FreeLists / si-list / [SI-LIST] Re: Crystal oscillator simulation in time domain by Pspice

["Sogo Hsu" <sogo.hsu@xxxxxxxxxxx>]

Hi, Partha and Peter,

In the simulation, we have put a noise source in the circuit. 
Actually, the circuit oscillated. However, the amplitude is too tiny 
to observe. We took Fourier Transformation for the tiny sinusoidal 
waveform. The 'oscillated' frequency depicted a negative feedback of 
complete close loop. I suspect that  the algorithm does merely pick 
the solution can meet convergence criterion.
 
Best Regards,

Sogo Hsu, Ph. D.

Simulation center/PCEG/Foxconn

--- In si-list@xxxxxxxxxxxxxxx, Parthasarathy Sampath <parthsv@xxxx> 
wrote:
> Hi Sogo,
>    We faced a similar problem when attempting design
> of crystal oscillators. This problem is acute for
> lower order frequencies. 
>    As you have said, pspice/hspice algorithm is unable
> to solve the circuit to develop oscillations. The main
> reason we belive is, crystal osc inductance has high
> 'Q', the energy concentrated at parallel resosance.
> Reducing the 'Q', spreads out this energy over a wider
> range of freq. Use parameters with lower 'Q' and you
> will certainly see oscillations.
>    Also, for lower order freq Crystals require higher
> resistance across the inverter(basically bias
> resistor) to enable more current to flow through
> crystal and you should see higher amplitude. But the
> drawback with higher resistor is, you start-up will be
> low - Reason, inverter takes long time to get itself
> autozeroed to its bias point - Higher RC delay.
> 
> Hope this Helps,
> 
> Regards,
> Partha!
> 
> PS: I did check out oscillator simulations on Spectre
> and results were pretty good. You may not require
> lower order 'Q' parameters.
> 
> 
> --- Sogo Hsu <sogo.hsu@xxxx> wrote:
> > Hi, Gurus,
> > 
> > I tried to simulate a typical oscillator and
> > investigate the start-up 
> > time by Pspice. The oscillator consists of an
> > inverter and crystal. 
> > the crystal was modeled by it's equivalent circuit.
> > However, we were 
> > unable to start up the oscillation successfully. It
> > seems that is the 
> > limitation of Newton-Raphson algorithm. The
> > algorithm ensures the 
> > circuit simulation can converge to solution.
> > Accordingly, it gives up 
> > the oscillation solution to avoid 'diverge' issue.
> > How can I solve 
> > this issue and bypass the converge requirement to
> > achieve 
> > oscillation? Thank you for your comments in advance.
> > 
> > Sogo Hsu Ph. D.
> > Foxconn
> > 
> >
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