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Low jitter transmission of LVDS signals

Discussion in 'Electronic Design' started by Spehro Pefhany, Apr 2, 2013.

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  1. I want to transmit a few LVDS clock signals (<= 10MHz) over a meter or
    so of wire each.

    What's the best kind of wire to use to minimize added jitter? Just
    need a single shielded twisted pair and (preferably) a wire for a
    ground reference.

    A low smoke/zero halogen type would be very good.


    Best regards,
    Spehro Pefhany
     
  2. Robert Macy

    Robert Macy Guest

    don't know about your low smoke requirement, but look at
    Belden 1800F
    I believe it's Zc = 110 ohms
     
  3. Not completely sure at the moment, but I think it has to be < 10ps for
    the added noise to be < 1 lsb. The source oscillator is claimed to
    have < 1ps jitter, so it should be negligible, but it's going through
    some logic too. It's a delta-sigma clock.
    Nice part, any reason not to standardize on it, other than a slight
    cost premium? No problems with ESD?

    I'm using ye olde SN65LVDS parts which I think are symmetric.
     
  4. Guest

    Have you checked National's LVDS Owner's Manual? Total jitter will depend on the length of cable too. Their measurements are way out of line with your objective.
    http://www.ti.com/lit/ml/snla187/snla187.pdf
     
  5. Guest

    True, but if he runs it any distance, attenuation causes his transition times to suffer putting him back to a humdrum 20-50ps RMS jitter just due to the comparator at the receiving end, and these signals are smallish.
     
  6. Bill Sloman

    Bill Sloman Guest

    ECL is current-steering logic, and ECL power rails have much less
    "grass" than rails feeding CMOS and other voltage-switching logic.
    Noise on the power rails feeds into the comparator that is detecting
    the edges (Power Supply Rejection Ratios - PSRRs - are lousy at high
    frequencies) This shifts the point where the comparator thinks that
    the in-phase and anti-phase inputs have crossed over and thus
    introduces jitter.

    From an analog design point of view, jitter is the voltage noise on
    the cross-over point projected onto the edge speed of the two signals
    being compared. The less dispersive your cable, the better the edge
    speed at the receiver end and the lower the jitter.
     
  7. brent

    brent Guest

    Wow, you could not have scripted that better if you had tried.
     
  8. brent

    brent Guest

    That is a great comeback
     
  9. Guest

    Okay, 1 m I can believe, missed that part in the OP.
     
  10. brent

    brent Guest

    My knee jerk reaction is to support a balance budget amendment,
    however, I believe that if it were implemented the budget would get
    balanced by never cutting spending (actually increasing it) and
    forever raising taxes because it is "constitutionally " required. It
    is better for the government to be insolvent.
     
  11. Guest

    So you were born on Feb 29th, 1940 ?
     
  12. josephkk

    josephkk Guest

    For your cable requirements i expect that TIA 568 certified Cat6 cable
    can do the job.

    ?-)
     
  13. A little fat and physically inflexible, but that would work.


    Best regards,
    Spehro Pefhany
     
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