Hi,
I am confused and I am sure I am getting something wrong. I have a very basic transimpdance circuit as shown in the picture. The input signal comes from a photodiode and has a max. frequency of 10kHz with an amplitude of approx. 0.1uA.
==> Based on those numbers, I thought there is no need to take a high-speed OpAmp. Everything with a GBP around 200kHz and a SR around 0,005 V/uS should be okay.
When I started to do the calculation for the compensation capacity I came across the formular: Cf=SQRT(CI/(2*pi*Rf*fc)) <-- True, as long as Cf >> CI
fc ist the unity gain cross-over frequency of the OpAmp (I assume, instead I can also take for this the GBP value).
==> Well ,,, the larger fc, the smaller Cf. Since I want to have Cf as small as possible, I should go with an OpAmp as fast as possible.
To go now with an OpAmp as fast as possible feels somehow wrong and I am wondering: if I take a very fast OpAmp to get the advantage of a low Cf, what would be the disadvantages?