Hi,
I have LPF built using OPA4188 in differential to single ended configuration.
Gain = 1.3 (RF = 133k, Rin = 100k, CF = 220p)
Now there is an external RC filter 1kohm and 1nF at the output, may be to reduce the overall noise profile.
My understanding from the AC analysis using break the loop method.
1. Phase margin we should check at the output of opamp where loop is closed, not at the external RC filter output., please confirm
2. External RC will not affect the loading of opamp, hence it wont contribute toward instability, is that correct.
3. Phase margin at the o/p of opamp is ~84 deg, which means circuit is stable
4. External RC will add to the delay of o/p signal by its time constant and will not affect the loading of opamp. The external C can be increased up to acceptable delay without loading the opamp, is that right?
Please refer below circuit and graphs
Thanks in advance!
Regards,
Sunney