NEAR FIELD RF COMMUNICATORS

• US 20120028574A1
• Filed: 07/23/2008
• Published: 02/02/2012
• Est. Priority Date: 07/23/2007
• Status: Active Grant

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Innovision Research & Technology PLC (Broadcom, Inc.)
• Inventors: Bangs, Joakim, Butler, Paul
• Granted Patent: US 8,422,946 B2
• Time in Patent Office: Days
• US Class Current: 455/41.1
• CPC Class Codes: H04B 5/00 Near-field transmission systems, e.g. inductive or capacitive transmission systems
• CPC Class Codes: H04B 5/26 using coils
• CPC Class Codes: H04B 5/72 for local intradevice communication
• CPC Class Codes: H04W 4/80 Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication

Abstract

A near field RF communicator has an inductive coupler (102) to couple inductively to an H field of an RF signal from another near field RF communicator in near field range to provide a received signal, a demodulator (300) coupled to extract any modulation from a source signal representing a received RF signal to provide an extracted modulation signal; and a controller (107) coupled to receive an extracted modulation signal from the demodulator. The demodulator (300) has a sampler (400) to sample the source signal in sampling periods and to compare signal samples with at least one of other signal samples and a clock or reference signal to remove or reject the carrier of the received RF signal and to extract the modulation.

Claims

1. A near field RF communicator for communicating with another near field RF communicator, the near field RF communicator comprising:

an inductive coupler operable to couple inductively to an H field of an RF signal from another near field RF communicator in near field range; and

a demodulator to sample a source signal representing the coupled RF signal and to compare a signal sample with at least one of;

another signal sample; and

a clock or reference signal, so as to extract modulation.

2. A near field RF communicator according to claim 1, wherein the demodulator is configured to compare successive signal samples

3. A near field RF communicator according to claim 1, wherein the demodulator comprises at least one capacitor configured to be charged in successive sampling periods to provide a voltage representing the voltage change in the source signal between those successive sampling periods.

4. A near field RF communicator according to claim 1, wherein the demodulator comprises a sampler having at least one input to receive a source signal and a demodulator controller to cause the sampler to sample a source signal in one of first and second sampling states and to compare the sampled signal with another sample of the source signal, a clock or a reference signal in the other of the first and second states.

5. A near field RF communicator according to claim 1, wherein the demodulator comprises a sampler having at least one input to receive a source signal, a sample capacitor and an output capacitor, and a demodulator controller to cause the sampler to operate in first and second sampling states such that, in the first sampling state, the output capacitor is charged or discharged in accordance with at least one reference voltage and the sample capacitor is charged in accordance with a voltage of the source signal received at the at least one input, and in the second sample state any change in the voltage of the source signal causes charge to move from the sample capacitor to the output capacitor to enable a voltage to be provided which represents the change in the source signal between successive samples of the source signal.

6. A near field RF communicator according to claim 1, wherein the demodulator comprises a sampler having at least one input to receive a source signal, a sample capacitor and an output capacitor, and a demodulator controller to cause the sampler to switch between the first and second sampling states or configurations, wherein in the first configuration the sampler is arranged to:

take a first sample of a source signal received at the at least one input;

to store charge on the sample capacitor, the stored charge being related to the source signal and a first reference voltage; and

to store a charge on the output capacitor, the stored charge being related to the first reference voltage and to a second reference voltage, and in the second configuration the sampler is arranged to;

take a second sample of a source signal received at the at least one input whereby any change in the source signal between the first and second samples causes charge to move from the sample capacitor to the output capacitor to enable a voltage to be provided which represents the change in the source signal between the first and second configurations.

7. A near field RF communicator according to claim 1, wherein the demodulator comprises a demodulator controller and a sampler having at least one input to receive at least one source signal and an output, wherein the input is coupled via at least one first switch and a sample capacitor to an inverting input of an amplifier, the other input of which is coupled to a first reference voltage source, the output of the amplifier is coupled to provide an output of the sampler, the output of the amplifier is coupled to its inverting input via a second switch and the output of the amplifier is coupled via a third switch to one plate of an output capacitor having its other plate coupled to the inverting input of the amplifier, the one plate of the output capacitor being coupled via a fourth switch to a second reference voltage source, wherein the demodulator controller is configured to cause the sampler to switch between a first sampling state in which the first, second and fourth switches are closed or conducting and a second sampling state in which the first and third switches are closed or conducting.

8. A near field RF communicator according to claim 7, wherein two first switches are provided in parallel and the modulation extraction controller is configured to close one of the first switches in the first state and to close the other of the first switches in the second state.

9. A near field RF communicator according to claim 4, wherein the demodulator controller is configured to cause break before make when switching between the first and second configurations.

10. A near field RF communicator according to claim 1, wherein the source signal comprises one or more of:

a signal direct from the received RF signal, a signal from a signal envelope detector, a signal from a regulator circuit; and

a signal from an AC supply rectifier.

11. A near field RF communicator according to claim 1, wherein the demodulator is coupled to sample differential source signals.

12. A near field RF communicator according to claim 1 further comprising at least one of:

one or more filters to filter the source signal;

a device to control a slew of the source signal.

13. A near field RF communicator according to claim 1, further comprising a voltage threshold detector coupled to provide a thresholded output representing the extracted modulation.

14. A near field RF communicator according to claim 13, wherein the voltage threshold detector comprises an n-bit digitiser which may be a single input or differential digitiser.

15. A near field RF communicator according to claim 1, wherein at least one of:

a controller of the near field RF communicator is arranged to determine modulation scheme being used by the other near field RF communicator from a modulation signal provided by the demodulator;

a controller of the near field RF communicator is arranged to determine the data carried by a coupled RF signal from a modulation signal provided by the demodulator;

the inductive coupler comprises a single-ended or differential antenna circuit;

the demodulator comprises a single-ended or differential circuit; and

the near field RF communicator is an NFC communicator.

16. A near field RF communicator according to claim 2, wherein the demodulator comprises at least one capacitor configured to be charged in successive sampling periods to provide a voltage representing the voltage change in the source signal between those successive sampling periods.

17. A near field RF communicator according to claim 2, wherein the demodulator comprises a sampler having at least one input to receive a source signal and a demodulator controller to cause the sampler to sample a source signal in one of first and second sampling states and to compare the sampled signal with another sample of the source signal, a clock or a reference signal in the other of the first and second states.

18. A near field RF communicator according to claim 2, wherein the demodulator comprises a sampler having at least one input to receive a source signal, a sample capacitor and an output capacitor, and a demodulator controller to cause the sampler to operate in first and second sampling states such that, in the first sampling state, the output capacitor is charged or discharged in accordance with at least one reference voltage and the sample capacitor is charged in accordance with a voltage of the source signal received at the at least one input, and in the second sample state any change in the voltage of the source signal causes charge to move from the sample capacitor to the output capacitor to enable a voltage to be provided which represents the change in the source signal between successive samples of the source signal.

19. A near field RF communicator according to claim 2, wherein the demodulator comprises a sampler having at least one input to receive a source signal, a sample capacitor and an output capacitor, and a demodulator controller to cause the sampler to switch between the first and second sampling states or configurations, wherein in the first configuration the sampler is arranged to:

take a first sample of a source signal received at the at least one input;

to store charge on the sample capacitor, the stored charge being related to the source signal and a first reference voltage; and

to store a charge on the output capacitor, the stored charge being related to the first reference voltage and to a second reference voltage, and in the second configuration the sampler is arranged to;

take a second sample of a source signal received at the at least one input whereby any change in the source signal between the first and second samples causes charge to move from the sample capacitor to the output capacitor to enable a voltage to be provided which represents the change in the source signal between the first and second configurations.

20. A near field RF communicator according to claim 2, wherein the demodulator comprises a demodulator controller and a sampler having at least one input to receive at least one source signal and an output, wherein the input is coupled via at least one first switch and a sample capacitor to an inverting input of an amplifier, the other input of which is coupled to a first reference voltage source, the output of the amplifier is coupled to provide an output of the sampler, the output of the amplifier is coupled to its inverting input via a second switch and the output of the amplifier is coupled via a third switch to one plate of an output capacitor having its other plate coupled to the inverting input of the amplifier, the one plate of the output capacitor being coupled via a fourth switch to a second reference voltage source, wherein the demodulator controller is configured to cause the sampler to switch between a first sampling state in which the first, second and fourth switches are closed or conducting and a second sampling state in which the first and third switches are closed or conducting.