Recovering data in a near field communications apparatus
View Patent ↗A communications device is disclosed that includes an antenna circuit with coupling connections that are used interchangeably as a receive coupling connection and a transmit coupling connection for an RF signal. A driver maintains a constant voltage or a constant current on a first coupling connection of the antenna circuit based on a drive signal that includes an output voltage and an output current. A demodulator extracts modulation from the RF signal based on a fluctuating voltage or a fluctuating current on a second coupling connection of the antenna circuit.
1. A communications device, comprising:
a coupling connection configured to receive a communication signal from another communications device, the communication signal causing an output current at the coupling connection to fluctuate;
a driver configured to adjust the output current to substantially compensate for the fluctuations of the output current to maintain a substantially constant voltage at the coupling connection;
a demodulator configured to extract modulation from a supply current, the supply current providing operational power to the driver and fluctuating in a substantially similar manner as the output current; and
a controller configured to control the driver to maintain the substantially constant voltage.
2. The communications device of claim 1 , wherein the driver is further configured to:
maintain the substantially constant voltage so that the fluctuations of the output current do not substantially vary the substantially constant voltage.
3. The communications device of claim 1 , wherein the output current is proportional to the substantially constant voltage divided by a sum of an output resistance and a load resistance.
4. The communications device of claim 1 , wherein the demodulator is further configured to:
detect the modulation based on the fluctuations of the supply current as the driver maintains the substantially constant voltage.
5. The communications device of claim 1 , wherein the output current is a second communication signal, and
wherein the coupling connection is further configured to transmit the second communication signal to the other communications device.
6. The communications device of claim 1 , wherein the driver is a differential amplifier.
7. The communications device of claim 1 , further comprising:
a sense resistor coupled between a power supply providing the supply current and the driver,
wherein the supply current is provided by the power supply through the sense resistor to the driver.
8. The communications device of claim 1 , wherein the driver comprises:
a plurality of variable current sources configured to provide the output current to the coupling connection.
9. The communications device of claim 8 , wherein the controller is further configured to control the plurality of variable current sources based on a sine synthesis signal.
10. The communications device of claim 1 , wherein the demodulator is further configured to detect the modulation based on the fluctuations of the output current at a load resistance.
11. A method, comprising:
receiving, by a communications device, a communication signal from another communications device at a coupling connection, the communication signal causing an output current at the coupling connection to fluctuate;
adjusting, by the communications device, the output current to substantially compensate for the fluctuations of the output current to maintain a substantially constant voltage at the coupling connection;
extracting, by the communications device, modulation from a supply current, the supply current providing operational power to a driver within the communications device and fluctuating in a substantially similar manner as the output current; and
controlling, by the communications device, the output current to maintain the substantially constant voltage.
12. The method of claim 11 , wherein the adjusting comprises:
providing the output current proportionally to the substantially constant voltage divided by a sum of an output resistance and a load resistance.
13. The method of claim 11 , further comprising:
detecting the modulation based on the fluctuations of the supply current as the substantially constant voltage is maintained.
14. The method of claim 11 , wherein the output current is a second communication signal, and further comprising:
transmitting a second communication signal from the coupling connection to the other communications device.
15. The method of claim 11 , further comprising:
detecting the modulation based on the fluctuations of the supply current as the communications device maintains the substantially constant voltage.