Passive entry and immobilizer at different frequencies using same antenna coil

• US 7,692,529 B2
• Filed: 04/05/2006
• Issued: 04/06/2010
• Est. Priority Date: 04/05/2005
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments Deutschland Gesellschaft Mit Beschrã¤Nkter Haftung (Texas Instruments, Inc.)
• Inventors: Aslanidis, Konstantin, Hagl, Andreas
• Primary Examiner(s): Bugg; George A
• Application Number:
  US11/278,736
• Publication Number:
  US 20060220786A1
• Time in Patent Office: 1,462 Days
• Field of Search: 340/5.61, 340/10.1, 340/10.2, 340/572.1, 340/5.2, 340/426.36, 307/10.3, 307/10.5, 336/83, 336/96, 343/788, 343/895
• US Class Current: 340/5.61
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user
• CPC Class Codes: G07C 2009/00357 and the lock having more than one limited data transmission ranges
• CPC Class Codes: G07C 2009/00777 by induction
• CPC Class Codes: G07C 2009/00793 by Hertzian waves
• CPC Class Codes: G07C 2209/61 Signal comprising different frequencies, e.g. frequency hopping
• CPC Class Codes: G07C 9/00309 operated with bidirectional data transmission between data carrier and locks

Abstract

A passive entry and immobilizer key for vehicles comprises an integrated front-end circuit (12b) with three battery-supplied receiver channels (14, 16, 18), each connected to an associated external antenna circuit with an inductor-capacitor combination (LR, CR) having a resonant frequency in the very low frequency range. The three antennas are arranged in a three-dimensional configuration. An immobilizer transponder (22) is supplied by energy received from an external transponder antenna circuit and stored in a storage capacitor (CL). The transponder antenna circuit includes an inductor-capacitor combination (LR, CR, CL) having a resonant frequency in the low frequency range. The transponder antenna circuit shares at least one inductive component (LR) with the antenna circuit of one of the three receiver channels. A capacitor in the transponder antenna circuit is selectively disconnected to change the resonant frequency from a frequency in the very low frequency range to a frequency in the low frequency range. Accordingly, one of the three antenna circuits has a dual function. A first function is that in a three-dimensional analog front end of a passive entry system that operates in the very low frequency range. A second function is that in a transponder of an immobilizer system that operates in the much higher low frequency range. As a result, only three antenna coils need to be implemented in the key.

Claims

1. A passive entry and immobilizer key for vehicles, comprising:

an integrated front-end circuit with three battery-supplied receiver channels each connected to an associated external antenna circuit including an inductor-capacitor combination having a resonant frequency in the very low frequency range, the antennas of the associated external antenna circuits being arranged in a three-dimensional configuration; and

at least one immobilizer transponder supplied by energy received from an external transponder antenna circuit and stored in a storage capacitor, the transponder antenna circuit including an inductor-capacitor combination having a resonant frequency in the low frequency range, wherein the external transponder antenna circuit shares at least an inductive component with one of the associated external antenna circuits of one of the three receiver channels, a capacitor in the transponder antenna circuit being selectively disconnected to change the resonant frequency from a frequency in the very low frequency range to a frequency in the low frequency range.

2. The passive entry and immobilizer key according to claim 1, wherein said selectively disconnected capacitor is switched in parallel with a permanently connected capacitor of the transponder antenna circuit.

3. The passive entry and immobilizer key according to claim 1, wherein said one receiver channel includes a frequency detector that detects a received frequency in the low frequency range even though the selectively disconnected capacitor is connected into the transponder antenna circuit, the frequency detector providing a detection signal when a low frequency signal is detected.

4. The passive entry and immobilizer key according to claim 1, and including a battery voltage detector that detects an applied battery voltage and provides a detection signal when a sufficient battery voltage level is detected.

5. The passive entry and immobilizer key according to claim 3, wherein the detection signals of said frequency detector and said battery voltage detector are combined by logic circuitry to provide a control signal for a switch that disconnects the selectively disconnected capacitor in the transponder antenna circuit.

6. The passive entry and immobilizer key according to claim 1, and comprising a plurality of transponder circuits each of which has an antenna circuit that shares an inductive component with an antenna circuit of a different one of the three receiver channels.

8. The passive entry and immobilizer key according to claim 2, wherein said one receiver channel includes a frequency detector that detects a received frequency in the low frequency range even though the selectively disconnected capacitor is connected into the transponder antenna circuit, the frequency detector providing a detection signal when a low frequency signal is detected.

9. The passive entry and immobilizer key according to claim 2, and including a battery voltage detector that detects an applied battery voltage and provides a detection signal when a sufficient battery voltage level is detected.

10. The passive entry and immobilizer key according to claim 3, and including a battery voltage detector that detects an applied battery voltage and provides a detection signal when a sufficient battery voltage level is detected.

11. The passive entry and immobilizer key according to 4, wherein the detection signals of said frequency detector and said battery voltage detector are combined by logic circuitry to provide a control signal for a switch that disconnects the selectively disconnected capacitor in the transponder antenna circuit.

12. The passive entry and immobilizer key according to claim 2, and comprising a plurality of transponder circuits each of which has an antenna circuit that shares an inductive component with an antenna circuit of a different one of the three receiver channels.

13. The passive entry and immobilizer key according to claim 3, and comprising a plurality of transponder circuits each of which has an antenna circuit that shares an inductive component with an antenna circuit of a different one of the three receiver channels.

14. The passive entry and immobilizer key according to claim 4, and comprising a plurality of transponder circuits each of which has an antenna circuit that shares an inductive component with an antenna circuit of a different one of the three receiver channels.

15. The passive entry and immobilizer key according to claim 5, and comprising a plurality of transponder circuits each of which has an antenna circuit that shares an inductive component with an antenna circuit of a different one of the three receiver channels.

7. A method of operating a passive entry and immobilizer key for vehicles, the key comprising an integrated front-end circuit with three battery-supplied receiver channels each connected to an associated external antenna circuit including an inductor-capacitor combination having a resonant frequency in the very low frequency range, the antennas of the associated external antenna circuits being arranged in a three-dimensional configuration, and the key further comprising an immobilizer transponder supplied by energy received from an external transponder antenna circuit and stored in a storage capacitor, the external transponder antenna circuit including an inductor-capacitor combination having a resonant frequency in the a low frequency range;

wherein the transponder antenna circuit shares at least an inductive component with the antenna circuit of one of the three receiver channels, comprising the steps of;

selectively connecting a capacitor into the transponder antenna circuit to change the resonant frequency from a low frequency to a very low frequency;

detecting a received frequency in the low frequency range while the selectively switched capacitor is connected into the transponder antenna circuit;

detecting an applied battery voltage; and

disconnecting the capacitor from the transponder antenna circuit to change the resonant frequency from the very low frequency to the low frequency when a sufficient battery voltage is not detected or when a received frequency in the low frequency range is detected.