High Speed Laser Receiver

[asimkumar]

i am designing a laser receiver for detecting a rotating laser( less than 1us pulse at 600meter), now am using reverse biased photo diodes as it gives highest speed due to low capacitance, but
why most of the good companies in this field uses photo diode without any biasing?

 

[keith1200rs]

A 1us pulse isn't high speed. I have designed quite a few high speed laser receivers and they always have reverse biased photodiodes. Where do you find the opposite to be true?

Keith

 

[asimkumar]

Thanks Keith for response

i have seen these in some patents , where they have used photodiodes with zero bias.
www.google.com/patents/US6750953
www.google.com/patents/US5886776

 

[keith1200rs]

I guess it depends on what you consider to be high speed. However, even at low speed the signal to noise ratio can suffer due to high photodiode capacitance which can be reduced by increasing the reverse bias. Some application notes here may be useful

**broken link removed**
**broken link removed**

A lot of my circuits are for laser rangefinders where pulses are 20ns to 40ns and so speed is important. Normally I am choosing the smallest photodiodes to get the lowest capacitance as well as reverse biasing them.

Keith.