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Simple Varactor Model: VRCTR

Symbol

Summary

VRCTR models a lossless varactor. Internally, this element is identical to the nonlinear capacitor model (NLCAP), but the nonlinear characteristics are extracted automatically from tabulated data.

Parameters

Name Description Unit Type Default
ID Device ID Text C1
CData Capacitance data Capacitance {1}
VData Voltage data Voltage {-1} V
PolyOrd Polynomial order   5
Tolerance Maximum fitting error   2

Parameter Details

The C/V data is entered in the CData and VData fields. It can be entered manually, for example:

CData = {30,15,10,5,4,3}

VData = {0,1,2,3,4,5}

or by referencing file-based data.

Suppose that measured C/V data is stored in a file called cv.txt. The data is column-ordered, with C in the first column and V in the second column.

Import the file by right-clicking on Data Files in the Project Browser and choosing Import Data File. In the Open dialog box, in Files of Type, select Text Data Files and then browse for cv.txt. Now, place the following equation on the schematic:

cv_data = DataFile("cv.txt");

cv_data is now a matrix with the C/V data in its columns.

Type the following equations in the CData and VData parameter fields to access the needed columns of cv_data:

For CData: Col(cv_data, 1)

For VData: Col(cv_data, 2)

PolyOrd is the order of the polynomial used for numerical fitting of the capacitance data. Higher polynomial orders may result in convergence problems, so it is best to keep it as low as possible. It is rarely necessary to specify orders higher than 5.

Once a numerical fit to C/V data has been performed, the model will compute the maximum relative error between the measured data and the polynomial prediction. If that number, measured in %, is larger than Tolerance, the model will report a warning.

Simulation of the model's C/V characteristic and hence the quality of the polynomial fit, is highly recommended. See the Examples\Circuit Design Types\Modeling\varactorplot.emp example project.

Layout

This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.

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