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Original question:

DS90UB936-Q1: minimum MIPI clock frequency?

DS90UB635-Q1: Narrow Mipi Data Rate (per CSI-2 lane)

ANDREW SAUTER
Intellectual 270 points
Part Number: DS90UB635-Q1
We are trying to use the arducam HQ (based on IMX477) which I believe can top out at about 2.5 gigabits per second 4k 60 Hz 12bit depth BUT our target res is currently 1080x1920 60 Hz (bit depth is not defined).
I am seeing a pretty narrow band of data rate per channel 832 ~ 700 Mbps for the DS90UB635/8 and 832 ~ 80 Mbps with the DS90UB953/4. We were previously looking at the THine THCV241/2 solutions for SerDes but had difficulty getting it functional, thought TI may be better.
Can you help me understand is there an encoding trick to achieve this narrow data rate? I believe the camera encoding of raw8 is represented below, but I am not clear on what is 'comp8' encoding which is also mentioned in the camera datasheet.
my math:
bottom up
resolution 1080
resolution 1920
RGB 3
Frame Rate 60
Bit Depth 8
Total 2986 Mbps
per channel 1493 Mbps
  • 0
    TI__Genius 11315 points

    Hi Andrew,

    The 635 has up to four CSI-2 data lanes which supports 600 Mbps - 832 Mbps per lane. This device has a narrower lane rate requirement compared to the 953 because it is part of our low-cost portfolio. Keep in mind that 635 can only operate with other 6xx deserializers. 

    You would divide the total CSI-2 video throughput by the number of lanes used to get the lane rate. Total CSI-2 video throughput = (HActive) x (VActive) x (Frame Rate) x (Data Type Bits-Per Pixel) x Overhead (~25% if unknown). Overhead includes pixel/line blanking plus CSI-2 protocol overhead.

    In your case for 1080x1920 @ 60Hz RAW8 (assuming 25% overhead), this would equal about 1.244Gbps of total CSI-2 payload. If you are using 2 CSI-2 lanes, 1.244Gbps/2 = 622Mbps/lane. 

    COMP8 seems to be a compressed form of RAW data. You can find more information in the MIPI CSI-2 Specification v1-3 document under Annex E. I also want to highlight that the 635 simply takes the received CSI-2 packets and passes them through without modification (unless the VCID is remapped). The number of bytes per line or data type do not matter, and no configuration is needed to support different data types, different line lengths, different virtual channels, or mixing of data types/VCIDs. You would just need to make sure that the bandwidth requirement is met. 

    Regards,

    Cindy

  • 0 in reply to Cindy Li
    Intellectual 270 points

    Hello Cindy, Thanks for the excellent reply.

    Can we buy the 953-EVM and the 954-EVM and replace the parts with the 635/8 parts? I only see two pins that are different connected to the second FPD Link 3 output which is not present on the 635 part.

    It appears we can purchase the 635/8 parts direct from TI at low quantity, whereas the 953/4 appears to be out of stock at most locations except for the secondary market, also we are targeting the 635/8 parts.

  • 0 in reply to ANDREW SAUTER
    TI__Genius 11315 points

    Hi Andrew,

    Yes the 635 and 638 can use the same EVM as the 953 and 954 respectively. 

    Regards,

    Cindy

  • 0 in reply to Cindy Li
    Intellectual 270 points

    May we recieve the altium design files for these EVMs?

  • 0 in reply to ANDREW SAUTER
    TI__Genius 11315 points

    Hi Andrew,

    Sure, we can provide them offline. I sent you an E2E friend request so we can message privately. 

    Regards,

    Cindy

  • 0 in reply to Cindy Li
    Intellectual 270 points

    Hello Cindy, 

    Can you tell me how does this data rate minimum work? 

    For example: If the camera is operating at 500 Mbps instead of the in the range 600 ~ 832 Mbps will it just operate with poor reliability? Will the back channel be corrupted? I realize these signals are capacitively coupled, and 635/8 are the lower performance and lower cost solution. does the narrow bandwidth allow the chip to have a lower cost circuit block on the transmit side? It appears the 638 is capable of a wider CSI-2 Mipi data rate 368 ~ 1664 Mbps. 

    Are there any tricks to up the data rate artifically while still operating the camera at 720p 30 Hz (or ~200 Mbps per channel) with the 635/8 solution which requires 600 Mbps? My understanding was that the high speed data does not have any configuration parameters in the SerDes chips but is merely a pass through.

    Best.

  • 0 in reply to ANDREW SAUTER
    Intellectual 270 points

    What is the length I could likely get for coax or ethernet?

  • +1 in reply to ANDREW SAUTER
    TI__Genius 11315 points

    Hi Andrew,

    ANDREW SAUTER said:
    Can you tell me how does this data rate minimum work? 

    6xx devices are part of the cost-optimized portfolio, so 635 has a narrower CSI-2 lane rate requirement and is not validated at rates below 600Mbps. We do not recommend going below this minimum value.

    The 638 CSI-2 transmitter frequency can be set to 400Mbps, 800Mbps, or 1.6Gbps. You can refer to section 7.4.19 in the 638 datasheet for more information.

    ANDREW SAUTER said:
    Are there any tricks to up the data rate artifically while still operating the camera at 720p 30 Hz (or ~200 Mbps per channel) with the 635/8 solution which requires 600 Mbps? My understanding was that the high speed data does not have any configuration parameters in the SerDes chips but is merely a pass through.

    Do you mean increasing the CSI-2 data rate per lane? If you decrease the number of lanes then each lane would have a higher rate. If using even one lane does not hit the 600Mbps minimum, you can see if more overhead (pixel/line blanking) can be applied. Another option is to use 953/954 since the 953 has a much lower minimum. 

    For the imager->serializer connection, you just need to make sure that the serializer bandwidth requirements are met. On the SER you can configure the number of CSI data lanes and the CSI clock lane configuration. These parameters should align with your camera settings. Then the CSI-2 data gets passed from the SER to the DES via the FPD-Link forward channel (up to 4.16Gbps). Finally the DES transmits the CSI-2 packets at a configurable transmitter frequency mentioned above.

    ANDREW SAUTER said:
    What is the length I could likely get for coax or ethernet?

    There are channel specifications which outline the allowed return and insertion loss of the interconnecting elements from a SER to a DES. Specific budgets are allocated between the cable and PCB. The cable and PCB losses can be reallocated depending on the application, but they must ultimately meet the total channel normative requirement. Therefore, the cable length you can achieve depends on the RF parameters of the other elements and the type of cable used. If you follow the budgets in the channel specs, then a 15m Coax cable can be achieved.

    Regards,

    Cindy