Near Field RF Communications

• US 20090137219A1
• Filed: 05/22/2006
• Published: 05/28/2009
• Est. Priority Date: 05/20/2005
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Broadcom Europe Ltd (Broadcom, Inc.)
• Inventors: Williams, Andrew
• Granted Patent: US 7,986,916 B2
• Time in Patent Office: Days
• US Class Current: 455/214
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10237 the reader and the record carrier being capable of selectively switching between reader and record carrier appearance, e.g. in near field communication [NFC] devices where the NFC device may function as an RFID reader or as an RFID tag
• CPC Class Codes: H04L 27/2075 in which the data are represented by the change in carrier phase

Abstract

A near field RF communicator has an IQ demodulator (100) and a demodulator processor (205) that identifies a transition between logical states on the basis of either: 1) a magnitude obtained by adding a first value representing a difference between positive and negative peaks in the in-phase modulation and a second value representing a difference between positive and negative peaks in the quadrature phase modulation; or 2) whether a combined value representing a rate of change in the in-phase modulation and in the quadrature phase modulation exceeds a threshold.

Claims

1. A near field RF communicator comprising:

a coupler operable to receive a modulated radio frequency signal by inductive coupling;

a signal generator operable to supply a radio frequency signal;

a demodulator operable to receive a modulated radio frequency signal inductively coupled to the coupler, wherein the demodulator comprises a first multiplier operable to multiply the received modulated radio frequency signal by a first radio frequency signal to produce an in-phase modulated signal, and a second multiplier operable to multiply the received modulated radio frequency signal by a second radio frequency signal in phase quadrature with the first radio frequency signal to produce a quadrature-phase modulated signal; and

a demodulation processor comprising a first peak detector coupled to receive in-phase modulation from the demodulator and operable to detect negative and positive peaks in the in-phase modulated signal, a second peak detector coupled to receive quadrature-phase modulation from the demodulator and operable to detect negative and positive peaks in the quadrature-phase modulated signal, a first difference calculator operable to determine a first difference between negative and positive peaks detected by the first peak detector, a second difference calculator operable to determine a second difference between negative and positive peaks detected by the second peak detector, a combiner operable to determine the length of a vector representing the difference between the negative and positive peaks by adding the first and second differences, and a controller operable to determine whether or not a logic state transition has occurred on the basis of the length of the vector determined by the combiner and so to enable data to be extracted from the received modulated RF signal.

2. A near field RF communicator according to claim 1, wherein the combiner is operable to scale at least one of the first and second differences before adding them.

3. A near field RF communicator according to claim 2, wherein the combiner is operable to scale the smallest of the first and second differences before adding them.

4. A near field RF communicator according to claim 2, wherein the combiner is operable to scale the smallest of the first and second differences by multiplying by 0.34275.

5. A near field RF communicator according to claim 1, wherein the first difference calculator is operable to determine a first current sample difference between the in-phase modulation for a current sample of the modulated radio frequency signal and one of the negative and positive peaks detected by the first detector, the second difference calculator is operable to determine a second current sample difference between the quadrature-phase modulation for the current sample of the modulated RF signal and one of the negative and positive peaks detected by the second detector, the combiner is operable to add said first and second current sample differences to produce a combined difference value and the controller is operable to determine whether or not a logic transition has occurred in dependence on whether or not the combined difference value is less than half the length of said vector determined by the combiner.

6. A near field RF communicator according to claim 5, wherein the controller is operable to determine whether the vector has a positive or negative angle and the first and second difference calculators are each operable:

1) to determine the difference between the current sample difference and the same one of the negative and positive peaks when the angle is positive; and

     2) to determine the difference between the current sample difference and different ones of the negative and positive peaks when the angle is negative.

7. A near field RF communicator according to claim 1, wherein a phase locker is provided to lock the phase of a radio frequency signal generated by the signal generator to that of a modulated a radio frequency signal inductively coupled to the coupler.

8. A near field RF communicator according to claim 1, wherein the first and second peak detectors are drooped peak detectors.

9. A near field RF communicator according to claim 1, wherein the first and second peak detectors each have a negative peak detector operable to provide a negative peak detection signal which drops to a minimum when the signal level of the received modulation drops below a current peak level and rises gradually when the signal level of the received modulation rises and each have a positive peak detector operable to provide a positive peak detection signal which rises to a maximum when the signal level of the received modulation rises beyond a current peak level and drops gradually when the signal level of the received modulation drops.

10. A near field RF communicator according to claim 1, wherein low pass filters are provided to derive the in-phase modulation and quadrature-phase modulation from the in-phase and quadrature-phase modulated signals produced by the first and second mixers.

19. A near field RF communicator according to claim 1, further comprising:

a data store operable to store data; and

a modulator operable to modulate a radio frequency signal in accordance with data to enable communication of data by the near field RF communicator.

20. A near field RF communicator according to claim 1, wherein the near field communicator is an NFC communicator and further comprises a data store operable to store data, a modulator operable to modulate a radio frequency signal in accordance with data, and a controller operable both to initiate near field radio frequency communication with another near field RF communicator and to respond to near field radio frequency communication initiated by another near field RF communicator.

21. A near field RF communicator according to claim 1, further comprising a power deliver operable to derive power from a radio frequency signal inductively coupled to the coupler.

24. A near field RF communicator according to claim 1, wherein the demodulator comprises a digital signal processor.

25. A device comprising a near field RF communicator in accordance with claim 1.

11. A near field RF communicator comprising:

a coupler operable to receive a modulated radio frequency signal by inductive coupling;

a signal generator operable to supply a radio frequency signal;

a demodulator operable to receive a modulated radio frequency signal inductively coupled to the coupler, wherein the demodulator comprises a first multiplier operable to multiply the received modulated radio frequency signal by a first radio frequency signal to produce an in-phase modulated signal, and a second multiplier operable to multiply the received modulated radio frequency signal by a second radio frequency signal in phase quadrature with the first radio frequency signal to produce a quadrature-phase modulated signal; and

a demodulator processor comprising a rate of change determiner operable to receive in-phase and quadrature phase modulated signals and to determine a combined rate of change on the basis of the in-phase and quadrature phase modulated signals, and a determiner operable to compare the combined rate of change with at least one threshold to determine whether or not a logic transition has occurred.

12. A near field RF communicator according to claim 11, wherein the a rate of change determiner comprises:

a first rate of change calculator coupled to receive in-phase modulation derived from an in-phase modulated signal supplied by the first multiplier and operable to determine the rate of change of the in-phase modulation;

a second rate of change calculator coupled to receive quadrature-phase modulation derived from an quadrature-phase modulated signal supplied by the second multiplier and operable to determine the rate of change of the quadrature-phase modulation; and

a combiner operable to combine the determined rates of change of the in- phase modulation and quadrature-phase modulation to produce a combined rate of change.

13. A near field RF communicator according to claim 12, wherein the combiner is operable to determine the combined rate of change by:

adding determined rates of change of the in-phase modulation and quadrature-phase modulation;

or scaling one of the determined rates of change of the in-phase modulation and quadrature-phase modulation and then adding them;

or squaring each determined rate of change to produced squared values, adding the squared values to produce a squared sum and then determining the square root of the squared sum.

14. A near field RF communicator according to claim 12, wherein the combiner is operable to determine the combined rate of change by scaling the smallest one of the determined rates of change and then adding the determined rates of change.

15. A near field RF communicator according to claim 12, wherein the first and second rate of change calculators are operable to determine the rate of change on the basis of the level of a current sample and the level of one or more previous samples.

16. A near field RF communicator according to claim 11, wherein the determiner comprises a threshold determiner operable to determine the threshold on the basis of a rate of change in at least one of a positive and a negative peak in the combined rate of change.

17. A near field RF communicator according to claim 11, wherein the determiner comprises a threshold determiner operable to determine the threshold on the basis of a rate of change in a positive peak in the combined rate of change multiplied by a scaling factor.

18. A near field RF communicator according to claim 17, wherein the threshold determiner is operable to determine a second threshold on the basis of a rate of change in the positive peak in the combined rate of change multiplied by a second smaller scaling factor and the determiner is operable to determine that no change in the modulation level is occurring when the combined rate of change is less than the second threshold.

22. A near field RF communicator having an IQ demodulator operable to determine whether or not a logic transition has occurred on the basis of a magnitude obtained by adding a first value representing a difference between positive and negative peaks in the in-phase modulation and a second value representing a difference between positive and negative peaks in the quadrature-phase modulation.

23. A near field RF communicator having an IQ demodulator operable to determine whether or not a logic transition has occurred by determining whether a combined value representing a rate of change in the in-phase modulation and in the quadrature-phase modulation exceeds a threshold.