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DS90UB949-Q1: Schematic review & Question

CHO SR
Genius 3415 points
Part Number: DS90UB949-Q1

Hi

Could you review schematic.

There was a lot of noise in the EMC part through LVDS cable, so I would like to request an improvement point guide.

1. The resistance value of the filter in the picture below is 260 ohm (100 mhz).
However, I understand that HDMI impedance should be set to 90ohm.
- Configured to match the design of the reference circuit, please check if there are any problems.

2. I know the setting of the picture below by using HDMI audio mode.
Is it possible for this part to affect EMC?

3. Request for review schematic
- Customer request: Schematics are confidential and should be considered in private.
- Please let me know your email address to send a schematic.

  • 0
    TI__Mastermind 25955 points

    Hi CHO SR,

    Please check the CMC symbol.  It appears that terminals 1 and 2, and 3 and 4 are accidentally shorted with a wire.  This would nullify any benefit of the CMC.

    The next portion shown are strap resistors.  These are simply voltage dividers off of a 1.8V rail.  There are connected to an ADC, which may generate some noise, however, the main EMC sources that should be first investigated would be clocks, high speed traces (proper high-speed pcb design), stubs, large current loops, fast switching power supplies, etc.

    There are many ways to reduce EMC/EMI once you have identified the weak spots in your design.  For example, if a clock at a set frequency is the source, SSCG may be employed to spread the energy among a larger range of frequencies.

    Please review the following material for more information on EMC/EMI considerations and requirements when designing your system.

    https://www.ti.com/lit/an/slyt636/slyt636.pdf

    https://www.ti.com/lit/an/snaa204/snaa204.pdf

    https://www.ti.com/lit/ug/snla187/snla187.pdf

    https://training.ti.com/automotive-emi-reduction-techniques-applications-and-solutions

    Next steps:

    1) Determine the source of EMI/EMC through testing (frequency, preferably point source as well)
    2) Understand the mechanism/feature causing the test the fail
    3) Mitigate the impact.  Mitigation steps will depend on the source, frequency and cause.

    Sincerely,
    Bryan Kahler

  • 0 in reply to Bryan Kahler
    Genius 3415 points

    Hi Bryan

    Thank you for your reply.

    In addition, Schematic need to be reviewed.

    Please let me know the email address to send the schematic.

  • 0 in reply to CHO SR
    TI__Mastermind 25955 points

    Hi CHO SR,

    The 949 EVM Schematic is a good starting point for designing the 949 into your system.

    To focus a schematic review, especially for EMC/EMI concerns, please take actions on points 1-3 above and share the results.  This will need to be done prior to set the scope appropriately. 

    Sincerely,

    Bryan Kahler