Hi,
I have an amplifier circuit build using TS9222 opamp, with gain = 40 and external EMI filter on the inputs. I want to understand the affect of filter capacitors at the input of opamp on stability of circuit.
I have simulated the circuit using LTSPICE and file is attached.
Observations:
- Pole in the feedback path is at ~366kHz
- phase margin is about 67 deg,
- And to counter the pole due to CL, output resistor is added outside the loop to add a pole-zero pair at ~56kHz
- BW of circuit is ~100KHz
Even though the pole in the feedback path is at 366KHz but the phase change starts as usual decade before. And as per bode plot or ROC method I see that phase change started before 100KHz (which is bandwidth of circuit). Even though phase margin is 67deg, do I need to add resistors on inv and non inv terminals. I referred one app note which says that I should but I am not getting the math behind it. (below is the link)
https://international.electronica-azi.ro/2017/05/09/using-op-amps-to-reduce-near-field-emi-on-pcbs/
Please help me to understand the issue and let me know if further information is required
