Simulator Reference: .AC

Syntax

.AC inner_sweep_spec [ F frequency ] [RUNNAME=runname] [ SWEEP outer_sweep_spec ]

Spice compatible frequency sweep:

.AC DEC|LIN|OCT num_points start stop

Instructs the simulator to perform a swept small signal AC analysis. SIMetrix AC analysis is not limited to a frequency sweep as it is with generic SPICE and derivatives. See General Sweep Specification and examples below for more details.

frequency	Frequency at which analysis will be performed for non-frequency sweeps. Default 0.
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.
num_points	LIN: total number of points DEC: number of points per decade OCT: number of points per octave
start	Start frequency for SPICE compatible mode
stop	Stop frequency for SPICE compatible mode
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

Except for frequency sweep, the frequency at which the analysis is being performed should be specified. If omitted, the frequency will be assumed to be zero.

For non-frequency sweeps, a new dc operating point may be calculated at each step depending on what is being swept. If a capacitor, inductor or an 'AC only' model parameter is being swept, then no new dc operating point will be required. Otherwise one will be performed. An 'AC only' parameter is one that does not affect DC operating point such as device capacitance.

Notes

An AC analysis calculates the small signal frequency response of the circuit about the dc operating point. The latter is automatically calculated prior to commencing the frequency sweep. One or more inputs may be specified for AC analysis by using voltage or current sources with the AC specification (See Voltage Source). The results of an AC analysis are always complex.

Examples

SPICE compatible. Sweep frequency from 1kHz to 1Meg

.AC DEC 25 1k 1MEG

Sweep voltage source V1 100 points from -100mV to 100mV. Frequency = 100kHz

.AC DEVICE V1 LIN 100 -100m 100m F=100k

Sweep parameter Rscale from 0.5 to 3 in steps of 0.1. Frequency=20Meg

.AC PARAM Rscale STP 0.5 3 0.1 F=20Meg

Sweep resistor R1 with values 10k 12k 15k 18k 22k 27k 33k, Frequency =1.1KHz

.AC DEVICE R1 LIST 10k 12k 15k 18k 22k 27k 33k F=1.1K

Monte Carlo sweep 100 steps. Frequency = 10K. This is useful if - say - you are interested in the gain of an amplifier at one frequency and it needs to lie within a defined tolerance. Previously you would need to repeat an AC sweep at a single frequency to achieve this which could take a long time especially if the circuit has a difficult to find operating point. The analysis defined by the following line will take very little time even for a large circuit.

.AC MONTE 100 F=10K

Examples of Nested Sweeps

As Monte Carlo above but repeated from 0 to 100C

.AC MONTE 100 F=10K SWEEP TEMP STP 0 100 10

... and at a number of frequencies

.AC MONTE 100 SWEEP FREQ DEC 5 1k 100k