Contactless communication system for exchanging data

A system for exchanging data, the system comprising:

• at least one terminal;
• a plurality of portable objects cooperating with the at least one terminal by contactless communication;
• wherein the contactless communication is a communication in which an operation of at least one of the plurality of portable objects is clocked by a clock signal remotely generated by the at least one terminal;
• wherein the at least one terminal includes a first tuned circuit having a first coil for emitting a magnetic field in free space, a first data transmitter cooperating with the first coil, the first data transmitter including an alternating signal generator and an amplitude modulator, a first data receiver cooperating with the first coil, and a clock generator for generating the clock signal;
• wherein the amplitude modulator of the at least one terminal provides amplitude modulation of the magnetic field emitted by the at least one terminal at a modulation ratio less than or equal to 50%,
• wherein the at least one of the plurality of portable objects includes an electric circuit remotely powered by the at least one terminal, the at least one of the plurality of portable objects including:
• a second tuned circuit having a second coil for at least one of interacting with the magnetic field emitted by the at least one terminal and producing a response by a modulated disturbance of a magnetic field,
• a converter cooperating with the second coil to transform a magnetic field signal induced in the second coil into a DC voltage for powering the electric circuit, the converter including a rectifier stage and a filter stage,
• a second data transmitter and a second data receiver cooperating with the second coil, the second data receiver including a demodulator demodulating an amplitude of the magnetic field signal induced in the second coil, the demodulator operating on a second signal output from the rectifier stage and the filter stage;
• digital processor;
• and
• a clock detector and extractor circuit for receiving a signal from the second tuned circuit and for extracting the clock signal and outputting the clock signal to the digital processor for clocking the digital processor.