NEAR FIELD COMMUNICATION CIRCUIT
A near-field communication circuit includes a first terminal coupled to a near-field communication antenna by a first resistor of the near-field communication circuit, a second terminal coupled to the near-field communication antenna by a second resistor of the near-field communication circuit, and a third resistor coupled to the first and second terminals and adapted to forming with each of the first and second resistors a voltage divider circuit. The third resistor is a resistor having an adjustable value.
1 . A near-field communication circuit comprising:
a first terminal coupled to a near-field communication antenna by a first resistor of the near-field communication circuit;
a second terminal coupled to the near-field communication antenna by a second resistor of the near-field communication circuit; and
a third resistor coupled to the first and second terminals and adapted to forming with each of the first and second resistors a voltage divider circuit, the third resistor being a resistor having an adjustable value.
2 . The near-field communication circuit according to claim 1 , further comprising an adjustment circuit for adjusting the third resistor, the adjustment circuit being coupled to the first and second terminals, and being configured to send a control signal to the third resistor to vary a value of the third resistor.
3 . The near-field communication circuit according to claim 2 , wherein the control signal results from an electric signal present at the first terminal and/or the second terminal.
4 . The near-field communication circuit according to claim 3 , wherein the electric signal is an AC voltage between the first and second terminals, and the adjustment circuit comprises:
a rectifier coupled to the first and second terminals and configured to transform the AC voltage into a DC voltage at an output of the rectifier;
an analog-to-digital converter coupled to the output of the rectifier and configured to convert the DC voltage into a digital signal at an output of the analog-to-digital converter; and
a control circuit coupled to the output of the analog-to-digital converter and configured to generate the control signal according to the digital signal and send it to the third resistor.
5 . The near-field communication circuit according to claim 4 , wherein the control circuit comprises:
a comparator configured to compare the digital signal with a limiting value, the control signal comprising:
a first state for controlling a decrease of the value of the third resistor if the digital signal is lower than the limiting value; and/or
a second state for controlling an increase of the value of the third resistor if the digital signal is greater than or equal to the limiting value; and
a memory configured to store the limiting value.
6 . The near-field communication circuit according to claim 5 , wherein the third resistor comprises an array of resistors coupled to a switching system adapted to selecting one or more resistors from among the array of resistors.
7 . The near-field communication circuit according to claim 6 , wherein the switching system comprises a plurality of switches, each resistor of the array of resistors being coupled to a dedicated switch adapted to switching a respective coupled resistor.
8 . The near-field communication circuit according to claim 7 , wherein the adjustment circuit is coupled to the switching system.
9 . The near-field communication circuit according to claim 8 , wherein the control signal is intended to control turning on and/or turning off of one or more switches among the plurality of switches, the control signal comprising a plurality of components.
10 . A method for controlling a third adjustable resistor of a near-field communication circuit comprising a first terminal coupled to a near-field communication antenna by a first resistor of the near-field communication circuit, a second terminal coupled to the near-field communication antenna by a second resistor of the near-field communication circuit, and the third adjustable resistor coupled to the first and second terminals and adapted to forming with each of the first and second resistors a voltage divider circuit, the method comprising adjusting a value of the third adjustable resistor according to an electric signal present at the first terminal and/or the second terminal.
11 . The method according to claim 10 , wherein adjusting the value of the third adjustable resistor is controlled by a control signal sent to the third adjustable resistor by an adjustment circuit comprised in the near-field communication circuit, the control signal resulting from the electric signal, the electric signal being a voltage between the first and second terminals.
12 . The method according to claim 11 , wherein the adjustment circuit converts the electric signal into a digital signal, compares it with a limiting value, and assigns to the control signal sent to the third adjustable resistor:
a first state for controlling a decrease of the value of the third adjustable resistor if the digital signal is lower than the limiting value; or
a second state for controlling an increase of the value of the third adjustable resistor if the digital signal is greater than or equal to the limiting value.
13 . The method according to claim 11 , wherein the third adjustable resistor comprises an array of resistors coupled to a switching system comprising a plurality of switches adapted to selecting one or more resistors from among the array of resistors, the control signal controlling turning on and/or turning off of one or more switches among the plurality of switches, the control signal comprising a plurality of components.
14 . The method according to claim 10 , wherein adjusting the value of the third adjustable resistor is performed:
in one or more iterations, by progressively increasing the value of the third adjustable resistor as long as the electric signal is below a threshold signal or a threshold value minus a margin; and/or
during a polling procedure of another near-field communication circuit.
15 . The method according to claim 10 , wherein:
the first terminal is coupled to a first terminal of the near-field communication antenna and the second terminal is coupled to a second terminal of the near-field communication antenna;
the near-field communication circuit further comprises a near-field communication controller, the first and second terminals being terminals of the near-field communication controller, the third adjustable resistor being an internal resistor of the near-field communication controller, and the first and second resistors being resistors external to the near-field communication controller;
the first and second terminals are input terminals of the near-field communication controller; or
the first and second terminals are output terminals of the near-field communication controller.
16 . A near-field communication device comprising a near-field communication circuit, the near-field communication circuit being coupled to at least one near-field communication antenna of the near-field communication device, wherein the near-field communication circuit comprises:
a first terminal coupled to the at least one near-field communication antenna by a first resistor of the near-field communication circuit;
a second terminal coupled to the at least one near-field communication antenna by a second resistor of the near-field communication circuit; and
a third resistor coupled to the first and second terminals and adapted to forming with each of the first and second resistors a voltage divider circuit, the third resistor being a resistor having an adjustable value.
17 . The near-field communication device according to claim 16 , wherein the first terminal is coupled to a first terminal of the at least one near-field communication antenna and the second terminal is coupled to a second terminal of the at least one near-field communication antenna.
18 . The near-field communication device according to claim 16 , wherein the near-field communication circuit further comprises a near-field communication controller, the first and second terminals being terminals of the near-field communication controller, the third resistor being an internal resistor of the near-field communication controller, and the first and second resistors being resistors external to the near-field communication controller.
19 . The near-field communication device according to claim 18 , wherein the first and second terminals are input terminals of the near-field communication controller.
20 . The near-field communication device according to claim 18 , wherein the first and second terminals are output terminals of the near-field communication controller.