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Tip of the Week: When should I use the pss/qpss Harmonic Balance vs. Shooting Newton Engine?

Comments(0)Filed under: RF design, Circuit design, Virtuoso Spectre, Virtuoso Spectre Simulator GXL, Spectre, Spectre RF, Virtuoso Spectre Simulator XL

Shooting Newton (shooting) and harmonic balance (HB) are complementary technologies and used for circuits that exhibit different behaviors.

The shooting Newton algorithm uses an adaptive time step control, which is particularly effective for sharp transitions. Convergence is robust and not as sensitive to model imperfections.

Harmonic balance is much faster for mildly nonlinear circuits. When the simulation parameters are set up properly, both should give accurate, very similar results (however, since the algorithms used are not identical, the results will not be identical).

Use harmonic balance for:

  • High dynamic range, weakly-nonlinear systems
    • RF front-ends (LNA, Mixer)
    • IQ modulators
  • Mildly nonlinear oscillators with resonators, such as
    • LC oscillators
    • Crystal oscillators
    • Negative-gain oscillators
  • Circuits with distributed components
    • Transmission lines
    • S-parameter models

Use shooting Newton for:

  • Circuits where input signals have sharp transitions
  • Strongly nonlinear circuits
    • Frequency dividers
    • Strongly-nonlinear resonatorless oscillators, such as
    •  
      • Ring oscillators,
      • Relaxation oscillators,
      • Oscillators containing digital control components,
      • Oscillators with dividers.

Important Note -- if simulating oscillators, see: 

http://sourcelink.cadence.com solution 11480630 - Guidelines for Simulating Oscillators in SpectreRF MMSIM 7.0.1

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