• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 33 subscribers
  • Views 829 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Use of magnetics/Balun on front end of SDI EQ Receivers

Dave Sharpe
Prodigy 140 points
Other Parts Discussed in Thread: LMH0394, LMH0366, LMH0346

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 10320 points

    Hi Dave,

    Please post this question in the Interface section of E2E.

    Gabe

  • 0 in reply to Gabe Ayala
    Prodigy 140 points

    Seems to me there should be a way of doing this without having to re-enter everything in again..

  • 0 in reply to Dave Sharpe
    TI__Genius 13475 points

    Dave - my apologies - we should have been able to move the forum for you.

    The SDI equalizers look at the signal that they receive, and from that, estimate the length of the cable attached to them.  They do this by looking at the energy in the signal in several different frequency bands.   Once the characteristics of the cable are determined, the high pass filtering section is configured to compensate for the cable loss.   For most SDI cables, the dominant loss is from the skin effect of the cable, which means that it follows a 1/(SQRT(f)) characteristic.   Magnetics have a different loss characteristic, so depending upon the bandwidth of the balun and the length of the cable attached to it, the equalizer can get confused as to what cable length is connected, which will result in not equalizing properly.

    Therefore, the answer to your question is that it depends upon which SDI signal you are using (270Mbps? - 3Gbps?), which equalizer you are using and which balun.   Can you help me to understand why you want to be using a Balun on an SDI signal?

  • 0 in reply to Mark Sauerwald88474
    Prodigy 140 points

    Ok let me throw another idea into the mix.. The LMH0394 is capable of a differential input, however there is no data in the datasheet to support this. I'm shooting for 100ohm differential input impedance (cable unknown). LMH0394 want's AC coupling, and it appears there is some input impedance flexibility and this may negate the need for a balun.

    I would like to get my eye's on an example..


    Dave