Controlling Output from Transient Analysis — Ansoft Designer 7.0 在线帮助文档，Ansys Designer 教程

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Controlling Output from Transient Analysis

By default, the output shows all node voltage values at the timesteps produced by the numerical integration. From the Schematic Editor, you can limit the output to specific variables with the Output Quantities dialog. From the netlist, you can specify a list of particular values with a .PRINT statement. For example, if the netlist input contains the following statements:

.TRAN 10ns 1us

.PRINT TRAN V(12), V(15)

Nexxim outputs just the voltages on nodes 12 and 15 at the internal timesteps. Without the .PRINT statement, the output would include voltages at all nodes in the circuit.

Nexxim performs quadratic interpolation between time steps. Unlike some Spice simulators, the output is not automatically interpolated to (uniform) TSTEP increments.

Stable Undershoot and Numerical Beating

When a periodic signal such as a sinusoidal or piecewise linear waveform is analyzed, the timesteps are selected to give an accurate representation of the periodic signal. Chance differences in the location of timepoints can lead to apparent errors when the wave is plotted.

Undershoot. In some cases, no time step falls at the exact high or low point of the waveform. When this happens, interpolation may cause the maximum and minimum values as plotted to appear less than the known high and low values. Quadratic interpolation used by Nexxim helps with this “stable undershoot” problem, but cannot fully resolve it.

Beating. Nexxim tries to set constant time points to sample at the same places each period of the waveform. When the period of the signal is not an integral multiple of the timestep, the apparent frequency implied by the time steps can be slightly different from the frequency of the signal. This frequency difference generates a “numerical beating” which appears in the plotted waveform. Decreasing the timestep improves the plots, but uses more analysis time.


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