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How Does SPICE Simulation Work?

Published Date
Author Cadence PCB Solutions

Formulas and electric schemes on a chalkboard

Chances are, you have come across the term “SPICE simulation” at some point in your career as an engineer. The term stands for simulation program with integrated circuit emphasis. It refers to computer programs used to simulate the behavioral properties of a circuit, particularly for analog designs. The SPICE simulator was first created during the growth of integrated circuits (IC) in electronics design. The intention of the SPICE simulator is to detect potential issues in design before the PCB is fabricated. In this article, we will explore how SPICE simulation works.

How Does SPICE Simulation Work?

The core functionality of a SPICE simulator centers around network analysis–if a source is provided or a current is injected into the circuit as designed, what is the response? Through mathematical approaches to solving the resulting differential equations formed from Kirchoff’s loop laws, the simulator is able to provide a quick and accurate solution with a high level of confidence.

So, how does SPICE simulation work, exactly? Behind the graphical chart and circuit diagram, the SPICE program works by utilizing models to represent the components. Component models are text-based parameters that are comprehensible to the SPICE programs. Today, various vendors have commercialized versions of SPICE simulators by adding their list of component models onto the code.

The SPICE engine analyzes circuits based on Kirchhoff’s current or voltage law. It assigns nodes to a circuit and attempts to solve the current and voltage values at the respective nodes. The SPICE simulator first generates nodal equations in the matrix format before solving them to obtain the values. Depending on the nature of the circuit, the iteration taken by the SPICE simulator to solve the nodal equations may differ.

Kirchhoff’s circuit, current, and voltage laws

Kirchhoff’s circuit laws form the fundamentals of SPICE simulators

For linear circuits, solving the nodal equations is a straightforward process. However, when non-linear circuits are involved, the SPICE simulator will need to replace each non-linear component with a representative linear component model before solving the equation. Based on the netlist of nodes and the component models, you’ll be able to get a detailed result into the electrical properties of the circuit. 

What Is the Purpose of a Spice Simulator?

While it’s easy to visualize how a SPICE simulator works for a simple resistive circuit, the true power of the SPICE simulator lies in its ability to analyze complicated behaviors of a circuit. Here are some practical advantages a SPICE simulation tool offers:

  • Cost - The single biggest driver of PSpice usage is to avoid manufacturing errors that could lead to defects and scrap. It is entirely infeasible to test components on a development board for both time and accuracy reasons. Simulators, while not perfect, are advanced and sophisticated, and can provide excellent approximations prior to fabrication and assembly.
  • Speed - Modern simulators can quickly incorporate circuit information from the netlist. The user doesn’t have to spend more time prototyping circuits with through-hole components that would ultimately provide a less predictive answer. This also eliminates any error caused by humans translating from schematic to breadboard - an exceedingly easy mistake to make.
  • Advanced functionality - In much the same way that a multimeter wouldn’t be expected to perform the duties of an oscilloscope, SPICE simulators possess wonderful features that provide additional analysis above and beyond what can be expected of users prototyping by hand.

Like the greater CAD tools, SPICE simulation has benefited immensely from the growth in personal and workstation computing power within the past few decades.

Where Is SPICE Simulation Used? 

Some of the most oft-utilized analyses are as follows, but note that simulators contain far greater features for network analysis today than ever before:

1. DC Analysis

In DC analysis, the SPICE simulator attempts to calculate the voltage and current of a circuit based on a range of DC input values. During a DC analysis sweep, reactive components like inductors and capacitors are translated into short and open circuits, respectively. 

2. AC Analysis

AC Analysis, or AC sweep, is done to determine the phase and magnitude of the nodes in a circuit. In AC analysis, the SPICE simulator uses the real and imaginary values of the components in the equation matrix. The equation is then solved for the range of frequency specified in the AC source input. 

3. Transient Analysis

Transient analysis is a process where the SPICE simulator uses an iterative model to provide insights into the behavior of the components throughout a specified timeframe. Before transient analysis commences, the SPICE simulator will first perform DC analysis to establish a DC operating point. Then it increments the time step and calculates the voltage and current values of the respective nodes.

Now that you have a clearer understanding of how SPICE simulation works and how it is used, it is important to talk with a vendor that offers a simulator that is packed with a vast library of accurate component models. OrCAD PSpice provides up to 34,000 models and is known for its accuracy in mixed-signal simulation.

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