Signal processing device, signal processing method, and receiving device

Abstract

This disclosure relates to a signal processing device, a signal processing method, and a receiving device that are capable of detecting response information at a high degree of accuracy from a carrier signal that is load-modulated based on the response information. A positive DC generating unit 61 generates a positive threshold based on a load-modulated carrier signal. A positive selecting unit 62 compares the voltage of the carrier signal with the positive threshold, and outputs the value of the larger one to an adding unit 65. A negative DC generating unit 63 generates a negative threshold based on the load-modulated carrier signal. A negative selecting unit 64 compares the voltage of the carrier signal with the negative threshold, and outputs the value of the smaller one to the adding unit 65. The adding unit 65 adds the output of the positive selecting unit 62 and the output of the negative selecting unit 64, and outputs the addition result to an IQ detecting unit 53. As a result of the combining, a signal that has smaller Vpp than that of the original carrier signal and maintains the fluctuation portions of the voltage is obtained. This disclosure can be applied to non-contact communication systems.

Claims

1. A signal processing device, comprising: a modulation generating unit configured to generate a positive threshold value and a negative threshold value based on an amplitude shift keying (ASK)-modulated carrier signal; a positive detecting unit configured to compare voltage the ASK-modulated carrier signal with the generated positive threshold value, and detect a first value of the voltage which is higher than the positive threshold value as a positive amplitude fluctuation portion; a negative detecting unit configured to compare the voltage of the ASK-modulated carrier signal with the generated negative threshold value, and detect a second value of the voltage which is lower than the negative threshold value as a negative amplitude fluctuation portion; and an adding unit configured to add the positive amplitude fluctuation portion and the negative amplitude fluctuation portion of the voltage of the ASK-modulated carrier signal.

2. The signal processing device according to claim 1, further comprising a shaping unit configured to shape a waveform that results from addition of the positive amplitude fluctuation portion and the negative amplitude fluctuation portion into a sinusoidal wave.

3. A signal processing method, comprising: in a signal processing device configured to attenuate a voltage of an amplitude shift keying (ASK)-modulated carrier signal: generating a positive threshold value and a negative threshold value using the ASK-modulated carrier signal; comparing the voltage of the ASK-modulated carrier signal with the generated positive threshold value; detecting a first value of the voltage which is higher than the positive threshold value as a positive amplitude fluctuation portion; comparing the voltage of the ASK-modulated carrier signal with the generated negative threshold value; detecting a second value of the voltage which is lower than the negative threshold value as a negative amplitude fluctuation portion; and adding the positive amplitude fluctuation portion and the negative amplitude fluctuation portion of the voltage of the ASK-modulated carrier signal.

4. A receiving device, comprising: a receiving unit configured to receive an amplitude shift keying (ASK)-modulated carrier signal; a modulation generating unit configured to generate a positive threshold value and a negative threshold value based on the received ASK-modulated carrier signal; a positive detecting unit configured to compare a voltage of the ASK-modulated carrier signal with the generated positive threshold value, and detect a first value of the voltage which is higher than the positive threshold value as a positive amplitude fluctuation portion; a negative detecting unit configured to compare the voltage of the ASK-modulated carrier signal with the generated negative threshold value, and detect a second value of the voltage which is lower than the negative threshold value as a negative amplitude fluctuation portion; an adding unit configured to add the positive amplitude fluctuation portion and the negative amplitude fluctuation portion of the voltage of the ASK-modulated carrier signal; and a detecting unit configured to detect a result of addition of the positive amplitude fluctuation portion and the negative amplitude fluctuation portion.

5. The receiving device according to claim 4, further comprising a shaping unit configured to shape a waveform that results from addition of the positive amplitude fluctuation portion and the negative amplitude fluctuation portion into a sinusoidal wave, wherein the detecting unit is further configured to detect the shaped sinusoidal wave.

6. The receiving device according to claim 4, wherein the detecting unit is further configured to detect response information included in the ASK-modulated carrier signal based on quadrature detection on the result of addition of the positive amplitude fluctuation portion and the negative amplitude fluctuation portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a circuit diagram showing an example structure of a conventional non-contact communication system.

(2) FIG. 2 is a diagram for explaining changes in the degree of modulation of a load-modulated carrier signal.

(3) FIG. 3 is a circuit diagram showing an example structure of a conventional reader/writer that detects amplitude changes in the voltage of a load-modulated carrier signal.

(4) FIG. 4 is a diagram showing a detection signal to be output from the reader/writer shown in FIG. 3.

(5) FIG. 5 is a circuit diagram showing an example structure of a reader/writer including an attenuator and a conventional IQ detector.

(6) FIG. 6 is a diagram showing amplitude changes in the voltage of an attenuated carrier signal that is input to the IQ detector in the reader/writer shown in FIG. 5.

(7) FIG. 7 is a diagram for comparing a case where Vpp of a carrier signal is attenuated by the conventional attenuator shown in FIG. 5 with a case where Vpp of a carrier signal is attenuated by a modulation adjusting unit of this disclosure.

(8) FIG. 8 is a diagram illustrating a technique attenuating Vpp without a decrease in the degree of modulation of the carrier signal.

(9) FIG. 9 is a block diagram showing an example structure of a reader/writer as an embodiment.

(10) FIG. 10 is a block diagram showing an example structure of the modulation adjusting unit.

(11) FIG. 11 is a block diagram showing a first example structure of an electronic circuit that realizes the modulation adjusting unit.

(12) FIG. 12 is a diagram showing a load-modulated carrier signal that is input to the first example structure of the modulation adjusting unit.

(13) FIG. 13 is a diagram showing the signal waveforms at respective parts of the first example structure of the modulation adjusting unit.

(14) FIG. 14 is a diagram showing the Vpp reduction effect achieved by the first example structure of the modulation adjusting unit.

(15) FIG. 15 is a diagram showing a definition of a degree of modulation.

(16) FIG. 16 is a flowchart for explaining a signal detecting operation to be performed by the reader/writer.

(17) FIG. 17 is a block diagram showing a second example structure of an electronic circuit that realizes the modulation adjusting unit.

(18) FIG. 18 is a diagram showing a load-modulated carrier signal that is input to the second example structure of the modulation adjusting unit.

(19) FIG. 19 is a diagram showing the signal waveforms at respective parts of the second example structure of the modulation adjusting unit.

(20) FIG. 20 is a diagram showing the Vpp reduction effect achieved by the second example structure of the modulation adjusting unit.

(21) FIG. 21 is a diagram showing waveforms output from the modulation adjusting unit.

(22) FIG. 22 is a block diagram showing another example structure of the reader/writer.

MODES FOR CARRYING OUT THE INVENTION

(23) The following is a detailed description of best modes (hereinafter referred to as embodiments) for carrying out the invention, with reference to the drawings.

Outline of This Disclosure

(24) First, the outline of this disclosure is described. FIG. 7 shows the difference between a case where Vpp of a carrier signal that is load-modulated based on response information is attenuated by the conventional attenuator shown in FIG. 5 (A in the drawing), and a case where Vpp of a carrier signal that is load-modulated based on response information is attenuated by a modulation adjusting unit 52 (FIG. 9) of this disclosure (B in the drawing).

(25) In the case where Vpp of a load-modulated carrier signal is attenuated by the conventional attenuator, the amplitude of the voltage is compressed overall as shown in A in the drawing. As a result, the amplitude change caused by response information or the degree of modulation of the carrier signal is reduced, and the accuracy of response information detection becomes lower. In view of this, this disclosure suggests a technique for attenuating Vpp of a carrier signal without a decrease in the degree of modulation of the carrier signal as shown in B in the drawing.

(26) FIG. 8 specifically illustrates this technique. The midpoint potential portion that is not affected by response information is removed from a pre-attenuation load-modulated carrier signal shown in A in the drawing, and a positive amplitude fluctuation portion and a negative amplitude fluctuation portion that are the amplitude change components of the voltage affected by response information are detected, as shown in B in the drawing. Further, the positive amplitude fluctuation portion and the negative amplitude fluctuation portion that are affected by response information are added to each other, as shown in C in the drawing.

(27) In this manner, a carrier signal that has Vpp attenuated but maintains the amplitude change components to be affected by response information (with the degree of modulation relatively increased) can be obtained. Accordingly, response information can be detected with a higher degree of accuracy by detecting this attenuated carrier signal.

Embodiment

Example Structure of a Reader/Writer

(28) FIG. 9 shows an example structure of a reader/writer as an embodiment in this disclosure.

(29) This reader/writer 50 is used in a non-contact communication system as shown in FIG. 1, for example. The reader/writer 50 receives a high-voltage (approximately 20 V) carrier signal that is load-modulated in accordance with response information at the transponder, performs quadrature detection, and detects the response information as a result of the detection.

(30) The reader/writer 50 includes an antenna 51, a modulation adjusting unit 52, and an IQ detecting unit 53.

(31) The antenna 51 receives a load-modulated carrier signal, and outputs the carrier signal to the modulation adjusting unit 52. The modulation adjusting unit 52 attenuates Vpp of the load-modulated carrier signal, and outputs the carrier signal to the IQ detecting unit 53, while maintaining the amplitude change components of the load-modulated carrier signal, as shown in FIG. 8. The IQ detecting unit 53 performs quadrature detection (IQ detection) on the carrier signal input from the modulation adjusting unit 52, and detects response information as a result of the detection.

Example Structure of the Modulation Adjusting Unit 52

(32) FIG. 10 shows an example structure of the modulation adjusting unit 52. The modulation adjusting unit 52 includes a positive DC generating unit 61, a positive selecting unit 62, a negative DC generating unit 63, a negative selecting unit 64, and an adding unit 65.

(33) Based on a load-modulated carrier signal that is input from the antenna 51, the positive DC generating unit 61 generates a positive threshold that is the positive DC component (a fixed value) of the voltage of the load-modulated carrier signal, and outputs the positive threshold to the positive selecting unit 62. Specifically, the positive threshold for extracting the waveform shown in the upper portion of B in FIG. 8 is generated from the load-modulated carrier signal shown in A in FIG. 8, for example.

(34) The positive selecting unit 62 compares the voltage of the load-modulated carrier signal input from the antenna 51 with the value of the positive DC component (the positive threshold) input from the positive DC generating unit 61, and outputs the larger value to the adding unit 65. As a result of this selection, the positive amplitude fluctuation portion of the voltage of the carrier signal is extracted as shown in the upper portion of B of FIG. 8, for example.

(35) Based on the load-modulated carrier signal that is input from the antenna 51, the negative DC generating unit 63 generates a negative threshold that is the negative DC component (a fixed value) of the voltage of the load-modulated carrier signal, and outputs the negative threshold to the negative selecting unit 64. Specifically, the negative threshold for extracting the waveform shown in the lower portion of B in FIG. 8 is generated from the load-modulated carrier signal shown in A in FIG. 8, for example.

(36) The negative selecting unit 64 compares the voltage of the load-modulated carrier signal input from the antenna 51 with the value of the negative DC component (the negative threshold) input from the negative DC generating unit 62, and outputs the smaller value to the adding unit 65. As a result of this selection, the negative amplitude fluctuation portion of the voltage of the carrier signal is extracted as shown in the lower portion of B of FIG. 8, for example.

(37) The adding unit 65 adds the output of the positive selecting unit 62 and the output of the negative selecting unit 64, and outputs the addition result (FIG. 12c) to the IQ detecting unit 53. As the addition result, a signal that has a lower Vpp than that of the original carrier signal and maintains the fluctuation portions of the voltage is obtained as shown in C in FIG. 8, for example.

First Example Structure of an Electronic Circuit that Realizes the Modulation Adjusting Unit 52

(38) FIG. 11 shows a first example structure of an electronic circuit that realizes the modulation adjusting unit 52. It should be noted that the components equivalent to those in FIG. 10 are denoted by the same reference numerals as those used in FIG. 10.

(39) In FIG. 11, the positive DC generating unit 61 is formed with a diode D11, a resistor R11, and a capacitor C11. The diode D11 passes only the positive voltage of a carrier signal that is input from the antenna 51 connected to the anode side. Accordingly, a positive voltage is applied to the capacitor C11. The resistor R11 prevents excess current from flowing into the capacitor C11. Accordingly, the value of the voltage accumulated in the capacitor C11 can be adjusted by changing the value of the resistor R11.

(40) The positive selecting unit 62 is formed with a diode D12 and a diode D13 that are connected in parallel. The positive voltage from the capacitor C11 connected to the anode side is applied to the diode D12. The positive voltage of the carrier signal from antenna 51 connected to the anode side is applied to the diode D13. As a result, the positive voltage accumulated in the capacitor C11 or the positive voltage of the carrier signal, whichever is higher, is output to the adding unit 65 of a later stage.

(41) The negative DC generating unit 63 is formed with a diode D21, a resistor R21, and a capacitor C21. The diode D21 passes only the negative voltage of the carrier signal that is input from the antenna 51 connected to the cathode side. Accordingly, a negative voltage is applied to the capacitor C21. The resistor R21 prevents excess current from flowing into the capacitor C21. Accordingly, the value of the voltage accumulated in the capacitor C21 can be adjusted by changing the value of the resistor R21.

(42) The negative selecting unit 64 is formed with a diode D22 and a diode D23 that are connected in parallel. The negative voltage from the capacitor C21 connected to the cathode side is applied to the diode D22. The negative voltage of the carrier signal from antenna 51 connected to the cathode side is applied to the diode D23. As a result, the negative voltage accumulated in the capacitor C21 or the negative voltage of the carrier signal, whichever is lower, is output to the adding unit 65 of a later stage.

(43) The adding unit 65 is formed with a resistor R12 and a resistor R22.

(44) When a load-modulated carrier signal having Vpp=40 V as shown in FIG. 12 is input to the first example structure of the modulation adjusting unit 52 shown in FIG. 11, the positive DC generating unit 61 can obtain a positive fixed value (a threshold) as shown in FIG. 13b. The positive threshold can be adjusted by changing the value of the resistor R11. The positive selecting unit 62 extracts the higher portion than the positive threshold shown in FIG. 13b from the carrier signal, and obtains a signal having the waveform shown in FIG. 13a.

(45) Meanwhile, the negative DC generating unit 63 can obtain a negative fixed value (a threshold) as shown in FIG. 13d. The negative threshold can be adjusted by changing the value of the resistor R21. The negative selecting unit 64 extracts the lower portion than the negative threshold shown in FIG. 13d from the carrier signal, and obtains a signal having the waveform shown in FIG. 13e.

(46) The adding unit 65 adds the waveform shown in FIG. 13a and the waveform shown in FIG. 13e, to obtain a signal having the waveform shown in FIG. 13c. The signal is output to a later stage.

(47) FIG. 14 shows the waveform of the voltage of the carrier signal that is shown in FIG. 12 and is input to the first example structure of the modulation adjusting unit 52, and the waveform of the voltage that is shown in FIG. 13c and is output from the adding unit 65, with the widths of the waveforms being adjusted. Specifically, the ordinate axis in A in FIG. 14 indicates the 20 V range, and the ordinate axis in B in FIG. 14 indicates the 2 V range. FIG. 15 shows a definition of a degree of modulation of a load-modulated signal. A degree of modulation is calculated by (AB)/(A+B), which uses the maximum Vpp A and the minimum Vpp B.

(48) As is apparent from FIG. 14, the maximum Vpp A of the carrier signal input to the first example structure of the modulation adjusting unit 52 is 40 V, and the minimum Vpp B is 36 V. Accordingly, the degree of modulation is 5.3%. On the other hand, the maximum Vpp A of the signal output from the adding unit 65 is 3.42 V, and the minimum Vpp B is 1.46 V. Accordingly, the degree of modulation is 40.2%.

(49) With the first example structure of the modulation adjusting unit 52 shown in FIG. 11, the degree of modulation can be made approximately 7.5 times higher, while Vpp of the carrier signal is reduced. Thus, a quadrature detection LSI having 2 V as the highest allowable Vpp can be used in the IQ detecting unit 53, and furthermore, detection based on amplitude changes in the voltage of the carrier signal can be performed.

Operation by the Reader/Writer 50

(50) FIG. 16 is a flowchart for explaining a signal detecting operation to be performed by the reader/writer 50.

(51) This signal detecting operation is performs on the assumption that a carrier signal load-modulated by the transponder is received by the antenna 51 of the reader/writer 50, and is input to the modulation adjusting unit 52.

(52) In step S1, the positive DC generating unit 61 of the modulation adjusting unit 52 generates a positive threshold based on the carrier signal input from the antenna 51, and outputs the positive threshold to the positive selecting unit 62. In step S2, the positive selecting unit 62 compares the voltage of the carrier signal input from the antenna 51 with the positive threshold from the positive DC generating unit 61, and outputs the value of the larger one to the adding unit 65.

(53) In step S3, the negative DC generating unit 63 generates a negative threshold based on the carrier signal input from the antenna 51, and outputs the negative threshold to the negative selecting unit 64. In step S4, the negative selecting unit 64 compares the voltage of the carrier signal input from the antenna 51 with the negative threshold input from the negative DC generating unit 62, and outputs the value of the smaller one to the adding unit 65.

(54) The procedures of steps S1 through S4 are simultaneously carried out in practice.

(55) In step S5, the adding unit 65 adds the output of the positive selecting unit 62 and the output of the negative selecting unit 64, and outputs the addition result (FIG. 12c) to the IQ detecting unit 53. In step S6, the IQ detecting unit 53 performs IQ detection on the signal that is input from the adding unit 65, has a lower Vpp than that of the original carrier signal, and maintains the fluctuation portions of voltage. As a result of the IQ detection, response information from the transponder can be obtained. The signal detecting operation is thus completed.

Second Example Structure of an Electronic Circuit that Realizes the Modulation Adjusting Unit 52

(56) FIG. 17 shows a second example structure of an electronic circuit that realizes the modulation adjusting unit 52. The same components as those of the first example structure shown in FIG. 11 are denoted by the same reference numerals and characters as those used in FIG. 11, and therefore, explanation of them will not be repeated.

(57) The second example structure differs from the first example structure in the structure of the adding unit 65. Specifically, the adding unit 65 is formed with the resistor R12 and the resistor R22 in the first example structure, but the second example structure further includes a resistor R31 and an operational amplifier 71.

(58) The resistor R31 has a smaller resistance value than that of the resistor R12 and the resistor R22, and functions as a feedback resistance for the operational amplifier 71. The operational amplifier 71 attenuates the sum of the output of the positive selecting unit 62 that is input via the resistor R12, and the output of the negative selecting unit 64 that is input via the resistor R22. The attenuated value is output to a later stage.

(59) When a load-modulated carrier signal having Vpp=40 V as shown in FIG. 18 is input to the second example structure of the modulation adjusting unit 52 shown in FIG. 17, the positive DC generating unit 61 can obtain a positive fixed value (a positive threshold) as shown in FIG. 19b. The positive threshold can be adjusted by changing the value of the resistor R11. The positive selecting unit 62 extracts the portion exceeding the positive threshold shown in FIG. 19b from the carrier signal, and obtains a signal having the waveform shown in FIG. 19a.

(60) Meanwhile, the negative DC generating unit 63 can obtain a negative fixed value (a negative threshold) as shown in FIG. 19d. The negative threshold can be adjusted by changing the value of the resistor R21. The negative selecting unit 64 extracts the portion lower than the negative threshold shown in FIG. 19d from the carrier signal, and obtains a signal having the waveform shown in FIG. 19e.

(61) The adding unit 65 adds the waveform shown in FIG. 19a and the waveform shown in FIG. 19e, to obtain a signal having the waveform shown in FIG. 19c. The signal is output to a later stage.

(62) FIG. 20 shows the waveform of the voltage of the carrier signal that is shown in FIG. 18 and is input to the second example structure of the modulation adjusting unit 52, and the waveform of the voltage that is shown in FIG. 19c and is output from the adding unit 65, with the widths of the waveforms being adjusted. Specifically, the ordinate axis in A in FIG. 20 indicates the 20 V range, and the ordinate axis in B in FIG. 20 indicates the 2 V range.

(63) As is apparent from FIG. 20, the maximum Vpp A of the carrier signal input to the second example structure of the modulation adjusting unit 52 is 40 V, and the minimum Vpp B is 36 V. Accordingly, the degree of modulation is 5.3%. On the other hand, the maximum Vpp A of the signal output from the adding unit 65 is 3.11 V, and the minimum Vpp B is 2.13 V. Accordingly, the degree of modulation is 18.7%.

(64) With the second example structure of the modulation adjusting unit 52 shown in FIG. 17, the degree of modulation can be made approximately 3.5 times higher, while Vpp of the carrier signal is reduced. Thus, a quadrature detection LSI having 2 V as the highest allowable Vpp can be used in the IQ detecting unit 53, and furthermore, detection based on amplitude changes in the voltage of the carrier signal can be performed.

Another Example Structure of the Reader/Writer

(65) The voltage of a carrier signal attenuated by the above described modulation adjusting unit 52 has the waveform shown in A of FIG. 21. This carrier signal may be input to the IQ detecting unit 53, and is subjected to detection. However, detection accuracy can be further increased, if the waveform is shaped into a waveform similar to a sinusoidal wave as shown in B of FIG. 21.

(66) FIG. 22 shows an example structure of a reader/writer 80 that can shape the waveform of the attenuated carrier signal into a waveform similar to a sinusoidal wave as described above, and input the carrier signal with the shaped waveform to the IQ detecting unit 53.

(67) The reader/writer 80 is the same as the reader/writer 50 shown in FIG. 9, except that a LPF 81 is provided between the modulation adjusting unit 52 and the IQ detecting unit 53. Other than the LPF 81, the components are the same as those of the reader/writer 50. The LPF 81 can make the waveform of the attenuated carrier signal similar to a sinusoidal wave by removing the high-frequency components of the attenuated carrier signal.

(68) With the reader/writer 80, response information can be detected with a higher degree of accuracy than that with the reader/writer 50.

(69) Having the modulation adjusting unit 52, each of the above described readers/writers 50 and 80 is very effective in detecting amplitude fluctuations in the voltage of a carrier signal. In a case where the distance between the reader/writer and the transponder is relatively long, load modulation is more often detected as an amplitude change than as a phase change. Therefore, this disclosure is particularly effective in extending the communication distance between the reader/writer and the transponder.

(70) The modulation adjusting unit 52 of this disclosure can be used not only in the reader/writer of a non-contact communication system, but also in a receiving device that receives load-modulated signals.

(71) In this specification, a system means an entire apparatus formed with more than one device.

(72) It should be noted that embodiments of this disclosure are not limited to the above described embodiments, and various modifications may be made to them without departing from the scope of this disclosure.

REFERENCE SIGNS LIST

(73) 50 Reader/writer, 51 Antenna, 52 Modulation adjusting unit, 53 IQ detecting unit, 61 Positive DC generating unit, 62 Positive selecting unit, 63 Negative DC generating unit, 64 Negative selecting unit, 65 Adding unit, 80 Reader/writer, 81 LPF