Patent ID: 8878549

Claim:
An AC impedance measuring device, comprising: a signal generator that provides a first signal on which a period signal is superimposed to a DUT (device under test); a Fourier transform unit that performs Fourier transform on current data and voltage data output from the DUT using a transformation window having a time width that is an integral multiple of a period of the first signal, while sequentially shifting a start time of the transformation window, thereby obtaining a plurality of Fourier transform data strings of the voltage data and the current data, wherein at least one of the current data and the voltage data includes a transient response; a difference sequence calculator that sequentially calculates a first difference sequence of the Fourier transform data strings of the voltage data and a second difference of the Fourier transform data strings of the current data; and and impedance calculator that calculates an impedance of the DUT based on a ratio of the first difference sequence and the second difference sequence.