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DS90UB914Q-Q1: The wavefom of VD signal is unstable

Shunsuke Yamamoto
Expert 4511 points
Part Number: DS90UB914Q-Q1

Hi team,

The waveform of VD signal looks unstable as attached slide. What do you think the cause? The connector is RJ-45 connector(2178415-1 from TE), and the LAN cable is CAT6a or CAT7.

Does this IC support LAN cable and RJ-45 connector? 

Best regards,

Shunsuke Yamamoto

FPDLinkIII_Waveform.TIF

  • 0
    TI__Guru* 83530 points

    Hello Shunsuke-san,

    can you please tell me what does "VD signal" means?

    Also, can you tell me what PCLK and what SER are you using?

  • 0 in reply to Hamzeh Jaradat
    TI__Expert 4511 points

    Hi,

    VD signal is 10kHz VSYNC. PCLK is a pixel clock of 74.25MHz.

    Is it possible to use RJ-45 connector, CAT6a or CAT7 cable?

    The customer uses DS90UB913Q1 as serializer.

    Best regards,

    Shunsuke Yamamoto

  • 0 in reply to Shunsuke Yamamoto
    TI__Guru* 83530 points

    Hello Shunsuke-san,

    Please note that this device has three operation modes:
    1) 12-bit Low-Frequency mode (PCLK= 10 to 50MHz)
    2) 12-bit high-frequency mode (PCLK= 15 to 75MHz), and
    3) 10-bit mode (PCLK= 20 to 100MHz).

    From your provided PCLK, I assume that you are using either the 10-bit mode, or the 12-bit high-frequency mode.
    For 10-bit mode, Line rate = PCLK/2 × 28 = 74.25MHz/2 x 28 = 1.04 Gbps, which means a nyquest frequency = 500.2MHz
    For 12-bit HF mode, Line rate = PCLK×(2/3) × 28 = 74.25MHz × (2/3) × 28 = 1.386 Gbps, which means a nyquest frequency = 693MHz

    Now, CAT6a cables are specified to support a max Frequency of 500MHz, which is below both above calculated Nyquist frequencies, which makes it not compatible.
    Where CAT7 can support a max frequency of 600MHz. which is okay to use if you are using the 10-bit mode, but not okay for 12-bit HF mode.

    Also, make sure the cables are twisted pairs and shielded. One more thing, the RJ45 connectors are not shielded hence not recommended.

  • 0 in reply to Hamzeh Jaradat
    TI__Expert 4511 points

    Hi,

    Thank you for your explanation, and I apologize for my late reply. I understood well.

    If so, which cables do you recommend?

    Best regards,

    Shunsuke Yamamoto

  • +1 in reply to Shunsuke Yamamoto
    TI__Guru* 83530 points

    We do recommend, for example, the Leoni Dacar 535