22.1 SPICE-based circuit simulators

SPICE-based circuit simulators are essential tools for analyzing electronic circuits. They model circuit behavior using mathematical equations, allowing engineers to predict performance without building physical prototypes. These simulators come in various flavors, from open-source options to commercial powerhouses.

Setting up a simulation involves creating a netlist, which describes the circuit's components and connections. Simulators then use this info to generate results like voltage and current waveforms. Understanding how to interpret these outputs is key to effective circuit design and troubleshooting.

SPICE Variants

Popular SPICE Simulators

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Top images from around the web for Popular SPICE Simulators

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  PSPICE 9.1 Student Version Download - Electronics Lab View original

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• 

  Inductor Simulation with LTspice – The Passives Times View original

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• 

  Electronic Circuit Design / Simulation Software - Electronics Lab View original

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  PSPICE 9.1 Student Version Download - Electronics Lab View original

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  Inductor Simulation with LTspice – The Passives Times View original

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• SPICE (Simulation Program with Integrated Circuit Emphasis) is the original open-source analog electronic circuit simulator developed at the University of California, Berkeley in the 1970s
• PSpice (Personal Simulation Program with Integrated Circuit Emphasis) is a commercial version of SPICE developed by MicroSim and currently owned by Cadence Design Systems, offering additional features and a user-friendly interface
• LTspice is a freeware SPICE simulator developed by semiconductor manufacturer Analog Devices (originally by Linear Technology), known for its ease of use and extensive library of component models
• NgSpice is a popular open-source SPICE simulator that is compatible with various SPICE variants and offers a command-line interface as well as graphical user interfaces through third-party applications (Gwave, KiCad)

Other SPICE-based Simulators

• HSPICE is a high-performance commercial SPICE simulator developed by Synopsys, widely used in the semiconductor industry for its accuracy and advanced features
• Xyce is an open-source, parallel, high-performance SPICE simulator developed by Sandia National Laboratories, designed for large-scale circuit simulations
• TINA-TI is a free SPICE-based simulator offered by Texas Instruments, which includes a library of TI components and a user-friendly schematic capture interface
• Micro-Cap is a commercial SPICE-based simulator developed by Spectrum Software, known for its intuitive interface and mixed analog-digital simulation capabilities

Circuit Simulation Basics

Simulation Setup

• Circuit simulation involves creating a mathematical model of an electronic circuit and analyzing its behavior under various conditions (DC, AC, transient) using a computer program
• A netlist is a text-based description of the circuit topology, including component values, connections, and simulation commands, which serves as an input to the SPICE simulator
• Model libraries contain mathematical models of electronic components (resistors, capacitors, transistors) that describe their electrical characteristics and are used by the simulator to predict circuit behavior
• Subcircuits are user-defined circuit blocks that can be reused multiple times within a larger circuit, simplifying the netlist and enabling modular design

Simulation Results

• SPICE simulators generate output data in the form of text files or plots, which can include node voltages, branch currents, and other circuit parameters (gain, bandwidth, power dissipation)
• Waveform viewers are used to visualize the simulation results, allowing users to analyze the circuit's time-domain and frequency-domain behavior (transient response, AC analysis, Fourier transforms)
• Monte Carlo analysis is a technique used to assess the impact of component variations on circuit performance by running multiple simulations with randomly varied component values (tolerance analysis)
• Sensitivity analysis helps identify the components that have the greatest influence on circuit performance by varying component values and observing the resulting changes in output parameters

Simulation Considerations

Convergence and Accuracy

• Convergence refers to the ability of the SPICE simulator to find a valid solution for the circuit equations within a specified tolerance and number of iterations
• Convergence issues can arise due to various factors (nonlinear components, floating nodes, initial conditions) and may require adjusting simulation settings or modifying the circuit topology to achieve a stable solution
• Simulation accuracy depends on the quality of the component models, the numerical methods used by the simulator, and the user-specified tolerance settings (relative tolerance, absolute tolerance)
• To improve simulation accuracy, users can employ more detailed component models (BSIM, EKV), use smaller time steps or tighter tolerances, and verify the results against experimental data or analytical calculations

Simulation Speed and Efficiency

• Simulation speed is affected by factors such as the circuit size, the complexity of the component models, the number of time points, and the computer hardware (CPU, RAM)
• To optimize simulation speed, users can employ various techniques (model simplification, time step control, parallel processing) and take advantage of the simulator's built-in performance optimization features
• Hierarchical design using subcircuits can help manage complexity and improve simulation efficiency by breaking down large circuits into smaller, more manageable blocks
• Behavioral modeling using Verilog-A or VHDL-AMS can be used to describe complex components (amplifiers, filters) using high-level mathematical equations, reducing the computational burden on the SPICE simulator