Patent ID: 6731199
Filing Date: 2004-05-04
Classification: G06K,H04B

Abstract:
A non-contact communication system comprising:a first communication unit for selectively radiating through a common tuning circuit thereof one of a radio wave for communication and a radio wave for detection, the radio wave for communication having alternately a period in which the radio wave is not modulated and a period in which the radio wave is modulated in accordance with data to be transmitted, the radio wave for detection having a smaller amplitude than the radio wave for communication and comprising only a carrier without including the data to be transmitted and data to be received; and a second communication unit for communicating with the first communication unit by modulating the radio wave for communication in accordance with reply data during said period in which the radio wave is not modulated, wherein the first communication unit generates a radio wave for detection; the second communication unit causes a frequency different from a frequency of the radio wave for detection to be superimposed on the radio wave for detection because an impedance with which the tuning circuit of the first communication unit is loaded when the second communication unit repeatedly switches between an operative state during which the second communication unit obtains power for functioning by tuning in to the radio wave for detection and a non-operative state during which the second communication unit obtains no power for functioning by detuning in to the radio wave for detection, and the first communication unit, by detecting said frequency which is different from the frequency of the radio wave for detection and superimposed on the radio wave for detection, recognizes that the second communication unit is present within a range communicable with the first communication unit and then starts transmitting the radio wave for communication.