You should be able to see in a simulation which real OP parameters have the greatest impact.
I guess, low gain will be a problem.
Do u mean replacing the op-amp (the error amplifier) with the differential one stage amp??A simple differential one-stage amp with constant current source and diode connection load should do. No stability problem.
Do u mean replacing the op-amp (the error amplifier) with the differential one stage amp??
Because i read about some CMFB architectures (check the images for examples)
View attachment 118988
The op amp with the ideal vcvs in the CMFB circuit still affects the Sigma Delta ADC performance greatly!!
I'm not sure if your CMFB circuit works in the right direction
Your diffstbprobes look like (non-inverting) buffers, but - if they work like iprobes - they might have a large output impedance
I'm not sure if your CMFB circuit works in the right direction
Are you sure that the CMFB part of the opAmp is the culprit for the SNR degradation?
Did you try with a LF low pass filter (e.g. a cap from the resistors' common connection point to GND), if this cures the degradation?
Did you try with a LF low pass filter (e.g. a cap from the resistors' common connection point to GND), if this cures the degradation?
Do u mean to compensate the CMFB detector? (i.e : add capacitors in parallel with the R_CMFB?)
Your Bode plots look quite well; I can't find any hint for so much SNR degradation.Ok, i think at this point it'd be better if i provide the whole op-amp plots
Here are the modified schematic along with the new bode plots, it looks the same.
So it's clear: not the CMFB part is the culprit, but the opAmp itself (in comparison to an ideal opAmp). Or did you perhaps change anything else, additionally?
What's the value of the feedback capacitors, in comparison to the inherent MOSFET caps (which do not exist for ideal cells)?
The feedback capacitor = 1pF
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