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    Relaxation Oscillator Jitter Simulation in cadence - Eye diagram confusion...

    Dear All,

    I am designing a conventional relaxation oscillator. The moninal frequency is around 2.85 MHz.

    When I try to run the transient noise simulation and use calculator to obtain the eye diagram, I got some weird diagram and i am very much confused.



    Attached you can see some waveforms obtained using the function eye diagram. The setting is pretty simple. Just set the start and stop time. The period is the oscillator output frequency period. I just took an average value for this. The weird thing is that when I changed the period by a little bit, the plotted diagram is very different.

    Can some expert help me with this? I don't know how i should proceed.

    For the first graph, the period is 351.5 ns; for the second one, the period is 351.3 ns; the last one has period of 351.25 ns.

    Please help me with this. thanks a lot guys.
    Last edited by FvM; 22nd December 2014 at 23:48. Reason: Deleted inappropriate text formatting

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  2. #2
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    Re: Relaxation Oscillator Jitter Simulation in cadence - Eye diagram confusion...

    What did you expect? a perfect sawtooth? I see a lot of instability modes with FM. I can guess but I"d rather see your design.
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
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    Re: Relaxation Oscillator Jitter Simulation in cadence - Eye diagram confusion...

    For an eye diagram you must look at only one or two waveform periods, not many as your graphs show.
    Zapper
    Curmudgeon Elektroniker



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  4. #4
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    Re: Relaxation Oscillator Jitter Simulation in cadence - Eye diagram confusion...

    He does not have a stable pattern to even view an eye pattern with. It is over modulating or something. One can only guess.
    A best design is easily achieved with good test specs™
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    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

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    Re: Relaxation Oscillator Jitter Simulation in cadence - Eye diagram confusion...

    Quote Originally Posted by wandola View Post
    ... the last one has period of 351.25 ns.
    I'd think this last one isn't so bad at all - I just wouldn't call it an eye diagram.

    In my eyes it depicts a time jitter of about 15ns, corresponding to a frequency jitter of about 60kHz at a mean frequency of 2.850MHz , or a phase jitter of about 15° .

    But may be I'm totally wrong. Let's wait for the experts!



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