Reader for electromagnetic transponders which functions with very short distance coupling

摘要

The terminal (1) uses inductive coupling to read from and write to a transponder, and includes a resonant circuit (Li,Ci) tuned to receive an AC HF excitation voltage. The resonant frequency may be altered so as to detune the LC in the event that a transponder is very close to the terminal. A capacitor (24) may be controlled by a control circuit (21) and with impedance (Li) to detect a gap of phase in relation to the signal of REF reference and to modify the capacity Ci of the capacitor (24). An Independent claim is included for a contactless system of data transmission.