Ford Motor Company Limited

Luke Aaron Perkins

David P Laude

Scott O Campbell

Lawrence P Kirk

William David Treharne

John F Kennedy

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.

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Security, CO, United States of America

Luke Aaron Perkins