Transient Analysis

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Description

A Transient analysis generates output similar to that normally shown on an oscilloscope, computing the transient output variables (voltage or current) as a function of time, over the user-specified time interval. An Operating Point analysis is automatically performed prior to a Transient analysis to determine the DC bias of the circuit, unless the Use Initial Conditions parameter is enabled.

Setup

Transient analysis is set up on the Transient/Fourier Analysis Setup page of the Analyses Setup dialog (after the dialog appears, simply click the Transient/Fourier Analysis entry in the Analyses/Options list). The default setup for this analysis type is shown in the image below:

Parameters

Transient Step Time or

(Transient Stop Time - Transient Start Time) / 50,

whichever is the smaller.

Notes

A Transient analysis always begins at time zero. In the time interval between zero and Transient Start Time, the circuit is analyzed but the results are not stored. In the time interval between Transient Start Time and Transient Stop Time, results are stored for display.

Although Transient Step Time is the nominal time increment used in the analysis, the actual time step is varied automatically to achieve convergence.

Typically Transient Step Time and Transient Max Step Time are set to the same value. As a starting point set both of these parameters to

(Transient Stop Time - Transient Start Time) / 1000.

If you are not sure what values to enter, press the Set Defaults button on the page to automatically calculate the Transient analysis parameters as follows:

Transient Stop Time = (1/FL) * Default Cycles Displayed

Transient Step Time = (1/FL) / Default Points Per Cycle

Transient Max Step Time = Transient Step Time

When using Initial Conditions, make sure that you first define the initial condition for each appropriate component in the circuit, or place .IC devices on the circuit. The IC value of a component overrides an .IC object attached to a net.

Data is saved for all signals in the Available Signals list, on the General Setup page of the Analyses Setup dialog.

The simulation results are displayed on the Transient Analysis tab of the Waveform Analysis window.

Examples

Consider the circuit in the image above, where a Transient analysis is defined with the following parameter values:

The entry in the SPICE netlist will be:

*Selected Circuit Analyses:

.TRAN 5E-7 0.0001 0 1E-6

and running the simulation will yield the output waveforms shown in the image below:

Links

Fourier Analysis

Operating Point Analysis

Simulation Analyses