Crystal Oscillator Waveform

Discussion in 'General Electronics Chat' started by HarwareGuy, May 7, 2015.

  1. HarwareGuy

    Thread Starter New Member

    Jan 17, 2013
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    0
    I've got a 32.768 kHz crystal running on a microprocessor and I'm concerned about the glitches I'm seeing on the waveform, should I be? The loading cap spec for the crystal is 12.5 pF (it's a CM8V from Golledge). I've loaded the crystal with 20 pF caps (tried to account for stray capacitances). I've attached a photo from my oscilloscope. My concern is, that if the crystal is fed into a schmitt trigger in the micro (silicon labs gecko), the glitches might cause frequency issues. Does this look normal, any tips?

    [​IMG]
     
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    2,689
    2,750
    You got your 0.1 uF caps installed?
     
  3. HarwareGuy

    Thread Starter New Member

    Jan 17, 2013
    3
    0
    The 20 pF loading caps are soldered on the PCB. Which 0.1 uF caps do you mean?

    I am running this PCB off USB, which isn't the cleanest of supplies, I know. I have moved the grounding clip on the oscilloscope closer to the crystal as not to pick up as much noise. The waveform is now looking as I expected and is a smooth sine wave, so it looks fine and was just measurement/user error.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,447
    3,362
    I think you're ok. What you are seeing is scope probe pick up from other digital signals on your board.
     
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