Crystal oscillator phase noise

Discussion in 'General Electronics Chat' started by electrojim, Dec 26, 2009.

  1. electrojim

    Thread Starter Member

    Jun 3, 2009
    Does anyone here have experience with those very tiny, cylindrical "watch" crystals, usually 32-and-some-odd kHz? They are available in a few other relatively low frequencies as well from DigiKey and Mouser.

    I'm trying to use a 100kHz crystal of this type as a timebase for a frequency synthesizer that has a loop frequency of 10kHz. These crystals don't work in the usual single inverting gate circuit, so I'm using two HC04 gates in tandem and an HC390 to divide by 10. The problem is that I'm seeing all kinds of phase noise, both as edge jitter on a 'scope display and sideband crud on the 'scope's FFT utility. Any help is appreciated.
  2. Wendy


    Mar 24, 2008
    I don't know if this is of any help, but have you looked at a 4060 oscillator? It was practically made for the 32.768Khz watch crystal, and the datasheet has a circuit.

    BTW, Welcome to All About Circuits. I see your jumping right in there!
    Last edited: Dec 26, 2009
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    Try amplifying the daylights out of the oscillator before applying the signal to the divider. This will make any threshold errors fade into insignificance.

  4. AlexR

    Well-Known Member

    Jan 16, 2008
    Possibly you are over-driving the crystal. Watch type crystals very sensitive to the amount of drive and too much will not only cause phase jitter but can also damage the crystal. It is common practice to put a few hundred K resistor in series with the crystal when driving it from a logic gate.
    See for a good article on watch crystals.