Transmit and receive performance of a near field communication device that uses a single antenna

• US 8,249,524 B2
• Filed: 09/10/2010
• Issued: 08/21/2012
• Est. Priority Date: 09/10/2010
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Darwhekar, Yogesh, Rajendran, Gireesh, Mukherjee, Subhashish, Sivadas, Apu, Joshi, Alok Prakash
• Primary Examiner(s): Dao, Minh D
• Application Number:
  US12/879,008
• Publication Number:
  US 20120064826A1
• Time in Patent Office: 711 Days
• Field of Search: 455/78, 455/82, 455/83, 455/41.1, 455/193.1, 455/195.1, 455/197.3, 455/197.2, 343/853
• US Class Current: 455/78
• CPC Class Codes: H04B 5/26 using coils
• CPC Class Codes: H04B 5/72 for local intradevice communication

Abstract

A near field communication (NFC) transceiver contains a transmitter portion to generate a transmit wireless signal, and a receiver portion to receive and process a receive wireless signal. The circuit further contains a shunt capacitor, a switch, and an antenna interface to couple the transmitter portion and the receiver portion to an antenna designed to communicate with external antennas by inductive coupling. The switch couples the shunt capacitor in parallel with the antenna in one operational mode, and decouples the shunt capacitor from the antenna in another operational mode. Transmit and receive performance of the NFC transceiver are enhanced as a result.

Claims

1. A circuit comprising:

an antenna interface to couple to an antenna designed to communicate with external antennas by inductive coupling;

a transmitter portion to generate a transmit wireless signal to be transmitted by the antenna;

a shunt capacitor;

a receiver portion to receive and process a receive wireless signal from the antenna; and

a switch operable in a first mode and a second mode,

wherein the switch couples the shunt capacitor in parallel with the antenna in the second mode,

the switch decoupling the shunt capacitor from the antenna in the first mode,

wherein the transmitter portion is designed to transmit the transmit wireless signal in a transmit interval, and the receiver portion is designed to receive the receive wireless signal from the antenna in a receive interval,

wherein the switch is operable in the first mode in the transmit interval and in the second mode in the receive interval,

whereby the switch couples the shunt capacitor in parallel with the inductance of the antenna to form a shunt resonant circuit in the receive interval to maximize a voltage generated at an input terminal of the receiver portion in the receive interval,

the switch to decouple the shunt capacitor from the inductance of the antenna in the transmit interval to enable maximization of a current generated in the antenna in the transmit interval.

2. The circuit of claim 1, wherein the transmitter portion and the receiver portion operate according to near field communication (NFC) techniques, wherein the transmit wireless signal and the receive wireless signal are NFC signals.

3. The circuit of claim 2, further comprising:

a series capacitor coupled in series with the antenna, the combination of the series capacitor and the inductance of the antenna forming a series resonant circuit in the transmit interval to maximize a current through the antenna in the transmit interval.

4. The circuit of claim 3, further comprising:

a resistor coupled in series with the antenna and the series capacitor, the resistor to increase the bandwidth of the series resonant circuit and the shunt resonant circuit.

5. A device comprising:

an application block to provide one or more user applications based on transmission and reception of near field communications (NFC) signals;

an NFC transceiver; and

an antenna designed to communicate with external antennas by inductive coupling, wherein the NFC transceiver comprises;

an antenna interface to couple to the antenna;

a transmitter portion to generate a transmit wireless signal to be transmitted by the antenna;

a shunt capacitor;

a receiver portion to receive and process a receive wireless signal from the antenna; and

a switch operable in a first mode and a second mode,

wherein the switch couples the shunt capacitor in parallel with the antenna in the second mode, the switch decoupling the shunt capacitor from the antenna in the first mode,

wherein the transmitter portion is designed to transmit the transmit wireless signal in a transmit interval, and the receiver portion is designed to receive the receive wireless signal from the antenna in a receive interval,

wherein the switch is operable in the first mode in the transmit interval and in the second mode in the receive interval,

whereby the switch couples the shunt capacitor in parallel with the inductance of the antenna to form a shunt resonant circuit in the receive interval to maximize a voltage generated at an input terminal of the receiver portion in the receive interval,

the switch to decouple the shunt capacitor from the inductance of the antenna in the transmit interval to enable maximization of a current generated in the antenna in the transmit interval.

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

a series capacitor coupled in series with the antenna, the combination of the series capacitor and the inductance of the antenna forming a series resonant circuit in the transmit interval to maximize a current through the antenna in the transmit interval.

7. The device of claim 6, wherein the NFC transceiver further comprises:

a resistor coupled in series with the antenna and the series capacitor, the resistor to increase the bandwidth of the series resonant circuit and the shunt resonant circuit.

8. A near field communication (NFC) transceiver comprising:

a baseband processor to generate a transmit baseband NFC signal, the baseband processor also to process a receive baseband NFC signal;

an up-converter to convert the transmit baseband NFC signal to a frequency band specified by the NFC standard to generate a transmit NFC signal;

a power amplifier to receive the transmit NFC signal and to generate a power-amplified NFC signal on a first pair of differential paths;

a low noise amplifier (LNA) to receive an NFC receive signal on a second pair of differential paths, and to generate an amplified receive NFC signal;

a down-converter to convert the amplified receive NFC signal from a frequency band specified by the NFC standard to generate the receive baseband NFC signal; and

an antenna interface, wherein the antenna interface comprises;

a first transistor and a second transistor, the control terminals of each of the first transistor and the second transistor being coupled to the baseband processor, wherein a first current terminal of each of the first transistor and the second transistor is coupled to a reference potential;

first shunt capacitor, wherein a first terminal of the first shunt capacitor is coupled to a first one of the paths in the first pair of differential paths, wherein a second terminal of the first shunt capacitor is coupled to a second current terminal of the first transistor;

a second shunt capacitor, wherein a first terminal of the second shunt capacitor is coupled to a second one of the paths in the first pair of differential paths, the second terminal of the second shunt capacitor being coupled to a second current terminal of the second transistor;

a third capacitor, wherein a first terminal of the third capacitor is coupled to the first one of the paths in the first pair of differential paths;

a first resistor, a first terminal of the first resistor coupled to a second terminal of the third capacitor, a second terminal of the first resistor to couple to a first terminal of an NFC antenna;

a second resistor, a first terminal of the second resistor to couple to a second terminal of the NFC antenna;

a fourth capacitor, a first terminal of the fourth capacitor coupled to the second one of the paths in the first pair of differential paths, a second terminal of the fourth capacitor coupled to a second terminal of the second resistor;

a fifth capacitor, a first terminal of the fifth capacitor coupled to a first one of the paths in the second pair of differential paths, a second terminal of the fifth capacitor coupled to the second terminal of the third capacitor; and

a sixth capacitor, a first terminal of the sixth capacitor coupled to a second one of the paths in the second pair of differential paths, a second terminal of the sixth capacitor coupled to the second terminal of the fourth capacitor.