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From: jewett@hpl-opus.UUCP
Newsgroups: sci.electronics
Subject: Re: Phase Jitter of a free-running oscillator
Message-ID: <1330001@hpl-opus.HP.COM>
Date: Wed, 18-Feb-87 14:27:01 EST
Article-I.D.: hpl-opus.1330001
Posted: Wed Feb 18 14:27:01 1987
Date-Received: Fri, 20-Feb-87 07:00:36 EST
References: <5246@reed.UUCP>
Organization: HP Labs, Instrument Tech. Dept.
Lines: 27

> What is the "phase jitter of a free-running oscillator" and what does it
> depend on?  Does anyone have any revealing references?   Mike

    To determine phase jitter of a waveform, compare the time of its zero
    crossings with the zero crossings of an ideal sinewave of the same
    frequency.  The difference in time can be plotted as a function of time:

    P  |       **  **                                  
    h  |   ** *  **  *                                 
    a  |  *  *            *         *        **        
    s  |*             * ** *                   *       
    e  +---------------*---------***--------*---*------> Time
       |                    *   *         *      *   * 
    E  |                     * *     *   * *      ***  
    r  |                      *       ***              
    r  |                                               

    Electronic circuits called phase detectors can compare the phases of two
    oscillators, and give a voltage proportional to the difference.  Often a
    very quiet crystal-controlled oscillator is used as a reference standard.

    You can do varous kinds of statistics on the resulting waveform, such as
    spectrum analysis to find probable noise sources (60Hz/120Hz due to the
    power supply is common).   See McGraw-Hill's "Electronic Instrument
    Handbook" for more details and references.

    Bob Jewett  hplabs!jewett