Visjnoe wrote on Aug 26th, 2008, 12:21am:When I mean faster, I indeed compare 'common' transient analysis to envelope analysis.
If you have interest only on steady state, you don't have to invoke envelope analysis. Rather just run simple steady state analysis such as HB or Shooting Newton.
Envelope analysis is time varied steady state analysis, so envelope analysis is redundant and slow, compared to simple time invariant steady state analysis.
Visjnoe wrote on Aug 26th, 2008, 12:21am:But let me ask this: if the envelope analysis has no benefit over a common transient analysis, why would all EDA vendors advocate/promote using this method?
This is dependent on situation for which you apply envelope analysis.
Envelope analysis is efficient if energy is concentrated on one harmonic.
If energies are distributed to many harmonics, envelope analysis is less efficient than common transient analysis.
And if a complex envelope(magnitude and phase) is varied fairly fast, envelope analysis is also less efficient.
These are true for both HB and Shooting Newton based envelope analysis.
Visjnoe wrote on Aug 28th, 2008, 2:09am:1. The transient analysis (using initial conditions) took 7hrs.
Your initial conditions are not good.
If you apply proper initial conditions with skipdc=yes(spectre) or uic=yes(hspice), it can reach steady state immediately.
Here initial conditions I mean are all node voltages and all state currents. Not only initial current of inductor.
Visjnoe wrote on Aug 28th, 2008, 2:09am:2. The steady-state analysis using harmonic balance took 2min.
You immediately can assess the steady-state conditions, but unlike transient analysis
you cannot see the detailed start-up behavior over time.
If you have interest on start-up behavior over time, use a time varied steady state analysis such as envelope analysis.
Visjnoe wrote on Aug 28th, 2008, 2:09am:I can see why the RF simulation using shooting-Newton methods might not gain you that much in simulation time,
Just your initial conditions are not good.
For very high Q osciilator, HB analysis is not always superior than Shooting Newton.
Again you have to consider the followings for rapid simulation of very high Q oscillator.
HB analysis require very accurate final state oscillation frequency.
Shooting Newton require good initial conditions.
For transient assisted HB analysis, both good guess of final state oscillation frequency and good initial conditions are useful.