db/double frequency? [Copy link]

How do we deduce that the roll-off gain of a general op amp is 6db/double frequency?

Is the op amp treated as a low-pass filter circuit? If so, the decibel gain formula of the op amp is as follows

lgAu1=10lg（1/（1+jwrc））

lgAu2=10lg(1/1+j2wrc))

Can we get the roll-off gain result of the op amp by comparing formula 1 with formula 2?

maychang

[How do you deduce that the roll-off gain of a general op amp is 6db/double frequency? ]

The capacitive reactance of the capacitor is obtained by dividing the voltage of the resistor.

maychang

[Can we get the roll-off gain of the op amp by comparing equation 1 with equation 2? ]

I don't know what formula 2 is, and the brackets don't match.

gmchen

It is not derived, but designed by the designer intentionally. The purpose is to make the op amp work stably in most cases.

gmchen

Why is it 6dB/octave? Because there is a pole inside the op amp. For a system with a pole, the amplitude above the pole frequency must roll off at 6dB/octave. For a detailed derivation, you can read any circuit theory book.