Contactless communication method between an object and a reader using active load modulation

1. A method of operating an object for contactless communication between the object and a reader using active load modulation, the method comprising:

detecting a sensing magnetic field emitted by the reader;

initializing a phase-locked loop of the object;

detecting a stopping of the sensing magnetic field emitted by the reader before initializing the phase-locked loop of the object is complete;

calibrating an oscillator of the phase-locked loop on the basis of an internal clock of the object;

after calibrating the oscillator, detecting a new sensing magnetic field of the reader; and

after detecting the new sensing magnetic field, implementing the phase-locked loop to adjust the phase of the oscillator.

2. The method according to claim 1 , further comprising responding to the reader after implementing the phase-locked loop to adjust the phase of the oscillator.

3. The method according to claim 1 , wherein calibrating the oscillator comprises:

measuring an output frequency of the oscillator;

comparing the measured output frequency with a desired frequency; and

calibrating the frequency of the oscillator depending on a result of the comparing.

4. The method according to claim 1 , wherein calibrating the oscillator comprises using a frequency-locked loop to lock the frequency of the oscillator onto the frequency of the internal clock.

5. The method according to claim 4 , wherein calibrating the oscillator comprises implementing the frequency-locked loop to calibrate and lock the frequency of the oscillator on the basis of a value stored in a register after detecting the stopping of the sensing magnetic field emitted by the reader.

6. The method according to claim 5 , wherein the phase-locked loop is implemented in response to detecting the new sensing magnetic field of the reader.

7. The method according to claim 5 , wherein the phase-locked loop is implemented by locking the frequency-locked loop that controls the oscillator in response to detecting the new sensing magnetic field of the reader.

8. An object capable of carrying out a contactless communication using active load modulation, the object comprising:

an internal clock;

a magnetic field detector; and

a phase-locked loop that includes an oscillator and is configured to lock a phase of the oscillator onto the detected magnetic field;

wherein the object is designed to initialize the phase-locked loop when sensing of a magnetic field is detected by the magnetic field detector, to calibrate the frequency of the oscillator of the phase-locked loop on the basis of the internal clock when the detector detects that sensing of the magnetic field has stopped before initializing of the phase-locked loop is complete, and to then adjust the phase of the oscillator when a new sensing magnetic field is detected.

9. The object according to claim 8 , wherein the object is designed to measure an output frequency of the oscillator, to compare the measured output frequency with a desired frequency, and to then calibrate the frequency of the oscillator depending on a result of the comparison.

10. The object according to claim 9 , further comprising a frequency-locked loop configured to lock the frequency of the oscillator onto the frequency of the internal clock.

11. The object according to claim 10 , wherein the object is designed to:

implement the frequency-locked loop to calibrate and lock the frequency of the oscillator on the basis of a value stored in a register when the detector detects that sensing of the magnetic field has stopped; and then

implement the phase-locked loop when the new sensing magnetic field is detected to adjust the phase of the oscillator.

12. The object according to claim 11 , wherein the object is designed to implement the phase-locked loop when the new sensing magnetic field is detected to lock the frequency-locked loop that controls the oscillator.

13. The object according to claim 9 , further comprising a counter divider having a first input coupled to an output of the oscillator and a second input coupled to a node carrying a reference signal operating at the desired frequency.

14. The object according to claim 8 , further comprising:

a counter divider having a first input coupled to an output of the oscillator and a second input coupled to a node carrying a reference signal;

a register;

a comparator having a first input coupled to the register and a second input coupled to an output of the counter divider; and

a frequency locked loop coupled between an output of the comparator and an input of the oscillator.

15. The object according to claim 8 , further comprising:

a first counter divider having a first input coupled to an output of the oscillator and a second input coupled to the internal clock;

a second counter divider having a first input coupled to an output of the oscillator and a second input coupled to receive a clock signal extracted from the magnetic field;

a first loop filter;

a first comparator having a first input coupled to an output of the second counter divider and an output coupled to the first loop filter;

a register;

a multiplexer having a first input coupled to the register and a second input coupled to an output of the first loop filter;

a second comparator having a first input coupled to an output of the multiplexer and a second input coupled to an output of the first counter divider; and

a second loop filter coupled between an output of the second comparator and an input of the oscillator.

16. The object according to claim 8 , further comprising a system configured to calibrate the frequency of the oscillator of the phase-locked loop on the basis of the internal clock when the detector detects that sensing of the magnetic field has stopped before initializing of the phase-locked loop is complete, and to then adjust the phase of the oscillator when the new sensing magnetic field is detected.

17. An object configured to be able to carry out a contactless communication with a reader by using active load modulation, the object comprising:

an internal clock;

means for detecting a sensing of a magnetic field of the reader;

a phase-locked loop including an oscillator and being configured to lock a phase of the oscillator onto the detected magnetic field of the reader, the phase-locked loop being configured to be initialized when sensing of the magnetic field is detected; and

means for calibrating the frequency of the oscillator of the phase-locked loop configured to calibrate the frequency of the oscillator on the basis of the internal clock when the sensing of the magnetic field of the reader is stopped before initializing the phase-locked loop is complete, and to then adjust the phase of the oscillator when a new sensing magnetic field of the reader is detected in order to be able to respond to the reader.

18. An object capable of carrying out a contactless communication using active load modulation, the object comprising:

an internal clock;

a magnetic field detector;

a phase-locked loop that includes an oscillator;

a first counter divider having a first input coupled to an output of the oscillator and a second input coupled to the internal clock;

a second counter divider having a first input coupled to an output of the oscillator and a second input coupled to receive a clock signal extracted from a magnetic field detected by the magnetic field detector;

a first loop filter;

a first comparator having a first input coupled to an output of the second counter divider and an output coupled to the first loop filter;

a register;

a multiplexer having a first input coupled to the register and a second input coupled to an output of the first loop filter;

a second comparator having a first input coupled to an output of the multiplexer and a second input coupled to an output of the first counter divider; and

a second loop filter coupled between an output of the second comparator and an input of the oscillator.

19. The object according to claim 15 , wherein the first loop filter comprises a phase locked loop and wherein the second loop filter comprises a frequency locked loop.

20. The object according to claim 15 , further comprising an adder coupled between the first comparator and the first loop filter.