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Setting Up An Analysis
AC Related Analyses
AC Related Analyses
The AC related analyses are:
• “AC Analysis” on page 224
• “Loop Stability Analysis” on page 229
• “Pole Zero Analysis” on page 230
• “Transfer Function” on page 237
See also “Noise Analysis” on page 239.
AC Analysis
A small-signal analysis that computes the magnitude and phase of output variables as a function
of frequency. Eldo first computes the circuit DC operating point (DCOP) with user-specifiable
initial conditions; thereafter the behavior of the linearized circuit is computed for a sine input of
user-specifiable amplitude, phase and frequency range.
Different types of AC analysis can be specified:
• Circuit frequency response analysis—.AC specified with the SWEEP parameter results
in a frequency response analysis within the frequency range fstart to fstop with a number
of points nb according to the sweep variation type.
• Parameter-driven analysis—The frequency response analysis can be performed while
sweeping a parameter or device.
• Data-driven analysis—.AC followed by the parameter DATA=dataname results in a
sweep of the values pre-defined in the .DATA command.
• List-driven analysis—A list of frequency points can be specified instead of a frequency
range.
• Adaptive analysis—An adaptive variant of AC analysis can be used when there are ports
in the design to generate an accurate touchstone file. Eldo will adjust the frequency
based on a tolerance value in order that sharp peaks in the AC response are not missed.
Whenever a .AC command, a .TRAN command, and a .OP command containing time
specifications are in the .cir file, then an AC analysis will be performed at each of these time
points. See Performing an AC Analysis During Transient Analysis for further details.
An adaptive variant of AC analysis can be used when there are ports in the design to generate an
accurate touchstone file. Eldo will then adjust the frequency in order that sharp peaks in the AC
response are not missed. See Adaptive AC Analysis Example for further details.
.MPRUN can be used to take advantage of multi-processor machines for data sweeps on the
.AC command.
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Eldo® User's Manual, 15.3