Electronic identification system with improved sensitivity

A tag for use with a reader, the reader establishing an alternating magnetic field in the proximity of the tag, the tag comprising:

• a coil;
• a capacitor;
• a means for coupling the capacitor to the coil and coupling the coil to at least one other means, the signal provided to the other means as a result of the coupling being called coupling-means signal, the combination of the coil, the capacitor and the coupling means being called the resonating circuit, the resonating circuit having a resonant frequency;
• a resonating means for automatically maintaining the resonating circuit in a tuned condition, a tuned condition being the condition where the difference between the resonant frequency and the frequency of the alternating magnetic field is a predetermined value in the range from a negative predetermined value to a positive predetermined value.

An identification system consisting of a reader and at least one tag, the reader comprising:

• a coil;
• at least one capacitor;
• a means for coupling the capacitor(s) to the coil and coupling the coil to at least one other means, the signal(s) provided to the other means as a result of the coupling being called coupling-means signal(s);
• a means for driving the coil through the capacitor(s) with a driving signal;
• a means for generating a driving signal which incorporates a bit-timing clock signal;
• a means for extracting data communicated by the tag from a coupling-means signal;
• the tag comprising:
• a coil;
• a capacitor;
• a means for coupling the capacitor to the coil;
• a means for driving the coil through the coupling means with a driving signal;
• a means for generating a bit-timing clock signal that is synchronized to the bit-timing clock signal embedded in the alternating magnetic field by the reader;
• a means for generating the driving signal which carries a sequence of bits to be communicated to the reader, the start of each bit being controlled by the bit-timing clock signal that is generated by the tag and synchronized to the bit-timing clock signal embedded in the alternating magnetic field.

An identification system consisting of a reader and at least one tag, the reader comprising:

• a coil;
• at least one capacitor;
• a means for coupling the capacitor(s) to the coil;
• a means for driving the coil through the capacitor(s) with a driving signal;
• a means for generating the driving signal;
• a means for transmitting a sequence of bits to the tag by modulating the driving signal, the start of each bit being determined by a bit-timing clock signal;
• a means for embedding the bit-timing clock signal in the alternating magnetic field;
• the tag comprising:
• a coil;
• a capacitor;
• a means for coupling the capacitor to the coil and coupling the coil to at least one other means, the signal(s) provided to the other means as a result of the coupling being called coupling-means signal(s);
• a means for generating a bit-timing clock signal that is synchronized to the bit-timing clock signal embedded in the alternating magnetic field by the reader;
• a means for identifying the bit being transmitted during each bit period, the identifying means being based on at least one weighted integration over a bit period of a demodulated coupling-means signal.