Self-Hosted SPICE Circuit Simulation: ngspice vs Qucs vs Xyce for Electronics Design

Why Self-Host Your Circuit Simulation?

Electronics design has traditionally relied on expensive commercial EDA suites like Cadence Virtuoso, Synopsys HSPICE, and Keysight ADS — tools that cost thousands of dollars per seat annually. Open-source SPICE simulators have matured to the point where they can handle professional-grade analog, digital, and mixed-signal circuit analysis without the licensing burden.

Self-hosting a SPICE simulation environment gives you unlimited parallel simulation capacity on your own hardware. Instead of waiting for cloud-based simulation queues or paying per-simulation-run fees, you can run parameter sweeps, Monte Carlo analyses, and corner simulations across your entire server fleet. For research labs and startups, this translates directly to faster design iteration.

The SPICE ecosystem also benefits from decades of community development. Open-source models for transistors, diodes, and passive components are widely available, and the open netlist format means your designs are never locked into a proprietary tool. You can start a simulation in ngspice and continue it in Xyce without converting your circuit description.

For broader scientific computing infrastructure, see our scientific simulation platforms guide. If you work with PCB design, our PCB visualization tools comparison covers complementary tools. For industrial control systems, check our SCADA platforms guide.

ngspice: The Universal SPICE Engine

ngspice is the most widely used open-source SPICE simulator, forked from Berkeley SPICE 3f5 and maintained by an active community of contributors. With 243+ GitHub stars and continuous development since 1993, it serves as the simulation engine behind KiCad, EAGLE, gEDA, and many other EDA tools.

Key Features:

• Full SPICE 3f5 compatibility plus XSPICE extensions for mixed-signal simulation
• Support for BSIM3, BSIM4, BSIM6, VBIC, and HICUM transistor models
• Post-simulation analysis with built-in plotting (interactive or batch PNG/SVG output)
• Verilog-A and C-language behavioral model support (XSPICE code models)
• Shared library mode (libngspice) for embedding in other applications
• Parameter sweeping, Monte Carlo analysis, and sensitivity analysis

Installation & Usage

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# Debian/Ubuntu installation
sudo apt install ngspice

# Run an interactive simulation
ngspice my_circuit.cir

# Batch mode simulation with data output
ngspice -b -r output.raw my_circuit.cir

# Run from Docker
docker run -v $(pwd):/work -w /work   hdlc/simulation:ngspice ngspice -b circuit.cir

Example Netlist (Differential Amplifier):

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* Differential Pair with Current Mirror Load
M1 3 1 5 5 NMOS W=10u L=1u
M2 4 2 5 5 NMOS W=10u L=1u
M3 3 3 0 0 PMOS W=20u L=1u
M4 4 3 0 0 PMOS W=20u L=1u
Ibias 5 0 DC 100u
Vdd 0 0 DC 3.3
Vin1 1 0 DC 1.65 AC 1
Vin2 2 0 DC 1.65
.op
.ac dec 10 1Hz 100MHz
.model NMOS NMOS (LEVEL=1 VTO=0.7 KP=200u)
.model PMOS PMOS (LEVEL=1 VTO=-0.7 KP=80u)
.end

Qucs: Schematic-Driven Simulation

Qucs (Quite Universal Circuit Simulator) takes a GUI-first approach, providing a graphical schematic editor that generates SPICE netlists under the hood. With 1,293+ GitHub stars, it bridges the gap between professional schematic capture and open-source simulation.

Key Features:

• Graphical schematic editor with component library (R, L, C, transistors, op-amps, digital gates)
• Built-in simulation types: DC, AC, S-parameter, harmonic balance, transient, parameter sweep
• Results viewer with Smith charts, polar plots, and Cartesian graphs
• Digital simulation via VHDL/Verilog co-simulation (via FreeHDL/Icarus Verilog)
• Export to SPICE netlist format for interoperability with other tools
• Component modeling with equation-defined devices

Installation

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# Debian/Ubuntu
sudo apt install qucs

# Docker (headless simulation via command-line interface)
docker run -v $(pwd):/work -w /work   ra3xdh/qucs:latest qucsator -i netlist.net -o result.dat

Xyce: Parallel High-Performance SPICE

Xyce is an open-source SPICE-compatible simulator developed by Sandia National Laboratories, designed from the ground up for parallel execution on large computing clusters. With 147+ GitHub stars but backed by a DOE national lab, it excels at simulations too large for single-threaded SPICE engines.

Key Features:

• MPI-based parallel execution — distributes circuit matrix across multiple nodes
• SPICE 3f5 compatible netlist syntax with extensions for parallel directives
• Support for BSIM3, BSIM4, BSIM-CMG, MEXTRAM, and HBT models
• Multi-level Newton methods for improved convergence on stiff circuits
• Krylov subspace methods for frequency-domain analysis of large circuits
• Hessian-based sensitivity analysis and uncertainty quantification

Installation & Usage

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# Build from source (requires Trilinos libraries)
git clone https://github.com/Xyce/Xyce.git
cd Xyce
mkdir build && cd build
cmake .. -DCMAKE_INSTALL_PREFIX=/opt/xyce
make -j$(nproc)
sudo make install

# Run a simulation (serial)
Xyce circuit.cir

# Parallel execution across 4 MPI processes
mpirun -np 4 Xyce circuit.cir

# Docker container (community-maintained)
docker run -v $(pwd):/work -w /work   xyce/xyce:latest mpirun -np 4 Xyce circuit.cir

Comparison Table

Convergence and Troubleshooting

SPICE simulation convergence issues are the most common frustration for new users. When a simulation fails to converge, it’s usually due to unrealistic component models, floating nodes, or inadequate initial conditions. Across all three simulators, the same troubleshooting steps apply: add parasitic resistances (1mΩ series, 1GΩ parallel), set initial conditions with .ic statements, use the gmin convergence aid, and simplify nonlinear models for DC operating point analysis. Xyce’s multi-level Newton methods provide the best convergence behavior for challenging circuits, while ngspice’s cshunt option offers a quick fix for many common convergence failures.

Choosing the Right Simulator

The choice between these three simulators depends on your workflow, circuit size, and deployment environment:

For general-purpose circuit design integrated with KiCad or other EDA tools, ngspice is the natural choice. Its libngspice library is already embedded in KiCad’s simulation interface, making it seamless for PCB designers who want to verify analog sections before fabrication.

For educational environments or situations where you prefer visual schematic entry, Qucs provides the most accessible experience. Students can draw circuits and immediately simulate them without learning netlist syntax.

For large-scale or computationally intensive simulations, Xyce is unmatched. If you’re simulating a power delivery network with thousands of nodes, a full-chip SRAM array, or running Monte Carlo analysis across hundreds of variations, Xyce’s MPI parallelization can reduce simulation time from hours to minutes.

FAQ

Can I use these tools with KiCad for PCB design?

Yes. KiCad integrates ngspice directly via its Simulation Inspector panel (since KiCad 6.0). You can assign SPICE models to schematic components and run AC, DC, and transient simulations without leaving the KiCad interface. Qucs and Xyce require exporting a netlist and simulating externally.

How accurate are open-source SPICE models compared to commercial tools?

The simulation engines (ngspice, Xyce) use the same numerical algorithms as commercial SPICE — modified nodal analysis with Newton-Raphson iteration. Accuracy depends on your device models, not the simulator. Industry-standard BSIM models (BSIM4, BSIM-CMG) are available for all three tools and produce results matching foundry-provided PDK simulations.

What’s the largest circuit these tools can handle?

ngspice and Qucs can handle circuits with tens of thousands of nodes on a modern workstation. Xyce, with MPI parallelization, has been demonstrated on circuits with millions of nodes running across hundreds of CPU cores. The practical limit depends more on your available RAM and compute time than the simulator itself.

Can I simulate RF and microwave circuits?

Qucs has the best RF simulation support among the three, with built-in S-parameter analysis, harmonic balance, and Smith chart visualization. Xyce supports harmonic balance for RF nonlinear analysis. ngspice can do basic AC analysis but lacks native S-parameter support — you can add it via XSPICE code models.

Do these tools support Verilog-A or Verilog-AMS models?

ngspice supports XSPICE code models (C language) and has experimental Verilog-A support via ADMS. Xyce supports compiled Verilog-A models through its ADMS integration. Qucs uses its own equation-defined device system but can co-simulate with digital Verilog via Icarus Verilog.

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