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SIMPLIS Adds Multi-Tone AC Analysis to Characterize Digital Control Loops

March 21, 2013 by Jeff Shepard

SIMPLIS Technologies’ Periodic Operating Point (POP) analysis followed by an AC Analysis has a proven record of quickly and accurately measuring the AC loop response of switching power supplies. This analysis works very well for stable systems where the feedback signals are represented by double precision numbers.

In digitally-controlled systems where the signals in the feedback loop are quantized into discrete levels, the POP / AC analysis is typically not applicable. The extremely small perturbation of the injected signal during the AC analysis is not large enough to produce a control loop response. The Multi-Tone AC analysis, now available in the Design Verification Module (DVM) in SIMetrix/SIMPLIS 7.1, is able to provide an AC analysis of such digitally controlled systems, including closed loop response, input and output impedance as well as conducted susceptibility.

Multi-Tone AC analysis is included in the Design Verification Module in the SIMetrix/SIMPLIS 7.10 release. Existing DVM customers will have access to the Multi-Tone AC feature by simply updating to the latest version of SIMetrix/SIMPLIS. DVM is an add-on module to SIMetrix/SIMPLIS.

The Multi-Tone AC Analysis injects multiple frequencies into the circuit under test during a transient simulation, and then calculates the AC results using a Fourier analysis. The signal amplitude is set by the user to be large enough to insure the control loop is perturbed and there will be a valid AC response to the perturbation. Because Multi-Tone AC analysis uses a transient simulation, the technique can be applied to any converter. POP convergence is not a requirement.

Both linear and decade frequency sweep modes are available with the four Multi-Tone tests objectives that are built in to DVM: Bode Plot, Output Impedance, Input Impedance and Conducted Susceptibility. Using the built-in test plans for dc-dc and ac-dc converters a working design can be converted to run the Multi-Tone AC analysis in 5 minutes or less.