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'Overclocking' LCDs. Any ill effects?

Discussion in 'Electronic Design' started by Al Borowski, Aug 27, 2004.

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  1. Al Borowski

    Al Borowski Guest

    Hi all,

    I'm working on a device with a low resolution, monochrome LCD (it
    appears to be "4-bit dual scan display mode (STN)"). I'm trying to get
    greyscale working properly at the moment. The LCD controller has
    hardware greyscale built in, but enabling it shows a fair amount of
    flicker in some shades, even with hardware dithering.

    If I increase the clock to the LCD controller by about 40%, this flicker
    basically disappears. Will problems will this cause in the long term?
    Could it damage the LCD?


  2. Al Borowski

    Al Borowski Guest

    I should mention: This is for a device which I have very little
    technical data. While the SoC is standard, the LCD isn't, and I know
    nothing about it.

    So, just as an educated guess, am I asking for trouble by increasing the
    clock rate over what the manufacturer is currently using?


  3. Bill Sloman

    Bill Sloman Guest

    Probably not, in the sense of permanently damaging anything. The clock
    rate of an LCD is (or used to be - it is a few years since I knew much
    about them) limited by the speed at which the molecules in the liquid
    crystal line themselves up with the changed electric field.

    The only risk you might be running is that the display will stop
    following the controlling field at low temperatures, when the
    viscosity of the liquid crystal material is higher.

    Higher clock rates do imply more capacitative current flowing through
    the tin oxide connections on the glass enclosing the liquid, but this
    ought not to be significant.

    Just my educated guess ...
  4. Tim Shoppa

    Tim Shoppa Guest

    IMHO if you see it flickering in grayscale pixels, it's because the
    dithering frequency is beating with the multiplexing frequency. This is a
    design flaw IMHO, the two clocks should be chosen to never fall close
    to each other (or the important divided-down freqs).
    If you see it flickering because of beating between the two clock rates,
    then the flickering pixels may have some short-term (well, over the time
    between flickers) DC bias on them, which
    is a not-so-good thing for LCD's. If you get rid of the flickering by tweaking
    clocks, then you're probably getting rid of the DC bias, and that's a good

  5. Al Borowski

    Al Borowski Guest

    thanks for the replies.


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