### Where To Find This Example

### 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.**

__Overview__

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.