what is the use of using opamp in photodiode circuit?

[liu93083]

Dear everyone,
Sorry to ask such simple question. My question is in designing the circuit for light detection, photodiode is used, what is the purpose of using opamp beside working as an amplifier to amplify the small signal?what is the theory behind it?can you explain for me?thank you very much..

 

[biomedicalEng]

Hello liu93083,

Photodiode generates a small current proportional to amount of light which is directed at it's face!

This current is very small, usually in range of micro amperes, so if we want to show amount of light in a screen whether digitally or even analog then we have to first change this small current to voltage and then amplify it to obtain the best resolution for showing it in a screen.

For example if you want to digitize the signal of photodiode to use it in a microcontroller based circuit or transfer it to computer, you have to amplify the signal up to the maximum input range of your A/D to obtain the maximum resolution and minimize the error of quantization.

A simple Op-Amp, if you use it in an invertive topology can do the most of this job for you!

I hope the above helped you to understand the theory of Photodiode's signal conditioning circuit.

Best regards,

Kasra Ravanbakhsh

email: kasra_ravanbakhsh@hotmail.com

 

[liu93083]

thank you very much for your help ar..haha..very understand..