Justifying the peak closed loop gain of an op-amp circuit

[ergospherical]

I'm just looking at a Bode plot of log(gain) vs log(frequency) for a an amplifier circuit. I'm trying to figure out whether I'm expecting to see a resonance in the gain at the frequency where I measured one. How could I, in principle, work out theoretically where the peak gain should occur - is this sort of information hidden somewhere in the data sheet? It's not clear to me from the schematics what the open loop gain $A$ or the feedback factor $b$ are (the internal components are not displayed). Thanks.

 

[berkeman]

I'm just looking at a Bode plot of log(gain) vs log(frequency) for a an amplifier circuit. I'm trying to figure out whether I'm expecting to see a resonance in the gain at the frequency where I measured one. How could I, in principle, work out theoretically where the peak gain should occur - is this sort of information hidden somewhere in the data sheet? Thanks.

The Bode plot of open loop gain for most opamps in their datasheets will show flat gain until the first pole ("dominant pole", set by an explicit capacitance), and then a straight rolloff down to the 2nd pole where it decreases even faster.

Can you post an example Bode plot that you're asking about? Most opamps would not have resonances or peaking in their open loop gain plots, in my experience.

 

[berkeman]

Like so:

https://toshiba.semicon-storage.com...-loop-and-closed-loop-gains-of-an-op-amp.html

 

[ergospherical]

I think you're right - at a second glance it doesn't look like a resonance so much as a little bump where the flat gain turns into a straight roll-off. I'll try and have a look for the manufacturer's version of that graph... thanks :)