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DS90UB953-Q1: Inconsistent clocks per frame and horizontal blanking jitter

Tim Lipsky
Prodigy 220 points
Part Number: DS90UB953-Q1

Hello,
My project is using  the DS90UB953 and DS90uB954 in CSI2 non-synchronous mode with a single 10-bit 1080p60 sensor.

I am seeing seeing horizontal blanking jitter at the '954's CSI2 outputs and the total number of clocks per frame is not consistent either(+/- 50 clocks per frame)  which is causing most monitors to not sync and display a scrolling right and very slow down pattern.   The line active is always correct at 1920 clocks.  I can add a line buffer to hide the horizontal blanking jitter and some monitors can sync and the data looks perfect.   But most monitors are not tolerant of the varying clocks per frame and I would like to avoid implementing a frame buffer.

BTW, the '953's pattern generator looks perfect with consistent clocks per frame but only when running the '953/954 in CSI-2 synchronous mode.   In CSI2 non-synchronous mode the monitor does not lock.    My clocks per frame and line jitter issues are the same in both CSI2 sync and non-sync modes.

Since the '953/954 are source synchronous to the sensor's CSI2 clock I would expect the number of clocks per frame to be consistent along with no line jitter.

Do you have any suggestions on how I can obtain consistent clocks per frame and no line jitter?

Thanks,
Tim

  • 0
    TI__Expert 3390 points
    Hi Tim,

    Have you tried to do sync mode with the imager? The fact that it works seamlessly in sync mode with patgen but has issues in non-sync, it could be related to the clock source itself or the imager. What's the ppm of the osc that is providing the clock source to the 953? Also, what is your Back channel rate? In Non-sync mode, the BC should be running at 10Mbps. You can check/set on register 0x58[2:0] on the 954. Additionally, maybe not as related but what are your AC-coupling cap values? For non-sync they should be 100nF for DOUT+ and 47nF for DOUT-

    Regards,
    Mandeep Singh
  • 0 in reply to Mandeep S
    Prodigy 220 points

    Hi Mandeep,

    Sync mode with the imager is the same issue.

    The '953 is using it's internal clock since it is in non-sync mode.   The sensor is using a +/- 100 PPM crystal.  The '954 is using a +/- 50 PPM oscillator.

    The Back channel rate is 10 Mbps.  '954 register 0x58 = 0x1A.

    The '953 AC-caps are 33nF(DOUT+) and 15nF(DOUT-).

    Thanks,

    Tim

  • 0 in reply to Tim Lipsky
    TI__Expert 3390 points
    Hi Tim,

    Register 0x58 doesn't have I2C_Pass_through enabled. This bit has to be enabled, so the 954 can communicate to the remote devices and forward their information. Please set reigster 0x58 = 0x5A and also set-up the serializer and camera device ID. The serializer ID should already be populated in reg 0x5B, you can use the same ID for the serializer alias in reg 0x5C. Set the Camera ID in register 0x5D and the camera alias in register 0x65. The camera alias can be the same as well because I am assuming you only have 1 serializer and 1 camera set-up right now. If you do start using another set, I recommend updating these so they are different for each remote device.

    If it doesn't work, let's debug this in sync mode and you can switch to the non-sync with internal clock mode after it starts working. So, set the BC rate on the 954 to 50Mbps in register 0x58 and repeat the steps above.

    If your still having issues, I'd like to ask if you've verified that the imager outputs correctly without the SERDES? Also, how do you have the CSI output set-up on the 954? Can you check register 0x33 on the 954. If CSI_Cont_Clk is disabled in reg 0x33, can you try enabling it and see if it makes a difference.

    Regards,
    Mandeep Singh
  • 0 in reply to Mandeep S
    TI__Expert 3390 points
    Hi Tim,

    I wanted to follow up with you and ask if you were able to resolve this or have any other questions.

    Regards,
    Mandeep Singh
  • 0 in reply to Mandeep S
    Prodigy 220 points

    Hi Mandeep,

    We have bypassed the back channel for now while we resolve this issue.

    Does setting BC rate on the 954 to 50Mbps place the both the '953 and '954 in sync mode?   I was hoping to avoid changing resistors to change modes.

    Thanks,

    Tim

  • 0 in reply to Tim Lipsky
    TI__Expert 3390 points
    Hi Tim,

    You don't have to change the hardware but along with the 50Mbps, you need to change register 0x03 on the DS90UB953 side. Set 0x03 = 0x10. This should put the 953/954 into Sync mode.

    I'm not sure if you're communicating to the 953 remotely from the 954. If you are then this might not work right away because you are the BC is set for 50Mbps and non-sync requires 10Mbps. If it doesn't work, then I recommend setting the BC rate on the 954 to 10Mbps and then set the 953 to sync mode and then set the 954 BC rate back to 50Mbps.

    Regards,
    Mandeep Singh