Charging a transponder in a security system
First Claim
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1. A method for adaptively energizing a transponder using a charging electromagnetic field created by a transceiver in a security system, said method comprising the steps of:
- transmitting a partial charging electromagnetic field in a manner providing a plurality of spaced frequency components so that one of said spaced frequency components energizes said transponder by an amount causing it to produce a partial transmission, thereby providing a calibration signal for identifying a frequency upon which said transponder will be transmitting, said spaced frequency components being spaced between a minimum frequency and a maximum frequency;
storing energy in said transponder from said partial charging electromagnetic field;
detecting within said transponder the ending of said partial charging electromagnetic field;
transmitting a partial transmission from said transponder including a frequency calibration signal;
receiving said frequency calibration signal in said transceiver;
transmitting a full charging electromagnetic field substantially limited to a single frequency component, said single frequency component determined in response to said frequency calibration signal;
storing energy in said transponder from said full charging electromagnetic field; and
transmitting a full transmission from said transponder including a security code.
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Abstract
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.
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Citations
13 Claims
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1. A method for adaptively energizing a transponder using a charging electromagnetic field created by a transceiver in a security system, said method comprising the steps of:
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transmitting a partial charging electromagnetic field in a manner providing a plurality of spaced frequency components so that one of said spaced frequency components energizes said transponder by an amount causing it to produce a partial transmission, thereby providing a calibration signal for identifying a frequency upon which said transponder will be transmitting, said spaced frequency components being spaced between a minimum frequency and a maximum frequency; storing energy in said transponder from said partial charging electromagnetic field; detecting within said transponder the ending of said partial charging electromagnetic field; transmitting a partial transmission from said transponder including a frequency calibration signal; receiving said frequency calibration signal in said transceiver; transmitting a full charging electromagnetic field substantially limited to a single frequency component, said single frequency component determined in response to said frequency calibration signal; storing energy in said transponder from said full charging electromagnetic field; and transmitting a full transmission from said transponder including a security code. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. Transceiver apparatus for adaptively charging a transponder using a charging electromagnetic field created by said transceiver apparatus in a security system, said transceiver apparatus comprising:
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a transceiver antenna for exchanging transmissions with said transponder when said transponder is located in the vicinity of said transceiver; an oscillator producing a reference frequency signal; a programmable divider coupled to said oscillator for selectably dividing said reference frequency signal to produce selected frequency signals; a frequency hop sequencer coupled to said programmable divider for commanding said programmable divider to produce said selected frequency signals according to a frequency hop sequence during a partial charging of said transponder; a frequency-sensitive decoder coupled to said transceiver antenna for receiving a charging frequency calibration signal from said transponder after partial charging thereof, said frequency-sensitive decoder identifying a specific frequency of said charging frequency calibration signal; and a natural frequency register coupled to said frequency-sensitive decoder and said programmable divider, said natural frequency register causing said programmable divider to produce a charging signal corresponding to said specific frequency during a full charging of said transponder.
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13. Transceiver apparatus for adaptively charging a transponder using a charging electromagnetic field created by said transceiver apparatus in a security system, said transceiver apparatus comprising:
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a transceiver antenna for exchanging transmissions with said transponder when said transponder is located in the vicinity of said transceiver; an oscillator producing a reference frequency signal; a signal generator producing a plurality of spaced frequency components simultaneously between at least a minimum frequency and a maximum frequency during a partial charging of said transponder; a frequency-sensitive decoder coupled to said transceiver antenna for receiving a charging frequency calibration signal from said transponder after partial charging thereof, said frequency-sensitive decoder identifying a specific frequency of said charging frequency calibration signal; a natural frequency register coupled to said frequency-sensitive decoder for storing a value proportional to said specific frequency; and a programmable divider coupled to said natural frequency register and said oscillator for dividing said reference frequency signal to produce a charging signal corresponding to said specific frequency during a full charging of said transponder.
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Specification