I'm trying to set up a transimpedance amplifier reading the response from an avalanche photodiode (Hamamatsu S12572-100P http://www.hamamatsu.com/resources/pdf/ssd/s12572-025_etc_kapd1043e03.pdf) and a low-noise operational amplifier (TI LMV793 http://www.farnell.com/datasheets/1771351.pdf).
The dark current is around 0.15 uA, and the signals I'm expecting to measure correspond to around 0.8 uA current on the APD. My feedback resistor is 1.27 MOhms. However, after building this circuit on a PCB I just get about 0.09V on the output of the amplifier, in a situation where it should saturate, and no variation at all. I've replaced both the APD and the op amp thinking they might be damaged, but the problem persists.
The biasing is being achieved by setting 70V across a 2 KOhm load and connecting a 1 KOhm resistor in series with the APD, as suggested by the datasheet. The breakdown on the APD is 67V, thus I assume the APD is pulling around ~35 mA from the biasing supply, but I don't get any output.
Best Answer
I'm assuming your circuit looks like
simulate this circuit – Schematic created using CircuitLab
and your expectation that "it should saturate" is exactly correct. It IS saturating. The op amp is trying to drive the output below zero, but it cannot since it's a single-supply amplifier.
If you're going to use a TIA you have to use a negative bias to get a positive output.
ETA: Oh yes, and just to make your day - you may well have killed your op amps. Maybe not, since designers have gotten pretty good at protecting chips against overload, but this is pretty extreme. Not as extreme as getting hit by lightning, but that kills most chips, too. You need to check them in a less stressful circuit if you want to reuse them.