Patent ID: 7548636
Filing Date: 2009-06-16
Classification: A61B,G06K

Abstract:
1. A biometric recognition apparatus comprising: a detection element which electrically contacts an object; a supply signal generating unit which generates an AC supply signal; a response signal generating unit which includes a resistive element connected between said supply signal generating unit and said detection element, applies the supply signal to said detection element through the resistive element, extracts, from one terminal of the resistive element, a response signal containing not less than one individual parameter which changes depending on whether or not the object is a living body, and outputs the signal; a waveform information detection unit which detects from said response signal at least one of the individual parameters as waveform information from the response signal, and outputs a detection signal representing the waveform information; and a biometric recognition unit which determines on the basis of the detection signal whether or not the object is a living body, wherein the individual parameters comprise a phase and amplitude of the response signal which change in accordance with an impedance of the object with which the apparatus is in contact through said detection element, said waveform information detection unit detects a phase difference between the supply signal and the response signal as the waveform information, and said detection element includes a first detection electrode which electrically contacts the object and is connected to a predetermined common potential, and a second detection electrode which electrically contacts the object, said supply signal generating unit includes an offset removing circuit which outputs an AC supply signal as the supply signal from which an offset is removed to make a central potential coincide with the common potential, said response signal generating unit applies the supply signal to the second detection electrode of said detection element, and outputs a signal as a response signal which changes in phase in accordance with the impedance of the object, said waveform information detection unit includes a level shift circuit which level-shifts the response signal to make a central potential of the response signal coincide with a central potential of a reference signal synchronized with the supply signal, detects, as waveform information of the response signal, a phase difference obtained by comparing a phase of the reference signal with the response signal level-shifted by the level shift circuit, and outputs a detection signal representing the waveform information, and said biometric recognition unit determines on the basis of the waveform information of the detection signal whether or not the object is a living body.