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How to Create an FM Source SPICE Model

Simulating the behavior for circuits using Frequency Modulation (FM) is critical as FM is one of the most common ways to transmit an analog signal with minimal noise. Circuits contained in consumer radios, mic packs, and more require an accurate source or input signal for a realistic analysis; however, creating a model for an FM source can be difficult. PSpice allows you to quickly define and create the required FM source SPICE model to produce a realistic simulation.

This quick how-to will provide step-by-step instructions on how to create SPICE Models for FM sources in OrCAD PSpice.

To follow along, download the provided files above the table of contents.

How-to Video

Creating an FM Source SPICE Model

Step 1: Open the provided design in OrCAD PSpice Designer.

Step 2: Select Place > PSpice Part > Modeling Application from the menu.

Creating an FM Source SPICE Model

Step 3: In the Modeling Application, expand Sources and select Independent Sources.

Step 4: The Independent Sources window opens. Select the FM tab.

Step 5: Select Voltage as the source type.

Step 6: Enter 0 for the Offset and 5m for the Amplitude.

Defining FM Source SPICE Model Parameters

Step 7: Enter the following parameters for the FM Source:

  • Carrier Frequency: 1meg
  • Modulation Index: 5
  • Modulation Frequency: 100k

Learn how to determine the required parameters for a FM source SPICE Model here.

Note: The SI prefix is not case-sensitive. Entering 1M into this field would be interpreted as 1 millihertz. AC and DC parameters can be set for AC Sweep and DC Sweep analyses.

Step 8: Select Place to attach the source to your cursor.

Placing an FM Source Model in PSpice

Step 9: Click to place the source in the schematic.

Running the Simulation

Step 10: Select PSpice > Run from the menu.

Viewing the Simulation Results

Step 11: View the simulation results. An FM signal is shown, as expected.

Modifying the FM Source SPICE Model

Step 12: Back in the schematic, right-click the source and select More > Edit Source Component.

Changing the FM Source SPICE Model Parameters

Step 13: Change the Carrier Frequency to 2meg and the Modulation Index to 15.

Step 14: Select Update.

Step 15: Select PSpice > Run from the menu.

Step 16: View the simulation results and effect of changing the FM source parameters.

Wrap Up & Next Steps

Quickly create SPICE Models for FM sources to accurately simulate circuit behavior with the modeling application in OrCAD PSpice. Test out this feature and more with a free trial of OrCAD. To learn how to determine the required parameters for a FM source SPICE Model for your circuit design, view our blog here.

Follow Along, Download the Pre-Packaged Design Files

Table of Contents

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