Mobile wireless communications device including NFC antenna matching control circuit and associated methods

Abstract

A mobile wireless communications device includes a near-field communications (NFC) transceiver, NFC antennas and an NFC control circuit. The NFC transceiver generates a received signal strength based on a received signal from an adjacent NFC device. The NFC control circuit includes an antenna switch circuit coupled between the NFC transceiver and the NFC antennas. A capacitance sensing circuit is coupled to the NFC antennas to determine capacitance values thereof. A processor operates the antenna switch circuit based upon the received signal strength and the capacitance values.

That which is claimed is:  
     
       1. An electronic device comprising:
 a near-field communications (NFC) transceiver that generates a received signal strength based on a received signal from an adjacent NFC device; 
 a plurality of NFC antennas; 
 a capacitance sensing circuit coupled to said plurality of NFC antennas and that determines capacitance values thereof; and 
 an antenna switch circuit coupled between said NFC transceiver and said plurality of NFC antennas and that operates based upon the received signal strength and the capacitance values. 
 
     
     
       2. The electronic device according to  claim 1  wherein said capacitance sensing circuit comprises a plurality of capacitance sensors, with each NFC antenna having a capacitance sensor associated therewith. 
     
     
       3. The electronic device according to  claim 2  wherein each capacitance sensor comprises a first plate adjacent a respective NFC antenna which functions as a second plate cooperating with the first plate. 
     
     
       4. The electronic device according to  claim 1  further comprising an NFC antenna tuning circuit coupled between said NFC transceiver and said antenna switch circuit. 
     
     
       5. The electronic device according to  claim 4  further comprising a signal rectification circuit coupled to said NFC antenna tuning circuit and configured to provide a peak-to-peak voltage signal thereto. 
     
     
       6. The electronic device according to  claim 1  further comprising:
 a signal coupling circuit coupled to said antenna switch circuit and comprising a reader mode output signal path and a card emulation mode output signal path; 
 a card emulation mode dynamic control circuit coupled to the card emulation mode output signal path; and 
 a reader mode dynamic control circuit coupled to the reader mode output signal path. 
 
     
     
       7. The electronic device according to  claim 6  wherein the signal received by said reader mode dynamic control circuit includes the received signal from the adjacent NFC device used by said NFC transceiver to generate the received signal strength. 
     
     
       8. The electronic device according to  claim 1  further comprising:
 a housing carrying said NFC transceiver, plurality of NFC antennas and switch circuit; and 
 a cellular transceiver carried by said housing. 
 
     
     
       9. A mobile wireless communications device comprising:
 a near-field communications (NFC) transceiver that generates a received signal strength based on a received signal from an adjacent NFC device; 
 a plurality of NFC antennas; 
 a respective capacitance sensor associated with each of said plurality of NFC antennas and that determines capacitance values thereof; and 
 an antenna switch circuit coupled between said NFC transceiver and said plurality of NFC antennas and that operates based upon the received signal strength and the capacitance values. 
 
     
     
       10. The mobile wireless communications device according to  claim 9  wherein each capacitance sensor comprises a first plate adjacent a respective NFC antenna which functions as a second plate cooperating with the first plate. 
     
     
       11. The mobile wireless communications device according to  claim 9  further comprising an NFC antenna tuning circuit coupled between said NFC transceiver and said antenna switch circuit. 
     
     
       12. The mobile wireless communications device according to  claim 11  further comprising a signal rectification circuit coupled to said NFC antenna tuning circuit and configured to provide a peak-to-peak voltage signal thereto. 
     
     
       13. The mobile wireless communications device according to  claim 9  further comprising:
 a signal coupling circuit coupled to said antenna switch circuit and comprising a reader mode output signal path and a card emulation mode output signal path; 
 a card emulation mode dynamic control circuit coupled to the card emulation mode output signal path; and 
 a reader mode dynamic control circuit coupled to the reader mode output signal path. 
 
     
     
       14. The mobile wireless communications device according to  claim 13  wherein the signal received by said reader mode dynamic control circuit includes the received signal from the adjacent NFC device used by said NFC transceiver to generate the received signal strength. 
     
     
       15. A method for operating an electronic device comprising a near-field communications (NFC) transceiver, a plurality of NFC antennas, a capacitance sensing circuit coupled to the plurality of NFC antennas, and an antenna switch circuit coupled between the NFC transceiver and plurality of NFC antennas, the method comprising:
 operating the NFC transceiver to generate a received signal strength based on a received signal from an adjacent NFC device; 
 operating the capacitance sensing circuit to determine capacitance values of the plurality of NFC antennas; and 
 operating the antenna switch circuit based upon the received signal strength and the capacitive values. 
 
     
     
       16. The method according to  claim 15  wherein the capacitance sensing circuit comprises a plurality of capacitance sensors, with each NFC antenna having a capacitance sensor associated therewith. 
     
     
       17. The method according to  claim 16  wherein each capacitance sensor comprises a first plate adjacent a respective NFC antenna which functions as a second plate cooperating with the first plate. 
     
     
       18. The method according to  claim 15  wherein the electronic device further comprises an NFC antenna tuning circuit coupled between the NFC transceiver and the antenna switch circuit, and further comprising controlling the NFC antenna tuning circuit to tune at least one of the plurality of NFC antennas. 
     
     
       19. The method according to  claim 18  wherein the electronic device further comprises a signal rectification circuit coupled to the NFC antenna tuning circuit to provide a peak-to-peak voltage signal. 
     
     
       20. The method according to  claim 19  wherein the electronic device further comprises a signal coupling circuit coupled to the antenna switch circuit and comprising a reader mode output signal path and a card emulation mode output signal path; a card emulation mode dynamic control circuit coupled to the card emulation mode output signal path; and a reader mode dynamic control circuit coupled to the reader mode output signal path. 
     
     
       21. The method according to  claim 20  wherein the signal received by the reader mode dynamic control circuit includes the received signal from the adjacent NFC device used by the NFC transceiver to generate the received signal strength. 
     
     
       22. The method according to  claim 20  further comprising operating the electronic device in a card emulation mode or in a reader mode based on receiving a control signal.