Crystal Oscillator Waveform

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

  1. HarwareGuy

    Thread Starter New Member

    Jan 17, 2013
    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?

  2. joeyd999

    AAC Fanatic!

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

    Thread Starter New Member

    Jan 17, 2013
    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


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