The AC Frequency Sweep Test is used to examine your circuit's behavior at different input frequencies. For example, a low-pass filter circuit could be analyzed to determine the cut off frequency of the filter, that is, the frequency above which the magnitude of the output is negligible.
{{Note | Before running an AC analysis, you have to designate one or more AC sources for your circuit and set their AC amplitudes (and phases). During an AC analysis, [[B2RF.Spice A/D]] shorts out all of the non-constant voltage sources that have a zero AC magnitude and opens all the non-constant current sources that have a zero AC magnitude. Make sure that the voltage and current sources used as inputs have non-zero AC voltage/current values.}}
All the sources with non-zero AC values are treated as sinusoidal sources with the specified peak voltage/current amplitudes and phases and default zero offsets. You can view or edit the AC values of voltage and current sources by double clicking on the parts and selecting the "Small-Signal AC and Distortion" tab of their property dialog. Make sure to check the "Use" checkbox in the section titled "AC Properties for Small-Signal AC Properties only". Given the specified voltage and current source values, the DC operating point of your circuit is calculated, and all nonlinear elements are replaced with their small-signal circuit models. If the DC operating point of your circuit with the sources shorted out is not where you want it, you may have to place some constant (DC) voltage sources in the circuit to compensate. Alternatively, you can set a nonzero value for the "Small-Signal Offset" parameter of an AC source as shown in the figure below.
[[File:b2MAN_Fig52.png|thumb|200px|AC Sensitivity Settings.]]
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===AC Sensitivity Test===