PROTECTION OF A RADIO FREQUENCY TRANSMIT-RECEIVE TERMINAL AGAINST ELECTROMAGNETIC DISTURBANCES

• US 20130119134A1
• Filed: 10/29/2012
• Published: 05/16/2013
• Est. Priority Date: 11/10/2011
• Status: Active Grant

• Current Assignee: STMicroelectronics SAS (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SAS (STMicroelectronics NV)
• Inventors: Tramoni, Alexandre
• Granted Patent: US 9,626,614 B2
• Time in Patent Office: Days
• US Class Current: 235/439
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• CPC Class Codes: G06K 7/10237 the reader and the record carrier being capable of selectively switching between reader and record carrier appearance, e.g. in near field communication [NFC] devices where the NFC device may function as an RFID reader or as an RFID tag

Abstract

An antenna circuit for a device of transmission/reception by inductive coupling, including a first inductive element in parallel with a capacitive element and, between each node of the parallel association and two terminals of a switch, a second inductive element.

Claims

1. An antenna circuit coupleable to a device of transmission/reception by inductive coupling, comprising:

a first inductive element in parallel with a capacitive element;

a first dual purpose inductance coupled between a first node of the parallel association and a first terminal of a switch; and

a second dual purpose inductance coupled between a second node of the parallel association and a second terminal of the switch, the first and second dual purpose inductances configurable by the switch to cooperate as a second inductive element in the parallel association.

2. The antenna circuit of claim 1 wherein the terminals of the switch are connectable to a circuit that generates an alternating current (A.C.) signal to excite the antenna circuit as an oscillating circuit.

3. The antenna circuit of claim 1 wherein said nodes of the parallel association are connectable to a circuit that interprets detected signals.

4. The antenna circuit of claim 1, comprising:

a circuit to generate an alternating current (A.C.) signal that excites the antenna circuit;

a circuit to interpret signals detected by the antenna circuit; and

a circuit to control the switch.

5. The antenna circuit of claim 4 wherein the switch is in an off position when the antenna circuit is configured to transmit the A.C. signal and configured to operate in reader mode.

6. The antenna circuit of claim 4 wherein the switch is in an on position when the antenna circuit is configured to transmit data and configured to operate in card mode.

7. The antenna circuit of claim 4 wherein the first and second dual purpose inductances are sized to match, at the frequency of the A.C. transmission signal, the antenna circuit to the output impedance of the A.C. signal generation circuit.

8. The antenna circuit of claim 6 wherein a sum of the first and second dual purpose inductances is selected to tune the excited antenna circuit to a frequency of an A.C. signal received from another device in the card mode operation.

9. A method to operate an antenna circuit of an inductively coupled transmission/reception device, comprising:

controlling a switch, the switch having a first terminal, a second terminal, and a control terminal, wherein the first terminal is coupled to a first dual purpose inductance, the first dual purpose inductance coupled to a first node of a parallel arrangement including a capacitive element and an antenna, wherein the second terminal is coupled to a second dual purpose inductance, the second dual purpose inductance coupled to a second node of the parallel arrangement, the controlling including opening the switch when the transmission/reception device is operating in a reader mode and closing the switch when the transmission/reception device is operating in a card mode.

10. The method of claim 9, comprising:

generating an alternating current (A.C.) signal to excite the antenna as an oscillating circuit.

11. The method of claim 10, comprising:

summing the first and second dual purpose inductances to tune the oscillating circuit to a frequency of an A.C. signal received from another device.

12. The method of claim 9, comprising:

interpreting detected signals induced on the antenna when the switch is open.

13. The method of claim 9, comprising:

transmitting data when the switch is closed.

14. A device having an antenna circuit inductively coupled to a transmission/reception circuit, comprising:

an antenna inductance;

a capacitive element connected in parallel with the antenna inductance, the parallel connection formed at a first node and a second node;

a switch having a first terminal and a second terminal;

a first dual purpose inductance coupled between the first switch terminal and the first node;

a second dual purpose inductance coupled between the second switch terminal and the second node; and

a control circuit to open and close the switch wherein closing the switch places the first and second dual purpose inductances in a series arrangement with each other, the series arrangement connected in parallel with the antenna inductance and the capacitive element.

15. The device of claim 14, comprising:

a reader mode circuit to generate an alternating current (A.C.) signal configured to excite the antenna circuit as an oscillating circuit, the reader mode circuit controllable by the control circuit.

16. The device of claim 15, comprising:

a circuit to interpret signals induced on the antenna inductance.

17. The device of claim 14, comprising:

a card mode circuit to configured to transmit data, the card mode circuit controllable by the control circuit.

18. The device of claim 14 wherein the first and second dual purpose inductances are sized to match, at a frequency of an A.C. transmission signal, the antenna inductance to an output impedance of an A.C. signal generation circuit.

19. The device of claim 14 wherein the sum of the first and second dual purpose inductances is selected to tune an oscillating circuit to a frequency of an A.C. signal received from another device in a card mode operation.