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

["Bob Weber" <rweber@xxxxxxx>]

In the commonly used single inverter crystal oscillator, the crystal
operates in the parallel resonance mode. In a manner of speaking, the
crystal itself provides the 'other' 180 degrees of phase shift. The
capacitors at the input and output serve two functions: providing capacitive
loading for the crystal (which is calibrated at some nominal capacitance,
say 20pf or so), and filtering high-frequencies to prevent the oscillator
from operating in harmonic modes, or even a parasitic mode that just uses
the body capacitance of the crystal to oscillate.
Bob W.

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
ViswanathanRavi@xxxxxxxxxxxxxx
Sent: Friday, January 10, 2003 7:17 AM
To: parthsv@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Parallel Resonance of crystall oscillator


U have missed the NOT gate in the crystal that provides 180 deg shift. Add
that to the 2 caps and u have 360 deg phase shift


-Ravi Viswanathan





Parthasarathy Sampath <parthsv@xxxxxxxxx>
Sent by: si-list-bounce@xxxxxxxxxxxxx
01/09/2003 08:29 AM
Please respond to parthsv


        To:     si-list@xxxxxxxxxxxxx
        cc:
        Subject:        [SI-LIST] Parallel Resonance  of crystall oscillator



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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