Methods of DC/DC converter transfer function measurements, based on data acquired in the time domain

The measurement of frequency characteristics, like magnitude and phase, related to a specific transfer function of DC-DC converters, can be a difficult task - especially when the measured signal approaches the boundary of a small-signal model validity (i.e. 1/3 of the switching frequency f(S)). It is hard to find a paper where authors mention the measurement techniques they use to draw frequency characteristics. Meanwhile the presence of noise in the output signal does not enable to directly measure the gain and the phase shift between the input and output signals. In such situations additional analysis is required in order to achieve a reliable result. This paper contains a description of a few methods that can be used to analyse measured signals in order to determine the gain and the phase shift of a specific transfer function. They enable to verify mathematical models in a wide range of frequencies (up to 1/3 f(S)). The methods use signals measured in the time domain and can be implemented in mathematical software such as Matlab or Scilab.