Anwesenheitsdetektor

摘要

In a human body detector, a wave-detection circuit (35) for detecting waves of a resonance voltage (V1) is connected to a sensor resonance circuit (35) that varies a constant frequency voltage in accordance with a change in the capacitance of a sensor electrode (37). The wave-detection circuit (36) is connected to a differentiator (41) that acquires a changing rate ( tau ) by differentiating the wave-detection voltage (V2) with respect to time, and allows a voltage to pass if the changing rate ( tau )of the voltage is greater than or equal to a predetermined value ( tau A). The differentiator (41) is connected to a high-pass filter (42) that allows passage of a voltage whose changing rate ()is greater than or equal to a second predetermined value ( tau B). The high-pass filter (42) is connected to a comparator (43) whose non-inversion input terminal (43b) is connected to a power source (44) that applies thereto a reference voltage (V4).