Transmitting and receiving system

摘要

A transmitting and receiving system including a transponder always maintains a transmission function even if circuit constants of circuit elements are deviated or such circuit constants are shifted in association with temperature changes. The transponder includes a transponder coil electromagnetically coupled to an antenna coil through which a response signal is transmitted, a resonance capacitor, a main modulation circuit including a first modulation capacitor, and a supplemental modulation circuit including a second modulation capacitor whose static capacitance value is different from that of the first modulation capacitor. A response signal is transmitted in changing an impedance of a transmitting and receiving portion by the main modulation circuit when a question signal is received and by the supplemental modulation circuit when a correction command signal is received.