Near-field communication (NFC) reader optimized for high performance NFC and wireless power transfer with small antennas
A device for near-field communication (NFC) and wireless power transfer. The device has an antenna resonant circuit that includes an antenna for transmitting and receiving signals, a multi-Q antenna matching circuit for adjusting a Q-factor of the antenna resonant circuit, and an antenna driver for driving the antenna through the multi-Q antenna matching circuit. The device also includes a microcontroller (MCU) configured to control the multi-Q antenna matching circuit to switch between a high-Q mode for wireless power transfer and a low-Q mode for NFC.
1. A device for near-field communication (NFC) and wireless power transfer, comprising:
an antenna resonant circuit that includes
an antenna for transmitting and receiving signals,
a switch and a resistor connected in series, the serially-connected switch and resistor being connected in parallel to the antenna, and
an antenna matching circuit, connected in parallel to the serially-connected switch and resistor, for adjusting impedance of the antenna,
the switch being configured to turn on or off to cause the antenna resonant circuit to enter respectively a high-Q mode in which the Q-factor of the antenna resonant circuit is no lower than 50, and a low-Q mode in which the Q-factor of the antenna resonant circuit is no higher than 25, and
an antenna driver for driving the antenna through the switch, the resistor and the antenna matching circuit; and
a microcontroller (MCU) configured to
turn off or on the switch, so as to switch a mode of the antenna resonant circuit between the high-Q mode and the low-Q mode, and control the antenna resonant circuit to transmit, via the antenna,
an unmodulated carrier signal when the antenna resonant circuit is in the high-Q mode, so as to transfer wireless power, and
a modulated signal when the antenna resonant circuit is in the low-Q mode, so as to perform near-field communication, wherein
the antenna resonant circuit has a lower bandwidth in the high-Q mode than in the low-Q mode.
2. The device of claim 1 , further comprising
a modulator connected to the antenna driver, for generating the modulated signal to be transmitted by the antenna;
a demodulator connected to the antenna, for demodulating a signal received by the antenna, the demodulator and modulator being connected to the MCU;
a data interface connected to the MCU via a FIFO (first in first out buffer) for data exchange with another device;
a power supply for providing power to the device; and
a clock system for providing clock signals to the device.
3. The device of claim 1 , wherein the antenna driver has output impedance smaller than 5 ohm.
4. The device of claim 1 , wherein the 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 100.
5. The device of claim 1 , wherein the MCU controls to switch the antenna resonant circuit between the high-Q mode and the low-Q mode in real-time.
6. The device of claim 1 , wherein the antenna matching circuit is a PI matching circuit.
7. A device for near-field communication (NFC) and wireless power transfer, comprising:
an antenna resonant circuit that includes
an antenna for transmitting and receiving signals,
a multi-Q antenna matching circuit for adjusting a quality factor (Q-factor) of the antenna resonant circuit, the multi-Q antenna matching circuit including
a Q-factor tuning switch configured to be turned on and off, and
a Q-factor tuning resistor connected in series with the Q-factor tuning switch,
the multi-Q antenna matching circuit being so configured that the turning-off and turning-on of the Q-factor tuning switch cause the antenna resonant circuit to enter respectively a high-Q mode in which the Q-factor of the antenna resonant circuit is no lower than 50, and a low-Q mode in which the Q-factor of the antenna resonant circuit is no higher than 25, and
an antenna driver for driving the antenna through the multi-Q antenna matching circuit; and
a microcontroller (MCU) configured to
turn off or on the Q-factor tuning switch, so as to switch a mode of the antenna resonant circuit between the high-Q mode and the low-Q mode, and control the antenna resonant circuit to transmit, via the antenna,
an unmodulated carrier signal when the antenna resonant circuit is in the high-Q mode, so as to transfer wireless power, and
a modulated signal when the antenna resonant circuit is in the low-Q mode, so as to perform near-field communication,
the antenna resonant circuit having a lower bandwidth in the high-Q mode than in the low-Q mode,
wherein the antenna matching circuit has an insertion loss smaller than 1 db.
8. The device of claim 7 , further comprising
a modulator connected to the antenna driver, for generating the modulated signal to be transmitted by the antenna;
a demodulator connected to the antenna via the multi-Q antenna matching circuit, for demodulating a signal received by the antenna, the demodulator and modulator being connected to the MCU;
a data interface connected to the MCU via a FIFO (first in first out buffer) for data exchange with another device;
a power supply for providing power to the device; and
a clock system for providing clock signals to the device.
9. The device of claim 7 , wherein the multi-Q antenna matching circuit further includes an antenna matching circuit, connected in parallel to the serially-connected Q-factor tuning switch and Q-factor tuning resistor, for adjusting impedance of the antenna.
10. The device of claim 9 , wherein the antenna matching circuit is a PI matching circuit.
11. The device of claim 7 , wherein the antenna driver has output impedance smaller than 5 ohm.
12. The device of claim 7 , wherein the 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 100.
13. The device of claim 7 , wherein the MCU controls to switch the antenna resonant circuit between the high-Q mode and the low-Q mode in real-time.
14. The device of claim 7 , wherein the serially-connected Q-factor tuning resistor and Q-factor tuning switch are connected to the antenna in parallel.