Measurements of 19+20kHz IMD of various opamps at gain 40dB

[AnalogSteph]

BTW the uber-guru of all hydrophone designers called me personally at my desk to tell me these common mode capacitance effects were nonsense and didn't exist.

That's funny. To be fair, I assume the normal signal levels encountered in hydrophone applications are substantially lower than those needed to make nonlinear input capacitance a major issue, so he may just never have seen it. You'd rarely be shooting for both sub-µV noise and +20 dBu signal levels (like Samuel Groner was testing at) at the same time.

 

[scott wurcer]

That's funny. To be fair, I assume the normal signal levels encountered in hydrophone applications are substantially lower than those needed to make nonlinear input capacitance a major issue, so he may just never have seen it. You'd rarely be shooting for both sub-µV noise and +20 dBu signal levels (like Samuel Groner was testing at) at the same time.

What bothered him the most was the concept of induced gate current noise, junction capacitance has a sheet resistance associated with one or both "plates" and this is a source of noise.

 

[AnalogSteph]

What bothered him the most was the concept of induced gate current noise, junction capacitance has a sheet resistance associated with one or both "plates" and this is a source of noise.

Mind = blown.
So you say the finite conductance of capacitor "plates" is a noise source?
I'll have to chew on that for a while.

 

[scott wurcer]

Mind = blown.
So you say the finite conductance of capacitor "plates" is a noise source?
I'll have to chew on that for a while.

Not much to chew on, a complete capacitor model has a series or parallel resistance that represents all the losses in the system, DA, simple series resistance, etc. These loses are in general all heat which means they have a statistical noise associated with them.

 

[John Dyson]

Here is an interesting document with lots of Opamp distortion measurements, also considering source resistance, dynamic effects, etc. Too bad that it is over 10yrs old, but maybe still somewhat useful:
https://www.nanovolt.ch/resources/ic_opamps/pdf/opamp_distortion.pdf