Probably not an issue, but the first stage amp bw is quite a bit lower than intended. OpAmp input capacitance? IIRC some feedback capacitance is needed to keep the OpAmp stable with a large feedback resistor, but the capacitor we currently have gives a 3dB point (according to LTSPice) of approx 75kHz.
To do (if anyone can be bothered) play with the simulation and do a transfer function/noise analysis and find a capacitor value that gives approx the BW we want without excessive ringing.
@pathfinder49 this probably explains why the RMS noise we measure is a little lower than we expect. 6.4mV/sqrt(1.57*75kHz)/2000=9nV/rtHz which is pretty close to the model. To get better agreement than that, we'd have to step through the circuit carefully, checking bandwidths and gains at various stages, but I'm pretty happy that there is nothing grossly wrong and everything seems to work as expected so far, which is good!
Probably not an issue, but the first stage amp bw is quite a bit lower than intended. OpAmp input capacitance? IIRC some feedback capacitance is needed to keep the OpAmp stable with a large feedback resistor, but the capacitor we currently have gives a 3dB point (according to LTSPice) of approx 75kHz.
To do (if anyone can be bothered) play with the simulation and do a transfer function/noise analysis and find a capacitor value that gives approx the BW we want without excessive ringing.
@pathfinder49 this probably explains why the RMS noise we measure is a little lower than we expect.
6.4mV/sqrt(1.57*75kHz)/2000=9nV/rtHzwhich is pretty close to the model. To get better agreement than that, we'd have to step through the circuit carefully, checking bandwidths and gains at various stages, but I'm pretty happy that there is nothing grossly wrong and everything seems to work as expected so far, which is good!