Near-field communication (NFC) tags optimized for high performance NFC and wireless power reception with small antennas

1. A device for concurrent near-field communication (NFC) and wireless power reception (WPR) using a magnetic field, comprising:

a low-Q antenna resonant circuit configured to perform the NFC, and including

a first antenna for magnetic flux of the magnetic field to flow therethrough, to thereby receive a NFC signal for the NFC, and

a first antenna matching circuit that is connected to the first antenna and is so configured that a quality factor (Q-factor) of the low-Q antenna resonant circuit is no higher than 25; and

a high-Q antenna resonant circuit configured to perform the WPR, and including

a second antenna for the magnetic flux of the magnetic field to flow therethrough, to thereby receive wireless power for the WPR, and

a second antenna matching circuit that is connected to the second antenna and is so configured that the Q-factor of the high-Q antenna resonant circuit is no lower than 50, wherein

the low-Q and high-Q antenna resonant circuits are separate from each other,

the high-Q antenna resonant circuit operates to perform WPR, responsive to strength of the magnetic field being larger than a predetermined threshold, and

the high-Q antenna resonant circuit and the low-Q antenna resonant circuit operate to perform NFC, responsive to the strength of the magnetic field being no larger than the predetermined threshold.

2. The device of claim 1 , wherein the high-Q antenna resonant circuit is configured to perform data transmission.

3. The device of claim 1 , further comprising:

a demodulator connected to the first antenna matching circuit and configured to demodulate the NFC signal received by the first antenna;

a data interface configured to transmit the demodulated NFC signal to a first external device;

a rectifier-and-regulator connected to the second antenna matching circuit and configured to convert the wireless power received by the second antenna to regulated DC (direct current) energy; and

an energy harvest interface configured to supply the regulated DC energy to a second external device.

4. The device of claim 3 , wherein

the second antenna is further configured to transmit another NFC signal, and has a load connected thereto;

the device further comprises a load modulator configured to modulate an impedance of the load for transmitting the another NFC signal; and

the data interface is further configured to receive data corresponding to the another NFC signal from the first external device, and to send the received data to the load modulator.

5. The device of claim 4 , wherein the load modulator includes a radio frequency (RF) switch that has an isolation value larger than 10 KOhm, an on-resistance value smaller than 50 Ohm, and a switching speed larger than 1 MHz.

6. The device of claim 3 , wherein the rectifier-and-regulator includes a switch for controlling a connection from the rectifier-and-regulator to the energy harvest interface.

7. The device of claim 1 , wherein each of the first and second antenna matching circuits utilizes an impedance transformation topology, and has an insertion loss smaller than 1 db.

8. The device of claim 1 , wherein the first antenna has at least one of an inductance value smaller than 4 uH,

a Q value smaller than 50, and

a coupling coefficient, with respect to an external antenna coupled thereto, is smaller than 0.1.

9. The device of claim 1 , wherein the second antenna has

an inductance in a range of 1 uH to 10 uH,

an area in a range of 100 mm 2 to 5000 mm 2 , and

a Q value higher than 50.