REDUCING EMISSIONS IN A NEAR FIELD COMMUNICATIONS (NFC) CAPABLE DEVICE

• US 20110287714A1
• Filed: 05/20/2011
• Published: 11/24/2011
• Est. Priority Date: 05/20/2010
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Dorning, Philip, Wilson, Robin Wyndham John
• Granted Patent: US 8,897,699 B2
• Time in Patent Office: Days
• US Class Current: 455/41.1
• CPC Class Codes: H04B 5/24 Inductive coupling

Abstract

A near field communications (NFC) device is disclosed that interacts with other NFC devices to exchange information and/or the data. Another NFC device inductively couples a received communications signal onto an antenna circuit of the NFC device to provide a recovered communications signal. An overvoltage protection module regulates a power level of the recovered communication signal by detuning the antenna circuit when the power level of the recovered communication signal may cause damage the NFC device. Active components of the overvoltage protection module, such as voltage controlled impedances, operate in their linear mode of operation to reduce unwanted emissions during this regulation process.

Claims

1. A near field communications (NFC) device, comprising:

an antenna circuit configured to receive a received communications signal to provide a recovered communications signal, the antenna circuit being optimally tuned to receive the received communications signal; and

near field operational components configured to recover information from the recovered communications signal, the near field operational components including;

an overvoltage protection module configured to detune the antenna circuit to regulate a power level of the recovered communications signal.

2. The NFC device of claim 1, wherein the near field operational components are further configured to transfer second information to another NFC capable device, and wherein the near field operational components further comprise:

a driver configured to gate a carrier wave in accordance with the second information to provide a modulated communication and to apply the modulated communication to the antenna circuit to provide a transmitted communications signal.

3. The NFC device of claim 1, wherein the near field operational components further comprise:

a demodulator configured to demodulate the recovered communication signal to provide the information.

4. The NFC device of claim 1, wherein the received communications signal is inductively coupled onto the antenna circuit.

5. The NFC device of claim 1, wherein the overvoltage protection module comprises:

a rectifier configured to rectify the recovered communications signal to provide a rectified output; and

a regulator configured to detune the antenna circuit when the rectified output is greater than a reference voltage.

6. The NFC device of claim 5, wherein the regulator comprises:

one or more variable impedances; and

a regulator controller configured to adjust an impedance of the one or more variable impedances to detune the antenna circuit when the rectified output is greater than the reference voltage.

7. The NFC device of claim 6, wherein the one or more variable impedances comprises:

a voltage controlled impedance; and

a capacitor coupled in series with the voltage controlled impedance.

8. The NFC device of claim 7, wherein the voltage controlled impedance is implemented using at least one selected from a group consisting of:

a metal oxide semiconductor field-effect transistor (MOSFET);

a bipolar junction transistor (BJT); and

a junction field effect transistor (JFET).

9. The NFC device of claim 5, wherein the reference voltage is less than a voltage level of the recovered communications signal that results from a maximally intense magnetic field being inductively coupled onto the antenna circuit.

10. The NFC device of claim 9, wherein the maximally intense magnetic field represents an intensity of a magnetic field at approximately a maximum operating range of the NFC enabled device as set forth in a NFC standard.

11. The NFC device of claim 9, wherein the maximally intense magnetic field represents an intensity of a magnetic field at approximately which increased intensities begin to damage the NFC enabled device.

12. The NFC device of claim 1, wherein the antenna circuit comprises:

an antenna interface; and

an inductive coupling element coupled to the antenna interface, the inductive coupling element being configured to receive the received communications signal.

13. The NFC device of claim 12, wherein the antenna interface comprises:

a notch filter configured and arrange to be parallel with the inductive coupling element.

14. A method for regulating a power level of a communications signal, comprising,

(a) receiving, by a near field communications (NFC) device, a received communications signal to provide a recovered communications signal, the NFC device being optimally tuned to receive the received communications signal;

and

(b) detuning the NFC device to regulate a power level of the recovered communications signal.

15. The method of claim 14, further comprising:

(c) demodulating the recovered communication signal to provide recover information.

16. The method of claim 14, wherein step (b) comprises:

(b)(i) rectifying the recovered communications signal to provide a rectified output; and

(b)(ii) detuning the NFC device when the rectified output is greater than a reference voltage.

17. The method of claim 16, wherein step (b)(ii) comprises:

(b)(ii)(A) adjusting an impedance of one or more variable impedances to detune the NFC device when the rectified output is greater than the reference voltage.

18. The method of claim 16, wherein the reference voltage is less than a voltage level of the recovered communications signal that results from a maximally intense magnetic field being inductively coupled onto the antenna circuit.

19. The method of claim 18, wherein the maximally intense magnetic field represents an intensity of a magnetic field at approximately a maximum operating range of the NFC enabled device as set forth in a NFC standard.

20. The method of claim 18, wherein the maximally intense magnetic field represents an intensity of a magnetic field at approximately which increased intensities begin to damage the NFC enabled device.