Hi guys!

I'm working with TIA photoreceivers and I've been encountering some troubles with the frequency response of my device when using Silicon Photodiodes.

Using a modulated laser as input signal, my PRs transfer function decreases from 10 KHz on, and it could be explained easily if the Quantum Efficiency of the device is actually frequency dependant (at least for frequencies higher than 10 KHz, since before it seems constant), but it's something I can't find anywhere.

Thanks in advance.

 

Could simply be the bandwidth is too low for your frequency. The photodiode should have specifications for bandwidth.

 

Thanks for your answer wayneh!

That's the thing, sometimes (I'd say, most of the time) the datasheet only specifies the rise-time of the photodiode as sth I could use to calculate the bandwidth. In my case, the bandwidth of my photodiode (0.35/rise_time) would be sth around 10 MHz, not 10 KHz.

On top of that, the drop of magnitude in the TF does not correspond to the equivalent drop in the phase that I'd expect due to a limited bandwidth (the drop in phase is around 10 MHz).

Since it's a magnitude-related thing, everything points into the Quantum-Efficiency - responsivity direction...

 

You need somebody that knows something. Rules me out.

 

Are you reverse biasing the PD sufficiently to drive the capacitance down?

Here's a real good application note for designing high-speed TIAs (using op amps).
http://www.ti.com/lit/an/sboa122/sboa122.pdf

 

Quantum frequency effects normally occur at very high frequencies. I suspect you have a circuit related problem. Post your circuit diagram.