An electronic identification tag, usually in very small size, responds to
a reader with an identification code unique to the object to which the
tag is attached. The stand-alone device responds to a reader signal by
storing energy received from the signal, then using the stored energy to
generate another signal that is encoded with identification information.
In operation, a reader generates RF energy which can reach a multiplicity
of such tags over a distance of several meters. The system minimizes
power requirements for the tag by minimizing intelligence in the IC. Use
of a transmit frequency which is different from the reader's power
frequency reduces interference between the power pulse and information
pulse, eliminates the need for filters and enables the multiplied clock
reference frequency as the transmit carrier frequency.