Ford Motor Company Limited

Lawrence P Kirk

John F Kennedy

David P Laude

Scott O Campbell

Luke Aaron Perkins

William David Treharne

Gregory A Marek

A security system utilizing a key-mounted transponder achieves fast and accurate charging of the transponder by using a frequency search and acquisition phase which attempts partial charging pulses at a plurality of spaced frequencies. After a successful partial charging, a frequency calibration signal is received from the transponder which provides a reference in the transceiver for producing a pulse for fully charging the transponder. Frequency search and acquisition allows robust system operation while using low cost and low tolerance parts.

Charging a transponder in a security system

A circuit and method of demodulating an FSK signal uses digital circuitry to convert the received signal into count values. For each reception an adaptive reference count value is determined by averaging the duration of received pulses during the preamble of the transmission. The adaptive reference count corresponds to a demodulated logic '1' or logic level '0'. The counts from the coded portion of the transmission are compared to the adaptive reference count. If the count is within predetermined windows from the reference count, the count value is converted to the corresponding digital signal.

Circuit for demodulating FSK signals

A method and apparatus for interrogating a transponder using a single transmitter-receiver antenna transmits an interrogation signal to the transponder. The transmit signal has two segments; a first segment for energizing the transmitter-receiver antenna and a second segment having a second phase for cancelling energy in the transmitter-receiver antenna. The amount of energy is reduced before the transponder transmits a response signal.

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Canton, MI, United States of America

Lawrence P Kirk