Hey all,

I have another question regarding my project. Hopefully some others will find this useful as well.

My design project requires that I amplify a signal from a photodiode in the range of 0.5 picoamps (pA). I was considering using a transimpedance (TIA) amplifier before but after doing a noise analysis it seems like the three noise sources of the design (resistor thermal noise, voltage noise, and current noise) all far exceed the signal in every case.

Is it possible to amplify a picoamp signal using a TIA? or is my analysis wrong?

I was looking at the LTC6244 (very low noise current), LT1028 (low noise voltage), and LT6200-10 (very low noise voltage and wide bandwidth). They are the lowest current and voltage noise op amps I could find and they're still in the nV/rootHz and pA/rootHz range which seems like too much.

I can provide more info if needed. Thanks for any and all help!

 

What is the bandwidth of the signal?

 

I was hoping to have the signal be at least 1kHz and as high as 100kHz but was waiting to see the analysis to get a better idea of how high I could push the frequency. It seems that not even 0.01Hz would give me enough gain to get above the noise floor...

 

Sorry to say but it does appear that your signal is below the level that can be practically amplified at those frequencies.

 

I am just thinking out loud here. Will you be able to use a lock-in amplifier aproach http://en.wikipedia.org/wiki/Lock-in_amplifier

 

I am just thinking out loud here. Will you be able to use a lock-in amplifier aproach http://en.wikipedia.org/wiki/Lock-in_amplifier

That might work if you have a single fixed frequency signal.