JP2008035104A - Communication apparatus and signal processing method - Google Patents

Abstract

The present invention can accurately demodulate a received carrier signal SA.
The present invention detects a signal level of a reception carrier signal SA as a detection value S using a first detection clock Ca and a second detection clock Cb having the same frequency as the reception carrier signal SA, and uses the detection signal S as a detection value S. An amplitude demodulated signal that indicates the presence or absence of modulation in the received carrier signal SA based on one detected signal that indicates that the corresponding signal level of the received carrier signal SA is the highest. And the amplitude demodulated signal is sent to the decoder unit 25.
[Selection] Figure 6

Description

  The present invention relates to a communication apparatus and a signal processing method, and is suitable for application to an IC card system that performs data communication with a non-contact IC card used for wireless communication at a short distance, for example.

  Conventionally, a non-contact type IC (Integrated Circuit) card system includes an IC card and a communication device that reads information from the IC card, and is widely used for commuter passes, electronic money, and the like. This IC card system is capable of data communication at a short distance, for example, within 30 cm.

  In this IC card system, when the IC card is brought close to a communication device, power is supplied to the IC card by an electromagnetic induction method using electromagnetic waves generated by the communication device, and data communication is performed (see, for example, Patent Document 1). ).

  That is, the IC card and the communication device each have an antenna coil, and when the antenna coils are close to each other, data communication is performed in an electromagnetically coupled state.

  That is, the communication device modulates a carrier signal having a predetermined frequency based on a read command for the IC card, and generates an electromagnetic wave by applying a voltage to the antenna coil in accordance with the modulated carrier signal.

  At this time, in the IC card, a current flows through the antenna coil due to the change of the electromagnetic wave, a demagnetizing field is generated by the current (hereinafter referred to as a reception current), and the reception current operates as a power source. Read command is read from the amplitude of.

  At this time, the IC card reads data corresponding to the read command from the storage unit, turns on / off the resistance or capacitance serving as a load based on this data, changes the impedance in the IC card 2, and generates the response generated from the antenna coil. Change the magnetic field.

  The communication device receives the change in the voltage value of the antenna coil due to the demagnetizing field as a modulation signal, detects the amplitude of the modulation signal using a detection clock having the same frequency as the modulation signal, and demodulates the IC card. The data transmitted from 2 is read out.

  At this time, in the IC card system, the communication distance between the IC card and the communication device is within an assumed range (for example, 0 to 30 cm) by adjusting a coupling coefficient representing the strength of electromagnetic coupling between the communication device and the IC card. In some cases, even if the communication distance changes, the phase of the modulation signal is not changed.

Thereby, the phase of the modulation signal and the phase of the detection clock can be matched, and the amplitude of the modulation signal can be detected with high accuracy.
JP-A-2005-319385

  By the way, in the IC card system, there are a plurality of different systems such as a modulation method and an encoding system, and there are, for example, those called Type A, Type B, and Type C. Type A is adopted as Mifare (registered trademark) of Philips, Type B is adopted as a basic resident register card, etc., and Type C is adopted as Felica (registered trademark of Sony Corporation).

  Further, in recent years, an NFC (Near Field Communication) system in which these three systems are standardized has been developed.

  Here, since the communication device corresponding to the NFC method is configured to perform data communication with respect to the three types of IC cards, the above-described coupling coefficient cannot be optimized to a specific method. As a result, there is a problem that the phase of the modulation signal changes according to the communication distance and the amplitude of the modulation signal cannot be detected with high accuracy, and the modulation signal cannot be demodulated with high accuracy.

  The present invention has been made in consideration of the above points, and intends to propose a communication device and a signal processing method capable of demodulating a modulated signal with high accuracy regardless of a change in the phase of the modulated signal. .

  In order to solve such a problem, in the present invention, in a communication device capable of receiving communication data in a contactless manner with a terminal device of a plurality of methods by an electromagnetic induction method, the terminal device is electromagnetically coupled with an antenna of the terminal device. A detection signal corresponding to a plurality of detection clocks by detecting the signal level of the modulation signal in synchronization with a plurality of detection clocks having the same frequency as the modulation signal and an antenna unit that receives communication data to be transmitted as a modulation signal And a signal processing for demodulating the modulation signal based on the detection signal having the highest signal level of the modulation signal represented by the detection signal among the detection signals. Part.

  Thereby, the accuracy when determining the presence or absence of modulation in the modulated signal can be increased.

  In a signal processing method for receiving communication data in a contactless manner with a terminal device of a plurality of methods by an electromagnetic induction method, a plurality of detections having the same frequency as a modulation signal received by an antenna unit electromagnetically coupled to the antenna of the terminal device By detecting the signal level of the modulation signal in synchronization with the clock, the amplitude demodulated signal generation step for generating the detection signal corresponding to the detection clock, and the signal level of the modulation signal represented by the detection signal among the detection signals is the highest. And a signal processing step of demodulating the modulation signal by determining whether or not the modulation signal is modulated based on one large detection signal.

  Thereby, the accuracy when determining the presence or absence of modulation in the modulated signal can be increased.

  ADVANTAGE OF THE INVENTION According to this invention, the accuracy at the time of judging the presence or absence of the modulation | alteration in a modulation signal can be improved, and thus the communication apparatus and signal which can demodulate a modulation signal with high precision irrespective of the change of the phase of a modulation signal A processing method can be realized.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) First Embodiment In FIG. 1, reference numeral 1 denotes an IC card system based on an NFC (Near Field Communication) system as a whole, and is composed of an IC card 2 and a communication device 3.

  As the IC card 2, those using the above-described Type A, Type B, and Type C methods are used, and the communication device 3 can communicate with the IC card 2 using any method.

  As shown in FIG. 2, the communication device 3 includes a CPU (Central Processing Unit), a ROM (Read Only Memory) in which various programs are stored, and a RAM (Random Access Memory) as a work memory of the CPU. The control unit 11 performs overall control.

  That is, the control unit 11 of the communication device 3 recognizes that the IC card 2 is approaching by the response to the recognition command that is continuously output, determines the method of the IC card 2, and determines the method of the IC card 2. In response to this, the data reading process is executed. Hereinafter, a case where the control unit 11 determines that the system of the IC card 2 is Type C will be described.

  The control unit 11 of the communication device 3 generates a read command for requesting data reading, such as a polling command specifying a modulation method or the like for the IC card 2, and sends the read command to the encoding unit 12.

  When encoding the read command by the Manchester encoding method, the encoding unit 12 switches the signal level of the baseband signal supplied to the modulation unit 13 based on the encoded read command, as shown in FIG.

  The modulation unit 13 synchronizes the carrier signal having the frequency of 13.56 [MHz] supplied from the carrier supply unit 14 with the baseband signal supplied from the encoding unit 12, thereby ASK (Amplitude Shift Keying) 10% A modulated carrier signal is generated by modulating with a method.

  That is, the modulation unit 13 generates a modulated carrier signal by changing the amplitude of the carrier signal by about 10% in accordance with the change in the signal level in the baseband signal supplied from the encoding unit 12.

  The transmission unit 15 amplifies the modulated carrier signal and sends it to the antenna unit 16 formed of an antenna coil. The antenna unit 16 generates an electromagnetic wave corresponding to the amplified modulated carrier signal when a voltage corresponding to the amplified modulated carrier signal is applied to the antenna coil.

  At this time, in the IC card 2, a current flows through the antenna coil electromagnetically coupled to the antenna unit 16 of the communication device 3 due to the change in the electromagnetic wave, and a demagnetizing field is generated by the current (hereinafter referred to as a reception current). At the same time, the received current operates as a power source, and a read command is read from the amplitude of the received current.

  At this time, the IC card 2 reads data corresponding to the read command from a storage unit (not shown), executes Manchester encoding, and generates a baseband signal. The IC card 2 changes the impedance in the IC card 2 by turning on / off a resistance or a capacitor serving as a load in accordance with the baseband signal, and changes the demagnetizing field generated from the antenna coil.

  The antenna unit 16 of the communication device 3 sends a modulated carrier signal whose voltage value has changed due to a change in the demagnetizing field to the receiving unit 21.

  The receiving unit 21 extracts a change in voltage value due to the demagnetizing field from the modulated carrier signal, generates a received carrier signal SA, and sends it to an LPF (Low Pass Filter) 22.

  The LPF 22 removes the noise component by removing the high frequency component in the reception carrier signal SA, and sends this to the detection processing unit 30.

  The detection processing unit 30 detects the amplitude of the received carrier signal SA by detecting in synchronization with a predetermined detection clock C supplied from the clock generation unit 24, converts it to a digital signal, and further demodulates it. Thus, it is sent to the decoder unit 25 as an amplitude demodulated signal. The decoder unit 25 decodes the amplitude demodulated signal and sends it to the control unit 11.

  In this way, the communication device 3 reads data from the IC card 2.

  By the way, as described above, the reception carrier signal SA received by the communication device 3 is load-modulated by the IC card 2, but the amplitude change according to the presence or absence of the modulation in the reception carrier signal SA is the ASK 10% method described above. Is even smaller. Therefore, the communication device 3 needs to detect the amplitude of the reception carrier signal SA as accurately as possible and determine whether or not there is modulation.

  Here, as described above, the communication device 3 corresponds to the IC card 2 having three methods. For this reason, the coupling coefficient determined by the communication distance and the circuit configuration in the IC card 2 and the communication device 3 cannot be matched with the IC card 2 of a specific method. As a result, the communication distance between the IC card 2 and the communication device 3 Accordingly, a phase change occurs in the reception carrier signal SA.

  For example, as shown in FIG. 4, in the period T1, the phase of the received carrier signal SA and the phase of the detection clock C, that is, the timing indicating the maximum and minimum signal levels in the received carrier signal SA (hereinafter referred to as amplitude timing). ) And the detection clock C serving as the detection timing match, the amplitude in the reception carrier signal SA can be detected as the detection value S in the detection signal Dw with high accuracy.

  On the other hand, since the phase change has occurred in the reception carrier signal SA in the period T2, the phase of the reception carrier signal SA and the phase of the detection clock C do not match, and the detection clock C deviates from the amplitude timing. Therefore, the detection value S in the detection signal Dw becomes smaller than the actual amplitude in the reception carrier signal SA.

  As a result, for example, when the detection clock C is shifted by 90 ° from the amplitude timing of the reception carrier signal SA, the detection value S becomes zero, and the amplitude of the reception carrier signal SA cannot be correctly reflected in the detection signal Dw.

  Therefore, in the present embodiment, detection is performed using the first detection clock Ca having the same frequency as the reception carrier signal SA, and the second detection clock Cb having a phase delayed by 90 ° with respect to the first detection clock Ca. So-called quadrature detection is performed.

  Then, as shown in FIG. 5, the detection processing unit 30 detects the first detection signal Dw1 obtained by detecting with the first detection clock Ca and the second detection obtained by detecting with the second detection clock Cb. The signal Dw2 is generated, and the detection clock C and the amplitude timing are close to each other, and the detection value S having a large detection value S is selected to generate an amplitude demodulated signal representing the amplitude of the reception carrier signal SA, and this is decoded. 25 (FIG. 1).

  That is, the signal separation unit 31 (FIG. 5) of the detection processing unit 30 detects the reception carrier signal SA in synchronization with the first detection clock Ca having the frequency 13.56 [MHz] supplied from the clock generation unit 24. As a result, the first detection signal Dw1 representing the signal level of the reception carrier signal SA in the first detection clock Ca is generated and sent to the analog / digital converter 32A.

  Further, the signal separation unit 31 also detects the second detection clock Cb by detecting in synchronization with the second detection clock Cb having a frequency of 13.56 [MHz] and having a phase delayed by 90 ° from the first detection clock Ca. The second detection signal Dw2 representing the signal level of the reception carrier signal SA at is generated and sent to the analog / digital converter 32B.

  Here, as shown in FIG. 6, the detection timings of the first detection signal Dw1 and the second detection signal Dw2 are shifted by 90 °, and therefore the first detection clock Ca and the amplitude timing of the reception carrier signal SA are close to each other. In the period T1, the amplitude of the reception carrier signal SA can be accurately expressed in the first detection signal Dw1 based on the first detection clock Ca.

  On the other hand, in the period T2 in which the first detection clock Ca and the amplitude timing of the reception carrier signal SA are separated, the second detection clock Cb and the amplitude timing of the reception carrier signal SA are close to each other. The amplitude of the reception carrier signal SA can be accurately expressed in the second detection signal Dw2 based on the detection clock Cb.

  The analog / digital converters 32A and 32B respectively convert the first detection signal Dw1 and the second detection signal Dw2 into a first digital detection signal and a second digital detection signal that are digital signals, and a signal processing unit 33 (FIG. 5). To send.

  When the first digital detection signal and the second digital detection signal are supplied from the analog / digital converters 32A and 32B, the signal processing unit 33 receives the received carrier signal represented by the first digital detection signal and the second digital detection signal. Based on whether or not the detection value S (S1 and S2), which is the SA signal level, is equal to or greater than a predetermined threshold value, the presence or absence of modulation of the received carrier signal SA is determined, and the received carrier signal SA is demodulated and demodulated Signals (first demodulated signal and second demodulated signal) are generated.

  Further, the signal processing unit 33 compares the first demodulated signal and the second demodulated signal, and indicates whether the received carrier signal SA is modulated based on one demodulated signal indicating that the signal level of the received carrier signal SA is high. An amplitude demodulated signal is generated and sent to the decoder unit 25.

  That is, for example, in the demodulated signal, the signal processing unit 33 outputs 1 when the unmodulated part is represented by 1 and the modulated part is represented by 0. If both indicate 0, 0 is output.

  As described above, the detection processing unit 30 generates the first detection signal Dw1 and the second detection signal Dw2 by performing quadrature detection using the first detection clock Ca and the second detection clock Cb having the same period as the reception carrier signal SA. In addition, an amplitude demodulated signal is generated based on one detection value S having a large detection value S.

  Thus, as shown in FIG. 7A, the phase of the detection value S1 detected by the first detection clock Ca and the second detection clock Cb when the relationship between the detection detection clock C and the amplitude timing changes. The phase of the detection value S2 detected by the step can always be shifted by 90 °.

  As a result, the detection value S1 and the detection value S2 intersect at the intersection P located at 45 ° from each vertex of the detection value S1 and the detection value S2, and the relation between the detection clock C and the amplitude timing is concerned. Instead, either the detection value S1 or the detection value S2 is always detected outside the intersection P.

  That is, as shown in FIG. 7B, when the detected value S detected when the amplitude timing and the detection clock C match is 1, the detected value at the intersection P deviated by 45 ° from the matched point. Since S is 0.71, even when the relationship between the amplitude timing and the detection clock C is changed, the detection processing unit 30 can detect either the first detection signal Dw1 or the second detection signal Dw2. The detection value S can be set to 0.71 or more. As a result, the signal processing unit 33 can generate an accurate amplitude demodulated signal based on the detection value S that holds 0.71 times or more of the actual amplitude in the reception carrier signal SA.

  In the above description, data reading from the IC card 2 made of Type C has been described. However, data reading is similarly executed for the IC card 2 made of Type A and Type B which are different in modulation method and coding method. . Even in this case, the same effect as in the case of Type C described above can be obtained.

  That is, when the communication device 3 determines that the IC card 2 method is Type A, the communication device 3 encodes the read command by the mirror method and modulates the carrier signal by the ASK 100% method. On the other hand, the IC card 2 encodes data by the Manchester method, and load-modulates the return carrier signal using a subcarrier of 847 [kHz].

  Further, when the communication device 3 determines that the system of the IC card 2 is Type B, the communication apparatus 3 encodes the read command by the NRZ (Non-Return to Zero) system and modulates the carrier signal by the ASK 10% system. On the other hand, the IC card 2 encodes data using the NRZ method and modulates the return carrier signal using the BPSK (Binary Phase Shift Keying) method.

(2) Second Embodiment In the present embodiment shown in FIGS. 8 and 9, the same reference numerals are assigned to the portions corresponding to those in the first embodiment shown in FIGS.

  As shown in FIG. 8, the detection processing unit 30 according to the present embodiment includes four detection clocks C (first to fourth detection clocks Ca to C) each having a phase difference of 45 ° supplied from the clock generation unit 24. Cd) is used to detect the amplitude of the received carrier signal SA to generate four detection signals, which are converted into digital detection signals composed of digital signals by the analog / digital converters 32A to 32D, respectively.

  The signal processing unit 33 demodulates the four digital detection signals to generate four demodulated signals, generates an amplitude demodulated signal based on the demodulated signal representing the highest amplitude value S, and sends it to the decoder unit 25. .

  As a result, as shown in FIG. 9A, the phases of the detection values S1 to S4 detected by the first to fourth detection clocks Ca to Cd can be shifted by 45 °, and the detection processing unit 30 Even if the amplitude timing and the detection clock C change as shown in FIG. 9B, the detection value S in the detection signal of any of the first detection signal Dw1 to the fourth detection signal Dw4 is 0.92. This can be done. As a result, the signal processor 33 can generate an accurate amplitude demodulated signal based on the detection value S that holds 0.92 times or more of the actual amplitude in the received carrier signal SA.

(3) Operation and Effect In the above configuration, the detection processing unit 30 of the communication device 3 uses the first detection clock Ca and the second detection clock Cb having the same frequency as the received carrier signal SA that is the received modulation signal. A signal level of the received carrier signal SA is detected as a detection value S, and a first detection signal and a second detection signal corresponding to the two detection clocks C are generated, respectively, and a first demodulated signal and a second demodulated signal obtained by demodulating them. By comparing the presence or absence of modulation in the signal, the reception carrier signal SA is demodulated by judging the presence or absence of modulation in the reception carrier signal SA based on one detection signal indicating that the signal level of the reception carrier signal SA is the highest. An amplitude demodulated signal is generated.

  As a result, the detection processing unit 30 generates an amplitude demodulated signal based on the detected value S that has not greatly decreased from the actual amplitude in the received carrier signal SA even when the phase of the received carrier signal SA has changed. The received carrier signal SA can be demodulated with high accuracy.

  The detection processing unit 30 also includes a first detection clock Ca, a second detection clock Cb having a phase delayed by 45 ° with respect to the first detection clock Ca, and a phase delayed by 90 ° with respect to the first detection clock Ca. By detecting the reception carrier signal SA using the third detection clock Cc having the fourth detection clock Cd having a phase delayed by 135 ° with respect to the first detection clock Ca, the detection processing unit 30 The received carrier signal SA can be demodulated with higher accuracy.

  According to the above configuration, the communication device 3 generates a plurality of detection signals using the plurality of detection clocks C, compares the detection values S in the detection signals, and selects the detection value S indicating the maximum value. By generating the amplitude demodulated signal, the received carrier signal SA can be accurately demodulated regardless of the phase of the received carrier signal SA.

(4) Other Embodiments In the above-described embodiment, the case where two detection clocks C and four detection clocks C are used as a plurality of detection clocks C has been described. The number of detection clocks C to be used is not limited.

  For example, the first detection clock Ca, the second detection clock Cb having a phase delayed by 60 ° with respect to the first detection clock Ca, and the first having a phase delayed by 120 ° with respect to the first detection clock Ca. By using the three detection clocks C including the three detection clocks Cc, the detection value S can be held at 0.87 times or more of the actual amplitude in the reception carrier signal SA, and the reception carrier signal SA can be obtained with high accuracy. It can be demodulated.

  In the above-described embodiment, the case where the clock generation unit 24 supplies the first detection clock Ca and the second detection clock Cb has been described. However, the present invention is not limited to this, and the clock generation unit 24 includes A clock of 54.24 [MHz] which is four times 13.56 [MHz] which is the frequency of the reception carrier signal SA is supplied, and the detection processing unit 30 selects and uses only the necessary clock. good.

  Further, in the above-described embodiment, the clock generation unit 24 has described the case where the phase difference is provided between the detection clocks C by an angle obtained by dividing 180 ° by the number of detection clocks C. However, the present invention is not limited to this, and the angle of phase difference is not limited.

  Furthermore, in the above-described embodiment, the case where the presence / absence of modulation in the first and second demodulated signals is compared has been described. However, the present invention is not limited to this, for example, detection in the first and second detected signals. The values S1 and S2 may be compared, and one detection value S indicating a high value may be selected to generate one detection signal, which may be demodulated. Even in this case, the same effects as those of the above-described embodiment can be obtained. The same applies to the first and second digital detection signals.

  Further, in the above-described embodiment, the communication device 3 as the communication device is configured by the antenna unit 16 as the antenna unit, the signal separation unit 31 as the detection signal generation unit, and the signal processing unit 33 as the signal processing unit. Although the present invention has been described, the present invention is not limited to this, and the communication device of the present invention may be configured by an antenna unit, a detection signal generation unit, and a signal processing unit having various other configurations. .

  The communication device and the signal processing method of the present invention correspond to a unified standard such as the NFC method, and can be used for various wireless communication systems in a short distance using an electromagnetic induction method.

It is a basic diagram which shows the IC card system by NFC. It is a basic diagram which shows the structure of a communication apparatus. It is an approximate line figure used for explanation of generation of a modulation carrier signal. It is a basic diagram with which it uses for description of the detection of the amplitude value by 1 axis | shaft detection. It is a basic diagram which shows the structure of the detection process part by 1st Embodiment. It is a basic diagram with which it uses for description of the detection of the amplitude value by 2-axis detection. It is a basic diagram with which it uses for description of the effect of biaxial orthogonal detection. It is a basic diagram which shows the structure of the detection process part by 2nd Embodiment. It is a basic diagram with which it uses for description of the effect of 4-axis detection.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... IC card system, 2 ... IC card, 3 ... Communication apparatus, 11 ... Control part, 12 ... Encoding part, 13 ... Modulation part, 14 ... Carrier supply part, 15 ... Transmission part, 16: Antenna unit, 21: Receiver unit, 22: LPF, 24: Clock generation unit, 25: Decoder unit, 30: Detection processing unit, 31: Signal separation unit, 32: Analog / digital Converter, 33... Signal processing unit, Ca... First detection clock, Cb... Second detection clock, Cc... Third detection clock, Cd ... Fourth detection clock, S1, S2.

Claims (5)

In a communication device capable of receiving communication data in a contactless manner with a terminal device composed of a plurality of methods by an electromagnetic induction method,
An antenna unit that receives the communication data transmitted from the terminal device as a modulation signal by electromagnetically coupling with the antenna of the terminal device;
Detecting signal levels of the modulation signals in synchronization with a plurality of detection clocks having the same frequency as the modulation signals, thereby generating detection signal generators respectively generating detection signals corresponding to the plurality of detection clocks;
A signal processing unit that demodulates the modulation signal based on the detection signal having the highest signal level of the modulation signal represented by the detection signal out of the detection signals. A communication device. The multiple detection clocks are
The communication apparatus according to claim 1, comprising a first detection clock and a second detection clock having a phase delayed by 90 ° with respect to the first detection clock. The multiple detection clocks are
The first detection clock, the second detection clock having a phase delayed by 60 ° with respect to the first detection clock, and the third detection clock having a phase delayed by 120 ° with respect to the first detection clock. The communication device according to claim 1, wherein: The multiple detection clocks are
A first detection clock, a second detection clock having a phase delayed by 45 ° with respect to the first detection clock, a third detection clock having a phase delayed by 90 ° with respect to the first detection clock, And a fourth detection clock having a phase delayed by 135 ° with respect to the first detection clock. In the signal processing method when receiving communication data in a non-contact manner with a terminal device having a plurality of methods by an electromagnetic induction method,
The detection signal corresponding to the detection clock is detected by detecting the signal level of the modulation signal in synchronization with a plurality of detection clocks having the same frequency as the modulation signal received by the antenna unit electromagnetically coupled to the antenna of the terminal device. An amplitude demodulated signal generation step for generating each;
A signal processing step of determining the presence or absence of modulation in the modulation signal and demodulating the modulation signal based on the detection signal having the highest signal level of the modulation signal represented by the detection signal among the detection signals; A signal processing method comprising the steps of:

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