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Low Jitter 20MHz oscillator

Discussion in 'Electronic Design' started by hbv, Mar 1, 2013.

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  1. hbv

    hbv Guest

    Hi all,

    We need a low jitter clock generator ( 3v3 or 1v8 CMOS output single
    ended ), 20Mhz (+-few percent...) and most important a low jitter on
    this output (few ps).

    Any ideas are welcomed. Habib.
  2. Conner-Winfield DV75C series has maximum integrated phase jitter 1ps
    RMS over 12kHz to 20MHz. Period jitter 5ps RMS maximum. Also very good
    temperature stability for a low-power non-ovenized oscillator (which I
    happen to need).

    Some info on jitter specs:- Documents/TechnicalDocs/AN256.pdf
  3. Jeroen

    Jeroen Guest

    Making an oscillator is easy. Making a low jitter oscillator isn't.
    A few uV of power supply noise would mess up the jitter specs of
    a 74HCU04 based oscillator. Minuscule temperature variations would
    probably do the same.

    Jeroen Belleman
  4. Jamie

    Jamie Guest

    Xtal base clock for 20 mhz should be ok..

    Digikey has lots of XC type osc that are surface
    mount that fits your needs.

  5. Hello Jim,

    What do you mean with "slap together with a U version" ? I believe an
    integrated oscillator will not gain benefit with an additional U version
    of anything.

    Best regards, Habib
  6. John,

    Measuring jitter is really the point (method based on something which
    ressemble on eye diag or something like that ... i don't know at the
    moment) the best is that i would not measure anything like that, just
    based on component spec.

    I need a CMOS low jitter oscillator (few ps in absolute way) only on
    specs for feeding the clock input of an16bits AD converter (is that so
    hard ?)

    Some guys said that a basic 74HCU would be sufficient ... i did'nt read
    anything such a thing on any 74HCUxx datasheet.

    I remember i had used IDT chips feeding a 100MHz PLL clock input for a
    PPC (AMCC PPC440) with something like 1 or 2 ps absolute jitter. I'm
    expecting that it's not so hard to find the equivalent on 20MHz.

    I will manage the point this week.

    Thx anyway for the topic. Habib
  7. Guest

    A 74HCU04,an xtal, 2 caps, 2 resistors and you have a very nice

  8. Really good point, thank you. But for the silabs solutions i think these
    guys are too obfuscated ... and i'm too in a hurry.

    Best Regards, Habib.
  9. Ahh ok a simple RC oscillator on 20MHz ! mmhhh ... i would not
    experiment such a basic thing when stable, cheap and reliable integrated
    oscillators exits for years with a jitter as low as 1ps.

    Thank anyway, Habib.
  10. Guest

    not an RC oscillator a crystal oscillator, the R's are for bias and
    the C's for the xtal

  11. Jim,

    I will never experiment a RC or Quartz + 74HCU or anything like that to
    achieve a low jitter oscillator. I leave this sort of thing to some
    flashers beginners. No offense.

    And the fact is i'm French has nothing to do with this.

  12. my turn : Jim tom tom tom ... -D
  13. Hi Jim, What's the advantage of the U version for xtal drive?

    George H.
  14. Tim Williams

    Tim Williams Guest

    Standard HC is buffered (one on the front, one on the back, plus whatever
    logic lies inbetween, so an HC04 is actually three inverters), which
    doesn't bias well. HCU is unbuffered, so it makes linear amps just as
    well as the old CD4000s did.

  15. Ok my first plan was to power the analog card with a 3V6 battery.

    I realize that driving modern ADC clock input is not so trivial (like
    Thx, Habib.
  16. Jim is a little bit condescendant with French guys like me but he must
    not as an analog innovatOR and as a good wines amatOR. I guess he spent
    too a long time in the cellar and returning here afterwards pissing on
    my shoes.

    These old men are incorrigible!

  17. Guest

    Jitter is a function of the phase noise profile.

    Set your jitter spec., calculate your jitter from the phase noise

    of your chosen oscillator.

    Then you don't need to argue with anybody.

    It's not difficult.
  18. Yes surely the single ended input clock requires more attention by us
    (PCB stack up issues, Power supplies and signal integrity) thank you for
    pointing these topics and we have been some experience on that subjects. Seems to be such a thing approching what we plan to do. Great piece of
    electronics design.
    That is always the same guys, Spehro, you and a few others who are
    speaking about electronics designs down here.

    Recently someone tells me to not question anything about electronics and
    just let some guys like Jim Thompson the great guru analog innovaTOR
    pissing me off.

    What a pity !

  19. Got it, thanks Jim (and Tim)

    George H.
  20. Guest

    you're talking about correlated system issues. goes without saying those components have to be dealt with. you don't want them setting your overall system spec. again, those contributions can be calculated.

    but ultimately timing systems specs starts with a master clock phase noise profile. in the case of downconverter all sources have to be considered.

    then it becomes obvious that spectral profiles can be shaped to maintain jitter, (time domain), specs.
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