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Increasing Sensitivity of CMOS Image Sensor.

Discussion in 'Electronic Components' started by david cowan, Apr 5, 2005.

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  1. david cowan

    david cowan Guest

    Hi,

    I'm engaged in a low light level application and I'm looking to
    increase the sensitivity of an image sensor by:
    1. Slowing the clock radically to allow more charge to accumulate.
    2. Obtaining a direct ANALOGUE signal from the sensor to allow me to
    digitise it with much higher resolution.

    In principal these devices are incredibly sensitive but unfortunately
    (for me )the tend to be aimed at high speed applications. I need only
    moderate resolution.

    Any thoughts or anyone know of such a device???

    Thanks again,

    David Cowan
     
  2. On 5 Apr 2005 02:55:25 -0700, the renowned
    You might want to look at what astronomers (including amateur
    astronomers) do with CCD and other image sensors. I think cooling the
    sensor is part of it.


    Best regards,
    Spehro Pefhany
     
  3. Remember that the 'point' of CMOS sensors, compared to CCD's, is that the
    complete camera can be built much more cheaply because major parts of the
    electronics can be included in the CMOS chip. Hence it is rare for them to
    provide access to the analogue signals. Also the presence of these
    components increases the thermal noise inside the chip.
    Realistically, what you want to do, is easier to do with a CCD. The Sony
    CCD's, are 'favoured', because they have some of the lowest dark current
    levels for any chip. Refrigerate the chip, and you can integrate the
    signal for minutes (hours!...).
    The cheapest 'mass production' camera on the market of this sort, is the
    Meade DSI. This has a 16bit ADC, instead of the normal webcam 8/10bit
    unit, and will accept exposure times of several minutes if required. It is
    limited by the fact that the CCD is not directly coooled, so thermal noise
    on the chip, builds relatively quickly. However for exposures up to a few
    minutes, it is the cheapest solution.
    Going slightly 'up market', Starlight Express in the UK, do a number of
    astronomical cameras based on the larger versions of this chip, and some
    industrial cameras based on the same chassis. These use unregulated
    Peltier cooling to keep the thermal noise better controlled. Some of the
    mono models o these have quantum efficiencies well over 60%. SBIG, do
    cameras based on the Kodak CCD's (which at room temperature, exhibit more
    dark current than the Sony CCD's), with multi-stage Peltier coolers, which
    allow the chips to be taken to around 45C below the ambient, and
    temperature regulated. Some models of their cameras, reach QE levels over
    85%, across quite a large piece of the visible spectrum, and are only
    bettered by rear illuminated CCD's costing vastly more.
    Look at the DSI. It may well be useable, if not the CCD is readily
    available, and sounds as if it might be usable as the basis of such a
    unit.

    Best Wishes
     
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