What is QUCS-S?

QUCS-S is a fork of the popular Qucs Circuit Simulator. The fork began in 2017.

The “S” in QUCS-S is for SPICE - the primary purpose of QUCS-S is to merge the user-friendly Qucs GUI with the power of the SPICE simulation ecosystem.

QUCS-S vs Qucs

The original Qucs project uses its own SPICE-incompatible simulator, called Qucsator. Qucsator has advanced RF and AC-domain simulation features, but is incompatible with most SPICE models used across industry.

QUCS-S vs QucsStudio

QucsStudio is another simulator package which is also based on the original Qucs project. QucsStudio is freeware, but not open-source. Apart from being forked from the same original Qucs project, QucsStudio has no relation to QUCS-S.

Simulation Backends

In contrast to Qucs and QucsStudio, QUCS-S does not include its own simulation backend at all. Rather, it serves as a frontend for several different simulation backends:

Analog/Digital/RF Simulators

  • ngspice (recommended): A powerful mixed-level/mixed-signal circuit simulator. Most SPICE models distributed across industry are compatible with it. It has excellent performance for time-domain simulation of switching circuits, and a powerful postprocessor. If you are unsure which simulation backend to use with QUCS-S, ngspice is recommended.

  • Xyce: A new SPICE-compatible circuit simulator, written from scratch by Sandia National Laboratory. Xyce has the notable advantage of supporting large-scale parallel computing platforms, making it a good fit for solving very large circuits (although it can run on an ordinary desktop platform as well).

  • SpiceOpus: A free general purpose circuit simulator, based on the Berkeley SPICE-3f5 codebas, specially suited for optimization loops.

  • QucsatorRF: A fork of Qucsator, the built-in simulation engine from the original Qucs project. QucsatorRF shares the original Qucsator netlist syntax, and all RF features. It’s primarily intended for RF simulation with microwave devices and microstrip lines. It is not generally recommended for general-purpose circuit simulation, since ngspice typically has better performance.

Digital-Only Simulators

  • Icarus Verilog: A digital-only simulation backend for simulating Verilog devices.

  • GHDL: A digital-only simulation backend for simulating VHDL devices. Fully supports the 1987, 1993, 2002 versions of the IEEE 1076 VHDL standard, and partially the latest 2008 revision (well enough to support fixed_generic_pkg or float_generic_pkg).

Notable Features

A few features of particular note are:

  • Basic and advanced simulation types: AC, DC, transient, S-parameter, FFT, distortion, pole-zero, parametric sweep.

  • Advanced RF simulation with Qucsator RF backend;

  • Quick switching of the simulation kernel without application restart;

  • Tuner simulation mode

  • Direct support of SPICE models from components datasheets;

  • Basic SPICE components: RCL, BJT, MOSFET, JFET, MESFET, switches;

  • Advanced SPICE components: Equation-defined sources and RCLs, transmission lines;

  • Parametric circuits (.PARAM) and SPICE postprocessor (Nutmeg)

  • Basic SPICE simulations: DC, AC, TRAN;

  • Advanced SPICE simulation: DISTO, NOISE, SENS (added in 0.0.20), Spectrum analysis;

  • Harmonic balance analysis with XYCE and Qucsator RF backends;

  • Nutmeg script simulation: direct access to the SPICE code and construct your own simulation;

  • XYCE script simulation type;

  • XYCE digital devices library;

Supported Platforms

QUCS-S is available for Windows and Mac OSX, as well as numerous Linux distributions.

Keep in mind that some simulation backends may need to be installed separately from QUCS-S, depending on your installation platform and method.

See Installing QUCS-S for more information.