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In the new runs, C1 varies from .1n to 4.6n and R1 varies from 12.5 to 50. The plot shows the functions vs. the C1 variable only. What about R1? Since a 2D plot can only show functions versus one variable, the plot itself is prepared for a single value of the other stepped variable. In this case the plot is for R1=12.5 only. To see other values, press F10, and select a new value from the R1.Value list box for each of the two plots. Here is the plot for R=25.

Figure 26-8 The Fall_Time performance plot for R=25

When two or more variables are stepped, there is another way to view the results. You can do a 3D performance plot. To illustrate, select Add 3D Window from the 3D Windows item on the Transient menu. From the 3D Properties dialog box select the Performance item from the Y Axis Type group, and select the Fall_Time function from the Function list box in the What To Plot group. Click OK. The result looks like Figure 26-9.

This 3D plot shows the Fall_Time function plotted along the (vertical) Y axis vs. C1 along the (horizontal) X axis and R1 along the (normal to paper) Z axis. It is the same data but presented a different way. In fact if you examine the 3D plot, you can see the 2D fall time plot within it.


Figure 26-9 The 3D Fall_Time performance plot

638 Chapter 26 Performance Functions

Chapter 27

3D Graphs

What's in this chapter

Micro-Cap provides 3D graphs for plotting and visualizing simulation results. This chapter shows you how to use them.

The chapter is organized as follows:

How 3D plotting works

3D example

The 3D dialog box

Cursor mode in 3D

3D performance functions

Changing the plot orientation

Scaling in 3D

Features new in Micro-Cap 7

Ability to use performance function expressions in 3D performance plots instead of single performance functions.


How 3D plotting works

In a 3D plot there are three variables. Each is associated with one of three mutually orthogonal axes, X, Y, and Z. The Z axis may be thought of as pointing out from the paper toward the user. The X and Y axes are coplanar with the paper.

Y Axis



y = f(x,z)






X Axis










Z Axis

The Y axis can plot one of two things:

Any expression (curve) plotted during the run.

Performance function expressions using curves plotted during the run.

Expressions can be plotted if either temperature stepping or parameter stepping has been employed during the run.

Performance functions expressions can be plotted if at least two variables have been stepped. One of the two can be temperature.

The first stepped variable is plotted along the Z axis. For example, if you stepped temperature and chose to plot V(1) on the Y axis, then T (Time) would normally be plotted on the X axis, and the stepped variable, temperature, would normally be plotted on the Z axis. If you stepped R(R1) and you chose to plot V(1) on the Y axis, then T (Time) would normally be plotted on the X axis, and the stepped variable, R(R1), would normally be plotted on the Z axis.

T or the second stepped variable is plotted along the X axis. For example, if you stepped R(R1) and C(C1), then you could plot an expression like V(1) vs. T on the X axis and either R(R1) or C(C1) on the Z axis, or a performance function like Rise_time vs. R(R1) on the X axis and C(C1) on the Z axis.

640 Chapter 27: 3D Plots

3D example

To illustrate how 3D plotting works, load the file 3D1. It looks like this:

Figure 27-1 The 3D circuit

The circuit consists of a resistor, R1, and a symbolic variable, Drop, which is dependent upon the resistance of R1 and T. Select Transient from the Analysis menu. The analysis limits look like this:

Figure 27-2 The analysis limits of 3D1

According to these limits T will vary from 0 to 8 with maximum steps of .1. We are plotting the value of the Drop variable. Since there are no capacitors or inductors in this circuit, the actual time step size starts small and quickly ramps up to the maximum of .1.


The Stepping dialog box looks like this:

Figure 27-3 R(R1) is stepped from 0 to 8

According to this dialog box, the value of R1 will be linearly stepped from 0 to 8 in steps of 0.1. Click OK. Press F2 to start the run. The results look like this:

Figure 27-4 The 2D analysis plot of Drop

The plot shows the value of the variable Drop, with T varying from 0 to 8 and R(R1) varying from 0 to 8. There are 81 runs (1+8.0/0.1).

642 Chapter 27: 3D Plots

Select the Drop vs. T vs. R1.Value item from the 3D Windows item from the Transient menu. This plots the value of the symbolic variable, Drop, along the Y axis, vs. T along the X axis, vs. R(R1) along the Z axis like this:

Figure 27-5 The 3D plot of Drop

In this case, we stepped only one variable R(R1). During the run, MC7 calculated 81 values of R(R1), the Z axis variable, and a little more than 81 values of T, the X axis variable, for each of the 81 values of R(R1). For each of these approximately 6400 values, it calculated the value of the Drop function.

When a 3D plot is requested, MC7 interpolates the specified number of data points from the simulation run at equally spaced values. It then produces a 3D plot where the intersection of the X and Z isolines mark the interpolated data points. The patches between the grid lines are colored according to the value at the adjacent isoline. The color used (color spectrum, gray, clear, etc.) is specified in the 3D Plot Properties dialog box.


The Properties dialog box for 3D plots

When you add or change a 3D graph you employ its properties dialog box. To see what it looks like press F10. The Plot panel of the dialog box looks like this:

Figure 27-6 The Plot panel of the 3D dialog box

The dialog box controls all aspects of the 3D graph. The command buttons at the bottom access the principal features of the graph:

OK: This accepts any changes made and exits the dialog box.

Cancel: This ignores any changes made and exits the dialog box.

Apply: This redraws the plot behind the dialog box using the current settings so you can see what the settings look like before committing to them.

Help: This accesses the Help system.

There are six panels:

Plot: This button accesses the main plot features of the 3D graph. In particular it includes these items:

644 Chapter 27: 3D Plots

Axis Variables:

Z Axis: This field lists the variables available for plotting along the Z axis. These include any stepped variable.

X Axis: This field lists the variables available for plotting along the X axis. If the Y Axis Type Performance item is enabled, this list will include all stepped variables except the one already selected for the Z axis. If the Performance item is not selected this list will include only the unique X expressions from the Analysis Limits dialog box. Usually this means only T (Time) or F (Frequency).


If more than one temperature has been run, and temperature is not being used as an axis variable, this field lets you select which run to plot.

Y Axis Type:

Performance: This option selects performance functions for the Y axis variable. If this option is enabled, any of the performance functions operating on any expression printed or plotted during the run may be used for the Y axis variable.

Expression: This option selects any of the expressions printed or plotted during the run.

What to Plot:

Top Row: This row lists excess stepped variables not already selected as axis variables. If a variable is not being used as an axis variable, you can select which of its stepped values you want to plot. Each value produces a different 3D surface plot.

Bottom Row: This row lists one of two things:

If the Performance item has not been selected:

The row lets you select an expression from the Analysis Limits Y Expression fields for plotting on the Y axis.

If the Performance item has been selected:

The row lets you select a performance function and its related data fields, Expression, Boolean, N, etc.


Options: This button accesses items which control the existence, quantity, or content of certain graph features. It looks like this:

Figure 27-7 The Options panel of the 3D dialog box

Title: This is the title of the 3D plot. The initial title is always of a form that reflects the names of the axis variables. Its format is "Y axis variable vs. X axis variable vs. Z axis variable". You can edit this field to change the title text if Auto is disabled. However, if the Auto field is enabled, the title will automatically revert to the axis name form as changes are made to axis variable names.

Options: These items control the existence of certain graph features:

Contour: This option plots a 2D contour of the Y axis variable.

Axes: If enabled, this option adds the three axes, X, Y, and Z. Note that the axes are colinear with the grid, so to see the effect of this feature, the Grid feature must be disabled.

Isolines: This option draws isolines on the plot along which X and Z are constant. The intersection of these lines comprise the boundaries of the colored surface patches of the 3D plot.

Grid: This option draws parallel grid lines in each coordinate plane to delineate equal fractional parts of the scale.

646 Chapter 27: 3D Plots

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