The AC Small Signal analysis computes the AC output variables as a function of frequency. The program first computes the DC operating point of the circuit and determines linearized, small-signal models for all of the nonlinear devices in the circuit. The resultant linear circuit is then analyzed over a user-specified range of frequencies. The desired output of an AC Small Signal analysis is usually a transfer function (voltage gain, transimpedance, etc). If the circuit has only one AC input, it is convenient to set that input to unity and zero phase, so that output variables have the same value as the transfer function of the output variable with respect to the input.

All independent voltage and current sources that have AC values are inputs to the circuit. During AC analysis, the only independent sources that have nonzero amplitudes are those using AC specifications. The SIN specification does not count, as it is used only during transient analysis.


To perform an AC 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.


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:

Collect Data For

Specifying the simulation data to be collected. Simulations, especially multiple simulations, can produce a large amount of data, causing excessive memory usage and lower simulation speed. This section allows you to specify which information resulting from the simulation should be stored. Select one of the following options:


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