Harmonic Balance
Understanding Harmonic Balance
Harmonic balance is the workhorse simulation technique for nonlinear RF circuit design. While S-parameter simulation handles linear circuits and transient simulation handles time-domain signals, HB is the tool for evaluating nonlinear behavior at specific frequencies.
| Amplifier Type | Noise Figure | Gain | Output Power |
|---|---|---|---|
| LNA | 0.3-2 dB | 10-25 dB | -10 to +10 dBm |
| Driver | 3-8 dB | 10-20 dB | +15 to +25 dBm |
| Power Amp | N/A | 8-15 dB | +30 to +50 dBm |
| Distributed | 3-6 dB | 5-12 dB | +10 to +20 dBm |
HB Simulation Capabilities
- Power sweep: Gain compression (P1dB), AM-PM conversion, efficiency vs power.
- Two-tone: IP3, IM3 products, spur levels.
- Large-signal match: Impedance at the operating power level (not small-signal S11).
- Mixer analysis: Conversion loss/gain, port isolation, spur chart.
- Oscillator analysis: Steady-state oscillation frequency, output power, harmonics.
Frequently Asked Questions
What is harmonic balance simulation?
HB is a frequency-domain method for simulating nonlinear RF circuits. It solves for steady-state response at each harmonic frequency by balancing linear and nonlinear subcircuits. The standard tool for PA, mixer, and oscillator design.
When do I use HB vs transient simulation?
HB: steady-state nonlinear analysis, gain compression, IP3, mixer performance. Transient: startup behavior, oscillator startup, digital modulation (time-varying signals). HB is much faster than transient for steady-state analysis.
What tools support harmonic balance?
Keysight ADS (industry standard), Cadence Spectre RF, NI AWR Microwave Office, ANSYS HFSS with circuit co-simulation. ADS is the most widely used HB simulator in RF industry.