Low power cordless magnetic field digitizer with differential gr

Details Low power cordless magnetic field digitizer with differential gr Low power cordless magnetic field digitizer with differential gr

1991-10-01

1993-06-08

Schreyer, Stafford

Telegraphy

Systems

Position coordinate determination for writing

178 18, G08C 2100

Patent

active

052181740

ABSTRACT:
A digitizing system includes a tablet and a cordless pointing device including a plurality of data grid conductors in the tablet and a plurality of clock grid conductors in the tablet, all receiving a magnetic field signal transmitted by the pointing device. A data channel circuit includes a differential amplifier and demodulating and filtering circuitry coupled to an output of the differential amplifier, having a clock input. An A/D converter has an input coupled to an output of the demodulating and filtering circuitry. Multiplexing circuitry selectively couples various grid conductor signals to the data channel circuit. A clock recovery circuit responsive to the clock grid conductors includes a phase-locked-loop circuit that generates a recovered clock signal which is synchronous with the magnetic field signal and is used as a reference for demodulating the phase and amplitude of signals multiplexed from the data grid conductors to the data channel circuit. Accurate determination of the pointer tip position is achieved simultaneously with accurate decoding of pointer commands represented by shifts in the frequency of the magnetic field signal.

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