Photodiode output emulation

[elki]

Does anyone know if there is a simple RC circuit that could emulate the current output of a photodiode? I wonder if it is possible to achieve starting from a function generator, pass it through an RC circuit, and then using the obtained current pulse as input to a transimpedance amplifier. Any suggestions are appreciated.

[tggzzz]

Does anyone know if there is a simple RC circuit that could emulate the current output of a photodiode? I wonder if it is possible to achieve starting from a function generator, pass it through an RC circuit, and then using the obtained current pulse as input to a transimpedance amplifier. Any suggestions are appreciated.

In the late 70s I did just that: function generator->resistor->transimpedance amplifier. Worked just fine for my purposes, i.e. measuring the amplitude of a 1pW to 50µW optical signal.

No idea whether or not it would work for your purposes depends on .... your purposes, oddly enough.

[KrudyZ]

This depends very much on how accurate you want to model the PD behavior.
The simplest would be to use a function generator and a resistor.
This works if your PD is zero voltage biased and your circuit can work with either side of the PD being at Earth ground as that's where your function generator ground will usually be at.
You are of course missing quite a few secondary effects of the PD, such as junction capacitance and non-linear behavior if voltage develops due to the TIA not maintaining the zero bias (during transients).
The latter also affects the accuracy of the current. To minimize the effect, you should set the output voltage of the function generator as high as possible and then adjust for the desired current by picking larger resistor values (ideal current sources have infinite source resistance and infinite compliance voltage).
That being said there are many PD configurations where what I described would not work, so we would need to see your schematics.

[elki]

Thanks a lot. I am using a photodiode that is voltage biased - cathode to positive power supply, anode to the input of the amplifier. If I understand correctly, the general approach would be just pass the pulse from function generator through a resistor to achieve the needed current.

[tggzzz]

This depends very much on how accurate you want to model the PD behavior.
The simplest would be to use a function generator and a resistor.
This works if your PD is zero voltage biased and your circuit can work with either side of the PD being at Earth ground as that's where your function generator ground will usually be at.

It works when simulating reverse-biassed PIN diodes, provided the input of the transimpedance amplifier is at (virtual) ground level.

You are of course missing quite a few secondary effects of the PD, such as junction capacitance and non-linear behavior if voltage develops due to the TIA not maintaining the zero bias (during transients).
The latter also affects the accuracy of the current. To minimize the effect, you should set the output voltage of the function generator as high as possible and then adjust for the desired current by picking larger resistor values (ideal current sources have infinite source resistance and infinite compliance voltage).
That being said there are many PD configurations where what I described would not work, so we would need to see your schematics.

Yup.

The frequency and transient response fidelity are key requirements in the OP's use case.