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.NOISE Statement

The .NOISE statement requests a noise analysis. It computes the noise contributions from each device and the total output noise spectral density over a range of frequencies.

Syntax

.NOISE V(<output_node>[, <ref_node>]) <input_source> <sweep_type> <points> <fstart> <fstop>
Parameter Description
V(<output_node>) Output node for noise measurement
<ref_node> Optional reference node (default: ground)
<input_source> Input source for input-referred noise
<sweep_type> DEC, OCT, or LIN
<points> Number of frequency points (per decade/octave, or total)
<fstart> Starting frequency (Hz)
<fstop> Ending frequency (Hz)

Example

Amplifier noise
V1 IN 0 AC 1
R1 IN OUT 10k
R2 OUT 0 10k
.NOISE V(OUT) V1 DEC 10 1 1MEG
.END

MNA View

Noise analysis is based on the linearized operating point, like .AC. The simulator first finds the DC bias point, then uses the small-signal MNA system to propagate each device's equivalent noise source to the requested output.

Conceptually:

solve DC operating point
linearize devices around that point
for each frequency:
  evaluate device noise sources
  solve small-signal matrix responses
  accumulate output and input-referred noise

The .NOISE statement itself does not create a normal circuit component. It asks the simulator to use the linearized MNA model and the devices' noise behaviors to compute spectral density.

For the related frequency-domain matrix view, see .AC.

C# API

var sim = model.Simulations.Single(); // Noise simulation
sim.EventExportData += (s, args) =>
{
    // Noise data available through exports
    Console.WriteLine(export.Extract());
};