I m using LMV794 as amplifier circuit for photodiode BPW34S.In first stage i put 5.6M resistor and 10Pf.The supply voltage is 3.3v.The first stage output is around 1.5-1.7v.In second stage one input is 0.9v dc and other is the output from first stage.I used 6.8k resistor to obtain 2v finally.But my waveform is like spikes.i dunno wat capacitor value sud be put? I need rectangular pulse... pl sumone help how to calculate both feedback resistor and capacitor.The frequency used is 4khz...

 

There's no DC path for the photodiode current. You need a high value resistor from the photodiode's anode to ground.