Patent ID: 6028503
Filing Date: 2000-02-22
Classification: G01S,G06K

Abstract:
A transmission and receiving device for contactless data transmission between the device and a transponder, the transmission and receiving device comprising a drive stage for generating a drive signal and a first antenna resonant circuit which includes a coil and a capacitor, the transponder comprising a second antenna resonance circuit, the drive signal being supplied to the first antenna resonance circuit, an RF signal occurring in the first antenna resonance circuit corresponding to the drive signal, and the RF signal being modulateable by load modulation in dependence on data to be transmitted to the transmission and receiving device by a transponder, the transmission and receiving device comprising an evaluation unit to which the RF signal is supplied for the purpose of evaluation, the evaluation unit being arranged to determine data contained in the RF signal due to the load modulation, and the transmission and receiving device comprising a measuring unit for determining measurement values of an electric variable which occurs in the first antenna resonant circuit, and a control unit for generating control information in dependence on the measurement values determined, characterized in that the evaluation unit is implemented as a synchronous demodulator which samples the RF signal at sampling instants for the purpose of demodulation, that the measuring unit is arranged to determine a respective phase shift between a reference signal and the electric variable, that the control unit and the synchronous demodulator are interconnected, that the control information generated by the control unit is applied to the synchronous demodulator, and that the sampling instants are automatically influenced by the control information in accordance with the determined phase shift, so as to adapt the sampling instances to a mode change of the synchronous demodulator between an amplitude demodulation mode and a phase demodulation mode.