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News:

Spectrum Software has released Micro-Cap 11, the eleventh generation of our SPICE circuit simulator.

For users of previous Micro-Cap versions, check out the new features available in the latest version. For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer.

 

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Curve Fitting

 

Did you know that Micro-Cap 11 has a built-in curve fitting function? Any plotted curve can be fitted to an N-degree polynomial. Consider this circuit:

A sample circuit for curve fittng

This circuit has a single voltage source whose output is:

B*X+A+RF*RND/2

where A, B, and RF are 3 , 6, and 1 respectively and X is set to the T (Time) variable. RND is a random number between 0 and 1. The E1 source then generates a line whose equation is

6*T+3 + RND/2.

If you run transient analysis on it you get this plot.

The transient analysis run


Here the line is drawn with its random element. The curve has been fitted to a linear equation per the instruction from the Curve Fit dialog box. It looks like this:


The Curve Fit dialog box


This dialog box lets you select the curve(s) to be fitted, the range over which the fit will occur, and the polynomial degree for the fit. You can also choose options for placing the equation and error text as well as options for numeric format, and text style.

The dialog box is selected from the Scope menu / Curve Fit or by using CTRL+ALT+C, or by right-clicking on any expression text in the analysis plot.

This example is a simple one. Next we'll try a more complex curve to fit.

Consider this circuit:

Another sample circuit for curve fitting

There are no sources, just .define statements specifying a quadratic (Y2) and a 6'th order polynomial (Y). Run transient analysis and you get this plot:


The transient run


The routine has fitted the quadratic curve as Y = -4 +-2*X + -3*X^2 and the 6'th order curve as Y = -1 -2*X -3*X^2 +200m*X^3 +1*X^4 +100m*X^5 +50m*X^6. Both fits have RMS errors of less than 1e-12.

 
Download Winter 2015 Circuit Files
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