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Screen Flicker using Channel Link III

Bradley Helsel
Intellectual 260 points
Other Parts Discussed in Thread: DS92LX2121, DS92LX2122

I am working on a design that is using the Channel link III SERDES chip sets DS92LX2121 Serializer and DS92LX2122 Deserializer. The devices are located in separate boxes connected through a 3m Cat5E shielded cable.

When any of the cables attached to Controller or the cable between the Controller and Display are subjected to any noise, such as RF or EFT pulses, the screen flickers. I believe I have tracked it down to being a common mode violation between the Serializer and Deserializer, but I'm not exactly sure how to verify this.

I can provide more details on the system as needed.

Does anyone have any suggestions on what else might cause the screen flicker or possibly have had the same issue?

Here is a block diagram of the system.

  • 0
    TI__Guru* 93670 points

    Hi Bradley,

    1). My understanding is that video flicker occurs because of the bit errors. I am assuming you see the devices are locked to one another. Can you please trigger your scope using Tx PCLK and then monitor Rx PCLK to make sure they are locked to one another and there is no drift or jumping in normal or when you have external RF noise.

    2). If we forget about the RF noise for a second, are you able to run the device at full data rate? i.e 50MHz pixel clock with back channel enabled? I am wondering if perhaps we have jitter margin issue. Even if you can run the device at 50MHz please run at higher frequency so we can see what kind of margin you have.

    3). Here is another link similar to your report but different part:

    http://e2e.ti.com/support/interface/high_speed_interface/f/138/t/222478.aspx

    4). Given when you apply the RF noise you see video flicker, this indicates signal to noise ratio decreases that causes bit error. Even though you have a shielded cable, this does not seem to reduce the cross coupling effect. So the first thing to consider or perhaps investigate is to make sure your cable is shielded properly and there is low impedance path to shiedling gnd. The RF noise seeks the path of least resistance but in this case, perhaps, the gnd shielding does not seem to be doing it's job as effectively.  

    Regards,,nasser

  • 0 in reply to Nasser Mohammadi
    Intellectual 260 points

    Hi Nasser,

    I am working on your suggestions now and will post the results.

    Thanks.

    Brad.