[SI-LIST] Re: Crystal oscillator simulation in time domain by Pspice
- From: Parthasarathy Sampath <parthsv@xxxxxxxxx>
- To: sogo.hsu@xxxxxxxxxxx
- Date: Wed, 9 Jun 2004 00:04:12 -0700 (PDT)
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@xxxxxxxxxxx> 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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