Electronic Devices - Operational Amplifiers - Discussion

There is a relationship between open-loop gain and cutoff frequency. Typically op-amps have a 6dB/octave or 20dB/decade rate for every increase or decrease in frequency. The reason why we employ closed-loop gains? To avoid the large change in gain due to a large change in frequency causing different output voltages at different frequencies.

In this problem, I think that because the frequency only dropped by 10 Hz it would be pretty much negligible since for the frequency to have a greater impact it needs to at least double/half its frequency or even multiply or divide by 10.

Example Problem:

An op-amp has an open-loop gain of 75, 000 and a cutoff frequency of 100 Hz. At 1 kHz the open-loop gain is down by?

Answer : 20dB.

Source: Operational Amplifiers. Electronic Devices " Electron Flow Version and Conventional Current Version 8th Edition by Thomas L. Floyd.

The answer is 20 dB because the frequency increased tenfold therefore the gain would decrease by 20dB following the rate of -20dB/decade.

There is no relationship between an open loop gain A0 and the signal frequency f. Therefore the gain will always be constant as long as the Op-amp is in its open loop mode.

Op-amp will amplify the any frequency signal with a constant output voltage.

Upto cut-off frequency it is constant, then it changes such that gain bandwidth product is constant.

Open loop condition op amp gain is infinite at any frequency.

There is no change i.e.its not dependent on frequency change.