I am working with a OPA197QDGKRQ1 and am seeing good results with 1MOhm resistors in Tina TI. Are there restrictions for high impedance with the OPA197?
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The selection of the Feedback R (and hence gain R) gets into several concerns -
2. phase margin as there is an added loop pole back to the V- node cap
Could you include your TINA file, attaching it using the the little paperclip symbol across the top here,
It is unnecessary to place 1Mohm resistor in OPA197 circuit. I changed from 1MOhm to 100kOhm, and you may still able to lower slightly. You will increase the unwanted thermal noises of the op amp circuit, see the attached plot.
I think that R31 = 100kOhm is your floating ground simulation?
Hey Zachary, thanks for the TINA file, makes it easy to check noise, a quick way to expose instability - yep the spike is at the output of the first stage, those 1Mohm R's are creating a low pole in the feedback network with the input C,
Here I changed those to 10kohm and reran, that took care of it,