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Interfacing LMH094 to Balun...

Dave Sharpe
Prodigy 140 points
Other Parts Discussed in Thread: LMH0394, LMH0387

What is the proper method of attaching a balun or transformer to the front end of the lower power LMH0394(2.5V) or similar. Input for this part is showing (typically) that it is capacitive coupled, likely do to a bias imposed by the LMH0394.. I have two areas of interest with the magnetics.. Balun specific to a customer request, and transformer for isolation of ground loops.. Balun at the SDI 1.25v offset 800mv swing level, transformer likely both the SDI and LVDS/CML levels, prior to the input of a reclocker such as the LMH0366 or LMH0346

-D

  • 0
    TI__Genius 13475 points

    Dave

    Please look at the answer to this thread: http://e2e.ti.com/support/interface/high_speed_interface/f/138/t/358814.aspx

    Since you are talking about the LMH0394, can I assume that you have a 3Gbps SDI signal?

    The '394 does rebias the input, but the main reason for the AC coupling caps is that this is standard practice in the broadcast video industry.   My primary concern with the Balun is that it will alter the shape of the cable insertion loss characteristic, which will lead the equalizer to under or over equalize - the easy solution is to use a balun with bandwidth much greater than the signal bandwidth, but when you are dealing with a 3Gbps signal, the options are quite limited...

  • 0 in reply to Mark Sauerwald88474
    Prodigy 140 points

    There are two primary reasons for wanting to use either a Balun or Transformer.. The balun reason comes direct from a customer and I suspect is due to a a specific signal path implementation. HD-SDI appears to be there current selected speed.. however there asking me about 3G. Second reason being the Transformer.. This is to provide DC isolation in prevention of ground loops. There is currently a balun that does 1.544Gbps/HD-SDI and is used in conjunction with our SD/HD/3G SDI distribution amplifier that has worked well for the customer. Most of our DA's use the LMH0387.

    Dave