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Clarification regarding LMH0387 SDI Configurable I O Demo

Suresha N S
Expert 1070 points
Other Parts Discussed in Thread: LMH0387

Hello ,

We are working on SDI driver / equalizer for one of our designs.

We watched the demo of LMH0387 chip and we observed that the input & output is run through two separate cables.

Since the input to the equalizer and the output of the driver is differential signals is it ok to run these signals on separate cables. We observed that these signals are routed   differentially and cable doesn't seem to maintain differentiality.

Do we need to use a special cable for running these differential signals or will two separate BNC cables are good enough ?

Thanks,

Suresha.N.S.

  • 0
    TI__Expert 4400 points

    The LMH0387 SDI configurable I/O device allows a single BNC to be used as either an SDI input or SDI output.  It is intended to be placed behind a BNC connector to interface to a 75 ohm coaxial cable.  The LMH0387 can be programmed to either drive an SDI signal over this cable or receive an SDI signal from the same cable.

    Please see the simplified diagram of the LMH0387 I/O connections below.

    The BNC_IO pin (left side in this diagram) connects to a single BNC connector, and provides either the single-ended output of the cable driver or the single-ended input to the equalizer, depending on how the LMH0387 is configured.  You would connect a single 75 ohm coaxial cable to this BNC.

    The other side of the LMH0387 (right side in the diagram) provides the differential cable driver input and differential equalizer output connections.  These signals would typically be routed differentially to an FPGA, Ser/Des, reclocker, crosspoint, or other chip, either located on the same PCB as the LMH0387, or located on a nearby PCB with a high speed connector to connect the differential signals between PCBs.  In any case, these cable driver input and equalizer output signals should each be routed with differential transmission lines.

    In our demo video we show our LMH0387 EVM which has SMA connectors for these differential cable driver input and differential equalizer output connections.  We use a matched pair of SMA cables for these connections to maintain the differential signals, but this would not be the case in typical applications as these connections would most commonly be made via PCB transmission lines.