[SI-LIST] Re: Crystal Oscillator
- From: "pankaj kumar" <pan_kmr@xxxxxxxxxxxxxx>
- To: "Ray Anderson" <Raymond.Anderson@xxxxxxx>
- Date: 25 Jul 2003 21:16:48 -0000
Hi Raymond,
Thanks for the detailed explanation. As you quoted
">When operated at parallel resonance the quartz resoantor
contributes
>180 degrees phase shift."
Could you Pl. explain how the quartz resoantor contributes
180 degree phase shift?
Thanks/-
Pankaj
On Sat, 26 Jul 2003 Ray Anderson wrote :
>
>Pankaj-
>
>A quartz crystal resonator has two resonant modes, series and
>parallel.
>(The series resonant frequency is (to a first order
>approximation)
>determined by the series combination of the motional inductance
>and
>motional capacitance of the quartz crystal.
>
>The parallel resonant frequency is determined by the series
>connection
>of the motional inductance and motional capacitance in parallel
>with
>the shunt holder capacitance. The series and parallel frequencies
>are
>very close to each other, typically separated by only a few
>kilohertz.
>
>Also note that when operated in the series resonant mode, the
>quartz
>resonator contributes ZERO degrees phase shift at resonance.
>When
>operated at parallel resonance the quartz resoantor contributes
>180 degrees phase shift.
>
>So an oscillator whose active element contributes 180 degrees
>phase
>shift (perhaps a single inverter) may be used at the parallel
>resonant
>frequency of the quartz resonator to sustain oscillation. (180 +
>180 =
>0 degrees or positive feedback).
>
>If your active elements contribute 0 degrees phase shift (say,
>two
>invertors), then the quartz resonator will operate in the series
>resonant
>mode (with zero degrees phase shift contributed by the crystal)
>to
>sustain oscillation at the series resonant frequency.
>
>Note that capacitive loading by the oscillator circuit can
>'pull'
>the actual frequency of oscillation slightly, and may
>contribute
>a small amount of phase shift that may cause the oscillator to
>actually
>operate slightly off the series or parallel resonant frequencies
>of
>the unloaded quartz resonator.
>
>I hope this explanation helps out.
>
>Ray Anderson
>Staff SI Engineer
>Sun Microsystems Inc.
>
>
> >
> >Hi Raymond,
> > I have some querry about crystal oscillator at parallel
>resonance. The
> >reason, I am asking you personally is because I posted the same
>question
> >in SI list, but unfortunately didn't get any response. Your
>help will be
> >really appreciated.
> > I understand in parallel resonance mode 180 degree(infact
> >180)
> >phase shift comes from inverter. Also, other 180 degree phase
>shift will
> >come from crystal and load. Now, crystal is modelled as
>inductor above
> >series resonance. That means, we are having inductor and
>capacitor, which
> >acts like tank circuit. But, tank circuit will give 0 degree
>phase shift.
> >So, I am wondering how we are getting the remaining 180 degree
>phase shift?
> > Any insight will be great help to me. Also, please forward me
>some
> >good links.
> >
> > Thanks in Advance.
> >
> >Pankaj Kumar
> >IO Design Engineer
> >ARTISAN COMPONENTS, INC.
> >
> >www.artisan.com
> >
>
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