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DS90UB960-Q1: Coax cable length and FPD link stability

Stefan Koncar
Genius 3050 points
Part Number: DS90UB960-Q1

Hi,

I have setup as shown on image below. I'm using Leoni Dacar coax cable to connect two boards. When using longer cable (~ 5 m), the link is very stable, but when using short cable (0.5 - 1 m) the link is completely unstable, pass/lock signals are not stable. So, my question is how I can make it work stable with any cable length (up to 5 m). Adaptive EQ is enabled and 0xD5 value is set to 0xF3. Registers 0xD2 - 0xD4 have their default values.

Can you help me with this problem with some suggestions or tips?

Best regards,

Stefan.

  • 0
    TI__Guru* 83890 points

    Hello Stefan,

    1) you need to change the REFCLK value on the 960. It should be between 23MHz to 26MHz.

    2) Please change the value in reg 0xD5 to 0xF0.

    3) Normally in a good design you should have a stable link for cable length from 0.5m up to 15m or more. If you still seeing instability even after doing the previous changes with very short cable this means you may have reflections problems on your board.

  • 0 in reply to Hamzeh Jaradat
    Genius 3050 points

    Hi Hamzeh,

    One more question for you. As I said, we are using Leoni Dacar coax cable, but on both ends we have some other cable  (SMA to FAKRA), about 25 cm length. I noticed that these cables tend to break quickly and they must be replaced. I attached specs for this cable and picture of this cable. I would like to hear you opinion about this. Maybe this could be my problem, maybe they produce attenuation ...

    1.13mm cable.pdf

    Best regards,

    Stefan.

  • 0 in reply to Stefan Koncar
    TI__Guru* 83890 points

    Hello Stefan,

    these cables are good for testing purposes, but their problem is they are very sensitive for bending or for multiple uses.

    You may want to try Fakra to SMA adapters from Rosenberger or other Connector manufacturers.