Smart card for effecting data transfer using multiple protocols

摘要

A data transaction device having a contactless mode of operation and comprising an antenna coil (15) coupled to a processing unit (14) via an antenna interface (16) for allowing contactless data transmission between the data transaction device and a remote transceiver. A circuit within the antenna interface includes a modulator (45) for modulating a signal transmitted by the remote transceiver and received by the antenna coil with outgoing data generated by the processing unit for transmitting via the antenna coil to the remote transceiver. The circuit further includes a variable loading means (45) connected in series with a load (14, 58) seen by the antenna coil and having a capacitance (57, 59) connected across the load so as to effect a change in impedance of the load seen by the antenna coil thus allowing amplitude and/or phase modulation of said signal without complete interruption thereof and regardless of the magnitude of an external capacitance (59) connected across the load. Preferably, the antenna interface (16) may be customized for different applications and the data transaction device also includes a contact field (11) thus allowing for either contact or contactless communication.