# .NOISE

.NOISE inner_sweep_spec [ V ] pos_node [ VN ] neg_node
+ [[ INSRC ] in_source ]
+ [ F frequency ] [RUNNAME=runname] [SWEEP outer_sweep_spec]
Spice Compatible:
.NOISE V(pos_node [, neg_out_node ])  in_source
+ DEC|LIN|OCT num_points start stop interval

This statement instructs the simulator to perform a small signal noise analysis.

pos_node Node on circuit at which noise is measured.
neg_node Node to which outputnode is referenced. Defaults to ground if omitted.
in_source Input source (i.e. voltage or current) to which the input noise measurement is referred.
inner_sweep_spec See General Sweep Specification for syntax. Defines sweep mode. FREQ keyword is optional.
outer_sweep_spec If specified, analysis will be repeated according to this specification. See General Sweep Specification for syntax.
LIN Analysis points are linearly spaced.
DEC Analysis points are logarithmically spaced in decades
OCT Analysis points are logarithmically spaced in octaves
num_points
 LIN: Total number of points DEC: Number of points per decade OCT: Number of points per octave
start Start frequency
stop Stop frequency
interval Currently does nothing. Provided for backward compatibility.
runname If specified, the value for runname will be passed to the simulation data group as a string variable with name UserRunName. This may be used to identify which analysis generated the data which is useful when running netlists with multiple analyses defined

In this topic:

## Notes

During noise analysis the simulator calculates the total noise measured between pos_node and neg_node at each frequency point. It also calculates and outputs this noise referred back to an input specified by in_source. As for all other analysis modes a DC operating point analysis is carried out first but, unlike AC analysis, the results of this analysis are not made available. The simulator outputs vectors covering the contribution from each noise generating device to the total output noise. The names of these vectors begin with the component reference of the device followed by a suffix to indicate the source of the noise within the device. A listing of the suffixes is given below. It is important to note that it is not the noise being generated by each device that is output but the proportion of that noise that is propagated to the output.

It is not necessary to specify a separate AC analysis alongside the noise analysis as it is with SPICE2 and commercial derivatives of SPICE2.

The magnitude of any AC independent voltage or current source on the circuit has no effect on the results of a noise analysis. Unlike SPICE and earlier versions of SIMetrix, it is not necessary to specify an AC parameter for the source used for the noise input source. For the first form shown above, the input source is in fact optional. If it is omitted the input referred noise will not be calculated.

All noise results are in $\text{V}/\sqrt{\text{Hz}}$ except input noise referred back to a current source which is in $\text{A}/\sqrt{\text{Hz}}$. In standard SPICE3 the noise values produced for MOS2 and BSIM3 devices are in $\text{V}^2/\sqrt{\text{Hz}}$. For consistency, these have now been changed to $\text{V}/\sqrt{\text{Hz}}$. The original SPICE3 behaviour can be restored by setting the simulator option OldMosNoise (see .OPTIONS).

## Device vector name suffixes

 Device Type Suffix and Description BJT #rc Noise due to collector resistance #rb Noise due to base resistance #re Noise due to emitter resistance #ic Shot noise in collector #ib Shot noise in base #1overf Flicker (1/f) noise no suffix Total transistor noise Diode #rs Noise due to series resistance #id Shot noise #1overf Flicker (1/f) noise no suffix Total diode noise JFET and MOSFETs level 1-3 and BSIM3 #rd Noise due to drain resistance #rs Noise due to source resistance #id Shot noise in drain #1overf Flicker (1/f) noise no suffix Total FET noise NXP MOS9 (all types see NXP Compact Models) #Sfl Flicker (1/f) noise #Sth Drain thermal noise #Sig Gate thermal noise #Sigth Gate-drain correlated thermal noise no suffix Total FET noise Resistor #therm Resistor thermal noise #1overf Flicker (1/f) noise #noise Total resistor noise Voltage controlled switch no suffix Total switch noise

## Creating Noise Info File

Noise analysis generates vectors in the same way as all other swept analyses. Individual vectors may also be tabulated in the list file using the .PRINT statement.

A noise output file may also be created from the front end. Select the command shell menu Graphs and Data | Create Noise Output File to create a text file with a summary of noise results. Included is a list of the integrated noise output for every device listed in order of magnitude. Select Graphs and Data | View Noise Output File to view the file. Note that this is a front end feature and is not implemented by the simulator.

## Examples

Run noise analysis from 100Hz to 1MHz with 25 points per decade. Calculate noise at node named vout and noise referred back to voltage source vin:

.NOISE V( vout ) vin dec 25 100 1meg

Decade sweep resistor RSource from 100 to 10K with 25 points per decade. Frequency = 1kHz

.NOISE DEVICE RSource DEC 25 100 10k F=1K