Author Options:

how to design a crystal oscillator for a particular frequency using quartz crystal Answered

can anyone please provide a link which speaks about this...for a beginner 
thank you in advance



Well you can't get them for a particular frequency, you can get them from a useful series, and then have to achieve particular frequencies by division/counting.

Unless you have good reasons not to use it, the classic inverter driven circuit that laserjocky suggests is actually pretty good. The only thing is, you have to be careful with the capacitors that load the crystal for good results. And contrary to what laserjocky says, the caps, they are more usually a few PICOfarads. Don't use 74 series, they're becoming hard to get, and 74HC or HCT work just as well.

Crystals can be cut in several ways which will give you Fundamental or Overtone modes. What crystal are you going to use or more importantly, what frequency are you after? Fundamental mode is the simplest. The crystal is usual cut to operate at that frequency (under 50MHz - Higher is usually very expensive and the crystal is very fragile and cannot be driven too hard as it will fracture). Overtone mode is running the crystal at the fundamental frequency but the oscillator circuit favours the higher harmonic frequency (the overtone). Overtone crystals are typically operated at the 3rd or 5th overtone (harmonic).

I've tried to find info on this online before and I had little luck. The easiest way to get started with this is to just get a crystal, a digital inverter and some capacitors.

This configuration has worked for me in the past:

Use a standard 7404 digital inverter (the triangle with the circle at the tip). The capacitors will be around 1nF.

You'll need to adjust the capacitor values until the oscillator maintains its rated frequency well. You can check frequencies by using an oscilloscope. Another way would be to use cascaded digital counters to divide the frequency to something more manageable.

For example, if you have a crystal rated for 65536Hz, that's 2^16 Hz, and feeding this into a 4 bit digital counter (74161) will cause the counter output to be 2^16/2^4 = 2^12. Feed this output to another 74161 to get 2^8, then to another to get 2^4, then to another to get a frequency of 1. You can attach an LED to this output pin and if the crystal is working properly you will see the LED blink every second.