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LMH0318: 2 input to 1 output mux for HD-SDI

Edwin Cho
Prodigy 70 points
Part Number: LMH0318
Other Parts Discussed in Thread: LMH0324, LMH0056, LMH0034, LMH0303

Is it possible to use LMH0318 to mux two single ended 75 Ohm HD-SDI inputs to one single ended 75 Ohm HD-SDI output? Could I just convert it from 75 Ohm to 50 Ohm on the input sides and terminate the inverted input or would I need a cable equalizer to convert it to 100Ohm before going into LMH0318? Thank you

  • 0
    TI__Guru* 93670 points
    Hi Edwin,

    Interesting way of using LMH0318.

    I think it is possible as long as cable length is limited to perhaps to 20 to 30m HD-SDI of B1694A cable length insertion loss or similar. You can do as you noted. For longer cable length then you would need a cable equalizer such as LMH0324. Please let me know your test result once you put this together. The good thing about LMH0318 is that it has onboard reclocker so this would be a clean 2:1 75-ohm mux/repeater.

    Regards,,nasser
  • 0 in reply to Nasser Mohammadi
    Prodigy 70 points
    Hi Nasser,

    Thank you, do you think passives would be okay for the conversion from 75 Ohm to 100 Ohm for the two inputs? How long can the 75 Ohm output be? We are looking to have the two HD-SDI inputs be under a meter while the output would be 100 meters, and we would be switching between the two inputs. Thank you
  • 0 in reply to Edwin Cho
    TI__Guru* 93670 points

    Hi Edwin,

    This should work. 100m reach or longer is a function of the receiver at the end of the cable. For example, LMH0324 reach can support 300m at HD. Under the same settings as you are planning to do, LMH0324 should be able to equalize HD-SDI up to 300m B1694A cable. LMH0318 retimes the signal and thus delivers lowest jitter to the cable - enabling longest cable reach.

    Regards,,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 70 points
    Hi Nasser,

    I will test this out sometime and also thinking of trying out making a 4:1 75 Ohm HD-SDI mux with a LMH0056, 4 LMH0034 , and a LMH0303. Do you have any thoughts about this 4:1 idea? Thank you
  • 0 in reply to Edwin Cho
    TI__Guru* 93670 points
    Hi Edwin,

    LMH0056 + 4 X LMH0034 + LMH0303 should work.

    Also, If HD-SDI input is going to be about one meter, you can do the same as what you are planning to do with LMH0318. That is use passive components to convert from 75-Ohm to 50-ohm, LMH0056, and finally LMH0303.

    Regards,,nasser