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photodiode noise

Discussion in 'Electronic Design' started by GregS, Feb 7, 2007.

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  1. GregS

    GregS Guest

    I have been thinking of try to cool down some op-amps and see how
    much this helps noise. Some of the lowered noise amps
    tend also to get hotter. Anybody try this?

    l also work with some Hamamatsu photodiode cameras. These things
    have bias circuits which also tend to have more noise with biasing,
    however the newer cameras have a new bias circuit suppy thats putting
    a 440 hz noise spike. I wanted to try cooling this camera, maybe
    also get rid of the bias circuit. A little scary working wwith $15K stuff.

    greg
     
  2. GregS

    GregS Guest

    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
     
  3. Wim Ton

    Wim Ton Guest

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

    Wim
     
  4. 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
     
  5. 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
     
  6. GregS

    GregS Guest

    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
     
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