Frequency adjustment of an NFC circuit

1. A near-field communication circuit comprising: an oscillating circuit having a controllable capacitor; a control circuit coupled to the oscillating circuit to control the controllable capacitor; and a battery coupled to the control circuit to enable control when the near-field communication circuit is in a standby mode, wherein the control circuit is configured to control the controllable capacitor based on stored data representative of a frequency tuning of the oscillating circuit based on a measurement performed before the circuit is set to standby; wherein the control circuit is further configured to control a controllable resistive dividing bridge according to the stored data.

2. The circuit of claim 1 , wherein the control circuit comprises a controllable resistive dividing bridge powered by the battery and having an output to control the controllable capacitor.

3. The circuit of claim 2 , wherein the control circuit further comprises a latch circuit coupled to the battery, the latch circuit configured to control the controllable resistive dividing bridge.

4. The circuit of claim 3 , wherein the control circuit further comprises a register, wherein the stored data are stored in the register.

5. The circuit of claim 4 , wherein the register includes a plurality of bits, states of the bits conditioning states supplied by the latch circuit.

6. The circuit of claim 2 , wherein the controllable resistive dividing bridge comprises:

a first resistor connected between a first terminal of application of a voltage supplied by the battery and an output terminal connected to a control terminal of the controllable capacitor; and

second resistors, each second resistor in series with a switch between the output terminal and a second terminal of application of the voltage supplied by the battery.

7. The circuit of claim 1 , wherein the stored data are obtained from an analysis of an amplitude and phase of a signal across the oscillating circuit.

8. A method of controlling a controllable capacitor of an oscillating circuit of a near-field communication circuit, the method comprising: measuring a frequency tuning of the oscillating circuit; storing data representative of the frequency tuning of the oscillating circuit; after storing the data, entering a standby mode of the near-field communication circuit; and during the standby mode, controlling the controllable capacitor according to the data stored before the near-field communication circuit entered the standby mode; wherein controlling the capacitor comprises controlling a controllable resistive dividing bridge that is powered by a battery during the standby mode.

9. The method of claim 8 , wherein storing the data comprises storing the data in a register.

10. The method of claim 9 , wherein controlling the controllable capacitor comprises latching the data into a latch circuit and configuring a resistive dividing bridge using the latch circuit.

11. The method of claim 10 , wherein the latch circuit and the resistive dividing bridge are powered by a battery during the standby mode.

12. The method of claim 8 , wherein measuring the frequency tuning of the oscillating circuit comprises analyzing an amplitude and phase of a signal across the oscillating circuit.

13. The method of claim 8 , wherein the controllable resistive dividing bridge comprises: a first resistor connected between a first terminal of application of a voltage supplied by a battery and an output terminal connected to a control terminal of the controllable capacitor; and second resistors, each second resistor in series with a switch between the output terminal and a second terminal of application of the voltage supplied by the battery.

14. A near-field communication device comprising:

an RF interface;

an oscillating circuit having a controllable capacitor coupled to the RF interface;

a controllable resistive dividing bridge having an output coupled to the controllable capacitor;

a latch circuit having an output coupled to the controllable resistive dividing bridge;

a register having an output coupled to an input of the latch circuit;

an analysis circuit coupled to the RF interface, the analysis circuit having an output coupled to the register; and

a battery coupled to the controllable resistive dividing bridge and the latch circuit, wherein the controllable capacitor is configured to be controlled based on data representative of a frequency tuning of the oscillating circuit based on a measurement performed before the near-field communication device is set to a standby mode, the battery configured to power the controllable resistive dividing bridge and the latch circuit in the standby mode.

15. The device of claim 14 , further comprising an antenna coupled to the RF interface.

16. The device of claim 14 , wherein the device is a mobile communication device.

17. A near-field communication device comprising:

an RF interface;

an oscillating circuit having a controllable capacitor coupled to the RF interface;

a controllable resistive dividing bridge having an output coupled to the controllable capacitor;

a latch circuit having an output coupled to the controllable resistive dividing bridge;

a register having an output coupled to an input of the latch circuit;

an analysis circuit coupled to the RF interface, the analysis circuit having an output coupled to the register; and

a battery coupled to the controllable resistive dividing bridge and the latch circuit, wherein the controllable resistive dividing bridge comprises:

a first resistor connected between a first terminal of application of a voltage supplied by the battery and an output terminal connected to a control terminal of the controllable capacitor; and

second resistors, each second resistor in series with a switch between the output terminal and a second terminal of application of the voltage supplied by the battery.