Why Quartz crystal used in Microcontrollers

Discussion in 'General Electronics Chat' started by electronicsLearner77, Sep 16, 2018.

  1. electronicsLearner77

    Thread Starter Active Member

    May 26, 2012
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    Generally a quartz crystal is used for generating clock timing for micro controllers. Why? Because of precision or some other reason?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Accuracy and stability. It is quite easy to manufacture oscillators with a quartz crystal that work at a given frequency plus or minus some small error. The frequency is stable over time, temperature, and supply voltage variations.
     
  3. electronicsLearner77

    Thread Starter Active Member

    May 26, 2012
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    What exactly is this accuracy? It is compared with what? Please advise.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    2,440
    Well, start with the datasheet for a typical crystal oscillator with a frequency of 4 MHz:

    https://www.mouser.com/datasheet/2/121/EC5720ETTS-4_000MTR-1011893.pdf

    The accuracy and stability are specified as 20 ppm (parts per million). You would compare this to a specifications for a ceramic resonator.

    https://www.murata.com/~/media/webr...alog/products/timingdevice/ceralock/p16e.ashx

    One possible specification calls for 0.07%

    So 20 ppm on 4 MHz = ± 80 Hz. for the crystal oscillator
    And 0.07% on 4 MHz = ± 2800 Hz.

    Now compare either of those to an oscillator using passive components with let us say a ± 10% tolerance and you begin to appreciate the differences.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    15,702
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    The Crystal in my digital watch, the quartz one not the face cover! Typically 32,768Khz, has lost <1min. in the last 6 years when I had changed the battery last.
    Max.
     
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