Importance

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Abstract

A reader interrogates an object. The object has a tag with a data source such as a read-only memory (ROM) which produces an identifying sequence of binary 1's and 0's in an individual pattern and transmits these signals to the reader. Each '1' or '0' is converted to a plurality of signal cycles at first and second harmonic frequencies. For example, a '1' may be identified by two signal cycles at the second frequency (e.g. 40 kHz) and then one signal cycle at the first frequency (e.g. 20 kHz) and a '0' may be identified by a signal cycle at the first frequency and then two signal cycles at the second frequency. The transponder also produces a plurality of signal cycles in an individual code (different from any combination of '1's' and '0's') to indicate the end of the transmission of the signal cycles identifying the object and the start of another transmission. The reader receives the signal cycles identifying the object and delays these signal cycles by (a) a first time such as 1/4 period of a cycle at the second frequency, (b) a second time such as 1/2 of such period and (c) a third time corresponding to such period. The reader compares the received signals and the first delayed signals to produce first phase-locked signals. The reader compares the received signals and the second delayed signals to produce additional phase-locked signals at the times that the first phase-locked signals are not produced. The reader then produces clock signals from the first and additional phase-locked signals. The reader produces information signals from a comparison of the received signals and the third delayed signals. The reader synchronizes the information signals with the lock signals to identify the object.

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First Claim