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TDES960: Cable length

Ville Keskilohko
Prodigy 190 points
Part Number: TDES960
Other Parts Discussed in Thread: TDES954, , TSER953

We are planning a surround view system based on TSER953 serializers in camera board and TDES960 and TDES954 in processor board for up to six cameras through two MIPI CSI-2 ports. The customer needs to have 30-40m cable lengths, which their current analog HD system is using. Currently, the cameras are 720p (1280x720), but the plan is to use full HD (1920x1080) in future. Ideally, the frame rate should be 60 Hz, but I guess 30Hz would be perfectly acceptable.

Without taking blanking or MIPI overhead into account, 30 fps 720p is roughly 700 Mbps and full HD about 1.5 Gbps (24 bpp). I'm a bit confused about TDES960 datasheet table 7-4:

Normally insertion loss is defined as positive number. What does the minimum insertion loss mean in this case? If we would use a low-loss coaxial cable with 10 dB/100ft attenuation @1GHz for full-HD, how can we calculate the approximate maximum cable length?

  • 0
    TI__Guru** 101115 points

    Hello Ville,

    The TSER953 and TDES960 used a fixed frequency link rate either 4Gbps (max 2GHz) or 2Gbps (max 1GHz) for the serial side regardless of how much video data is being passed. From a channel specs perspective, if you are planning to run at 4Gbps, then you would need to consider the whole channel spec above. If you run at 2Gbps, then you only need to worry about the channel specs up to 1GHz.

    With 2Gbps link rate, the maximum supported CSI-2 throughput is 1.6Gbps total, so it may be possible to implement both of the above with 2Gbps link rate. 

    For the insertion loss above, it would probably be more accurate if the IL was defined as S21 rather than S12 which is why the number is negative. This is the maximum loss that is allowed across the operating frequency ranges. 

    If you are able to find a coax assembly which can meet the above loss then it could work, but also keep in mind that you need to factor in losses from the PCB trace and connector as well into the budget above. 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Prodigy 190 points

    So the "minimum insertion loss" specified in datasheet is actually maximum transmission coefficient? For example at 1GHz the total attenuation needs to be below 14 dB, right? Low-loss coax cable 10 dB/100ft attenuation @1GHz would then imply 140 ft (~42m) maximum cable length. Then 30 m cable (~100 ft, 10 dB attenuation) should be ok, if PCBs and connectors attenuation is below 4 dB.

  • 0 in reply to Ville Keskilohko
    TI__Guru** 101115 points

    Ville,

    Yes, that is correct. 

    Can you share what kind of cable you are evaluating here?

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Prodigy 190 points

    I'm not yet evaluating any cable. The project is in concept phase and this was just to check, if FPD-Link / V3Link would be feasible for 30-40m cable lengths. So, FPD-Link should be ok for long cables if we just use a high-quality low-loss cable.