y capacitors with XTAL-oscillator

[uogian]

Hi friends!
Can anyone of u help me understand Why we use capacitors with XTAL-oscillator?

Waiting 4 ur posts

Baber

 

[mvs sarma]

Hi friends!
Can anyone of u help me understand Why we use capacitors with XTAL-oscillator?

Waiting 4 ur posts

Baber

This link explains
www.eetkorea.com/ARTICLES/.../2001SEP06_AMD_AN.PDF

 

[MikeMl]

Good article.

Short answer: A crystal is a two-terminal network which has a complex impedance between it's two terminals. At a frequency near "series-resonance", the impedance across the two-terminals becomes real only, and fairly low. It is possible to build an oscillator (without extra capacitors) based on series-resonance of a crystal.

Most crystals are operated on what is called "parallel resonance", where an external capacitance is place in parallel with the crystal terminals, where the external capacitor resonates with the effective inductance of the crystal. Usually, to create an oscillator, you need to create either a voltage step-up, or a phase reversal, so the external capacitor is split into two series capacitors, creating a three terminal network which is incorporated into the oscillator circuit.

 

[Ghosty_Ghoul]

The capacitor values are normally given on the data sheet.

 

[mneary]

Please don't double post.

 

[Ghosty_Ghoul]

Did I double post?

If so, it was an accident, sorry.

 

[Hero999]

Not you, the origional poster made a duplicate thread.
http://www.electro-tech-online.com/threads/y-use-capacitors-before-xtal.96371/

Making duplicate posts does not help you get more help, it annoys the people who are trying to help and puts them off.