Radio-frequency communication device

• US 20090130981A1
• Filed: 10/03/2008
• Published: 05/21/2009
• Est. Priority Date: 04/03/2006
• Status: Active Grant

• Current Assignee: Brother Kogyo Kabushiki Kaisha (Brother Industries Limited)
• Original Assignee: Brother Kogyo Kabushiki Kaisha (Brother Industries Limited)
• Inventors: Ohashi, Tsuyoshi, Nagai, Takuya, Taki, Kazunari, Takeda, Michihiro, Hirata, Hironori
• Granted Patent: US 8,233,872 B2
• Time in Patent Office: Days
• US Class Current: 455/63.100
• CPC Class Codes: G01S 7/038 Feedthrough nulling circuits
• 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: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal

Abstract

There is provided a radio-frequency communication device that can sufficiently eliminate a leakage signal from a transmission side included in a received signal. The communication device includes a cancel amplitude controlling unit 62 selectively suppressing supply of a cancel signal to a cancel signal synthesizing unit 52, a received-signal terminating unit 50 selectively terminating a received-signal input terminal 64i, a signal strength detecting unit 78 detecting a signal strength, a memory unit 82 storing a signal strength detected by the signal strength detecting unit 78, a signal strength comparing unit 80 comparing a plurality kinds of signal strengths read out from the memory unit 82, and a cancel signal controlling unit 72 controlling an amplitude and/or a phase of the cancel signal based on a result of the comparison by the signal strength comparing unit 80. Thus, suppressing the cancel signal by the cancel amplitude controlling unit 62 enables accurate detection of a strength of the received signal, as well as terminating the received signal by the received-signal terminating unit 50 enables accurate detection of a strength of the cancel signal.

Claims

1. A radio-frequency communication device comprising a splitting unit splitting a carrier wave component of a transmitted signal transmitted via a transmission antenna, an amplitude controlling unit controlling an amplitude of the carrier wave component split by the splitting unit, a phase controlling unit controlling a phase of the carrier wave component split by the splitting unit, and a cancel signal synthesizing unit adding a cancel signal generated with the carrier wave component via the amplitude controlling unit and the phase controlling unit to a received signal received via a reception antenna, the radio-frequency communication device characterized by:

a cancel signal supply suppressing unit that selectively suppresses supply of the cancel signal to the cancel signal synthesizing unit;

a received-signal terminating unit that selectively terminates a received-signal input terminal from the reception antenna to the cancel signal synthesizing unit;

a signal strength detecting unit that detects a strength of the cancel signal, the received signal, or a synthesized signal of the cancel signal and the received signal;

a memory unit that stores the signal strength detected by the signal strength detecting unit;

a signal strength comparing unit that compares a plurality kinds of signal strengths read out from the memory unit with each other, or compares the plurality kinds of signal strengths with the signal strength detected by the signal strength detecting unit; and

a cancel signal controlling unit that controls an amplitude and/or a phase of the cancel signal via the amplitude controlling unit and/or the phase controlling unit based on a comparison result by the signal strength comparing unit.

2. The radio-frequency communication device of claim 1, wherein the received-signal terminating unit includes a circuit switching unit that switches a circuit between the reception antenna and the received-signal input terminal, and a termination resistance connected to the circuit switching unit;

and upon detection of the strength of the cancel signal, the circuit switching unit connects the received-signal input terminal to the termination resistance.

3. The radio-frequency communication device of claim 2, wherein the received-signal terminating unit includes, at a side of the reception antenna relative to the circuit switching unit and the termination resistance, a second circuit switching unit that switches a circuit between the reception antenna and the circuit switching unit and a second termination resistance connected to the second circuit switching unit, and upon detection of the strength of the cancel signal, the second circuit switching unit connects the reception antenna and the second termination resistance.

4. The radio-frequency communication device of claim 1, wherein upon detection of the strength of the received signal, the cancel signal supply suppressing unit controls the amplitude of the carrier wave component such that an output from the amplitude controlling unit is maximally reduced.

5. The radio-frequency communication device of claim 1, wherein the cancel signal supply suppressing unit includes a third circuit switching unit that switches a circuit between the amplitude controlling unit and a cancel signal input terminal and a third termination resistance connected to the third circuit switching unit, the cancel signal supply suppressing unit connecting the cancel signal input terminal and the third termination resistance upon detection of the strength of the received signal.

6. The radio-frequency communication device of claim 1, wherein the transmission antenna and the reception antenna are individually provided as separate antennas.

7. The radio-frequency communication device of claim 1, wherein the transmission antenna and the reception antenna are integrally provided as an antenna commonly used for transmission and reception.

8. The radio-frequency communication device of claim 1, wherein upon detection of the strength of the cancel signal, the transmission antenna transmits a transmitted signal having a signal strength smaller than that of a transmitted signal to communicate with a predetermined communication object.

9. The radio-frequency communication device of claim 1, wherein first, in a state allowing the cancel signal supply suppressing unit to suppress cancel signal supply to the cancel signal synthesizing unit, the cancel signal controlling unit allows the signal strength detecting unit to detect a strength of the received signal and then allows the memory unit to store a result of the detection;

next, in a state releasing the suppression of the cancel signal supply to the cancel signal synthesizing unit and allowing the received-signal terminating unit to terminate the received-signal input terminal, the cancel signal controlling unit controls an amplitude of the cancel signal such that a cancel signal strength detected by the signal strength detecting unit is made equal to the strength of the received signal stored in the memory unit; and

then, in a state releasing the termination of the received-signal input terminal by the received-signal terminating unit, the cancel signal controlling unit controls a phase of a cancel signal such that the strength of a synthesized signal of a received signal and the cancel signal detected by the signal strength detecting unit is maximally reduced.

10. The radio-frequency communication device of claim 1, wherein first, in a state allowing the cancel signal supply suppressing unit to suppress cancel signal supply to the cancel signal synthesizing unit, the cancel signal controlling unit allows the signal strength detecting unit to detect a strength of each of an in-phase component and a quadrature component of the received signal and then allows the memory unit to store a result of the detection;

next, in a state releasing the suppression of the cancel signal supply to the cancel signal synthesizing unit and allowing the received-signal terminating unit to terminate the received-signal input terminal, the cancel signal controlling unit controls the amplitude and/or the phase of the cancel signal such that a strength of each of the in-phase component and the quadrature component of the cancel signal detected by the signal strength detecting unit is made equal to the strength of each of the in-phase and the quadrature components of the received signal stored in the memory unit; and

then, after controlling the phase of the cancel signal to be rotated by 180 degrees, the cancel signal controlling unit releases the termination of the received-signal input terminal by the received-signal terminating unit.

11. The radio-frequency communication device of claim 1, wherein first, in a state allowing the cancel signal supply suppressing unit to suppress cancel signal supply to the cancel signal synthesizing unit, the cancel signal controlling unit allows the signal strength detecting unit to detect respective strengths of an in-phase component and a quadrature component of the received signal and then allows the memory unit to store a result of the detection;

next, in a state releasing the suppression of the cancel signal supply to the cancel signal synthesizing unit and allowing the received-signal terminating unit to terminate the received-signal input terminal, the cancel signal controlling unit controls the amplitude and/or the phase of the cancel signal such that respective in-phase and quadrature components of the cancel signal detected by the signal strength detecting unit are made equal to the respective strengths of the in-phase and the quadrature components of the received signal stored in the memory unit, whereas plus and minus signs of the in-phase and the quadrature components of the cancel signal are opposite to those of the in-phase and the quadrature components of the received signal; and

then the cancel signal controlling unit releases the termination of the received-signal input terminal by the received-signal terminating unit.

12. The radio-frequency communication device of claim 1, wherein the cancel signal controlling unit executes the cancel signal control prior to transmission of information to the predetermined communication object.

13. The radio-frequency communication device of claim 1, wherein the cancel signal controlling unit executes the cancel signal control during transmission of information to the predetermined communication object.

14. The radio-frequency communication device of claim 1, wherein the cancel signal controlling unit executes the cancel signal control at every switching of a frequency of the transmitted signal.

15. The radio-frequency communication device of claim 1, wherein the cancel signal controlling unit executes the cancel signal control, when the strength of the synthesized signal of the received signal and the cancel signal detected by the signal strength detecting unit is equal to or larger than a predetermined value.

16. The radio-frequency communication device of claim 1, wherein the transmission antenna includes an array antenna having a plurality of transmission antenna elements as the transmission antenna and a transmission phase controlling unit that controls respective phases of transmitted signals sent to the respective transmission antenna elements to control a transmission directivity, and upon a phase change of the transmission phase controlling unit, the cancel signal controlling unit executes the cancel signal control.

17. The radio-frequency communication device of claim 1, wherein the reception antenna includes an array antenna having a plurality of reception antenna elements and a reception phase controlling unit that controls respective phases of received signals sent from the respective reception antenna elements to control a reception directivity, and upon a phase change of the reception phase controlling unit, the cancel signal controlling unit executes the cancel signal control.

18. The radio-frequency communication device of claim 1, further comprising a homodyne detection circuit as a demodulating unit for the received signal.

19. The radio-frequency communication device of claim 1, wherein the radio-frequency communication device is a radio-frequency communication tag device that transmits a predetermined transmitted signal via the transmission antenna to a radio-frequency tag, and receives, via the reception antenna, a reply signal returned from the radio-frequency tag in response to the transmitted signal to perform information communication with the radio-frequency tag.

20. A radio-frequency communication device that transmits a transmitted signal via a transmission antenna, and receives, via a reception antenna, a reply signal returned from a communication object in response to the transmitted signal to thereby perform information communication with the communication object, the radio-frequency communication device characterized by:

a direct wave detecting unit that detects a direct wave component from a transmission side in a received signal received via the reception antenna;

a signal processing unit that processes the direct wave component detected by the direct wave detecting unit;

a cancel signal generating unit that generates a cancel signal suppressing the direct wave component from the transmission side in the received signal based on a processing result by the signal processing unit; and

a cancel signal synthesizing unit that synthesizes the cancel signal generated by the cancel signal generating unit and the received signal received via the reception antenna.

21. The radio-frequency communication device of claim 20, wherein the cancel signal generating unit includes a cancel phase controlling unit controlling a phase of the cancel signal and/or a cancel amplitude controlling unit controlling an amplitude of the cancel signal.

22. The radio-frequency communication device of claim 20, further comprising a circuit switching unit that switches a first circuit supplying the received signal received via the reception antenna to the signal processing unit, and a second circuit supplying the direct wave component detected by the direct wave detecting unit to the signal processing unit.

23. The radio-frequency communication device of claim 20, further comprising an A/D converting unit that digitally converts the received signal received via the reception antenna or the direct wave component detected by the direct wave detecting unit to supply the converted signal or component to the signal processing unit.

24. The radio-frequency communication device of claim 23, wherein the direct wave detecting unit includes a direct wave extracting unit that extracts the direct wave component in the received signal in accordance with a difference between the received signal received via the reception antenna and a predetermined reference signal;

a reference adjusting unit provided between the direct wave extracting unit and the A/D converting unit to determine a reference value of the A/D converting unit, and a switch that connects or disconnects a circuit between the direct wave extracting unit and the reference adjusting unit.

25. The radio-frequency communication device of claim 24, wherein the signal processing unit calculates a calculation value for determining the phase and/or the amplitude of the cancel signal based on the reference value and an actual output value in the digital conversion of the direct wave component by the A/D converting unit, using a predetermined relationship;

and the cancel signal generating unit controls the phase and/or the amplitude of the cancel signal based on the calculation value using a predetermined relationship.

26. The radio-frequency communication device of claim 25, wherein the signal processing unit includes a memory unit storing a signal supplied from the A/D converting unit to allow the memory unit to store the reference value prior to the digital conversion of the direct wave component by the A/D converting unit.

27. The radio-frequency communication device of claim 20, further comprising a quadrature demodulating unit that demodulates the received signal received via the reception antenna as mutually quadrature I-phase component and Q-phase component.

28. The radio-frequency communication device of claim 27, wherein the direct wave detecting unit, the A/D converting unit and the circuit switching unit are provided corresponding to each of the I-phase component and the Q-phase component demodulated by the quadrature demodulating unit.

29. The radio-frequency communication device of claim 27, wherein the direct wave detecting unit, the A/D converting unit and the circuit switching unit are provided corresponding to each of the I-phase component and the Q-phase component demodulated by the quadrature demodulating unit;

and

further comprising a reference adjusting unit provided between the direct wave extracting unit and the A/D converting unit corresponding to each of the I-phase component and the Q-phase component to determine reference values of the A/D converting units, a switch that connects or disconnects a circuit between the direct wave extracting unit and the reference adjusting unit corresponding to each of the I-phase component or the Q-phase component, and a second circuit switching unit that switches a first circuit supplying an output from the direct wave extracting unit provided corresponding to the I-phase component to the switch and a second circuit supplying an output from the direct wave extracting unit provided corresponding to the Q-phase component to the switch.

30. The radio-frequency communication device of claim 28, wherein, regarding each of the I-phase and the Q-phase components supplied via the direct wave detecting unit and the A/D converting unit, the signal processing unit calculates an calculation value determining the phase and/or the amplitude of the cancel signal based on a reference value and an actual output value by the digital conversion by the A/D converting unit using a predetermined relationship.

31. The radio-frequency communication device of claim 30, wherein, regarding each of the I-phase and the Q-phase components supplied via the direct wave detecting unit and the A/D converting unit, the signal processing unit obtains a difference between the reference value and the actual output value by the digital conversion by the A/D converting unit to calculate a square root of a sum of squares of the respective differences corresponding to the I-phase and the Q-phase components as the calculation value.

32. The radio-frequency communication device of claim 31, wherein the cancel signal generating unit controls the phase and/or the amplitude of the cancel signal such that the calculation value calculated by the signal processing unit is maximally reduced.

33. The radio-frequency communication device of claim 30, wherein the cancel signal generating unit controls the phase and/or the amplitude of the cancel signal based on a larger one of the difference between the reference value and the actual output value in the digital conversion by the A/D converting unit calculated corresponding to the I-phase component, and the difference between the reference value and the actual output value in the digital conversion by the A/D converting unit calculated corresponding to the Q-phase component by the signal processing unit.

34. The radio-frequency communication device of claim 20, wherein the signal processing unit processes the direct wave component in the received signal received via the reception antenna in response to a carrier wave or a signal including a predetermined command transmitted via the transmission antenna.

35. The radio-frequency communication device of claim 20, wherein the communication object is a radio-frequency tag that enables writing and/or reading of information via a radio-frequency communication;

and

the radio-frequency communication device transmits a predetermined transmitted signal to the radio-frequency tag by the transmission antenna, and receives, via the reception antenna, a reply signal returned from the radio-frequency tag in response to the transmitted signal to perform information communication with the radio-frequency tag.

36. A radio-frequency communication device transmitting a transmitted signal via a transmission antenna and receiving, via a reception antenna, a reply signal returned from a communication object in response to the transmitted signal to perform information communication with the communication object, the radio-frequency communication device characterized by:

a transmission amplifier that modulates a carrier wave based on a predetermined transmission data to output the transmitted signal;

a cancel signal generating unit that includes a cancel phase shifting unit controlling a phase of a cancel signal based on the carrier wave, and a cancellation amplifier having substantially the same characteristics as those of the transmission amplifier for amplifying the cancel signal; and

a cancel signal synthesizing unit that adds a cancel signal generated by the cancel signal generating unit to a received signal received via the reception antenna.

37. The radio-frequency communication device of claim 36, wherein the transmission antenna is an array antenna comprised of a plurality of antenna elements, and includes a transmission amplifier having, in response to each of the antenna elements, substantially the same characteristics as those of the cancellation amplifier.

38. The radio-frequency communication device of claim 36, wherein the transmission amplifier and the cancellation amplifier are variable gain amplifiers capable of varying an amplification factor thereof.

39. The radio-frequency communication device of claim 36, further comprising a transmission filter disposed in a signal transmission path between the transmission amplifier and the transmission antenna, and a cancellation filter disposed in a signal transmission path between the cancellation amplifier and the cancel signal synthesizing unit and having substantially the same characteristics as those of the transmission filter.

40. The radio-frequency communication device of claim 38, wherein the cancel signal generating unit generates the cancel signal by controlling, via the cancellation amplifier, an amplitude of a carrier wave component of the transmitted signal transmitted via the transmission antenna.

41. The radio-frequency communication device of claim 40, wherein the cancel signal generating unit generates the cancel signal by modulating, via the cancellation amplifier, the carrier wave component of the transmitted signal transmitted via the transmission antenna based on the transmission data.

42. The radio-frequency communication device of claim 36, further comprising a phase shifting unit controlling a phase of the transmitted signal transmitted via the transmission antenna or a phase of the received signal received via the reception antenna.

43. The radio-frequency communication device of claim 42, wherein the phase shifting unit has substantially the same characteristics as those of the cancel phase shifting unit.

44. The radio-frequency communication device of claim 36, further comprising a cancel signal controlling unit that controls a phase and/or an amplitude of the cancel signal generated by the cancel signal generating unit such that the amplitude of the cancel signal is made equal to that of the received signal and the phase of the cancel signal is made opposite to that of the received signal, received via the reception antenna.

45. The radio-frequency communication device of claim 36, wherein the radio-frequency communication device is a radio-frequency communication tag device that transmits a predetermined transmitted signal via the transmission antenna to a radio-frequency tag as the communication object, and receives, via the reception antenna, a reply signal returned from the radio-frequency tag in response to the transmitted signal to perform information communication with the radio-frequency tag.

46. A radio-frequency communication device transmitting a transmitted signal via a transmission antenna, and receiving, via a reception antenna, a reply signal returned from a communication object in response to the transmitted signal to perform information communication with the communication object, the radio-frequency communication device characterized by:

a cancel signal generating unit that generates a cancel signal controlling a leakage signal from a transmission side based on a carrier wave component of the transmitted signal transmitted via the transmission antenna;

a cancel signal synthesizing unit that synthesizes the cancel signal generated by the cancel signal generating unit and a received signal received via the reception antenna;

a signal strength detecting unit that detects a signal strength of a synthesized signal synthesized by the cancel signal synthesizing unit; and

a cancel signal controlling unit that controls a phase and/or an amplitude of the cancel signal such that a signal strength detected by the signal strength detecting unit falls within a predetermined designated range not including zero.

47. The radio-frequency communication device of claim 46, wherein the signal strength detecting unit detects a signal strength of the received signal received via the reception antenna;

and the cancel signal controlling unit controls the amplitude of the cancel signal such that a signal strength of the cancel signal is made smaller than the signal strength of the received signal detected by the signal strength detecting unit.

48. The radio-frequency communication device of claim 47, wherein the cancel signal controlling unit controls the cancel signal such that the signal strength of the synthesized signal detected by the signal strength detecting unit falls within the predetermined range and the signal strength of the cancel signal is maximally reduced.

49. The radio-frequency communication device of claim 46, further comprising a quadrature demodulating unit that executes quadrature-demodulation of the synthesized signal output from the cancel signal generating unit, and wherein the signal strength detecting unit detects a signal strength of a direct current component of a demodulated signal demodulated by the quadrature demodulating unit.

50. The radio-frequency communication device of claim 46, further comprising a splitting unit that splits the synthesized signal output from the cancel signal synthesizing unit into parts, and wherein the signal strength detecting unit detects a signal strength of the part of the synthesized signal split by the splitting unit.

51. The radio-frequency communication device of claim 46, wherein upon initial setting of the cancel signal, a carrier wave is transmitted via the transmission antenna to allow the cancel signal controlling unit to control a cancel signal in accordance with a received signal received via the reception antenna in response to the carrier wave, and the amplitude and/or the phase of the cancel signal are/is stored in the memory unit as initial values at a moment when the signal strength of the synthesized signal detected by the signal strength detecting unit falls within the predetermined range.

52. The radio-frequency communication device of claim 51, wherein after the initial setting of the cancel signal, the cancel signal controlling unit controls the phase and/or the amplitude of the cancel signal based on the initial values stored in the memory unit.

53. The radio-frequency communication device of claim 52, wherein the memory unit stores the phase and/or the amplitude of the cancel signal as a control history of the cancel signal whenever necessary, and when the signal strength of the synthesized signal detected by the signal strength detecting unit is outside the predetermined range upon control of the phase and/or the amplitude of the cancel signal based on the initial values stored in the memory unit, the cancel signal controlling unit controls the phase and/or the amplitude of the cancel signal based on the control history stored in the memory unit.

54. The radio-frequency communication device of claim 46, further comprising an amplifying unit that amplifies the synthesized signal output from the cancel signal synthesizing unit, and a quadrature demodulating unit that executes quadrature-demodulation of the synthesized signal amplified by the amplifying unit, and wherein the predetermined range is determined in advance such that the signal strength of the cancel signal is maximally reduced within a range causing no saturation of the amplifying unit or the quadrature demodulating unit.

55. The radio-frequency communication device of claim 54, wherein the predetermined range is less than a saturation-starting input value of the amplifying unit or the quadrature demodulating unit, and is within a range from the saturation-starting input value to 3 or 10 dB.

56. The radio-frequency communication device of claim 46, wherein the predetermined range corresponds to a ringed region surrounding a predetermined region where the synthesized-signal strength is minimal in an xy orthogonal projection of a three-dimensional quadrature coordinate system with an x axis representing the amplitude of the cancel signal, a y axis representing the phase of the cancel signal, and a z axis representing the synthesized-signal strength.

57. The radio-frequency communication device of claim 46, further comprising a transmission and reception common antenna used as the transmission antenna and the reception antenna, wherein the transmission and reception common antenna is connected to a transmission-side circuit and a reception-side circuit via a transmission and reception separating unit.

58. The radio-frequency communication device of claim 46, wherein the radio-frequency communication device is a radio-frequency communication tag device that transmits a predetermined transmitted signal to a radio-frequency tag as a communication object via a transmission antenna, and receives, via the reception antenna, a reply signal returned from the radio-frequency tag in response to the transmitted signal to perform information communication with the radio-frequency tag.