Running PSS for an oscillator with a driving signal in some other part of the circuit.

This can be done with hb/hbnoise; it's not possible with PSS, since that requires a single tone only, and the common frequency with a driven signal + oscillator would be chaotic (highly nonlinear). Shooting QPSS also doesn't support it because it would essentially have to start again as it tried to solve for the oscillator frequency. 

So we have added it for multi-tone harmonic balance analysis, but it's only been added via the HB analysis form itself. The feature is called "semi-autonomous harmonic balance", and there's an example (if my memory is correct) in the SpectreRF workshop at <MMSIMinstDir>/tools/spectre/examples/SpectreRF_workshop/rfworkshop.tar.Z (there's a database and a PDF inside).

Regards,

Andrew.

 Dear Andrew,

Thnaks a lot for your reply.

I want to know whether the hb analysis is suitable for hard-non-linearity( inverter based ) oscillator as compared to a LC based Oscillator.

Also:-

Could you please reply to my query :- http://www.cadence.com/Community/forums/p/26723/1325269.aspx#1325269 ? It has stopped me for doing pnoise analysis further. I think you may be the most suitable person who can clear the doubts ( though I couldn't get any clear-cut answer by reading the documnets ).

Kind Regards,

Hi RF Stuff...

Regarding:  want to know whether hb analysis is suitable for hard-non-linearity (inverter based) oscillator as compared to an LC oscillator.

If you have a semi-autonomous circuit (oscillator with a driven source), you MUST use hb with the semi-autonomous option.  Only hb has the semi-autonomous capability.  Since the circuit is strongly nonlinear, you will need to increase oversample (4 or higher) and also increase the number of harmonic (as compared to a nearly sinusoidal oscillator).

If this is strictly an oscillator and it is a strongly nonlinear oscillator, then use pss analysis (rather than harmonic balance.).

Please see post: /blogs/rf/archive/2008/09/03/tip-of-the-week-when-to-use-harmonic-balance-engine-vs-shooting-newton-engine.aspx?postID=11093

 best regards,

Tawna

Dear Andrew,

Is it a good option to go for Transient Noise Analysis ( i.e. direct time domain analysis) in these type of chaotic cases ?

Kind Regards,

I always say that transient noise is the option of last resort. The only reasons to use it are if the circuit is non-periodic in nature and can't be simulated with a more efficient method (such as semi-autonomous HB as described before) or if you need to be able to see a large signal response to the noise (e.g. the noise is large enough to cause distortion or significant intermodulation).

Transient noise is always a challenge, because you need to have sufficient accuracy to allow the noise (which is small for most circuits) to be observed given the usual dynamic range of transient analysis; low frequency noise needs a long simulation, and high frequency noise needs short time steps. So that's short time steps over a long simulation with high accuracy; that tends to mean long simulation times!

Small signal noise analyses are much more efficient and generally more accurate because you don't lose the noise below the numerical noise floor in the simulator, plus you don't need to run over multiple periods to see the average noise effect. So they're nearly always preferable if you can use them.

Regards,

Andrew.