Circuit Frequency Domain Analyses

Nexxim provides a variety of analysis methods for simulating circuit designs in the frequency domain.

Harmonic Balance Analysis

Harmonic balance analyzes the periodic or quasi-periodic steady-state response of a circuit to a periodic input by solving the circuit equations in the frequency domain. Time domain equations are represented by their Fourier series equivalents. In a one-tone or periodic analysis, the input is a sine wave at a specified frequency, and the response is measured over a specified range of harmonics of that frequency. In a multi-tone or quasi-periodic analysis, the input is a combination of sine waves at different frequencies, and the response is a spectrum containing the DC response, the harmonics of the input frequencies, and the sums and differences of the harmonic frequencies.

See Nexxim Harmonic Balance Analysis.

HB Load Pull Analysis

Load-pull analysis is used to determine the optimum load on a circuit. Nexxim load-pull analysis measures the output calculated by harmonic balance while varying the reflection coefficient of one input. The load-pull input is set up as a passive tuner.

See Nexxim Harmonic Balance Analysis.

Oscillator Analysis Tool

Oscillator analysis uses harmonic balance analysis techniques to find the oscillating frequency of a resonant circuit. The resonant frequency is an unknown, although the process of finding it can be aided by providing an estimate that is close to the true value.

The analysis has two phases. First, initial estimates of the oscillating frequency and test voltage are made, either from user input or as directed by simulator options, and those estimates are assigned to the probe. Second, multiple harmonic balance analyses are performed while adjusting the probe frequency and voltage, until a more accurate, final resonant frequency is found.

Oscillator analysis can be set up for single-tone or multi-tone calculations. In single-tone analysis, a single resonant frequency is calculated. In multi-tone analysis, two or more unknown oscillations are analyzed. Including the effects of one or more driving frequencies is optional.

The simulation can be directed to run just the initial estimate phase (resonant frequency search), or to run both the initial and the final phases of oscillator analysis.

The simulation can include phase noise analysis as part of the oscillator analysis.

See Nexxim Oscillator Analysis.

Envelope Analysis

Envelope analysis is commonly used to analyze systems where harmonic balance or transient analysis alone is not adequate. Such systems include circuits with two inputs, where one input is a fast-changing periodic or quasi-periodic source such as a clock or Local Oscillator (LO) and the other input is a non-periodic source such as a baseband RF modulator that changes on a timescale that is orders of magnitude slower than the timescale of the fast-changing input. Transient analysis requires a small timestep to capture the fast-changing input, but then requires a very large number of timesteps to simulate the slowly changing non-periodic input. Harmonic balance fails to analyze the non-periodic input.

Envelope analysis uses transient analysis to simulate the slowly moving signal in the time domain, plus harmonic balance to analyze the fast-moving signal in the frequency domain. The time-domain analysis can use a varying timestep that is appropriate to the slowly changing waveform. At each timestep of the transient analysis, an HB analysis is run. The frequency coefficients at each timestep are stored and returned as the result. From these coefficients, obtain a variety of results including a transient-like time-domain result.

See Envelope Analysis.

Time-Varying Noise Analysis

Time-varying noise analysis (TV-Noise) calculates the response of a circuit to shot, thermal, and flicker noise sources analyzed as small-signal AC perturbations around the periodic steady-state operating point calculated by harmonic balance. The circuit elements are linearized by a DC operating point calculation prior to the harmonic balance analysis. The user specifies the range of frequencies over which the noise is to be calculated, one output whose response is to be calculated, and the output harmonic frequencies of interest. Optionally, an input can be specified to use as an input-referred noise (IRN) source. The response matrix shows the noise power spectrum at the specified harmonic frequencies.

See Nexxim Time-Varying Noise Analysis.

Periodic Transfer Function Calculation

The TV Noise analysis can be extended to include periodic transfer function analysis. Periodic transfer function analysis computes the small-signal transfer function from multiple input sources at multiple frequencies to one output at one frequency, or using the sweep of output frequencies on the TV noise analysis setup. A typical application for periodic transfer function analysis is to determine image rejection.

See Nexxim Time-Varying Noise Analysis.

Linear Network Analysis

Linear network analysis (LNA) computes the frequency-dependent scattering, impedance, and admittance parameters for a linearized circuit. Linear network analysis performs a linear frequency-domain analysis. Circuit components are analyzed using Y-matrix analysis, and any nonlinear devices are linearized around their bias points when computing the bias values.

Optionally, LNA can include group delay analysis. Group delay analysis determines the delay of the propagation of energy at a given frequency point. This analysis is defined as the derivative of the phase of a network parameter with respect to frequency, using the S-parameters as a basis for calculation.

Optionally, LNA can include DC noise analysis. Noise analysis calculates the noise spectral density at designated outputs due to thermal, flicker, and shot noise sources in a circuit that has been linearized around the DC bias operating point.

Optionally, LNA can calculate the AC small-signal transfer functions relating outputs to inputs at selected test frequencies. AC analysis calculates the response of a circuit to small-signal AC perturbations around the DC bias operating point.

See Nexxim Linear Network Analysis.

Smith Tool

The Ansys Smith Tool is an interactive Smith chart utility for the design of amplifiers, oscillators, and matching networks. The Smith Tool is available after a successful linear network analysis.

See Smith Tool.