Noise analysis measures the noise generated by resistors and semiconductor devices in the circuit. Capacitors, inductors and controlled sources are treated as noise free.

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 (V2/Hz and A2/Hz for spectral density, V2 and A2 for integrated noise).

The following noise measurements can be made:


To perform an Noise analysis, the circuit must contain at least one independent source that has defined the parameters for the amplitude and phase of the AC signal. These parameters must be specified in the SPICE attributes of the symbol.


Enter a brief description of the type of analysis. The text entered is the title of the document in which the simulation results will be stored.

Analysis Range

In this section, you must specify the frequency range for which the analysis is to be performed.

Sweep Type

Defines how test points are determined within the specified frequency range.

Start Frequency

The initial frequency for the sine wave generator (in Hz).

Stop Frequency

The final frequency for the sine wave generator (in Hz).

Number of Points

Specifies the number of points to be analysed. If the frequency varies linearly, this parameter specifies the total number of points otherwise it indicates the number of points to be analysed for each decade or octave.

Points Per Summary

Determines the amount of data generated by the noise analysis. It is an integer number that indicates how many frequency values, in the frequency range specified for the analysis, a detailed report must be generated on the noise produced by each resistor and semiconductor device in the circuit. For example, if a decadic variation has been selected for analysis with numpoints per decade and numdec decades within the specified frequency range, numdec*numpoints/PointsPerSummary+1 values are reported for each noise generator. Setting this parameter to 0 will cause input and output noise to be measured only.

Noise Source

An independent voltage source in the circuit which is to be used as an input reference for the noise calculations.

Output Node

The node in the circuit at which the total output noise is to be measured.

Reference Node

The node in the circuit used as a reference for calculating the total output noise at the desired Output Node. By default, this parameter is set to GND. If set to any other node, the total output noise is calculated as: V(Output Node) - V(Reference Node).


Specifying the simulation data to be collected. Click on the button to activate the Vectors dialog box in which to specify the names of the vectors.


Specify the temperature at which the simulation will be performed.

Analysis Mode

Specify whether a single or multiple analysis should be performed. The multiple analysis performs several consecutive simulations, varying the value of some parameters at each step. When a multiple analysis is selected, the Setup button is activated. Click on the button to activate the dialog in which to set the specific parameters for the selected analysis mode.

The following analysis modes are supported, click a link to learn more about that analysis mode:


Click on this button to activate the dialog box in which to set the options of the simulator. The options set are only valid for the current analysis and replace those defined in the general tab of the simulator options.


Click on this button to activate the dialog box in which to set the diagrams and the list of vectors to be included in the diagrams. See the Plot dialog box.

See also