Quite Universal Circuit Simulator

Quite Universal Circuit Simulator

Quite Universal Circuit Simulator (Qucs) is a open source electronics circuit simulator software released under GPL. It gives you the possibility to set up a circuit with a graphical user interface and simulate the large-signal, small-signal and noise behaviour of the circuit. Pure digital simulations are also supported using VHDL and/or Verilog.

Qucs supports a growing list of analog and digital components as well as SPICE sub-circuits.

Analysis Types

  • S-parameter, including noise
  • AC, including noise
  • DC
  • Transient Analysis
  • Harmonic Balance (not yet finished)
  • Digital simulation: VHDL as well as Verilog-HDL
  • Parameter sweeps

Features at a glance

  • Easy to use graphical interface for schematic capture.
  • Simulation data representation in various types of diagrams, i.e., Smith-Chart, Cartesian, Tabular, Polar, Smith-Polar combination, 3D-Cartesian, Locus Curve, Timing Diagram and Truth Table.
  • Transmission line calculator.
  • Filter synthesis.
  • Smith-Chart tool for power and noise matching.
  • Attenuator design synthesis.
  • Device model and subcircuit library manager.
  • Optimizer for analog designs.
  • Verilog-A interface.
  • Support for multiple languages (GUI and internal help system).
  • Subcircuit (including parameters) hierarchy.
  • Powerful data post-processing possible using equations.
  • Symbolically defined nonlinear and linear devices.
  • Documentation including
    • many useful tutorials (WorkBook),
    • reports (ReportBook),
    • technical description of the simulator.

Tool Suite

Qucs consists of several standalone programs interacting with each other through the GUI. There are

  • the GUI itself
  • :The GUI is used to create schematics, setup simulations, display simulation results, writing VHDL code, etc.
  • the backend analogue simulator
  • :The analogue simulator is a command line program which is run by the GUI in order to simulate the schematic which you previously setup. It takes a netlist, checks it for errors, performs the required simulation actions and finally produces a dataset.
  • a simple text editor
  • :The text editor is used to display netlists and simulation logging informations, also to edit files included by certain components (e.g. SPICE netlists, or Touchstone files).
  • a filter synthesis application
  • :The program can be used to design various types of filters.
  • a transmission line calculator
  • :The transmission line calculator can be used to design and analyze different types of transmission lines (e.g. microstrips, coaxial cables).
  • a component library
  • :The component library manager holds models for real life devices (e.g. transistors, diodes, bridges, opamps). It can be extended by the user.
  • an attenuator synthesis application
  • :The program can be used to design various types of passive attenuators.
  • a command line conversion program
  • :The conversion tool is used by the GUI to import and export datasets, netlists and schematics from and to other CAD/EDA software. The supported file formats as well as usage information can be found on the manpage of qucsconv.

Additionally the GUI steers other EDA tools. For digital simulations (via VHDL) the program FreeHDL is used. And for circuit optimizations ASCO is configured and run.


  • Lumped components
  • Sources
  • Probes
  • Transmission lines
  • Nonlinear components (diodes, transistors, etc.)
  • Digital components
  • File containers (S-parameter datasets, SPICE netlists)
  • Paintings

Transistor models

  • HICUM L0 v1.12
  • HICUM L0 v1.2
  • HICUM L2 v2.1
  • HICUM L2 v2.22
  • HICUM L2 v2.23
  • MESFET (Curtice, Statz, TOM-1 and TOM-2)
  • SGP (SPICE Gummel-Poon)
  • JFET

External links

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