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LMH1218EVM: LMH1218 4K 50, 59.94 and 60fps don't work

Marcelo Hebling
Prodigy 120 points

Part Number: LMH1218EVM
Other Parts Discussed in Thread: LMH1218, LMH1219, LMH1228

Hello everyone!

I am developing a bidirectional fiber-optic to 4K SDI converter using the LMH1219 as the TX and the LMH1218 as the RX.
The fiber-optic transceiver is bidirectional and suitable for 12G video transmission and reception.
Transmission via the LMH1219 works normally—we tested it against a competitor's device, and the same applies when using that device as the transmitter and our board as the receiver; in other words, when using an external device as the transmitter and our board as the receiver, the 4K signal (at 50, 59.94, and 60 fps) displays correctly on the monitor.
However, when we close the loop on the transceiver—injecting the signal into the SDI TX and connecting the monitor to the SDI RX—nothing appears on the screen for 4K signals at 50, 59.94, and 60 fps.
In that same setup, the image *does* appear on the monitor for 4K signals at frame rates below 50 fps.
I would like to ask the community for help in resolving this issue.
Thank you all for your attention, and I look forward to your replies.

Best regards,
Marcelo

  • 0
    TI__Guru**** 190881 points

    Marcelo

    Can you please share your design schematic for review?

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 120 points

    David

    I'm so sorry but I can't to share my design schematic because this is a project for a customer.

  • 0 in reply to Marcelo Hebling
    TI__Guru**** 190881 points

    Marcelo

    Are you seeing the 6G_enable register on the LMH1218 set when passing 6G data through?

    Have you also tried to tune the De-Emphasis and VOD value on LMH1219 and tune EQ Boost on LMH1218 when transmitting 4k@60Hz video?

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 120 points

    David

    All others frame rates and bit rates the board is okay, only when is injected 12G 50, 59.94 and 60fps occur the problem.

    I'm already using this command that you send me above and much others commands.

    But I believe that I could found the problem, I will test my idea and if it correct I come back to say to you what happened.

    Thanks

    Marcelo

  • 0 in reply to David (ASIC) Liu
    Prodigy 120 points

    Hi David

    Following up on my last message, here are my results:

    1- The code structure written to configure the LMH1219 and LMH1228 was incorrect; I have fixed it;
    2- I realized from a previous board that separating the ground planes is crucial; the ground plane for the output connectors needs to be completely isolated from the other planes;
    3- I added coupling capacitors to the LMH1219 output connecting to the LMH1228, and to the LMH1228 output connecting to the next LMH1228. This significantly improved the signal displayed on the monitor, but it wasn't enough. The signal appears at 50, 59.94, and 60 fps but flickers; I need to eliminate this flicker;
    4- I used aluminum tape on the output connectors to act as a shield; this improved the signal but didn't provide a definitive solution;
    5- I isolated the SDI input connector; this led to a significant signal improvement but still wasn't the final solution.

    I spoke with my client regarding your previous message, in which you suggested I send the schematic to your private email. If it is still possible, please let me know your email address so I can send the schematic to you; if you agree, we can continue discussing this matter via email.

  • 0 in reply to Marcelo Hebling
    TI__Guru**** 190881 points

    Marcelo

    Would you accept my friendship request and you can then send me the board design file in a private E2E message?

    Thanks

    David