PD33fsi, an 3.4um peak InAs photodiode, local manufacture.Which device are you using? What temperature are you running it at?
Scattered sunlight would likely be the primary source.what source you are using.
In place it would have to do a reading about 1000 times a second, with absolute values.Also curious if it is an AC or DC measurement you are trying to make.
Well, it would be looking into the background through a tiny hole, so it's either works or not fixable.There's an app note from Hamamatsu that describes two effects, a charge build up at room temperature, and a background noise current due to background light. They recommend limiting the FOV of the photodiode or throwing two pieces of black tape on the front of the diode to reduce background noise current. **broken link removed**
Which turned to be exactly the solution for that part of the problem. Luckily, the op-amp have the feature.it's OP offset voltage converted to current by the low shunt resistance. In the latter case, a thorough offset null adjustment would remove the apparent diode current.
This is all about temperature drift, which in fact can't be exactly distinguished from low frequency noise. The thermal drift of the OP as such isn't severe, it mainly becomes a problem in combination with the low shunt resistance. Just as an example, the nominal shunt resistance at 20°C results in a DC gain of about 2500 in your circuit. The most severe temperature effect is caused by the shunt resistance's temperature dependency, even with the rather low AD820 offset voltage.The noise is certainly thermal - just breathing lightly into the box (~0.1 m³) drops the reading off the scale, and i can't imagine the PD heating up as much as a tenth of a degree from that.
That happens in case of target Rf=2.2GΩ, not the testing 1MΩ shown in the diagrams above for the earlier issue.but you got me with the "shoots off scale" comment. If the amplifier is pegging out at 5V (~5 uA of current) with a small temperature change, then I must be missing something. If we were relying on the noise gain transfer function of the amplifier and the input voltage noise, this would mean that the input voltage noise is around 2 mV, which is about 15k times the value I would expect you to see. Unless there's that much IR in the heat from your breath.
Good to know. 2.2G/400 equals 5.5*10e6 DC gain, the OP is operating more or less open loop. This effectively can't work.That happens in case of target Rf=2.2GΩ, not the testing 1MΩ shown in the diagrams above for the earlier issue.
The drifting is in ±2nA range with the box left alone.
I don't really understand how that could work.I would recommend you step back to the 1 M resistor, or even 500k, and use two stages, one transimpedance, one voltage gain.
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