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THS7372: VGA rise/fall time test fail

daniel
Genius 5095 points
Part Number: THS7372
Other Parts Discussed in Thread: THS7376

Hi Team,

Now we get VGA rise/fall time test fail (>spec time)as attached test report.

We concern about the down resistor, series resistors and pi filter on the VGA trace.

Please kindly double check the schematic, and advice how to improve the rise/fall time.

Thanks

2U Steel_Front VGA_Test_Results-0828.xlsx

  • 0
    TI__Expert 8670 points

    Hi Daniel, 

    With the THS7372, you shouldn't need any additional filtering because you can use the internal filters for the part. However, if I am understanding your specification correctly, it looks like you are targeting less than 2.5 ns of rise and fall time? Unfortunately the THS7372 can only achieve about 4.5ns of rise and fall time on the HD channels due to the bandwidth. 

    Regards, 

  • 0 in reply to Jacob Freet
    Genius 5095 points

    Hi Jacob,

    Thanks for your help.

    The rise/fall time 2.5ns spec comes from VESA as attached file page8.

    So, should we try to remove the pi filter to see any improve?

    Also, could you help clarify the data sheet shows THS7372 can support FHD but you mentioned HD only?

    Thanks

    VESA_VSIS_1.1, March 29, 2000.pdf

  • 0 in reply to daniel
    TI__Expert 8670 points

    Hi Daniel, 

    The THS7372 was design to the SMPTE standard to transmit component RGB (G'B'R') analog video at full HD. It looks to me like you are trying to send digital RGB video signals, which is a different standard than analog component RGB. The component RGB signals require reconstruction filters on the output of the video DAC that are limited to 72 MHz and therefore would slow the edge rates of the signals. In this case, you can look at the THS7376, which is a very similar device, but features a filter bypass mode that allows for a full 300 MHz of bandwidth on the HD channels. That would yield a rise time around 1.6ns typically, which should fit your requirements. 

    Regards,