Harmonic Balance Assisted Harmonic Balance

This topic describes the automated harmonic balance assisted harmonic balance simulation (HBAHB). Using this method when performing a multi-tone harmonic balance simulation allows the simulator to decide automatically which tones to use in generating the final HB solution. For example, instead of simulating a three-tone circuit directly, it is possible to simulate a one-tone, then use the result as an initial guess for a two-tone, and finally use that result as an initial guess for the third tone. HBAHB is both fast and robust, particularly for large multi-tone simulations of mixer circuits to determine gain and IP3.

HBAHB applies only to multi-tone simulations. By default, this feature is enabled within the HB simulator. The simulator determines the optimal sequence of tones to simulate. Depending upon various conditions, the simulator may decide to simulate a three-tone HB simulation with only the first tone, then use that result as an initial guess directly for a three-tone.

If you are not familiar with the harmonic balance simulator, see Harmonic Balance Basics.

The following topics describe details about automated HBAHB:

• Modes of HBAHB Operation
• HBAHB, Parameter Sweeps, and Noise
• HBAHB and TAHB
• HBAHB and Non-Convergence

Modes of HBAHB Operation

There are three modes for the HBAHB - Auto, On, and Off. The default mode is Auto.

To set the HBAHB mode:

1. Place the HB controller on the schematic and open its setup dialog box.
2. On the Initial Guess tab, in the HBAHB section, select the mode.
   • In the Auto mode, the simulator decides whether or not to perform the HBAHB, and the optimal sequence of tones to simulate.
   • In the On mode, the HBAHB always performs a simulation at each tone.
   • In the Off mode, the HBAHB is not performed at all. When the HBAHB is off, a standard multi-tone HB simulation is performed.

For additional setup information, see Setting Up the Initial Guess.

When selecting Solver parameters for a harmonic balance simulation with the HBAHB set to Auto, it is recommended that you set Convergence Mode to Auto and Solver Type to Auto (see Selecting a Harmonic Balance Solver Technique). These settings ensure that simulation of the intermediate tones is both fast and robust, and that the optimal solver is selected when simulating the different tones.

HBAHB, Parameter Sweeps, and Noise

When performing a swept simulation, HBAHB occurs only for the first, or innermost, sweep point. When simulating a noise analyses, the HBAHB occurs prior to the noise. This means that the noise analyses is not performed at the intermediate tones.

HBAHB and TAHB

HBAHB will not be performed if TAHB takes place. The HB analysis will read in the transient solution as the initial guess.

If you provide an initial guess using Initial Guess parameters InFile and UseInFile, HBAHB will not be performed so long as the supplied initial guess file exists. If the file does not exist, the simulator will decide whether or not to perform HBAHB. Details about setting parameters for Initial Guess, HBAHB, and TAHB are located in Setting Up the Initial Guess.

HBAHB and Non-Convergence

At any point of time during the HBAHB analysis, if non-convergence occurs, the simulation will stop HBAHB and resort to a standard multi-tone HB analyses. A new DC initial guess will also be recomputed. If TAHB was enabled, then the transient initial guess will be restored.