Passivity Checking: Iterated Fitting of Passivity Violations Low Frequency (IFPVLF)

Iterated Fitting of Passivity Violations Low Frequency (IFPVLF) is the latest passivity enforcement algorithm. It builds upon the default passivity enforcement algorithm (Iterated Fitting of Passivity Violation) by providing a better fit to “Z” at DC and low frequencies.

In a dynamic link simulation, Circuit receives the calculated Scattering Parameter data (S-data) from the field solver. Circuit performs state-space fitting, which generates a macromodel that represents the input/output behavior of the structure modeled within the field solver, and performs time or frequency domain simulations. In many applications such as power delivery networks, Circuit must fit the S-data while also preserving its fit of the corresponding Z-data. This fitting process is called “Z-fitting”.

Often, the generated macromodel is not passive. When passivity enforcement is invoked using the default Iterated Fitting of Passivity Violation (IFPV) method, there is no guarantee that the Z-fit to DC and low frequencies are preserved. Preserving the fit to Z-data at DC and low-frequency can be very important (e.g., due to inaccuracies of the fit to Z-data at DC and low frequencies, a DC-DC buck converter may not converge to a correct steady state voltage regulated value. To remedy this issue, Circuit offers a DC/low frequency Z-fitting passivity enforcement called Iterated Fitting of Passivity Violation at Low Frequency. IFPVLF enforces passivity while providing a better fit to Z-data at DC and low frequencies. Use IFPVLF for passivity enforcement when a better Z-fit at DC and low frequencies are appropriate).