Charging a transponder in a security system

• US 5,790,014 A
• Filed: 04/21/1997
• Issued: 08/04/1998
• Est. Priority Date: 04/21/1997
• Status: Expired due to Term

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Ford Motor Company
• Inventors: Perkins, Luke Aaron, Campbell, Scott O., Kirk, Lawrence Peter, Laude, David Philip, Treharne, William David
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Pope, Daryl C.
• Application Number:
  US08/844,569
• Time in Patent Office: 470 Days
• Field of Search: 340/426, 340/425.5, 340/825.54, 340/825.31, 340/825.72, 340/825.34, 340/543, 340/572, 340/505, 235/382, 235/382.5, 342/51, 342/30, 342/44, 307/9.1-10.8
• US Class Current: 340/10.34
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user
• CPC Class Codes: B60R 25/406 Power supply in the remote key
• CPC Class Codes: G07C 2009/00603 by power transmission from lock

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.

Claims

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.

2. The method of claim 1 wherein said spaced frequency components are substantially evenly spaced according to a spacing interval, said spacing interval being less than or equal to a receiving bandwidth of said transponder.

3. The method of claim 1 wherein said plurality of spaced frequency components are transmitted sequentially.

4. The method of claim 1 wherein said plurality of spaced frequency components are transmitted simultaneously.

5. The method of claim 3 wherein said transceiver attempts to receive said frequency calibration signal after each sequential transmission of a respective spaced frequency component, and wherein further transmissions of said spaced frequency components are terminated once said frequency calibration signal is received.

6. The method of claim 3 wherein a frequency of sequentially transmitted frequency components follows a predetermined hop sequence commencing with a center frequency substantially midway between said minimum frequency and said maximum frequency.

7. The method of claim 6 wherein said hop sequence alternates above and below said center frequency in successive transmissions.

8. The method of claim 1 wherein said frequency calibration signal is comprised of a beginning portion of a programmed response message of said transponder using frequency-shift keying modulation, said beginning portion consisting of a transmission at a resonant frequency at which said transponder charges and corresponding to one modulation frequency of said frequency-shift keying modulation.

9. The method of claim 1 wherein said single frequency component used for said full charging electromagnetic field is selected as a closest transmittable frequency of said transceiver to the frequency of said frequency calibration signal.

10. The method of claim 9 wherein said single frequency component is not equal in frequency to any of said plurality of spaced frequency components.

11. The method of claim 1 further comprising the steps, following said storing of energy in said transponder from said full charging electromagnetic field, of:

transmitting a pulse-width modulated code from said transceiver to said transponder; and

determining said security code in said transponder by manipulating said pulse-width modulated code according to a predetermined procedure stored in said transponder.

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:

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.

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:

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.