Circuit tuning for device detection in near-field communications

• US 8,977,197 B2
• Filed: 10/11/2012
• Issued: 03/10/2015
• Est. Priority Date: 10/11/2012
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Krishnan, Koushik, Gaethke, Rainer, Sabouri, Faramarz
• Primary Examiner(s): WEST, LEWIS G
• Application Number:
  US13/649,801
• Publication Number:
  US 20140106668A1
• Time in Patent Office: 880 Days
• Field of Search: 455/41.1, 455/41.2, 455/41.3, 455/73, 310/10.1, 340/10.1
• US Class Current: 455/41.1
• 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 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device
• CPC Class Codes: H04B 17/12 of transmit antennas, e.g. of the amplitude or phase
• CPC Class Codes: H04B 5/24 Inductive coupling
• CPC Class Codes: H04B 5/72 for local intradevice communication

Abstract

A near-field communications (NFC) device includes an NFC antenna, a matching network coupled to the NFC antenna, and a transmitter coupled to the matching network. The transmitter applies a signal to the matching network and a capacitance of the matching network is varied. A parameter is measured while varying the capacitance of the matching network and while applying the signal. A peak value of the parameter is identified and compared to a threshold. A communication protocol is initiated in response to a determination that the peak value satisfies the threshold.

Claims

1. A method of operating a first near-field communications (NFC) device comprising an NFC antenna, a matching network coupled to the NFC antenna, and a transmitter coupled to the matching network, the method comprising:

applying a signal from the transmitter to the matching network;

varying a capacitance of the matching network;

measuring a parameter while varying the capacitance of the matching network and applying the signal;

identifying a first peak value of the parameter;

detecting a second NFC device, the detecting comprising comparing the first peak value to a threshold and determining that the first peak value satisfies the threshold; and

initiating a communication protocol in response to detecting the second NFC device.

2. The method of claim 1, wherein the parameter comprises a current consumed while varying the capacitance of the matching network and applying the signal.

3. The method of claim 1, wherein the parameter comprises a voltage measured across the NFC antenna while varying the capacitance of the matching network and applying the signal.

4. The method of claim 1, wherein:

measuring the parameter comprises performing a first series of measurements and a second series of measurements;

the first peak value is identified from the first series of measurements; and

the method further comprises;

configuring an output impedance of the transmitter to have a first value while performing the first series of measurements;

configuring the output impedance of the transmitter to have a second value while performing the second series of measurements;

identifying a second peak value of the parameter from the second series of measurements; and

calibrating the transmitter and the antenna based at least in part on the first and second peak values of the parameter, wherein the comparing is performed in accordance with the calibrating.

5. The method of claim 4, wherein the calibrating comprises determining the output impedance of the transmitter and a resistance of the antenna based at least in part on the first and second peak values of the parameter.

6. The method of claim 5, wherein the calibrating further comprises determining the threshold based on the determined output impedance of the transmitter and resistance of the antenna.

7. The method of claim 4, wherein the calibrating comprises determining the threshold based at least in part on the first and second peak values of the parameter.

8. The method of claim 1, wherein the signal comprises an oscillating signal.

9. The method of claim 1, wherein varying the capacitance of the matching network comprises sweeping the capacitance across a range of values.

10. The method of claim 1, wherein:

the matching network comprises a variable capacitor; and

varying the capacitance of the matching network comprises varying a capacitance of the variable capacitor.

11. The method of claim 10, wherein the variable capacitor is situated in series with the NFC antenna.

12. The method of claim 10, wherein the variable capacitor is situated in parallel with the NFC antenna.

13. The method of claim 1, wherein:

the matching network comprises a capacitor and a switch situated in series between a node of the matching network and ground; and

varying the capacitance of the matching network comprises selectively opening and closing the switch.

14. The method of claim 1, wherein initiating the communication protocol comprises initiating a polling procedure.

15. A first near-field communications (NFC) device, comprising:

an NFC antenna;

a matching network coupled to the NFC antenna and having a variable capacitance;

a transmitter, coupled to the matching network, to provide a signal to the matching network;

one or more processors; and

memory storing one or more programs configured to be executed by the one or more processors, the one or more programs comprising;

instructions to vary the capacitance of the matching network;

instructions to measure a parameter while varying the capacitance of the matching network and while the transmitter provides the signal to the matching network;

instructions to identify a first peak value of the parameter;

instructions to detect a second NFC device, comprising instructions to compare the first peak value to a threshold; and

instructions to initiate a communication protocol in response to detecting the second NFC device.

16. The NFC device of claim 15, wherein:

the instructions to measure the parameter comprise instructions to perform a first series of measurements and a second series of measurements;

the instructions to identify the first peak value comprise instructions to identify the first peak value from the first series of measurements; and

the one or more programs further comprise;

instructions to configure an output impedance of the transmitter to have a first value or a second value, wherein the output impedance of the transmitter is to have the first value while performing the first series of measurements and the second value while performing the second series of measurements;

instructions to identify a second peak value of the parameter from the second series of measurements; and

instructions to calibrate the transmitter and the antenna based at least in part on the first and second peak values.

17. The NFC device of claim 16, wherein the instructions to calibrate the transmitter and the antenna comprise instructions to determine the output impedance of the transmitter and a resistance of the antenna based at least in part on the first and second peak values.

18. The NFC device of claim 17, wherein the instructions to calibrate the transmitter and the antenna further comprise instructions to determine the threshold based on the determined output impedance of the transmitter and the resistance of the antenna.

19. The NFC device of claim 16, wherein the instructions to calibrate the transmitter and the antenna comprise instructions to determine the threshold based at least in part on the first and second peak values.

20. The NFC device of claim 15, wherein:

the matching network comprises a variable capacitor; and

the instructions to vary the capacitance of the matching network comprise instructions to vary a capacitance of the variable capacitor.

21. A first near-field communications (NFC) device, comprising:

an NFC antenna;

a matching network coupled to the NFC antenna;

a transmitter, coupled to the matching network, to provide a signal to the matching network;

means for varying a capacitance of the matching network;

means for detecting a second NFC device based on a peak value of a parameter measured while varying the capacitance of the matching network and while the transmitter provides the signal to the matching network; and

means for initiating a communication protocol in response to detecting the second NFC device.