THS8200: The VGA picture output by THS8200 is blurry

Part Number: THS8200

The VGA picture output by THS8200 is blurry. It seams that the bandwidth and sharpness of the signal is very limmited. Therefore the legibility of the HDMI output is much better than the VGA output. Is there any technique to impove the legibility of the VGA output?

8 Replies

  • The THS should provide a sharp image up to UXGA resolutions.

    What is your display resolution? What digital input format (444, 420, RGB, YUV) ?

    What external filtering do you have?

    Can you share your schematics?

    BR,

    Steve

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  • In reply to Steve Clynes:

    The resolution is 1280*720. The input format is YUV 422.
    When we use VGA output, the horizontal direction is blurry, while the vertical direction is ok.
    We removed ferrite bead, the output seams better, while it's still blurry. I think we didn't use other external filters.
    About schematics, I'm applying for the approval to send you schematics.
  • In reply to Steve Clynes:

    I can't find your email address. Could you kindly send me a email to chen.juneric@zte.comm.cn? I send you the schematics.
  • In reply to Eric Chen95:

    OK, the first issue you will have is that 422 is inherently decimated in the color domain so colors will look blurred.

    I assume you are trying to display text/computer graphics etc... and not 'video' i.e. cameras etc...?

    As a test can you display pure monochrome to see if the blurry image is present with that since the luma channel is not decimated with 422?

    Bottom line, you will never get a sharp color display using 422 formats.

    BR,

    Steve

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  • In reply to Steve Clynes:

    We are using text/computer graphics, and we tryed pure monochrome display, the blurry is the same.
    BTW, the HDMI output of the same 422 graphics is not blurred.
    Thanks for your support.
  • In reply to Eric Chen95:

    422 will never be as sharp as 444 for color images.

    Have you executed the monitor's "auto phase alignment" ? All analog monitors have an option somewhere to adjust the analog ADC sample point to ensure correct sampling phase alignment. If this is not performed then the edges can 'shimmer' due to sampling the analog signal close to the transition edges.

    Are you using good quality VGA cables? The cables can have a huge impact on image quality, especially if they are not correctly impedance matched, causing reflections and hence 'shadowing'.

    BR,
    Steve

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  • In reply to Steve Clynes:

    I've tried "auto phase alignment", but the burr have not improved.
    I've switched VGA cables, using the best quality cables I can find. The burr was still there.
  • In reply to Eric Chen95:

    OK, please send me your schematics and layout, sclynes@ti.com

    BR,
    Steve

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