| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a proximity sensor detecting existence of a body to be detected, and also detecting a distance between the body to be detected and itself. Ž<P>SOLUTION: This proximity sensor includes an LC resonance circuit 1 having a detection coil 10, an oscillation circuit 2 which supplies a feedback current to oscillate the LC resonance circuit 1, a detection circuit 3 to detect the oscillation amplitude of the LC resonance circuit 1, a control part 4 having a resistance circuit 40 to adjust the magnitude of the feedback current in accordance with the duty ratio of a semiconductor switching element QP, and a PWM control part 41 to PWM-control the semiconductor switching element QP so that the negative conductance of the oscillation circuit 2 reaches a critical value (a critical value at which the LC resonance circuit 1 can oscillate) based on the detected result of the detection circuit 3, and a signal processing circuit 5 to make a detecting signal indicating the distance between a body to be detected and the detection coil 10 based on an electric signal used for setting the duty ratio in the PWM control part 41. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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