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Where To Find This Example

Understanding AWR .emz Files

Design Notes

Capacitance vs Voltage Analysis of a Varactor Model

This example demonstrates plotting Capacitance vs Voltage for the varactor model. The varactor model (VRCTR) can be found in the Element Browser under Nonlinear > Capacitor.


The model reads in data from a file, "bby58_02V", as seen by the equations in the "Varactor Bias" Schematic. The data file includes capacitance data on the first row and voltage data on the second.

Measurement Setup

The Swept Variable simulation control is used to plot the Capacitance vs Voltage (C-V) graph.

Using the advanced harmonic balance settings (Options > Default Circuit Options > Harmonic Balance tab > Advanced button), the project can be configured so that the charge can be measured across the varactor and the capacitance can then be derived.

Linear Cv vs Freq Graph

This graph shows the simulated capacitance versus frequency as computed using the C_SRC measurement which computes the capacitance at the input as a series RC. Corresponding with the data the capacitance is flat over frequency.

Linear Cv vs Voltage Graph

The Capacitance vs Voltage measurement was done in two different ways. The first way computed C vs V using the C_SRC measurement and setting the voltage as the x-axis values while holding frequency constant.

Use the tuner to change the swept voltage setting

DC Linearized C vs V Graph

The alternative way to measure Capacitance vs. Voltage is to use the CDC measurement, which computes DC Linearized capacitance. This graph shows this measurement being used to computer C vs V while holding the frequency constant.

Schematic - Varactor_Bias

Graph - Linear Cv vs Voltage

Graph - DC Linearized C vs V

Graph - Linear Cv vs Freq