Antenna driving device for transponder

• US 6,154,635 A
• Filed: 03/25/1998
• Issued: 11/28/2000
• Est. Priority Date: 06/22/1995
• Status: Expired due to Fees

• Current Assignee: Fujitsu Ten Limited (DENSO Corporation)
• Original Assignee: Fujitsu Ten Limited (DENSO Corporation)
• Inventors: Ohta, Mitsuru
• Primary Examiner(s): Bost, Dwayne D.
• Assistant Examiner(s): LEGREE, TRACY MICHELLE
• Application Number:
  US08/945,097
• Time in Patent Office: 979 Days
• Field of Search: 342/374, 70/257, 343/866, 455/41, 379/55.1, 340/10.3, 340/10.4, 340/10.41, 340/10.42, 340/10.1, 340/825.31, 340/870.31, 340/854.8
• US Class Current: 455/41.1
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• CPC Class Codes: G06K 19/0715 the arrangement including means to regulate power transfer to the integrated circuit
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: G06K 7/10861 sensing of data fields affixed to objects or articles, e.g. coded labels postal sorting B07C3/14, conveying articles B65G47/48

Abstract

An antenna coil (21) for generating a magnetic field (25) to supply power to a transponder (26) is energized through switching devices (23 and 24) connected between Vcc and GND of a D.C. power supply (20) and having contacts S1 and S2 that are actuated in opposite phases in accordance with a carrier signal. Both of the switching devices (23 and 24) are turned OFF while the carrier signal is absent. Accordingly, the oscillating current flowing through a series resonance circuit of the antenna coil (21) and a capacitor (22) quickly attenuates, thereby dropping the intensity of the magnetic field (25).

Claims

1. An antenna driving device for a transponder which drives an antenna coil in accordance with a carrier signal in order to generate a magnetic field for a magnetically coupled transponder, the device comprising:

a resonant circuit in which an antenna coil and a resonant capacitor are connected in series;

switching means for alternately switching between a state in which the resonant circuit forms a closed loop including a DC power supply for providing a current flowing in one direction, and a state in which a closed loop is formed for providing a current flowing in another direction in accordance with the carrier signal; and

controlling means for controlling the switching means such that the closed loop of the resonant circuit is maintained when the carrier signal continues and such that the closed loop of the resonant circuit is disconnected when the carrier signal is halted.

2. The antenna driving device for a transponder of claim 1, wherein

the switching means comprises:

one switching element connected between one output of the DC power supply and one end of the resonant circuit and alternately switched between a conducting state and a cutoff state in accordance with the carrier signal; and

another switching element connected between another output of the DC power supply and the one end of the resonant circuit and alternately switched between a conducting state and a cutoff state in accordance with the carrier signal, such that the another switching element is in a phase opposite to that of the first switching element, and wherein

the controlling means controls such that the first and second switching elements are simultaneously in the cutoff states when the carrier signal is halted.

3. The antenna driving device for a transponder of claim 1, wherein

the switching means comprises:

a change-over switching element for switching such that one end of the resonant circuit is alternately connected to the one and another outputs of the DC power supply in accordance with the carrier signal; and

an on off switching element connected to another end of the resonant circuit and the another output of the DC power supply, which is in a conducting state when the carrier signal continues, and wherein

the controlling means controls such that the on-off switching element is in a cutoff state when the carrier signal is halted.

4. The antenna driving device for a transponder of claim 1, wherein

the switching means comprises a change-over switching element and an on-off switching element;

the change-over switching element is alternately switched to connect one end of the resonant circuit to one output of the DC power supply, or to connect the one end of the resonant circuit to the another output of the DC power supply through the on-off switching element in accordance with the carrier signal; and

the controlling means controls such that the on-off switching element is in a conducting state when the carrier signal continues and the on-off switching element is in a cutoff state when the carrier signal is halted.

5. The antenna driving device for a transponder of claim 1, wherein

the switching means comprises:

a first switching element for connecting or disconnecting one end of the resonant circuit and one output of the DC power supply in accordance with the carrier signal;

a second switching element for connecting or disconnecting the one end of the resonant circuit and another output of the DC power supply in accordance with the carrier signal such that the second switching element is in a phase opposite to that of the first switching element;

a third switching element for connecting or disconnecting another end of the resonant circuit and the one output of the DC power supply in accordance with the carrier signal such that the third switching element is in the phase opposite to that of the first switching element;

a fourth switching element for connecting or disconnecting the another end of the resonant circuit and the another output of the DC power supply in accordance with the carrier signal such that the fourth switching element is in the same phase as that of the first switching element, and wherein

the controlling means controls such that at least either the first and second switching elements or the third and fourth elements are simultaneously in a cutoff state when the carrier signal is halted.

6. The antenna driving device for a transponder of claim 1, wherein the controlling means controls the switching means such that the resonant circuit forms a closed loop to allow reception of a signal from the transponder.

7. An antenna driving device for a transponder which drives an antenna coil in accordance with a carrier signal for supplying electric power to a magnetically coupled transponder, the device comprising:

a resonant circuit in which an antenna coil and a resonant capacitor are connected in series;

switching means for alternately switching between a state in which the resonant circuit forms a closed loop including a DC power supply for providing a current flowing in one direction, and a state in which a closed loop is formed for providing a current flowing in another direction in accordance with the carrier signal; and

controlling means for controlling the switching means such that the closed loop of the resonant circuit is maintained when the carrier signal continues and such than the closed loop of the resonant circuit is disconnected when the carrier signal is halted.

8. The antenna driving device for a transponder of claim 7, wherein

the switching means comprises:

one switching element connected between one output of the DC power supply and one end of the resonant circuit and alternately switched between a conducting state and a cutoff state in accordance with the carrier signal; and

another switching element connected between another output of the DC power supply and the one end of the resonant circuit and alternately switched between a conducting state and a cutoff state in accordance with the carrier signal, such that the another switching element is in a phase opposite to that of the first switching element, and wherein

the controlling means controls such that the first and second switching elements are simultaneously in the cutoff states when the carrier signal is halted.

9. The antenna driving device for a transponder of claim 7, wherein

the switching means comprises:

a change-over switching element for switching such that one end of the resonant circuit is alternately connected to the one and another outputs of the DC power supply in accordance with the carrier signal; and

an on-off switching element connected to another end of the resonant circuit and the another output of the DC power supply, which is in a conducting state when the carrier signal continues, and wherein

the controlling means controls such that the on-off switching element is in a cutoff state when the carrier signal is halted.

10. The antenna driving device for a transponder of claim 7, wherein

the switching means comprises a change-over switching element and an on-off switching element;

the change-over switching element is alternately switched to connect one end of the resonant circuit to one output of the DC power supply, or to connect the one end of the resonant circuit to the another output of the DC power supply through the on-off switching element in accordance with the carrier signal; and

the controlling means controls such that the on-off switching element is in a conducting state when the carrier signal continues and the on-off switching element is in a cutoff state when the carrier signal is halted.

11. The antenna driving device for a transponder of claim 7, wherein

the switching means comprises:

a first switching element for connecting or disconnecting one end of the resonant circuit and one output of the DC power supply in accordance with the carrier signal;

a second switching element for connecting or disconnecting the one end of the resonant circuit and another output of the DC power supply in accordance with the carrier signal such that the second switching element is in a phase opposite to that of the first switching element;

a third switching element for connecting or disconnecting another end of the resonant circuit and the one output of the DC power supply in accordance with the carrier signal such that the third switching element is in the phase opposite to that of the first switching element;

a fourth switching element for connecting or disconnecting the another end of the resonant circuit and the another output of the DC power supply in accordance with the carrier signal such that the fourth switching element is in the same phase as that of the first switching element, and wherein

the controlling means controls such that at least either the first and second switching elements or the third and fourth elements are simultaneously in a cutoff state when the carrier signal is halted.

12. The antenna driving device for a transponder of claim 7, wherein the controlling means controls the switching means such that the resonant circuit forms a closed loop to allow reception of a signal from the transponder.