Introduction to Mixed Signal Circuit Simulation

Mixed signal circuit simulation is a powerful tool for designing and analyzing electronic circuits that combine both analog and digital components. It allows engineers to model and simulate the behavior of complex systems, including the interactions between analog and digital domains. One of the most widely used mixed signal circuit simulators is PSpice, which is integrated into the Altium Designer PCB design software.

What is PSpice?

PSpice is a SPICE (Simulation Program with Integrated Circuit Emphasis) based analog circuit simulator that has been extended to support mixed signal simulation. It was originally developed by MicroSim and later acquired by Cadence Design Systems. PSpice is now part of the Altium Designer suite, providing seamless integration with PCB design tools.

Key Features of PSpice

• Analog and digital circuit simulation
• Behavioral modeling using Verilog-A and VHDL-AMS
• Extensive model libraries for various components
• Waveform analysis and visualization
• Integration with Altium Designer for PCB design

Setting Up PSpice in Altium Designer

To start using PSpice for mixed signal circuit simulation in Altium Designer, you need to ensure that it is properly installed and configured.

Installation

1. Install Altium Designer on your computer.
2. During the installation process, make sure to select the option to install PSpice.
3. Follow the on-screen instructions to complete the installation.

Configuration

1. Launch Altium Designer.
2. Go to “Tools” > “PSpice Simulation Settings.”
3. Configure the simulation settings according to your project requirements.
4. Set the paths for model libraries and other necessary files.

Creating a Mixed Signal Circuit in Altium Designer

To create a mixed signal circuit in Altium Designer, follow these steps:

1. Create a new schematic document.
2. Place the analog and digital components on the schematic.
3. Connect the components using wires and buses.
4. Assign appropriate models to the components.
5. Define the simulation parameters and stimuli.

Analog Components

Analog components in PSpice include resistors, capacitors, inductors, diodes, transistors, op-amps, and more. These components are modeled using mathematical equations that describe their electrical behavior.

Digital Components

Digital components in PSpice are represented using behavioral models or VHDL/Verilog descriptions. These models define the logical behavior of the digital elements, such as gates, flip-flops, and multiplexers.

Connecting Analog and Digital Domains

To connect the analog and digital domains in a mixed signal circuit, you need to use special interface components. These components act as bridges between the two domains, converting signals from one form to another.

Examples of interface components include:

• Analog-to-Digital Converters (ADCs)
• Digital-to-Analog Converters (DACs)
• Comparators
• Level shifters

Running Mixed Signal Simulations

Once you have created your mixed signal circuit in Altium Designer, you can run simulations to analyze its behavior.

Simulation Types

PSpice supports various types of simulations, including:

• Transient analysis
• AC sweep
• DC sweep
• Monte Carlo analysis
• Parametric sweep

Setting Up Simulation Parameters

To set up a simulation in PSpice:

1. Open the simulation settings dialog.
2. Select the desired simulation type.
3. Configure the simulation parameters, such as time step, duration, and convergence criteria.
4. Define the simulation stimuli, such as voltage sources and current sources.

Running the Simulation

To run the simulation:

1. Click on the “Run Simulation” button in the PSpice toolbar.
2. Wait for the simulation to complete.
3. View the simulation results in the waveform viewer.

Analyzing Simulation Results

PSpice provides a comprehensive set of tools for analyzing simulation results.

Waveform Viewer

The waveform viewer allows you to visualize the simulation results in the form of time-domain waveforms. You can zoom in/out, pan, and measure signal values using cursors.

Measurement Functions

PSpice offers a wide range of measurement functions to extract specific information from the simulation results. These functions include:

• RMS value
• Peak value
• Average value
• Rise/fall time
• Delay
• Frequency

Plotting and Graphing

You can create plots and graphs to visualize the relationships between different signals or parameters. PSpice supports various plot types, such as:

• X-Y plots
• Smith charts
• Polar plots
• Histograms

Advanced Topics in Mixed Signal Simulation

Behavioral Modeling

Behavioral modeling allows you to describe the behavior of complex components or systems using mathematical equations or algorithmic descriptions. PSpice supports behavioral modeling using Verilog-A and VHDL-AMS languages.

Hierarchical Design

Hierarchical design is a technique for managing the complexity of large mixed signal circuits. It involves breaking down the circuit into smaller, more manageable subcircuits and defining the interactions between them.

Analog Behavioral Modeling

Analog behavioral modeling enables you to describe the behavior of analog components using mathematical equations or transfer functions. This is useful for modeling complex analog systems or creating custom components.

Digital Behavioral Modeling

Digital behavioral modeling allows you to describe the behavior of digital components using higher-level abstractions, such as state machines or algorithmic descriptions. This is particularly useful for modeling complex digital systems or creating custom digital blocks.

FAQs

1. What is mixed signal circuit simulation?
   Mixed signal circuit simulation is the process of modeling and simulating electronic circuits that contain both analog and digital components. It allows engineers to analyze the behavior of complex systems that span across the analog and digital domains.

2. What is PSpice, and how is it related to Altium Designer?
   PSpice is a SPICE-based analog and mixed signal circuit simulator. It is integrated into the Altium Designer PCB design software, providing seamless integration between circuit simulation and PCB design.

3. How do I set up PSpice in Altium Designer?
   To set up PSpice in Altium Designer, you need to install Altium Designer with the PSpice option selected. Then, configure the simulation settings and paths for model libraries in the PSpice Simulation Settings dialog.

4. What types of simulations can I run in PSpice?
   PSpice supports various types of simulations, including transient analysis, AC sweep, DC sweep, Monte Carlo analysis, and parametric sweep. These simulations allow you to analyze the circuit behavior under different conditions and scenarios.

5. How can I analyze the simulation results in PSpice?
   PSpice provides a waveform viewer for visualizing simulation results in the time domain. It also offers measurement functions to extract specific information from the waveforms, such as RMS values, peak values, and rise/fall times. Additionally, you can create plots and graphs to visualize relationships between signals or parameters.

Conclusion

Mixed signal circuit simulation is a valuable tool for designing and analyzing electronic circuits that combine analog and digital components. PSpice, integrated into Altium Designer, provides a powerful and user-friendly environment for mixed signal simulation. By following the steps outlined in this article, you can set up PSpice, create mixed signal circuits, run simulations, and analyze the results effectively. With the advanced features like behavioral modeling and hierarchical design, PSpice enables you to tackle complex mixed signal design challenges and optimize your circuits for better performance and reliability.

Simulation Type	Description
Transient	Analyzes circuit behavior over time
AC Sweep	Analyzes circuit response to varying frequencies
DC Sweep	Analyzes circuit response to varying DC input values
Monte Carlo	Performs statistical analysis with parameter variations
Parametric	Sweeps multiple parameters simultaneously

Remember to leverage the extensive model libraries provided by PSpice and utilize the integration with Altium Designer for seamless PCB design and simulation workflows. Happy mixed signal circuit designing!