FreeLists / si-list / [SI-LIST] Re: Parallel Resonance of crystall oscillator

[super cop <super_uvais@xxxxxxxxxxx>]

Hi Parthasarthy, 

Your inferance on the capacitice reactances &
inductive reactances are correct. Integrated Circuit
or transistor based crystal oscillator circuit which
can be either a stand-alone or part of an even larger,
more complex circuit are called Pierce-type
oscillators. These use an inverter to provide 180
degrees of phase shift, with the remaining 180 degrees
being supplied by two pi capacitors which are
connected to the two ends of the crystal. The loop
gain can be optimized by specifying a lower output
capacitance value than that of the input. 

Pls check this link . This might help you 
http://www.microchip.com/download/appnote/pic16/00588b.pdf


Hope this helps. 

Thanks,
Uvais. 


 --- Parthasarathy Sampath <parthsv@xxxxxxxxx> wrote:
> 
> Hi all,
>  I have a question regarding crystall oscillator
> operating at parallel resonance.
>   At parallel resonance, the impedance offered by
> series resonant ckt within crystal oscillator is
> inductive. This inductive reactance is cancelled by
> the capacitive reactance offered by parallel
> capacitance in the crystall oscillator and the load
> capacitance. So there should not be any phase in the
> circuit since the reactances get cancelled. However
> a
> lot of articles say load capacitance provide a phase
> shift of 180 in order to oscillate in closed loop.
> Since the load capacitance is included in the
> parallel
> resonance to cancel inductive reactance, how can it
> contribute 180 degress phase shift.
> 
> Thanks in advance,
> Partha
> 
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