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Ansoft Designer / Ansys Designer 在线帮助文档：

Nexxim Simulator >
   Nexxim Simulation Process >
       Nexxim Analyses           

Nexxim Analyses

Nexxim provides a variety of analysis methods for simulating circuit designs. The Nexxim simulation engine incorporates DC analysis, transient analysis, harmonic balance analysis, and linear network analysis. Any of these analyses can include a sweep of circuit parameters. The next several sections introduce each of these analysis types.

DC Operating Point Analysis

DC analysis provides the DC operating point voltages and currents. In turn, the DC operating point provides the initial values for DC sweep analysis, harmonic balance, and transient analyses. It also provides the large signal bias operating point for small signal AC analysis, noise analysis, and linear network analysis.

See Nexxim DC Analysis.

Transient Analysis in Nexxim

Transient analysis computes the response of a circuit over time, using a system of differential/algebraic equations derived from information provided by the circuit topology and by the device models. Transient analysis can calculate its initial values by running a DC operating point simulation, or can be set to use initial values supplied in the netlist.

See Nexxim Transient Analysis.

Harmonic Balance Analysis

Harmonic balance analyzes the periodic or quasiperiodic 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 quasiperiodic 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.

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.

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 from the TV noise analysis setup. A typical application for periodic transfer function analysis is to determine image rejection.

See Nexxim Time-Varying Noise 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, optionally including the effects of one or more driving frequencies.

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 quasiperiodic source such as a clock or Local Oscillator (LO) and the other input is a nonperiodic 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 would require a small timestep to capture the fast-changing input, but then would require a very large number of timesteps to simulate the slowly-changing nonperiodic input. Harmonic balance would fail to analyze the nonperiodic 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 time step are stored and returned as the result. From these coefficients, you can obtain a variety of results including a transient-like time-domain result.

See Envelope Analysis.

Monte Carlo Simulation

The Nexxim DC and transient analyses can be performed multiple times while using randomly generated values of one or more component parameters. The random-value method is referred to as Monte Carlo analysis.

Monte Carlo analysis is supported in Nexxim netlists. Designer does not provide a setup dialog for Nexxim Monte Carlo analysis.

See Monte Carlo Analysis.

Statistical Eye Diagram Analysis

Statistical eye analysis is commonly used to perform bit error rate (BER) simulations on high-speed communications channels. Statistical eye analysis uses statistical post-processing to calculate the performance of a serial channel given the channel parameters including jitter.

Nexxim’s QuickEye analysis uses simplifying assumptions to calculate the BER from a transient analysis of single transitions. Nexxim’s VerifEye analysis uses a fully statistical approach to calculate the BER.

See VerifEye And QuickEye Analyses.

AMI Analysis

The Algorithmic Modeling Interface (AMI) allows time-domain simulation of a linear channel using customer-supplied models for the transmitter and receiver. Reports include eye diagrams and bit-error-rate (BER) contours like those available for QuickEye.

For details on Nexxim AMI Analysis, see AMI Analysis.

Nexsys Discrete Time-Domain Analysis

In a Nexsys design, functional and electrical components and subdesigns may be connected arbitrarily. Nexsym analysis seamlessly integrates with NexximTransient analysis and Envelope analysis to solve mixed-mode design problems at differing levels of abstraction. Nexsys time domain analysis allows the simulation of arbitrary wired/wireless communications system topologies and other system-level applications.

For details on Nexsys Analysis, see Nexsys Analysis.

Variable Parameter Sweep

Any of the analyses described above can be augmented with a sweep of variable parameters. The analysis is run multiple times over a specified range of values for the given variable, which can be the circuit temperature, a circuit voltage or current, a device model parameter, a device instance parameter, or a user-defined netlist or subcircuit parameter.

See Variable Sweep.

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