DC or Small-Signal AC Sensitivity Analysis

The sensitivity of out_var to all non-zero device parameters is calculated when the SENS analysis is specified.

.SENS <out_var> [AC <sweep type> <points> <start frequency> <end frequency>]



Is a circuit variable (node voltage or voltage-source branch current).

sweep type

Must be LIN, OCT, or DEC, as described below.

Sweep type Description
LIN Linear sweep. The frequency is swept linearly from the starting to the ending frequency. The points is the total number of points in the sweep.
DEC Sweep by decades. The frequency is swept logarithmically by decades. The points is the number of points per decade.
OCT Sweep by octaves. The frequency is swept logarithmically by octaves. The points is the number of points per octave.


Specifies the number of points in the sweep, using an integer.

start frequency

Is the starting frequency.

end frequency

Is the final frequency.


Spice will calculate either the DC operating-point sensitivity or the AC small-signal sensitivity of an output variable with respect to all circuit variables, including model parameters. Spice calculates the difference in an output variable (either a node voltage or a branch current) by perturbing each parameter of each device independently. Since the method is a numerical approximation, the results may demonstrate second order affects in highly sensitive parameters, or may fail to show very low but non-zero sensitivity. Further, since each variable is perturb by a small fraction of its value, zero-valued parameters are not analyized (this has the benefit of reducing what is usually a very large amount of data).

To calculate the sensitivity of the output variable with respect to the analysis DC, specify only the name of the variable without the term AC. Specify the term AC and its parameters to calculate the sensitivity with respect to the analysis AC.

The output values are in dimensions of change in output per unit change of input (as opposed to percent change in output or per percent change of input).


.SENS V(OUT) AC DEC 10 100 100k

See also