초록 ▼

A non-propagating magnetic field-based communication system transmits and receives digital data within a limited coverage area environment. The system includes a compact transmitter unit, such as that contained in an `tracking' tag affixed to an object, and a digital detector/demodulator unit. In or

A non-propagating magnetic field-based communication system transmits and receives digital data within a limited coverage area environment. The system includes a compact transmitter unit, such as that contained in an `tracking' tag affixed to an object, and a digital detector/demodulator unit. In order to generate and FSK-modulate a non-propagating magnetic field in accordance with modulation signals representative of the digital data, the transmitter unit contains a magnetic field coil and one or more capacitors controllably switched in circuit with the coil in accordance with the data, so as to change the resonant frequency of an inductor-capacitor transmitter resonant circuit. The receiver unit includes a magnetic field-sensing coil in circuit with a capacitor, to form a receiver resonant circuit that resonates at a frequency between the FSK frequencies modulated by the transmitter unit. A digital receiver/demodulator detects whether received frequencies are valid FSK frequencies and derives digital data using differences between valid detected FSK frequencies.

대표청구항 ▼

1. A communication system comprising:a transmitter unit that is operative to generate and FSK-modulate a non-propagating magnetic field in accordance with modulation signals representative of digital data to be transmitted, said transmitter unit including a magnetic field producing-coil and one or m

1. A communication system comprising:a transmitter unit that is operative to generate and FSK-modulate a non-propagating magnetic field in accordance with modulation signals representative of digital data to be transmitted, said transmitter unit including a magnetic field producing-coil and one or more capacitors controllably switched in circuit with said magnetic field coil in accordance with said digital data, thereby changing the resonant frequency of an inductor-capacitor transmitter resonant circuit formed thereby, to effect FSK-modulation of said magnetic field; and a receiver unit including a magnetic field-sensing coil in circuit with an associated capacitor, forming a receiver resonant circuit that resonates at a frequency between FSK frequencies employed by said transmitter unit, and a digital receiver/demodulator, that is operative to detect valid FSK frequencies modulating said non-propagating magnetic field, and derives said digital data from valid detected FSK frequencies, with said digital receiver/demodulator being referenced to a clock frequency representative of a difference between FSK modulation frequencies, and including two signal sample paths that process alternate sample periods of one-half the period of the received data modulation, and produce output values from which said digital data can be recovered.