Understanding Photodetectors

[lefenzy]

Hi, I need some help understanding the circuit diagram for a photodetector.

If you could go here Text and click the graphs tab, you'll get the circuit diagram. I understand that the photodiode creates a current and you can either measure current or measure voltage across R-load. The battery creates a negative bias which makes it more accurate? I'm not sure about how that works. Also, what is the purpose of the capacitor?

 

[PottedMeat]

Looks to be a diode in the photoconductive mode - a voltage to keep the reverse bias, a resistor for current limiting, and a capacitor as bias filtering ( maybe ):

http://en.wikipedia.org/wiki/Photodiode

More noise in exchange for quicker response time.

 

[Biftheunderstudy]

I would think its a low pass filter to get rid of high frequency laser noise and also make the diode have a decent response time with a time constant given by 1/2*Pi*R*C.

 

[TuxDave]

It's hard for me to guess mainly because I have no clue what the "BNC" is in that schematics.

 

[PottedMeat]

Originally posted by: TuxDave
It's hard for me to guess mainly because I have no clue what the "BNC" is in that schematics.

The bayonet connector?

 

[TuxDave]

Originally posted by: PottedMeat

Originally posted by: TuxDave
It's hard for me to guess mainly because I have no clue what the "BNC" is in that schematics.

The bayonet connector?

The what? (had to go wiki it)

So the bayonet connector connects two things together so why is there three terminals in the schematics?

 

[Biftheunderstudy]

There are only 2 terminals, an internal singnal conductor and a outer grounded connector. That is why there were a few things all connected to it since they are all ground. BNC is the standard interconnect these days in industry/research.

 

[TuxDave]

Originally posted by: Biftheunderstudy
There are only 2 terminals, an internal singnal conductor and a outer grounded connector. That is why there were a few things all connected to it since they are all ground. BNC is the standard interconnect these days in industry/research.

Ah, so the ground connection the to BNC signal is just indicating the outer part of it is grounded. Yeah I don't deal with connecting this to the outside world. Packaging and all that is something that I dealt with once in school and never saw again.