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Issue with DS92LV2412 clock recovery below 10Mhz

Charles H
Intellectual 895 points
Other Parts Discussed in Thread: DS92LV2412, DS92LV2411, AM3703

The issue I found was that the LOCK signal being asserted indicating a loss of clock recovery at the DS92LV2412 deserializer. This occurred with the pixel clock set to 10MHz. When I increase the pixel clock frequency to 20MHz the LOCK signal never asserted and my pixel clock output is uninterrupted.

Is there any reason that the DS92LV2412 deserializer clock recovery would fail at lower (< 10MHz) clock frequencies? This error might originate in the serializer. Any reason that the serializer would have issues with (< 10MHz) pixel clock frequencies?

 

  • 0
    TI__Genius 13475 points

    CHarles

    The DS92LV2411/2412 pair should operate with clock frequencies from 5MHz to 50MHz - a few questions about your system:

    1)  I assume that you are driving the DS92LV2412 with the output of a DS92LV2411 - if so, what is between the serializer and deserializer - cable? - what type, length, is the link AC coupled, or direct?  How do you have the De-Emphasis settings of the serializer set? what are the VOD settings for the serializer?

    2)  What data is being provided to the DS92LV2411 - are you trying to use the BIST mode?

    3) Do you have the serial bus connected to the serializer/deserializer? - are we able to examine the register status in your system?

     

    Mark Sauerwald

     

     

  • 0 in reply to Mark Sauerwald88474
    Intellectual 895 points

    The DS92LV2411/2412 pair should operate with clock frequencies from 5MHz to 50MHz - a few questions about your system:

    1)  I assume that you are driving the DS92LV2412 with the output of a DS92LV2411 - if so, what is between the serializer and deserializer - cable?

    The link is PCB-PCB through a Hirose FX8C board-to-board connector. 90 ohm differential pair traces are routed on both PCBs.

    - what type, length, is the link AC coupled, or direct? 

    There is AC coupling at the serializer  - 0.1uf

    How do you have the De-Emphasis settings of the serializer set? what are the VOD settings for the serializer?

    All settings are default. I have tried changing VOL to high with no improvement.

    2)  What data is being provided to the DS92LV2411 - are you trying to use the BIST mode?

    The serializer is receiving output from the LCD controller of TI AM3703 application processor. 24bit with PCLK, VSYNC, HSYNC as control signals. I have tested in BIST mode and the LOCK errors  are present in BIST mode as well.

    3) Do you have the serial bus connected to the serializer/deserializer? - are we able to examine the register status in your system?

    Yes – I can read and write both SER/DES in this system.

  • 0 in reply to Charles H
    TI__Guru* 93570 points

    Hi Charles,

    1). In your first post, you had specified: "When I increase the pixel clock frequency to 20MHz the LOCK signal never asserted and my pixel clock output is uninterrupted.". So it is my understanding that either at 20MHz or 10MHz or below you have not been able to get the device to lock at all. Could you please confirm.

    2). What are the configuration or strap settings. I mean pin # 13 and 12. Can we have copied of your DS92LV2412 and DS92LV2411?

    3). Is it possible if you could please send us picture or video of your test setup? A block diagram would be fine as well.

    4). Finally please send us register dump for both DS24LV2411 and DS92LV2412.

    Even though the device is rated at 5Mhz, based on our testing we should be able to operate even at lower frequency(i.e 2MHz). So we are thinking, perhaps, there is something in the setup that we do not understand.

    Regards,,nasser