FreeLists / si-list / [SI-LIST] Re: Crystal Oscillator Overtones.

[Parthasarathy Sampath <parthsv@xxxxxxxxx>]

Hi Merrick,
   The phase crosses '0' at three different points
corresponding to Fundamental, 2nd overtone and 3rd
overtone.
   The impedance offered by tank at 3rd overtone(the
case for which I have highest gain at this freq) is
infact Inductive!!!!
    This is what is more confusing for me. How will
this circuit oscillate when I have one load as
capacitive and another as inductive?  and I cannot get
any good gain at 3rd overtone if the tank impedance is
capacitive. 
   
Thanks 

Regards,
Partha!
--- "Moeller, Merrick" <mmoeller@xxxxxxxxxxxxxxx>
wrote:
> How does the phase shift look at your
> peak AC Gain? 
> 
> The initial condidtions on your simulation
> can provide misleading oscillations. If the
> signal dies out you probably aren't actually
> running. Check the phase.
> 
> Run Neg R. It will represent a combination of
> phase and gain. 
> 
> The High frequency of your tank circuit may be
> misleading your gain measurements. What is the
> tank impedance?
> 
> M
> 
> -----Original Message-----
> From: Parthasarathy Sampath
> [mailto:parthsv@xxxxxxxxx]
> Sent: Friday, May 30, 2003 5:06 PM
> To: Moeller, Merrick
> Cc: si-list@xxxxxxxxxxxxx
> Subject: RE: [SI-LIST] Re: Crystal Oscillator
> Overtones.
> 
> 
> Yes, it does include 1nf cap in series with tank
> circuit.
>   First i test for ac gain whihc inlcudes the
> invertor
> and crystal oscillator and once i achieve required
> gain with correct inverter size, I go for transient
> analysis to make other measurements.
>    Another peculiar thing is, with tank ckt freq
> twice
> the 3rd overtone, I have good ac gain, while in
> transient analysis, the ouput dies out.
>  
> Regards,
> Partha
> --- "Moeller, Merrick" <mmoeller@xxxxxxxxxxxxxxx>
> wrote:
> > First, are you using a decoupling cap from 
> > your tank inductor to ground? Second what 
> > type of simulation are you running...
> > A negative R simulation is good in this 
> > case you should see your negative R cross
> > 0 at your tank resonant frequency.
> > 
> > Merrick
> > 
> > 
> > -----Original Message-----
> > From: Parthasarathy Sampath
> > [mailto:parthsv@xxxxxxxxx]
> > Sent: Friday, May 30, 2003 3:01 PM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Crystal Oscillator
> Overtones.
> > 
> > 
> > >   My question is at freq above tank corner freq,
> > the
> > > tank becomes inductive and whole circuit becomes
> > > imbalanced. 
> >   'The above statement should be "At freq below
> tank
> > frequency, the tank should become inductive and
> the
> > whole circuit becomes inductive with one load of
> > crystal being capacitor and other inductor(due to
> > tank)".
> >    
> > 
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