ECAD using KiCad: SPICE Modeling

BME253L - Fall 2025

Author
Affiliation

Dr. Mark Palmeri, M.D., Ph.D.

Duke University

Published

September 24, 2025

SPICE Modeling

What is SPICE?

  • Simulation Program with Integrated Circuit Emphasis (SPICE)
  • Model and analyze the behavior of electronic circuits before they are physically constructed.
  • Input schematic representations of circuits (e.g., resistors, capacitors, transistors, diodes, etc.)
  • Simulate circuit performance by computing current, voltage, and power, across these components under different conditions.

Why model circuits?

  • Reduce design costs.
  • Breadboards / thru-hole prototyping is not realistic for complex circuits.
  • Most components are now surface mount.
  • Model \(\rightarrow\) Breakout Boards \(\rightarrow\) PCB

SPICE vs. Non-SPICE Components

  • SPICE components are defined by their mathematical models.
  • Non-SPICE components are defined by their physical characteristics.
  • KiCad has a library of SPICE models for common components.
  • SPICE models are not always available for all components, but can be downloaded and added to some libraries.
  • SPICE models can be edited / created for custom components.

Limiting Scope of SPICE Simulation

  • We usually want to simulate as simple of a circuit as possible.
  • We can limit the scope of the simulation by excluding components from the braoder schematic from the sub-circuit that we want to simulate:
    1. Drag select all of the components you want to exclude to highlight them.
    2. Right Click: Attributes -> Exclude from Simulation
    3. Repeat this for other sheets / circuits in the schematic.
    4. In the Simulation window, Confirm that your SPICE Netlist reflets what you actually want to simulate.

Setting Component Simulation Parameters

  • The SPICE model can be set in the component properties.
  • The component must have a SPICE model to be included in the simulation.
  • Only certain components allow certain simulation parameters to be varied (e.g., resistors vs. potentiometers).

Setting Analysis Parameters

  1. AC Sweep: frequency analysis
  2. DC Sweep: sweep voltage, current, resistance, capacitance
  3. Operating Point: analysis at a specific point in time
  4. Transient: time-domain analysis

Run Simulation and Probe Components

  • Simulations are Run (Blue Arrow in Simulation window).
  • Probes can be added by parameter and component name or interactively.
  • Choose a New Analysis and what components you want to sweep.
    • Avoid setting any values to 0 as they can cause numerical instability!
  • After you hit Ok, choose the parameters from the right side of the window that you would like to plot.
  • If you change your schematic, be sure to re-Run the simulation.
    • You may want to create a new analysis tab to make sure that the simulation reflects the latest changes.
  • All open analysis tabs must be valid for the running simulation to be successful!

Examples

Voltage Divider with Potentiometer (DC Sweep)

RC Filter (AC Sweep)

Resources