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.