y use capacitors before XTAL

[uogian]

I m unable to understand that why we use capacitors with XTAL-oscillator.
Friendz if anyone of u know its logic, plz reply me
thanx


Baber Mustafa

 

[Nigel Goodwin]

Because they are part of the oscillator circuit, and required to make it oscillate.

 

[einton]

because they make oscilator frequency more stable.

 

[Speakerguy]

The crystal looks inductive in a narrow region near its resonance (actually, between its series and parallel resonances). That's 90 degrees of phase shift. You need another 90 degrees (provided by either of the caps) to get 180 degrees phase shift between in and out, which is the main condition for oscillation. That's about as simple as I can describe it.

 

[Hero999]

because they make oscilator frequency more stable.

Not the capacitors are a requirement and aren't optional, although if you've got large PCB traces it is possible for it to oscillate without capacitors but it's a silly idea and not stable.