MOBILE BODY IDENTIFICATION DEVICE

摘要

PURPOSE: To extend a communication available range between a reader/writer and a data carrier. CONSTITUTION: A transmission reception resonance circuit 10 of a data carrier B receives a carrier from a reader/writer A. A reverberation vibration is generated in the transmission reception resonance circuit 10 for a period when the carrier is lost. A reception resonance circuit 5 of the reader/writer A receives the reverberation vibration and a level discrimination circuit 19 compares the reception level with a prescribed threshold level. When the reception level of the reverberation vibration exceeds the threshold level, the level discrimination circuit 19 gives a control signal to a coding circuit 1. The coding circuit 19 receiving the control signal controls an ASK modulation circuit 3 to decrease number of carrier pulses by one and to extend the stop period by one pulse. Thus, the start of generation of the reverberation vibration is quickened and the reverberation vibration is sufficiently attenuated within the stop period. Then delimiter of transmission of the reader/writer A is made clear and a communication available range is extended.