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.tran Line

The transient analysis portion of WRspice computes the transient output variables as a function of time over a user-specified time interval. The initial conditions are automatically determined by a dc analysis. All sources which are not time dependent (for example, power supplies) are set to their dc value. The transient time interval is specified on a .tran control line.

General Form:
.tran tstep1 tstop1 [tstart1 [tmax]] [tstep2 tstop2 ... tstepN tstopN] [uic]
[scroll | segment base delta] [dc dc_args]
Examples:
.tran 1ns 100ns
.tran 1ns 1000ns 500ns
.tran 10ns 1us uic

The tstep values are the printing or plotting increments for output, in the ranges

tstep1: tstart < = time < tstop1
tstep2: tstop1 < = time < tstop2
...
tstepN: tstopN-1 < = time < tstopN

The tstart is the initial time, assumed 0 if not given. The transient analysis always begins at time zero internally. In the interval [0, tstart), the circuit is analyzed (to reach a steady state), but no outputs are stored. Subsequently, the circuit is analyzed and outputs are stored. The parameter tmax is the maximum internal timestep size that WRspice will use. The internal timestep is computed dynamically from the circuit. The output generated at the specified tstep points is interpolated from the ``real'' internal time points. The tmax parameter can be used when one wishes to guarantee a computing interval which is smaller than the output increment, tstep.

The uic keyword (use initial conditions) is an optional keyword which indicates that the user does not want WRspice to solve for the quiescent operating point before beginning the transient analysis. If Josephson junctions are present, uic will always be taken as if set. If this keyword is specified, WRspice uses the values specified using ic=... on the various elements as the initial transient condition and proceeds with the analysis. If the .ic line has been given, then the node voltages on the .ic line are used to compute the initial conditions for the devices. See the description of the .ic line (2.4.2) for its interpretation when uic is not specified.

The scroll keyword is useful in the tran command in interactive mode. If the scroll keyword is given, the simulation will continue indefinitely, until stopped by a stop command or interrupt. The time range of data tstop - tstart behind the current time is retained in the plot.

If the segment keyword is given, along with a character string token base and real value delta, individual rawfiles are output for each range of delta as the simulation advances. The internal plot data are cleared after each segment is output. The files are named with the base given, as base.s00, base.s01, etc. This will not happen if a rawfile is being produced. If scroll is also given, it is ignored. If a dc analysis is chained, it is legitimate to pass a delta of zero, in which case a file is produced for each cycle. Otherwise, the delta should be a multiple or submultiple of tstop, or the files will be difficult to interpret. It is an error if delta is nonpositive if there is no chained dc analysis. The purpose of this feature is to facilitate extremely lengthly transient analysis runs.

The optional dc sweep is a dc analysis specification which will cause the transient analysis to be performed at each point of the dc sweep. The dc operating point is reevaluated at every sweep point, and output vectors will be multidimensional. The optional parameters before dc can be omitted in this case, as the parser recognizes the ``dc'' keyword as the start of a dc sweep specification. If the scroll keyword is given, the dc sweep is not available.

In interactive mode, the tran command, which takes the same arguments as the .tran line, can be used to initiate transient analysis.

During transient analysis, a special vector @delta maps to the (most recent) internal time step. To use in a plot, it must be saved first (using a .save line or the save command). It is sometimes useful or interesting to see how the internal timestep varies in a simulation.


next up previous contents index
Next: Output Generation Up: Analysis Specification Previous: .tf Line   Contents   Index
Stephen R. Whiteley 2006-10-23