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SN75LVDS82 LCD image distortion, sync signal inversion

George Biner12801
Intellectual 2395 points
Other Parts Discussed in Thread: SN75LVDS82, SN65LVDS94

Hello:  (I am posting this for a customer -- G Biner, TI AFA Los Angeles)

      ... we are using the SN75LVDS82 IC to convert a 18bit LVDS video signal to a TTL signal to drive a Sharp 640x480 10.4 inch LCD. What I am seeing is some distortion on the LCD screen, as seen on the picture attached. I am also seeing that the VSYNC and HSYNC signal are inverted to what I expected, as seen on the attached document.

Is there anything else I can do to try to fix the distortion?

Is there any white papers that will help it his matter?

Is there another IC that is better suited for my application?

 

26207-3-SCH_REV-_2011-5-2.zip
  • 0
    TI__Mastermind 20985 points

    What pixel clock are you running at? (this is of course based on refresh rate and blanking)

    The standard clock for 640x480@60Hz is 25.175MHz.  If you are running at that, that could be your problem, as the LVDS82 is spec'd for 31-68MHz.  The LVDS94 is pin-compatible and supports 20-68MHz.

    Thanks,
    RE

  • 0 in reply to RE
    Prodigy 20 points

     I am starting a new LVDS-toTTL design for LCD display and I was planning on using the 75LVDS82.

      Would the 65LVDS94 be a better part to use with its extended frequency range?

     

       Thanks

       RG

  • 0 in reply to Ralph Garvin
    TI__Genius 16430 points

    If you are running at the lower pixel frequency, then yes, I would recommend the SN65LVDS94.  Of course the SN75LVDS82 has a higher upper end frequency, so it depends on the pixel clock range you need to support.  The above example is a relatively low pixel frequency, so the LVDS94 would be the best fiot for that application. 

  • 0 in reply to Ralph Garvin
    TI__Mastermind 20985 points

    Ralph, if your pixel frequency is within the supported range of both the LVDS82 and LVDS94, then either device will equally work.

    LVDS94  -  4:28, 20-68MHz, -40C to 85C
    LVDS82  -  4:28, 31-68MHz, 0C to 70C

    Thanks,
    RE