• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 33 subscribers
  • Views 405 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

DS90UB960-Q1: cable effect

DS90UB953-Q1: How to caculate the cable data rate

guihui yang
Prodigy 100 points
Part Number: DS90UB953-Q1

We used 953/960 for our application.

Resolution: 720x2560

fps: 30

format: YUV422

The cable manufacturer want to know the operating frequency and attenuation requirements about the cable.

(1)How to caclute the data rate?

(2)Where can I get the attenuation requirements?

Thanks.

  • 0
    TI__Mastermind 28020 points

    Hi Guihui,

    1) The line rate of the 953/960 application depends on their configured MODE of operation. The UB953 can support up to 3.3Gbps of video data throughput, but the actual data transfer rate over the cable depends on the MODE used.

    In the UB960 datasheet, you can refer to Section 7.4.1 CSI-2 Mode and Section 7.4.2 RAW Mode to calculate the line rate of the Forward Channel for each MODE. In CSI-2 Synchronous, the line rate depends on the REFCLK input on the deserializer. In CSI-2Non-Synchronous mode, the cable line rate depends on the external CLK_IN used on the serializer. In the DVP RAW mode, line rate depends on the PCLK input at the serializer.

    The Back Channel rate is fixed and depends on the MODE used.

    The frequency over the cable is half the line rate. If data is being transferred with a Forward Channel rate of 4Gbps and a Back Channel rate of 50Mbps, the frequency range of the FPD-Link channel is 25MHz - 2GHz.

    2) In the UB953 datasheet, Table 8-2. Suggested Characteristics for Single-Ended PCB Traces With Attached PoC Networks shows the required Return Loss for the PCB and the cable as well. For detailed Insertion Loss requirements for the cable, we have a channel specification document, but it is under NDA. Please contact your local TI Sales/FAE so you can sign an NDA and obtain this information.

    Best,

    Justin Phan

  • 0 in reply to Justin Phan
    Prodigy 100 points

    Hi Justin,

    Thank you for your reply.

    We use CSI-2 Non-Synchronous mode, so the cable line rate depends on the external CLK_IN used on the serializer.

    Should the CLK_IN be 50MHz? Or is it determined by our image size?

    Maybe 1920x1080@60 uses 50MHz and 720x2560@30 uses 27MHz?

  • 0 in reply to guihui yang
    TI__Mastermind 28020 points

    Hi Guihui,

    Yes, if the external CLK_IN used on the serializer is 50MHz, then the data transferred over the Forward Channel will be about 4Gbps. The Back Channel rate will be constant at 10Mbps in this MODE. This results in a frequency bandwidth of 5MHz - 2GHz.

    The serializer specifications determine the max supported video throughput of the camera sensor. The UB953 supports up to 3.328Gbps video throughput (832Mbps per data lane). Other signals are being transferred over the Forward Channel as well, such as I2C, GPIO, etc..., so the supported video throughput does not take up the entire Forward Channel bandwidth.

    You just need to make sure that the imager has a video throughput less than 3.328Gbps and that you can enable enough data lanes on the CSI-2 receiver on the SER to support the video throughput.

    Video Throughput = HActive x VActive x (Frame Rate) x Bits-Per-Pixel x Overhead (Assume 25% if unknown)

    I also recommend checking to see if the UB960 can support the CSI-2 aggregation bandwidth, if you are using multiple sensors. If you can provide the camera specs mentioned above and the total vertical blanking, then I can calculate it for you.

    Best,

    Justin Phan

  • 0 in reply to Justin Phan
    Prodigy 100 points

    h-active = 2560
    hfp = 176
    hpw = 88
    hbp = 296
    v-active = 720
    vfp = 8
    vpw = 10
    vbp = 72
    fps = 30

    H-total = 3120

    V-total = 810

    3120x810x30x12 = 909,792,000 = 909.792Mbps.

    909.792Mbps is much smaller than 3.328Gbps, so maybe can we change the CLK_IN  to 25MHz to let the cable run at 2Gbps to reduce the pressure on the cable?

  • +1 in reply to guihui yang
    TI__Mastermind 28020 points

    Hi Guihui,

    You can use a 25MHz external reference clock at the UB953, which will set the Forward Channel rate to 2Gbps and the allowable input CSI-2 bandwidth to be about 1.6Gbps, as defined in Table 7-6 in the UB953 datasheet:

    Just keep in mind that there are 4 CSI-2 data lanes, which requires an input data rate between 80Mbps to 832Mbps, as defined in the datasheet:

    The reference clock sets the allowable CSI-2 input bandwidth at the UB953 receiver and the Forward Channel rate in the overall cable. You can select whichever option suits your application. I also recommend looking at Synchronous mode, since that would allow the REFCLK to be sent from the DES to the SER, and eliminate the need to add an external oscillator on the SER board.

    Best,

    Justin Phan