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I am often asked for guidelines on maximizing speed vs. accuracy for
SpectreRF harmonic balance simulations.
Today, I'll discuss part 2 of the 3 part series consisting of:
Which Engine: Spectre or APS?Oversample vs Number of HarmonicsHarmonic Trimming
The first post in this series focused on the "which engine" question.
Another aspect of speed vs accuracy in Harmonic Balance Simulations is specifying the number of harmonics and the value of oversample.
Note: You may also want to look at Solution 11670194 Guidelines for setting "Oversample vs Number of Harmonics" in Harmonic Balance simulation. (https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1Od0000000nTyDEAU&pageName=ArticleContent )
Below are three scenarios I'll consider:
Circuit with sinusoidal voltage and current waveforms
Circuit with sinusoidal input but has some non-sinusoidal currents (for example) in the circuit
Circuit with square wave input or signals generated in the circuit are digital-like
If your circuit has sinusoidal voltage and current waveforms, start with setting oversample=1
Circuit has a sinusoidal input but currents are non-sinusoidal:
If your circuit has a sinusoidal input but currents (for example) in the circuit are non-sinusoidal -- say in the case of a diode mixer, you can still use harmonic balance, but you need to use considerably more harmonics.
Circuit contains square waves or digital-like signals
If your input is a square wave or signals generated in the circuit are digital (e.g. mixer + divider)... as mentioned above, see Solution 11670194 Guidelines for setting "Oversample vs Number of Harmonics" in Harmonic Balance simulation. (https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1Od0000000nTyDEAU&pageName=ArticleContent )
In general, the more non-sinusoidal the waveform, the higher you need to set oversample. Typically for "sharp" edges use oversample=8. For "rounded" edges, use oversample=4.
Finally, some circuits just do not play well with Harmonic Balance. Extremely nonlinear (but periodic) circuits may be better suited for the Shooting Newton engine.
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Stay tuned....next time I'll talk about Knob 3....Harmonic Trimming!