hy,
i wan to make a 5 Mbps digital photoreciever for white light, i bought bpw34 as photodiode but i am no able to get an output for higher freqencies, the circuit which i made works for nearly 50 khz but after that i doesn't. can some body suggest any thing.

 

can some body suggest any thing.

Yes: post a complete, accurate schematic diagram of your circuit, showing all components and connections. Until you do that, no one can even guess what your problem might be.

 

hy,
i wan to make a 5 Mbps digital photoreciever for white light, i bought bpw34 as photodiode but i am no able to get an output for higher freqencies, the circuit which i made works for nearly 50 khz but after that i doesn't. can some body suggest any thing.

Opto devices are notoriously slow - it might still be possible to obtain fiber optic discrete PD components.

Photo current is very small - that means large resistances and vulnerability to parasitic capacitance.

 

The accepted approach is to connect the photodoide to the input of a transimpedance amplifier.



The bpw34's high capacitance will increase noise and make 5 MHz harder to reach, so use the maximum reverse bias available to you.

What is your current circuit?

 

The accepted approach is to connect the photodoide to the input of a transimpedance amplifier.

View attachment 122861

The bpw34's high capacitance will increase noise and make 5 MHz harder to reach, so use the maximum reverse bias available to you.

What is your current circuit?

AFAICR: The BPW34 was a popular device in TV remote front panel units - I'm sure there must be faster devices out there.

Hamamatsu is a good place to look, even if you don't intend ordering their parts. They have a decent selection of application notes and example circuits - and most likely; advice on optimising frequency response.

 

hy,
i wan to make a 5 Mbps digital photoreciever for white light, i bought bpw34 as photodiode but i am no able to get an output for higher freqencies, the circuit which i made works for nearly 50 khz but after that i doesn't. can some body suggest any thing.

Are the photodiode and receiver coupled through a fiber-optic cable or is the receiver exposed to room light. If the receiver sees room light then using white light will make your problem a lot harder since ambient light can not be easily filtered your of your signal.

 

I have never thought about what type of photo detectors are used for high frequencies so I thought looking for a schematic of a GBIC (Used for fibre optic communications to convert from electrical signals to optical signals.) might give some information. I could not find a schematic but I found that some use avalanche photodiodes so that information may help the TS to find a suitable device.

Les.