Photodiode Amplifier question

[Ronnie]

hello,

Can anyone explain the theory of operation of the attached circuit, I saw allot of application notes explaining that in this connection there is no voltage across the photo diode- only current, but if there is no voltage across the diode-what produces the current? Also my basic understanding of op amp is that slight voltage between the + and - pin will produce a voltage at the amplifier output. how does this settle with the idea that there is no voltage across the diode?


I also don't have any equations for this circuit.

If anybody can help me I will be grateful.

Thanks

 

[kspalla]

i guess you removed circuit near by, which is essential to understand.

I also guess this is for digital application than analog communication.

Regards,

 

[mtwieg]

A zero bias on the diode can work fine, depending on the diode. Photons striking the diode's depletion region create free electron-hole pairs, which are separated by the built in electric field (which exists even with no external bias voltage). This leads to current at the terminals.

Often a larger negative bias is applied to the diode in order to increase sensitivity and bandwidth, but it's not always necessary.

However, the 1M and 100K resistors in your schematic will only harm performance. The 1M should be shorted, and the 100K should be left open.