Modification of TAMA PD (2)

As reported in elog2437, I modified TAMA PD based on Pierre's design. But since we don't have an exact capacitor of design value (the capacitor in parallel with the photodiode, we call it Cpp), we don't have the resonant peak at the design frequency.

As mentioned in elog2437, Cpp's design value is 160pF while the one in place is 150pF. So I tried to put a capacitor with 7pF and 10pF in parallel with the 150pF Cpp. However, after putting them, I found the noise spectrum has changed from the measurement on 20210405. The noise spectrum measurement is shown in the attached figure.

I will investigate more why this happens. In the worst case, I will solder this circuit again with a new op-amp. Then check if the noise spectrum becomes reasonable.