photodiode noise

I might add, I'm guessing it would be better to cool the photodiode rather than the amp if one had the option, but there is also that gigohm resistor around the amp.

grge

Have a look at some of the astronomy sites. They seem to cool CCD cameras to reduce noise AFIAR.

Wim

Hi Greg

May be this one is your main noise source. Try to cool everyone alone and you will see, wich one you have to cool.

Marte

Yes. The 'simpler' units, have Peltier coolers (often dual stage), giving temperatures like -30C, while the professional units, at extreme, get into things like liquid nitrogen cooling. It is the thermal _signal_ (dark current), that is reduced. Most CCD's, will gain electrons from thermal effects, at a rate proportional to the temperature. This will be specified with a figure like 0.5e/p/s at 0C (an average of 0.5 electrons per pixel, per second at 0C). This signal then (of course) has a 'noise' component itself. Reducing the temperature, reduces the rate at which this signal accrues, and with it the contribution from it's noise component. The typical rate of change, is about a 50% drop in the signal, for every 6 to

7C drop in temperature. The noise, is approximately proportional to the square root of the dark current. So dropping the temperature by (say) 30C from ambient, gives about a twenty fold decrease in the signal, and about a 4.5* decrease in the thermal noise.

Best Wishes

I will get a chance when I build a new project. The camera system has 512 individual channels of amplification and filtering. A little difficult to check there.

greg