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Running a Simulation

Use the Simulation Workbench to select a supported circuit scope, configure the engine and analysis, prepare sources and loads, run preflight, and inspect results.

Open the workbench

With a schematic active, select Simulation → SPICE Simulation Panel or press F5.

The current sidebar contains:

  • Setup;
  • Blocks;
  • Testbench;
  • Signals;
  • Models;
  • AI.

Older documentation referring to a separate Analysis tab or a different sidebar layout has been removed.

Image — Current Simulation Workbench

Image needed

Capture the complete workbench with the current six sidebar tabs, the waveform area, and run controls visible. Use a small circuit with at least one selectable block and signal. Suggested size: 1600 × 900 px.

1. Select an engine and analysis

In Setup:

  1. Select an available simulation engine.
  2. Choose the analysis type.
  3. Set its values, such as transient stop time and step.
  4. Add any required SPICE directives.

Configure external engine paths in Preferences → Simulation. A release build normally includes or locates Ngspice; alternative engines must be installed and selected explicitly.

2. Choose the circuit scope

Open Blocks and select:

  • Entire schematic; or
  • one or more recognized functional blocks.

Use Only runnable to select blocks with enough models and connectivity for simulation. Read the reason shown for any block that is not runnable.

Short video — Select runnable simulation blocks

Video needed

Record 10–15 seconds showing Re-scan, Only runnable, selection of two blocks, and the scope summary changing. Use a schematic containing at least one unsupported block so the reason is visible. 1080p.

3. Add sources and loads

In Setup, add sources to the intended nets. In Testbench, add loads and assertions.

Check source polarity, units, waveform parameters, and reference ground. A source added to the wrong net can produce a plausible but irrelevant waveform.

4. Run preflight

Select Simulation → Pre-flight Validation Checklist before running.

Resolve blockers such as:

  • missing ground;
  • missing or incompatible SPICE models;
  • invalid source or analysis values;
  • disconnected required pins;
  • unsupported selected blocks;
  • engine not found.

Warnings require review even when the Run action remains available.

5. Select signals

Open Signals and select the nets to plot. Use Named nets for a concise view or All when investigating an unknown issue. Too many traces can make the plot difficult to read.

6. Run and inspect

Start the simulation and wait for Last run to update. Review:

  • completion status;
  • assertion results;
  • simulation log;
  • selected waveform traces;
  • cursor measurements when required.

If the run fails, open AI and use Why did the last run fail? or Review preflight blockers, then verify the explanation against the log and circuit.

Short video — Preflight, run, and inspect

Video needed

Record 15–20 seconds showing a successful preflight, selecting two signals, running the simulation, and the waveform plus Last run result appearing. Replace older clips that show obsolete controls. 1080p.

Stop or repeat a run

Stop an active run only when required. After changing component values, source settings, models, scope, or analysis parameters, run preflight again before comparing results.

Common failures

Result Check
Engine unavailable Preferences → Simulation engine path and executable
No runnable blocks Models, ground, connectivity, and block reasons
Empty waveform Selected signals and completed analysis
Flat output Source waveform, ground reference, operating point, and load
Assertion not measured Signal selection, analysis window, and assertion metric
Different engines disagree Dialect, model version, sources, load, and analysis settings

See also