Sensormatic Electronics Corporation

Ericsson Gmbh

Pulse Electronics Gmbh

David L Roberson

Brent F Balch

Harry E Watkins

A technique for reducing low frequency baseband interference noise is disclosed. The low frequency baseband interference noise typically takes the form of low frequency magnetic interference emanating from a power source providing low frequency switching currents. The power source typically has a supply current terminal and an oppositely disposed return current terminal. The technique is realized by enclosing the power source in an electrically conductive sheath, wherein the electrically conductive sheath has an input terminal disposed proximate the supply current terminal and an output terminal disposed proximate the return current terminal. The output terminal is electrically connected to the return current terminal. Also, the electrically conductive sheath has an opening proximate the supply current terminal for allowing access to the supply current terminal.

Technique for reducing low frequency interference noise

An electronic article surveillance (EAS) system includes a transmitting antenna, a driver operable for exciting the transmitting antenna, a receiving antenna and circuitry connected to the receiving antenna for improving the quality of transmissions from the transmitting antenna. The driver excites the transmitting antenna at a preselected system operating frequency and the circuitry connected to the receiving antenna improves the quality of transmissions from the transmitting antenna by lessening harmonics of the operating frequency in the transmissions. The harmonics are attributable to protection diodes connected to the receiving antenna for limiting voltages impressed thereon and otherwise adversely impacting on the receiver tag signal processing circuitry. The harmonic lessening circuitry is connected in parallel with the protection diodes and is operative to lessen protection diode harmonic generation.

Pulsed electronic article surveillance systems

A direct sequence digital spread spectrum receiver acquires and maintains synchronization in a reliable, yet simple manner, even under severe multipath and interference conditions. A sliding correlator and a voltage controlled crystal oscillator (VCXO) cooperate to acquire initial synchronization, and once synchronization is acquired, the VCXO is linearly frequency modulated (FM) for accurate tracking. The difficult problem of keeping the receiver code clock synchronized to that of the transmitter under severe multipath and interference conditions is solved by virtue of a dual switched bandwidth low pass filter section of the tracking circuit, allowing a wide bandwidth for initial acquisition and tracking but once the clocks are aligned, a narrow loop takes over that follows the transmitter closely. A commercially available intermediate frequency (IF) integrated circuit (IC) is used as an amplitude modulated (AM) detector to achieve the large dynamic range required. The IF IC has an internal received signal strength indicator (RSSI) output which is used to demodulate the amplitude variations generated by the tracking circuit.

Initial synchronization and tracking circuits for spread spectrum

A transmitter for an electronic article surveillance system having a power amplifier for forming a drive signal for causing a current to flow through an antenna. The magnitude of the current flowing through the antenna is sensed and, based upon the sensed current, the drive signal is continuously controlled.

Linear power amplifier utilizing current feedback

A method and apparatus for determining the amplitude of a first magnetic field at a first fundamental frequency in a zone in which a second magnetic field is able to be present wherein first and second transmissions of a magnetic field at the fundamental frequency and different phases is carried out at different times, the field in the zone is detected for each transmission and the detected fields are processed to determine the magnitude of the first magnetic field.

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Forest, VA, United States of America

David L Roberson