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Design >> Analog Design >> how to use the crystal osc.?
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Message started by trashbox on Sep 13^th, 2005, 7:55pm

Title: how to use the crystal osc.?
Post by trashbox on Sep 13^th, 2005, 7:55pm

Hi all,
In the applicaiton of crystal oscillator, there are always an invertor and some capacitors. How to decide the values of the capacitors? Is there any application note?
Thank you!

Title: Re: how to use the crystal osc.?
Post by Paul on Sep 14^th, 2005, 1:06am

I'm not sure to understand your question correctly. Does this appnote help?

http://www.eettaiwan.com/ARTICLES/2001MAR/PDF/2001MAR21_CT_AN998.PDF

Paul

Title: Re: how to use the crystal osc.?
Post by keble on Sep 14^th, 2005, 4:43am

The crystal manufacturer specifies the resonant frequency at a specific capacitance load across the crystal. At any other value of loading the frequency will be different - incidentally that provides a way of changing frequency slightly.
So if you want the frequency to be on spec you need to have the right capacitance.

The inverter provides some transconductance - for a given set of electrical parameters it is possible to work out how much you need to get oscillation to occur.

See E. Vittoz, High-Performance Crystal Oscillator circuits: Theory and Application IEEE Journal of Solid state circuits, vol. 23, No. June 1988 pp.774- 783.