Bandpass transimpenance amp simulation with analog switch

I have a transimpedance amplifier circuit for a photodiode. The circuit is below.




There are other parts in this circuit as well. There is the photodiode, analog switch and another non-inverting gain stage that has a digital pot on the feedback resistor.

The photodiode model is below:




The Analog switch with input and output capacitance, series resistance and on leakage current is below:
Switch P# = SN74LVC1G66DCKR




Gain stage with digital pot is below. Digital pot is circled in red:
Digital Pot P# is MCP4011-103E/SN






Here is the simulation parameters of the photodiode current source:





Here is the output of the simulation:








Questions:
1) If I put a phase plot to the output, it looks like the circuit is unstable since the phase starts at -180deg and there is gain greater than 1 when it goes below -180. Is this circuit really unstable or am I reading it wrong?




2) I want to add a high pass filter to the design to filter out low frequencies. I am only interested in pulses between 7uS and 20uS. Where would this best be achieved? Before or after the 2nd gain stage? I would be ok with a -3db point at 10kHz on the low end and a -3db at 1MHz on the high end.

3) Am I modeling the analog switch correctly?



ADIsimPE Simulation file is attached.

Stability will be analyzed in loop in loop gain frequency response. The diagram doesn't seem to show the loop gain. How is it generated?

The pulse response suggests a stable circuit with sufficient phase margin.

It is generated by ADIsim with the phase probe. How it generates the graph I am not sure. I did post this question on the Analog Devices Forum hoping I would get an answer for that information. I don't see any settings or configuration on the probe that could effect this. The pulse response does seem to be a critically damped and stable.

I'll post that question by itself instead of the other 2 I asked here since it's really a software usage specific question.

- - - Updated - - -

To clarify, the green curve is the gain in dB and the red is the phase.

Hi,

The transimpedance amplifier acts as inverting amplifier, for sure it shows 180° at DC.
But this doesn't mean it is unstable.

Klaus

So the TIA does -180, and the 2nd amp is non-inverting. So does that mean a phase shift of -360 is where I look for gain margin?

Here is a zoomed image of when the phase crosses -360deg.



When phase is -360deg the gain is around 15dB.