How to get a stable frequency using a crystal oscilltor

Discussion in 'General Electronics Chat' started by dumindu89, Jun 30, 2012.

  1. dumindu89

    Thread Starter Member

    Oct 28, 2010
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    I want to output a stable frequency using a crystal oscilltor. I have 4 MHz crystal oscillator (SD4.00000) and I need to get a square wave (High level: 5 V and low level 0 V) with a stable frequency of 4MHz.

    How Can I achieve this from this crystal oscillator? Do I need extra components or circuit?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Crystal oscillators come in different parts. You are confusing the output drivers with the base oscillator.

    THE_RB has some neat circuits on his website. One is a way to tweak the output time base with a PIC, another is to make a super simple crystal oven for a crystal, which is one way to really stabilize a oscillator. The norm in most test equipment, matter of fact.

    http://www.romanblack.com/

    [SIZE=-1]Make a OCXO (xtal oven) for $1[/SIZE]
     
    Last edited: Jun 30, 2012
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  3. MrChips

    Moderator

    Oct 2, 2009
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    A quartz crystal by itself does not oscillate. You need in create an oscillator circuit that uses the crystal as a feedback element.

    Alternatively, you can purchase a crystal oscillator module that has a ready made crystal oscillator. You apply power and ground (usually +5V and GND) and the output pin provides the oscillator signal at TTL voltage levels. Some modules will also provide outputs at frequencies that have been divided down from the crystal frequency.

    Crystal oscillators are generally stable to a few parts per 1,000,000.
     
  4. dumindu89

    Thread Starter Member

    Oct 28, 2010
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  5. MrChips

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    Oct 2, 2009
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    dumindu89 likes this.
  6. Wendy

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    Mar 24, 2008
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    The simple fact is the crystal element is much more stable than you will ever get from any kind of LC oscillator. It was considered a vital skill during WWII, and has been pretty much automated since. This is not going to change anytime soon.
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Is that one of those square can crystal oscillators with a leg on each corner? If so that is already a complete oscillator and should produce a logic level 4MHz output.

    Just watch the output loading, they won't drive a lot of current so it's best to feed that into a high impedance input like a CMOS input etc.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I couldn't find much on your part, from the limited data here it seems to be a complete oscillator: you give it power and it gives you an output wave. I don't see if it is a sine or square wave, but in either case it is a 3.3V part so you will need to buffer the output to get your 5V levels.

    Such a buffer should make a sine into at least a pulse wave. The frequency will be fine but it may not be a square wave 50% duty cycle.

    Good luck determining the pinout :D
     
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