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.dc Line

The dc analysis portion of WRspice determines the dc operating point of the circuit with inductors shorted and capacitors opened. The dc analysis is used to generate dc transfer curves: a specified voltage or current source is stepped over a user-specified range and the dc output variables are stored for each sequential source value.

General Form:
.dc src1 start1 [stop1 [incr1]] [src2 start2 [stop2 [incr2]]]
Examples:
.dc vin 0.25 5.0 0.25
.dc vds 0 10 .5 vgs 0 5 1
.dc vce 0 10 .25 ib 0 10u 1u
.dc vdd 5 6

The .dc line defines the dc transfer curve source and sweep limits. The variation may be in one or two dimensions, depending upon whether the second block is provided. The src parameter is the name of a voltage or current source to vary. The start, stop, and incr parameters are the starting, final, and incrementing values, respectively. If incr parameter is not supplied, analysis will be performed at the start and stop. If in addition the stop parameter is not given, analysis will be performed at start, i.e., the level is fixed. A parameter can be omitted only if all parameters to the right are also omitted.

A second source (src2) may optionally be specified with associated sweep parameters. In this case, the first source will be swept over its range for each value of the second source. This option can be useful for obtaining semiconductor device output characteristics.

The first example will cause the value of the voltage source vin to be swept from 0.25 volts to 5.0 volts in increments of 0.25 volts.

In WRspice, other types of analysis (ac, noise, transfer function, sensitivity, and transient) can be chained to a dc analysis specification. In this case, the requested analysis is performed at each successive operating point, as specified by the dc part of the analysis specification. The resulting circuit variables are saved as multi-dimensional vectors, which can subsequently be saved in a rawfile or plotted (together or as individual traces).

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

If Josephson junctions are present in the circuit, they will be taken as shorted (actually, a resistance of 1uV/Ic) during DC analysis. It is in general not possible to perform this type of analysis on Josephson junctions. The approach taken here may be useful when working with hybrid semiconductor/superconductor circuits, but in no case should one expect DC analysis of Josephson circuits to ``work''. Transient analysis, which takes into account the past history of the Josephson excitation, is required for a complete simulation.


next up previous contents index
Next: .disto Line Up: Analysis Specification Previous: .ac Line   Contents   Index
Stephen R. Whiteley 2012-09-24