ANTENNA IMPEDANCE MODULATION METHOD

• US 20080212346A1
• Filed: 02/27/2008
• Published: 09/04/2008
• Est. Priority Date: 09/02/2005
• Status: Active Grant

• Current Assignee: Stmicroelectronics France (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Moreaux, Christophe, Kari, Ahmed, Naura, David, Rizzo, Pierre
• Granted Patent: US 8,022,889 B2
• Time in Patent Office: Days
• US Class Current: 363/60
• CPC Class Codes: G06K 19/0713 the arrangement including a power charge pump
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs

Abstract

A method for modulating the impedance of an antenna circuit supplying pump signals to a charge pump comprising at least one first pump stage and one last pump stage, the last pump stage supplying a continuous voltage. The output of the first pump stage is short-circuited by means of a switch and the last pump stage goes on pumping electric charges and supplying the continuous voltage. Application in particular to RFID passive transponders.

Claims

1. A method for modulating the impedance of an antenna circuit supplying pump signals to a charge pump having at least a first pump stage and a last pump stage, the last pump stage supplying a continuous voltage, the method comprising a step of applying a short-circuit to the charge pump, wherein the short-circuit is applied to the output of the first pump stage in order to allow the last pump stage to continue pumping electric charges and supplying the continuous voltage.

2. The method according to claim 1 wherein the charge pump comprises at least one intermediary pump stage between the first and the last pump stages, and wherein the short-circuit of the charge pump is applied to the output of the first pump stage in order to allow the intermediary pump stage to continue pumping electric charges.

3. The method according to claim 1 wherein the short-circuit is applied to an output capacitor of the first pump stage.

4. The method according to claim 1, applied to the charge pump wherein each pump stage includes an input diode and an input capacitor, an output diode and an output capacitor, the cathode of the input diode connected to the anode of the output diode and to a first terminal of the input capacitor, a second terminal of which receives a first antenna signal as first pump signal, the cathode of the output diode connected to a first terminal of the output capacitor, a second terminal of which receives a second antenna signal as second pump signal.

5. The method according to claim 1 wherein the short-circuit is applied by means of a modulation switch which has a low intrinsic serial resistance and does not comprise any additional serial impedance.

6. A contactless integrated circuit, comprising:

an antenna circuit;

a charge pump driven by pump signals supplied by the antenna circuit, the charge pump comprising at least a first pump stage and a last pump stage, the last pump stage supplying a continuous voltage; and

at least one switch for modulating the impedance of the antenna circuit, arranged for short-circuiting the charge pump when it is in the conducting state, the modulation switch arranged for short-circuiting the output of the first stage of the charge pump in order to allow the last stage of the charge pump to go on pumping electric charges and supplying the continuous voltage.

7. The integrated circuit according to claim 6 wherein the charge pump comprises at least one intermediary pump stage between the first and the last pump stages, which goes on pumping electric charges when the modulation switch short-circuits the output of the first stage of the charge pump.

8. The integrated circuit according to claim 6 wherein the modulation switch is arranged for short-circuiting an output capacitor of the first stage of the charge pump.

9. The integrated circuit according to claim 6 wherein each pump stage comprises an input diode and an input capacitor, an output diode and an output capacitor, the cathode of the input diode connected to the anode of the output diode and to a first terminal of the input capacitor, a second terminal of which receives a first antenna signal as first pump signal, the cathode of the output diode connected to a first terminal of the output capacitor, a second terminal of which receives a second antenna signal as second pump signal.

10. The integrated circuit according to claim 6, electrically powered by the continuous voltage supplied by the last stage of the charge pump.

11. The integrated circuit according to claim 6 wherein the modulation switch has a low intrinsic serial resistance and does not comprise any additional serial impedance, to apply a total short-circuit to the output of the first stage of the charge pump.

12. An electronic portable object comprising a portable support and an integrated circuit according to claim 6 fixed onto, or integrated into the portable support.

13. A circuit for modulating the impedance of an antenna while maintaining a supply of voltage from signals received on the antenna, the circuit comprising:

a charge pump coupled to the antenna, the charge pump comprising a plurality of charge pump stages adapted to supply power extracted from the received signals on the antenna, each charge pump stage having an input coupled to the antenna and an output coupled to a succeeding charge pump stage, with the output of the last charge pump stage coupled to a voltage supply output; and

a switch element coupled between the antenna and the output of one of the charge pump stages that is not the last charge pump stage to couple and uncouple the output of the one of the charge pump stages that is not the last stage to the antenna in response to a control signal while the succeeding charge pump stage or stages continue supplying voltage on the voltage supply output.

14. The circuit of claim 13, in which the antenna is a dipole antenna, and wherein the switch element is coupled to a pole of the dipole antenna.

15. The circuit of claim 13, comprising a control circuit adapted to generate the control signal as a binary signal to open and close the switch element in response to data stored in the circuit.

16. A method for modulating the impedance of an antenna while maintaining a supply of power from signals received on the antenna through a charge pump coupled to the antenna, the charge pump having a plurality of charge pump stages adapted to supply power extracted from the received signals, each charge pump stage having an input coupled to the antenna and an output coupled to a succeeding charge pump stage, with the output of the last stage coupled to a voltage supply output, the method comprising:

generating a control signal; and

applying the control signal to a switch to periodically couple and uncouple at least one charge pump stage that is not a last charge pump stage of the charge pump to the antenna while allowing succeeding charge pump stages to continue supplying voltage to the voltage supply output.

17. The method of claim 16 wherein generating the control signal comprises generating a binary signal to open and close the switch in response to binary data read from a memory.

18. The method of claim 16 wherein coupling and uncoupling the at least one charge pump stage with respect to the antenna comprises coupling and uncoupling the at least one charge pump stage to one pole of a dipole antenna.

19. A radio frequency identification device, comprising:

an antenna;

a charge pump circuit coupled to the antenna and adapted to extract power from signals received from the antenna and to output a supply voltage; and

a switch coupled to the charge pump circuit and the antenna and adapted to connect a portion of the charge pump circuit to the antenna in a manner to modulate an impedance of the antenna while a remaining portion of the charge pump circuit continues to supply voltage to the voltage supply output.

20. The device of claim 19 wherein the charge pump comprises series connected charge pump stages and the switch is coupled to an output of one of the series connected charge pump stages that is not a last stage, the switch having a control terminal adapted to receive a control signal that is generated by a control circuit utilizing binary data stored in the device.

21. The device of claim 19 wherein the antenna comprises a dipole antenna, and wherein the switch is coupled to one pole of the dipole antenna.