Reducing emissions in a near field communications (NFC) capable device
View Patent ↗A near field communications (NFC) device is disclosed that interacts with other NFC devices to exchange information and/or the data. Another NFC device inductively couples a received communications signal onto an antenna circuit of the NFC device to provide a recovered communications signal. An overvoltage protection module regulates a power level of the recovered communication signal by detuning the antenna circuit when the power level of the recovered communication signal may cause damage the NFC device. Active components of the overvoltage protection module, such as voltage controlled impedances, operate in their linear mode of operation to reduce unwanted emissions during this regulation process.
1. A near field communications (NFC) device, comprising:
an antenna circuit configured to receive a communications signal to provide a recovered communications signal, the antenna circuit being tuned to receive the communications signal; and
near field operational components configured to recover information from the recovered communications signal, the near field operational components comprising:
a rectifier configured to rectify the recovered communications signal to provide a rectified output; and
a regulator configured to detune the antenna circuit to regulate a power level of the recovered communications signal when the rectified output is greater than a reference voltage.
2. The NFC device of claim 1 , wherein:
the near field operational components are further configured to transfer second information to another NFC device, and
the near field operational components further comprise a driver configured to gate a carrier wave in accordance with the second information to provide a modulated communication and to apply the modulated communication to the antenna circuit to provide a transmitted communications signal to transfer the second information to the other NFC device.
3. The NFC device of claim 1 , wherein the near field operational components further comprise:
a demodulator configured to demodulate the recovered communications signal to provide the information.
4. The NFC device of claim 1 , wherein the communications signal is inductively coupled onto the antenna circuit.
5. The NFC device of claim 1 , wherein the regulator comprises:
a variable impedance; and
a regulator controller configured to adjust an impedance of the variable impedance to detune the antenna circuit when the rectified output is greater than the reference voltage.
6. The NFC device of claim 5 , wherein the variable impedance comprises:
a voltage controlled impedance; and
a capacitor coupled in series with the voltage controlled impedance.
7. The NFC device of claim 6 , wherein the voltage controlled impedance is implemented using at least one of:
a metal oxide semiconductor field-effect transistor (MOSFET);
a bipolar junction transistor (BJT); and
a junction field effect transistor (JFET).
8. The NFC device of claim 1 , wherein the reference voltage is less than a voltage level of the recovered communications signal, the recovered communications signal resulting from a maximally intense magnetic field being inductively coupled onto the antenna circuit.
9. The NFC device of claim 8 , wherein the maximally intense magnetic field represents an intensity of a magnetic field at approximately a maximum operating range of the NFC device as set forth in an NFC standard.
10. The NFC device of claim 8 , wherein the maximally intense magnetic field represents an intensity of a magnetic field at approximately which increased intensities begin to damage the NFC device.
11. The NFC device of claim 1 , wherein the antenna circuit comprises:
an antenna interface; and
an inductive coupling element coupled to the antenna interface, the inductive coupling element being configured to receive the communications signal.
12. The NFC device of claim 11 , wherein the antenna interface comprises:
a notch filter configured and arranged to be parallel with the inductive coupling element.
13. A method for regulating a power level of a recovered communications signal, the method comprising,
receiving, by a near field communications (NFC) device, a communications signal to provide the recovered communications signal, the NFC device being tuned to receive the communications signal;
rectifying the recovered communications signal to provide a rectified output; and
detuning the NFC device to regulate the power level of the recovered communications signal when the rectified output is greater than a reference voltage.
14. The method of claim 13 , further comprising:
demodulating the recovered communications signal to provide recovered information.
15. The method of claim 13 , wherein the detuning the NFC device comprises:
adjusting an impedance of a variable impedance to detune the NFC device when the rectified output is greater than the reference voltage.
16. The method of claim 13 , wherein the reference voltage is less than a voltage level of the recovered communications signal, the recovered communications signal resulting from a maximally intense magnetic field being inductively coupled onto an antenna circuit of the NFC device.
17. The method of claim 16 , wherein the maximally intense magnetic field represents an intensity of a magnetic field at approximately a maximum operating range of the NFC device as set forth in an NFC standard.
18. The method of claim 16 , wherein the maximally intense magnetic field represents an intensity of a magnetic field at approximately which increased intensities begin to damage the NFC device.