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 > > > > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxx with 'unsubscribe' in > > the Subject field > > > > or to administer your membership from a web page, go > > to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxx with 'help' in the > > Subject field > > > > List FAQ wiki page is located at: > > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > List technical documents are available at: > > http://www.si-list.org > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > > Old (prior to June 6, 2001) list archives are > > viewable at: > > http://www.qsl.net/wb6tpu > > > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu