Hi team,
if I am going to sample 220V/50Hz voltage signal, could I directly using a differential circuit with gain around 0.003 and have a 1.65V as bias voltage for the non-inverting port. The 0.1V resolution is okay.
If I have this 0.003 gain circuit, what spec of amplifier should I focus most?
I think input offset could be ignored, since the gain is so small, as well as the input bias current.
Right now I am thinking of the input voltage density may cause some problem here because of the 6.5MHz GBW of opa4374. Even though the gain is 0.003, the noise gain is 1+0.003 here. And the En_in=en_in*square[1.57*fc], fc here could be 6.5MHz*1.003 also around 6.5MHz, then we have En_in=15nV*square[1.57*6.5M]=~0.048mV on the input, and we have output En=0.048*1.003=0.048mV. And it seems okay with the resolution since I have LSB= 0.1*0.003=3mV. Could you please help to check if my calculation is correct?
Besides the noise density, do you have other concerns for this circuit?
James