Capacitive modulation in an electromagnetic transponder

• US 6,356,198 B1
• Filed: 12/20/1999
• Issued: 03/12/2002
• Est. Priority Date: 12/21/1998
• Status: Expired due to Term

• Current Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Wuidart, Luc, Bardouillet, Michel
• Primary Examiner(s): Lee, Benjamin C.
• Application Number:
  US09/467,603
• Time in Patent Office: 813 Days
• Field of Search: 340/572.5, 340/572.1, 340/10.4, 340/10.3, 340/10.1, 340/10.2, 235/451, 235/492, 235/384, 235/380, 343/895, 343/742, 343/741, 343/867, 343/866, 342/44, 342/51, 342/27, 375/258, 455/41
• US Class Current: 340/572.5
• 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
• CPC Class Codes: G06K 19/07777 the antenna being of the inductive type

Abstract

An electromagnetic transponder is provided that includes an oscillating circuit, an electronic circuit, a rectifying circuit, and a capacitive modulation circuit. The oscillating circuit includes an inductive clement and the electronic circuit includes a transmission circuit for transmitting digitally-coded information. The rectifying circuit is coupled to the oscillating circuit to provide a DC supply voltage to the electronic circuit, and the capacitive modulation circuit is coupled to both end terminals of the inductive element and to the reference potential of the electronic circuit. In a preferred embodiment, the capacitive modulation circuit includes two capacitors, with capacitor being coupled between one end terminal of the inductive clement and the reference potential and the other capacitor being coupled between the other end terminal of the inductive element and the reference potential. Also provided is a system of electromagnetic transmission that includes at least one transponder and a terminal that generates an electromagnetic field for communicating with the transponder when the transponder is in the electromagnetic field.

Claims

1. A system of electromagnetic transmission including at least one transponder and a terminal that generates an electromagnetic field for communicating with the transponder when the transponder is in the electromagnetic field, said transponder comprising:

an oscillating circuit including an inductive element having two end terminals;

an electronic circuit for transmitting digitally-coded information to the terminal;

a rectifying circuit coupled to the oscillating circuit to provide a DC supply voltage to the electronic circuit; and

a capacitive modulation circuit coupled to both of the end terminals of the inductive element and to the reference potential of the electronic circuit.

2. The system of claim 1, wherein the capacitive modulation circuit includes two capacitors, one of the capacitors being coupled between one of the end terminals of the inductive element and the reference potential of the electronic circuit and the other of the capacitors being coupled between the other of the end terminals of the inductive element and the reference potential of the electronic circuit.

3. The system of claim 1, wherein the capacitive modulation circuit includes two MOS transistors, one of the transistors being coupled between one of the end terminals of the inductive element and the reference potential of the electronic circuit and the other of the transistors being coupled between the other of the end terminals of the inductive element and the reference potential of the electronic circuit.

4. The system of claim 3, wherein the gate of each of the transistors receives a modulation signal transmitted by the electronic circuit.

5. The system of claim 3

wherein the capacitive modulation circuit includes two capacitors, and

each of the transistors is associated in series with one of the capacitors such that each transistor acts as a switch to control the associated capacitor.

6. The system of claim 1, wherein the inductive clement of the oscillating circuit includes a midpoint that provides the reference potential of the electronic circuit.

7. The system of claim 1, wherein said transponder further comprises a resistive modulation circuit coupled in parallel with a capacitor to filter the DC supply voltage provided by the rectifying circuit.

8. The system of claim 7, wherein one signal controls both the capacitive modulation circuit and the resistive modulation circuit.

9. The system of claim 7, wherein the resistive modulation circuit is controlled by a circuit for enabling a control signal for the capacitive modulation circuit.

10. An electromagnetic transponder comprising:

an oscillating circuit including an inductive element having two end terminals;

an electronic circuit including a transmission circuit for transmitting digitally-coded information;

a rectifying circuit coupled to the oscillating circuit to provide a DC supply voltage to the electronic circuit; and

a capacitive modulation circuit coupled to both of the end terminals of the inductive element and to the reference potential of the electronic circuit.

11. The transponder of claim 10, wherein the capacitive modulation circuit includes two capacitors, one of the capacitors being coupled between one of the end terminals of the inductive element and the reference potential of the electronic circuit and the other of the capacitors being coupled between the other of the end terminals of the inductive element and the reference potential of the electronic circuit.

12. The transponder of claim 10, wherein the capacitive modulation circuit includes two MOS transistors, one of the transistors being coupled between one of the end terminals of the inductive element and the reference potential of the electronic circuit and the other of the transistors being coupled between the other of the end terminals of the inductive element and the reference potential of the electronic circuit.

13. The transponder of claim 12, wherein the gate of each of the transistors receives a modulation signal transmitted by the electronic circuit.

14. The transponder of claim 12,

wherein the capacitive modulation circuit includes two capacitors, and

each of the transistors is associated in series with one of the capacitors such that each transistor acts as a switch to control the associated capacitor.

15. The transponder of claim 10, wherein the inductive element of the oscillating circuit includes a midpoint that provides the reference potential of the electronic circuit.

16. The transponder of claim 10, further comprising a resistive modulation circuit coupled in parallel with a capacitor to filter the DC supply voltage provided by the rectifying circuit.

17. The transponder of claim 16, wherein one signal controls both the capacitive modulation circuit and the resistive modulation circuit.

18. The transponder of claim 16, wherein the resistive modulation circuit is controlled by a circuit for enabling a control signal for the capacitive modulation circuit.