MICROPOWERED RF DATA MODULES

摘要

A low-power wireless data communication system, in which base stations (110) can automatically interface to batter-powered portable data modules (210) as they are brought within range. In the data modules (210), each receive antenna (121) is directly connected to a gain-controlled comparator (420A, 420B). Bandpass filtering (448) is accomplished economically by use of simple digital circuits. The two-level digital output from the comparator (420A, 420B) is fed (through an intersymbol detector, a counter, and a ripple-through magnitude comparator) to a state machine (552), which decodes the resulting digital waveform to a conventional serial-bus format. The internal data bus (701D) provides an interface to memory chips (262) and (optionally) to other chips, such as an electronic key. The decoder chip (220) also provides a secondary power supply to the other chips (230), and modulates the power supply (250) to assist detection of transitions on the reset-bar line of the serial bus (206). The modules (230) use widely different frequencies for read and write operations. (Transmissions by the base station (110) use a pulse-width modulation scheme where the most commonly used signals correspond to the shortest pulse. A "read" command is encoded as the same pulse width as one of the two write commands). In addition, a pair of touch contacts (270) can be used to override the RF link. Error-checking (Fig. 7E) is performed on incoming commands before memory access (260) is permitted. "Freshness seal" logic (510) prevents any battery drain until the module is initially turned on (by placing it in a strong field).