.GRAPH

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Parameters

.GRAPH supersedes the older and less flexible .TRACE. The latter is, however, still supported and may sometimes be convenient for specifying multiple signals on one line.

Using Multiple .GRAPH Statements

If specifying several .GRAPH statements to plot a number of curves on the same graph, you should make sure that the various parameters are consistent. If for example, a conflict arises if you specify xmin and xmax for two .GRAPHs that plot curves in the same graph sheet, and the values for xmin and xmax are different for each. You can specify xmin and ymin for just one of the .GRAPH statements or you can specify for all and make sure they are all the same. The same applies to other non-Boolean parameters i.e. ymin, ymax, xlabel, ylabel, xunits and yunits. The parameter initXLims, however must be specified with the same value for all .GRAPH statements specifying the same graph sheet.

Conflicting values of ylog and xlog are resolved by plotting the curves on separate axes or graph sheets respectively.

Creating X-Y Plots

To create an X-Y plot, use the XY() function (Script Reference Manual/Function Reference/XY for full details of available functions). You should also specify "initXLims=false". E.g.

The above will create a Nyquist plot of the vector VOUT.

Using .GRAPH in Subcircuits

Using Expressions with .GRAPH

You can enter an expression as well as single vectors to be plotted. A problem arises when plotting expressions incrementally that are regularly updated while the simulation is running. SIMetrix versions prior to v5 could not incrementally evaluate expressions, so each time the plot of an expression was updated, the expression had to be recalculated from the beginning. This was inefficient and it has always been recommended that the complete=true flag was added in these circumstance to inhibit incremental plotting.

SIMetrix - from version 5 - now has the ability to incrementally evaluate some expressions and there is no longer a recommendation to set complete=true. However, certain expression cannot be incrementally evaluated and when such expressions are entered, incremental plotting will automatically be disabled and the plot won't appear until the run is complete.

A notable example of expressions that cannot be incrementally evaluated is anything containing the phase() function. This is because the phase() function uses a state machine to determine when the phase wraps from -180 to 180 and back. An offset is then applied to make the phase plot continuous. Because of the state machine, it is always necessary to evaluate this function from start to finish which makes incremental evaluation difficult. An alternative is to use instead the arg() function. This is the same as phase, but does not have the state machine and always gives an output that lies between +/- 180 degrees.

Plotting Spectra with .GRAPH

You can use .GRAPH to create spectrum plots using FFTs or Fourier. However, FFT is quite difficult to use on its own as it needs interpolated data. So, a new user defined function called Spectrum() has been developed that is especially designed for use with .GRAPH. Usage is:

Examples

Plots the vector C2_P and gives it the label 'Amplifier output'. As NOWARN is TRUE, no warning will be given if C2_P does not exist.

The above illustrates the use of the parameters AXISTYPE and AXISNAME. Both the vectors specified by the above .GRAPH statements will be plotted on the same but separate grid. Because both grids have been given the AXISNAME grid1, each curve will be plotted on the same one. If the values of axisname for the above were different, each curve would be plotted on a separate grid. The ANALYSIS parameter has been specified in both cases, so plots will only be created for transient and dc sweep analyses.