The noise analysis portion of * WRspice* performs analysis of
device-generated noise for the given circuit. When provided with an
input source and an output node or current, the analysis calculates
the noise contributions of each device (and each noise generator
within the device) to the output node voltage or current. It also
calculates the level of input noise from the specified input source
to generate the equivalent output noise. This is done for every
frequency point in a specified range -- the calculated value of the
noise corresponds to the spectral density of the circuit variable
viewed as a stationary Gaussian stochastic process.

This is the classic frequency-domain SPICE noise analysis. * WRspice*
also provides the capability of simulating thermal noise in the time
domain. See the description of the

After calculating the spectral densities, noise analysis integrates these values over the specified frequency range to arrive at the total noise voltage/current (over this frequency range). This calculated value corresponds to the variance of the circuit variable viewed as a stationary Gaussian process.

- General Form:
`.noise`*out**src*`dec|oct|lin`*pts fstart fstop*[*summary_pts*] [dc| sweep*args*]

- Examples:
`.noise v(5) vin dec 10 1khz 100mhz`

.noise v(5,3) v1 oct 8 1.0 1.0e6 1 dc vee -5 -3 1

Above, *out* represents the output, which can be a node voltage
in the standard form

v(or the current through a voltage source (or inductor) in one of the standard and equivalent formsout[,ref])

Vsource

Vsource#branch

i(Vsource)

This directive initiates a noise analysis of the circuit. The
parameter *out* is the point at which the total output noise is
desired, and if this is a voltage and *ref* is specified, then
the noise voltage v(*out*) - v(*ref*) is calculated. By
default, *ref* is assumed to be ground. The parameter *src* is the name of a voltage or current source to which input
noise is referred, with *pts*, *fstart* and *fstop*
being the `.ac` parameters that specify the frequency range over
which analysis is desired. The optional *summary_pts* is an
integer; if specified, the noise contributions of each noise
generator is produced every *summary_pts* frequency points.

The `.noise` analysis produces two plots -- one for the Noise
Spectral Density curves and one for the total Integrated Noise over
the specified frequency range. All noise voltages/currents are in
squared units (V^{2}
/Hz and A^{2}
/Hz for spectral density, V^{2}
and
A^{2}
for integrated noise).

The optional dc sweep is a dc analysis specification which will cause the noise analysis to be performed at each point of the dc sweep. The small-signal parameters are reevaluated at every sweep point, and the output vectors will be multidimensional.

In interactive mode, the **noise** command, which takes the same
arguments as the `.noise` line, can be used to initiate noise
analysis.

Noise analysis is not available if Josephson junctions are included in the circuit.