This circuit just doesn't do what it says it should do. Need to inject waveform at FP1test and probe at each stage. Then compare against LISO model. If something is busted we need to know at which point we are getting this extra zero in the response. There is a lot not great about this particular board but it should just have a flat response above 488 Hz.
I don't think AD602 is in the LISO library. Should be able to add it as some kind of hack op amp with fixed gain, 100nV/rtHz of noise (with 10 Hz corner) and some appropriate current noise with corner of 1 kHz. Maybe check the AD602 datasheet.
We need to clean this up this week or do something drastic like replacing electronics with minicircuits or removing MC altogether. For now we need to move onto solving bigger problems like the ISS, thermal stability, PLL readout noise
Also, on the ISS do you now have a prototype working servo circuit and photodetector?
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We earlier found that the intended LPF isn't working so we thought of this external LPF idea. So I checked today the PZT input with LCR meter to see if it is in good condition or not. It gave C = 406.4nF, L=60.6 mH and R = 31kOhm. From the spec sheet, the C value looks 20% below the rated value but the spec value has uncertainity of +- 15%, so maybe our PZT is still good.
With the measured values, I calculated again (fitted using LISO) what good value of output resistor would make it closest to 10Hz pole. The value came out to be 37.1k Ohm. I have replaced this output resistor with 39k Ohm now. I'm attaching updated schematic for future reference.
keywords for search: PMC North Driver Board Schematic
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should probably put back the 30k resistor. It makes a low pass filter with the PZT capacitance (not the cable capacitance). This is to prevent shorting of the HV drive.
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