Running Simulations

Running a Single Cell

Every SPICE cell has a Run button in its toolbar. Clicking it sends the cell’s netlist to the backend, which:

1. Writes the netlist to a temp file
2. Invokes the selected engine (ngspice or LTspice)
3. Parses the raw output into structured WaveformData
4. Returns results to the browser and saves them in the cell’s outputs array

Results appear inline beneath the cell — either a data table (for .op) or a waveform plot (for .tran, .dc, .ac).

Run All

The toolbar’s Run All button executes every SPICE cell in the notebook from top to bottom, sequentially. Each cell’s results are saved before the next cell runs.

This is useful for notebooks where later cells depend on understanding earlier results, or when you want to regenerate all outputs after changing the engine.

Analysis Types

The analysis directive in your netlist determines what kind of results you get:

DC Operating Point (.op)

V1 1 0 DC 5
R1 1 2 1k
R2 2 0 2k
.op
.end

Returns a single set of node voltages and branch currents. Displayed as a table.

Transient (.tran)

V1 1 0 PULSE(0 5 0 1n 1n 5u 10u)
R1 1 2 1k
C1 2 0 100n
.tran 10n 50u
.end

Returns time-series data. Displayed as an XY waveform plot with time on the horizontal axis.

DC Sweep (.dc)

V1 1 0 DC 5
R1 1 2 1k
R2 2 0 2k
.dc V1 0 10 0.5
.end

Sweeps a source value and returns node voltages at each step. Displayed as a waveform plot with the swept parameter on the horizontal axis.

AC Analysis (.ac)

V1 in 0 AC 1
R1 in out 1k
C1 out 0 1u
.ac dec 100 1 1meg
.end

Returns complex frequency-domain data. Displayed as a Bode plot — magnitude in dB and phase in degrees versus frequency on a log scale.

Tip

AC analysis results include y_magnitude_db and y_phase_deg fields in the waveform data. The viewer automatically switches to Bode plot mode when these are present.

Output Format

Every simulation returns a SimulationResponse:

{
  "success": true,
  "waveform": {
    "variables": [{"name": "v(out)", "type": "voltage"}],
    "points": 100,
    "x_data": [0.0, 0.001, ...],
    "y_data": {"v(out)": [0.0, 0.5, ...]},
    "x_type": "time",
    "is_complex": false
  },
  "log": "ngspice output...",
  "error": null,
  "elapsed_seconds": 0.42
}

If the simulation fails (syntax error, convergence failure), success is false and error contains the diagnostic message. The simulator log is always available in the log field for debugging.

Engineering Notation

SPICE uses its own suffix convention for component values — be aware that M means milli (10⁻³), not mega. Use meg for 10⁶.

Suffix	Multiplier	Example
T	10¹²	1T
G	10⁹	2.2G
meg	10⁶	1meg
k	10³	4.7k
m	10⁻³	10m
u	10⁻⁶	100u
n	10⁻⁹	47n
p	10⁻¹²	10p
f	10⁻¹⁵	1f