.NOISE — Perform a Noise Analysis

This is a frequency domain analysis that computes the noise due to Johnson, shot and flicker noise. The output data is noise spectral density per unit square root bandwidth.

Syntax:

.noise V(<out>[,<ref>]) <src> <oct, dec, lin> <Nsteps> <StartFreq> <EndFreq>

The frequency is swept between frequencies <StartFreq> and <EndFreq>. The number of steps is defined with the keyword oct, dec, or lin and <Nsteps> according to the following table:

Keyword	Nsteps
oct	No. of steps per octave
dec	No. of steps per decade
lin	Total number of linearly spaced steps between StartFreq and EndFreq

.noise V(<out>[,<ref>]) <src> list <FirstFreq>[ <NextFreq> [<NextFreq> ...]]

The noise analysis is performed at the listed frequencies. The list can contain only one entry, which is useful in combination with .step. It allows you to plot noise densities as a function of a stepped parameter.

.noise V(<out>[,<ref>]) <src> file=<Filename>

The list of frequencies is read from the file <Filename>. This file can contain comments like a regular netlist. The numbers must be separated by whitespace or commas as described here.

V(<out>[,<ref>]) is the node at which the total output noise is calculated. It can be expressed as V(n1, n2) to represent the voltage between two nodes. <src> is the name of an independent source to which input noise is referred. <src> is the noiseless input signal.

Output data trace V(onoise) is the noise spectral voltage density referenced to the node(s) specified as the output in the above syntax. If the input signal is given as a voltage source, then data trace V(inoise) is the input-referred noise voltage density. If the input is specified as a current source, then the data trace inoise is the noise referred to the input current source signal. The noise contribution of each component can be plotted. These contributions are referenced to the output. You can reference them to the input by dividing by the data trace "gain".

The waveform viewer can integrate noise over a bandwidth by <Ctrl-Key> + left mouse button clicking on the corresponding data trace label.