JP4634896B2 - Reception apparatus and received signal data demodulation method - Google Patents

Description

  The present invention relates to a receiving device for receiving a signal from a medium equipped with an IC using a frequency shift keying communication method or an amplitude shift keying communication method, and a data demodulation method for a received signal, and particularly to an IC card, an IC tag, etc. The present invention relates to a receiving device in a reader and / or writer that reads and / or writes data from / to a medium, and a method for demodulating received data.

  A reader / writer equipped with an IC for exchanging data with a recording medium such as an IC card or IC tag equipped with an IC is widely used. The reader / writer is provided with an antenna for data transmission / reception with the recording medium, and an induced current flows through the recording medium due to electromagnetic waves emitted from the antenna. The recording medium operates by using the induced current as a power source, and the recording medium transmits a desired response to the reader / writer by placing it on the electromagnetic wave. As a communication system with such a recording medium, an amplitude shift keying (hereinafter referred to as ASK) communication system or a frequency shift keying (hereinafter referred to as FSK) communication system is used.

In ISO15693, which is an international standard, communication standards based on the ASK communication system and the FSK communication system are used. In the ASK communication system, there are a non-modulation period and a modulation period based on a carrier frequency, and data values “1” and “0” are assigned according to the presence or absence of the modulation period. Further, the FSK communication system has two different carrier frequencies, and is assigned to data values “1” and “0”, respectively, according to the carrier frequency. Hereinafter, such a carrier is referred to as a subcarrier, and a carrier used for transmitting the subcarrier is simply referred to as a carrier.
Conventionally, in the FSK communication system, when receiving a response from a recording medium, a band pass filter or notch filter is configured by an analog circuit or a digital circuit, and a pulse having one frequency included in the response signal from the recording medium. Is detected, and only the pulse having the other frequency is detected, and the original data values “1” and “0” are obtained by using an envelope detection circuit or the like, and then the data analysis is performed by sampling by the CPU or the like. Do.

  In the ASK communication method, two subcarrier frequencies are not used, and only one subcarrier frequency is used. Therefore, a band filter and a notch filter are not necessarily required. The original data values “1” and “0” are obtained using an envelope detection circuit or the like, and then analyzed by sampling with a CPU or the like. The received signal is sampled using a general-purpose microcomputer at a speed higher than the data frequency to be received, and once the sampling data is accumulated in the memory, the analysis is performed.

FIG. 3 is a block diagram showing an example of the internal configuration of a reader / writer that communicates with a recording medium equipped with an IC that uses the FSK communication method (see, for example, Patent Document 1).
In FIG. 3, arrows indicate the data flow when receiving a response from the recording medium, and the data flow when transmitting to the recording medium is omitted.
The response from the recording medium 110 is sent to the antenna 101 using inductive coupling between the recording medium 110 and the antenna 101 of the reader / writer 100 in response to a request from the personal computer (hereinafter referred to as a PC) 111. It is told.
The signal from the recording medium 110 detected by the antenna 101 includes one or two subcarriers that are pulses having a specific period, and the subcarrier detection circuit 102 obtains a signal of only the subcarrier. That is, only the specific subcarrier is extracted, and pulses having other periods such as the carrier and noise are removed.

Here, a section where subcarrier A having one frequency is present is a data value “1” in the response of the recording medium, and a section where subcarrier B having the other frequency is present is a data value “0”. The assignment of data values “1” and “0” in the FSK communication system is defined by a standard that the recording medium complies with.
Subcarrier removal circuit 103 detects only subcarrier A or subcarrier B in the FSK communication system, or removes only subcarrier A or subcarrier B. By detecting or removing only one of the two subcarriers, a signal composed of a section where subcarrier A exists and a section where there is no subcarrier A is obtained, as in the ASK communication system.
The envelope detection circuit 104 extracts the envelope of the signal waveform obtained by the subcarrier removal circuit 103. By extracting the envelope with the envelope detection circuit 104, it becomes clear that the section in which the subcarrier exists is the data value “1”.
The A / D conversion circuit 105 converts the signal obtained by the envelope detection circuit 104 into a digital signal, and the digital signal is sampled and analyzed by the CPU 106. The result analyzed by the CPU 106 is sent to the PC 111.
JP 2005-38228 A

  In the ISO15693 standard, the carrier frequency is 13.56 MHz, the subcarrier A frequency in the FSK communication system is 423.75 kHz, and the subcarrier B frequency is 484.28 kHz. Thus, the frequencies of the subcarriers A and B are close to each other, and the subcarrier discrimination and data demodulation can be performed with high accuracy by the digital circuit, which is extremely important for improving the communication quality between the reader / writer and the recording medium. is important. In the ISO15693 standard, communication is performed using an induced current, and therefore there are many factors that degrade communication performance in the communication path. For this reason, it is necessary to correct the communication waveform or to perform subcarrier discrimination while allowing an assumed frequency error.

  However, the conventional reader / writer as described above requires a band-pass filter or a notch filter for extracting or removing only a pulse having one subcarrier frequency in the FSK communication system. In such filtering of the subcarrier frequency by the band pass filter or the notch filter, when the two subcarrier frequencies employed in the FSK communication method are close to each other, the extraction or removal cannot be reliably performed. Furthermore, depending on the communication environment, the subcarrier frequency is not always obtained according to the standard, and in this case as well, the wrong signal is to be subjected to subsequent processing.

Further, in the FSK communication system and the ASK communication system, an envelope detection circuit that generates a demodulated signal for detecting a data value by sampling is required. However, even if an incorrect signal is generated by the filter circuit as described above, there is no means for correcting the envelope detection circuit, and it is necessary to introduce such a correction function in order to prevent demodulation errors of received data. It was.
In addition, the data demodulating circuit formed of an analog circuit as shown in FIG. 3 cannot reduce cost and power consumption.

  The present invention has been made to solve the above-described problems, and performs data demodulation after performing A / D conversion on the detected subcarriers, thereby reducing power consumption, cost, and cost. It is an object of the present invention to obtain a receiving apparatus and a received signal data demodulation method capable of realizing performance enhancement.

A receiving apparatus according to the present invention is a receiving apparatus for receiving a signal from a medium equipped with an IC using a frequency shift keying communication method or an amplitude shift keying communication method via an antenna.
A subcarrier detection circuit unit that detects and outputs a subcarrier that is a carrier of a specific frequency from a signal received from the medium via the antenna;
An A / D conversion circuit unit that performs A / D conversion on the signal output from the subcarrier detection circuit unit; and
Extracting a signal having a preset period from the output signal of the A / D conversion circuit unit, and outputting a variation edge of a signal level in the extracted signal,
A waveform shaping circuit unit that generates and outputs a pulse signal of a predetermined signal level for a time corresponding to the period of the subcarrier when the variant edge is output from the variant edge detection circuit unit;
A data extraction circuit unit that analyzes an output signal of the waveform shaping circuit unit and extracts data output from the medium;
Is provided.

  Further, the waveform shaping circuit unit performs correction for advancing a terminal edge of each pulse of the generated pulse signal by a predetermined time, and outputs the result to the data extraction circuit unit.

  Further, the mutated edge detection circuit unit, the waveform shaping circuit unit, and the data extraction circuit unit are integrated in one IC.

The data demodulation method according to the present invention is a data demodulation method for a signal received from a medium equipped with an IC using a frequency shift keying communication method or an amplitude shift keying communication method.
Detecting a subcarrier which is a carrier of a specific frequency from a signal received from the medium;
A / D conversion of the detected subcarrier,
Extracting a signal with a preset period from the A / D converted signal,
Detection of a signal level variation edge in the extracted signal,
When the mutated edge is detected, a pulse signal having a predetermined signal level is generated for a time corresponding to the period of the subcarrier,
Data from the medium was obtained from the generated pulse signal.

  Further, correction is performed so that the end edge of each pulse of the generated pulse signal is advanced by a predetermined time, and data from the medium is obtained from the signal obtained by the correction.

  According to the receiving apparatus and received signal data demodulation method of the present invention, a subcarrier having a specific frequency is detected from a signal received from the medium, the detected subcarrier is A / D converted, and the A / D conversion is performed. A signal having a preset period is extracted from the detected signal, and a signal level variation edge is detected in the extracted signal. When the variation edge is detected, a predetermined time period corresponding to the subcarrier period is detected. A signal level pulse signal is generated, and data from the medium is obtained from the generated pulse signal. For this reason, most of the data demodulation processing of the signal received from the medium can be performed using the dedicated LSI, and the power consumption can be reduced. Furthermore, the configuration can be made independent of the communication method, and the size and cost of the dedicated LSI can be reduced.

  Further, when a variation edge is detected, a pulse signal having a predetermined signal level is generated for a time corresponding to the subcarrier period, so that subcarrier fluctuations due to fluctuations in subcarrier period, noise, or other factors It is possible to correct the disappearance and improve communication performance.

Next, the present invention will be described in detail based on the embodiments shown in the drawings.
First embodiment.
FIG. 1 is a diagram illustrating a configuration example of a receiving device according to the first embodiment of the present invention. In FIG. 1, a reader / writer that performs data writing and data reading with respect to a recording medium equipped with an IC that uses the FSK communication method is taken as an example of a receiving apparatus, and a circuit that operates when data is received from the recording medium. Only the part is shown.
In FIG. 1, a reader / writer 1 writes data to or reads data from a recording medium 11 such as an IC card or IC tag equipped with an IC using the FSK communication system based on an instruction from an external PC 10. Is to do.

The reader / writer 1 includes an antenna 2, a subcarrier detection circuit 3, an A / D conversion circuit 4, and an LSI 5.
The signal transmitted from the recording medium 11 is received by the antenna 2, and the subcarrier detection circuit 3 removes the carrier, noise, etc. from the received signal, and extracts only the subcarrier A and subcarrier B of a specific frequency. And output. As described above, in the ISO15693 standard, the frequency of the carrier is 13.56 MHz, the frequency of the subcarrier A in the FSK communication system is 423.75 kHz, and the frequency of the subcarrier B is 484.28 kHz.
The A / D conversion circuit 4 A / D converts the signal output from the subcarrier detection circuit 3 and outputs it to the LSI 5. Subsequent signal processing is performed by the dedicated LSI 5 and is managed by software that controls the LSI 5.

As shown in FIG. 2, the LSI 5 includes a period measurement circuit 21, a waveform shaping circuit 22, a register 23, and a CPU 24, and preset values for controlling the period measurement circuit 21 and the waveform shaping circuit 22 are stored in the register 23 in advance. Managed and stored by software. The cycle measuring circuit 21 includes a rising edge detecting circuit 31 and a cycle measuring count circuit 32. The subcarrier detection circuit 3 is a subcarrier detection circuit unit, the A / D conversion circuit 4 is an A / D conversion circuit unit, the period measurement circuit 21 and the register 23 are mutant edge detection circuit units, the waveform shaping circuit 22 and The register 23 forms a waveform shaping circuit unit, and the CPU 24 forms a data extraction circuit unit.
The rising edge detection circuit 31 receives a signal composed of the subcarrier A and the subcarrier B, and the rising edge detection circuit 31 detects the rising edge in the subcarriers A and B. The rising edge is the timing at which the input signal changes from “0” to “1”, but the falling edge, which is the timing at which the data value changes from “1” to “0”, is detected. May be.

  The period measurement count circuit 32 measures the time from one rising edge to the next rising edge obtained by the rising edge detection circuit 31, that is, the pulse period. In the FSK communication system, since the rising edge of the signal consisting only of subcarriers A and B is detected, two periods of subcarriers A and B are measured as pulse periods. Here, the value of the period for determining the period of the subcarrier A as the data value “1” is set in the register 23 in advance, and the period measurement count circuit 32 is set in the register 23 with the measured period. When the period to be determined as the data value “1” is measured, the rising edge used for the period measurement is recognized as the edge of the subcarrier to be determined as the data value “1”, and the subsequent stage To the waveform shaping circuit 22.

  Further, when a period different from the period to be determined as the data value “1” is measured, the period measurement count circuit 32 determines the rising edge used for the period measurement of the subcarrier to be determined as the data value “1”. The edge is not recognized and is not output to the subsequent waveform shaping circuit 22. As a result, only the edge signal detected from the subcarrier having a period to be determined as the data value “1”, which is set in the register 23 in advance, from the signal composed of the subcarriers A and B is the period measurement count circuit. 32. For this reason, the edge signal detected from the subcarrier to be determined as the data value “0” is removed by the period measurement count circuit 32.

  The waveform shaping circuit 22 receives the rising edge signal of the subcarrier A that exists in the section to be determined as the data value “1” generated by the processing in the period measurement circuit 21. When the rising edge signal is input, the waveform shaping circuit 22 outputs a high level signal indicating the data value “1”, and holds the data value “1” until the period of the subcarrier A elapses. A level signal is output, and the next rising edge signal is input. When the next rising edge signal is input while the waveform shaping circuit 22 holds the data value “1”, the waveform shaping circuit 22 further holds the data value “1” until the period of the subcarrier A elapses. If the next rising edge signal is not obtained while the data value “1” is held, a low level signal indicating the data value “0” is output, and the input of the next rising edge signal is awaited. As a result, the waveform shaping circuit 22 outputs a high-level pulse signal having a pulse width in a section where the subcarrier A exists.

On the other hand, there is a possibility that the subcarrier A, which should be present due to noise or other factors, may disappear by one pulse. The time for holding the data value “1” in advance is set in the register 23 as a correction setting value. The waveform shaping circuit 22 compensates for the disappearance of the pulse as described above by holding the data value “1” in accordance with the correction setting value set in the register 23.
Here, in the above description, the holding period for holding the data value “1” is set to the period of the subcarrier A, but here, specifically, it is set to three times the period of the subcarrier A. By setting the correction setting value so that the holding period for holding the data value “1” is three times the period of the subcarrier A, the waveform shaping circuit 22 can receive the rising edge signal and then input the subcarrier. The data value “1” continues to be held even if the next rising edge signal is not input after the time twice as long as the period A has elapsed. The waveform shaping circuit 22 further holds the data value “1” when the next rising edge signal is input after the rising edge signal is input until the time three times the period of the subcarrier A elapses. To do. That is, the waveform shaping circuit 22 complements the two pulse disappearances.

  In addition, the waveform shaping circuit 22 sets the data value to “0” and outputs the output signal if the rising edge signal is not input during the time three times the period of the subcarrier A has elapsed since the rising edge signal was input. In this case, the period of the data value “1”, that is, the period of the high level becomes longer than the original data signal. For this reason, the waveform shaping circuit 22 corrects the signal output to the CPU 24 so that the timing of falling from the high level to the low level is advanced by a time twice as long as the period of the subcarrier A. The CPU 24 samples and analyzes the data signal input from the waveform shaping circuit 22, obtains a response from the recording medium 11 in response to a request from the PC 10, and outputs it to the PC 10.

In the above description, the FSK communication method has been described as an example, but the same processing as that of the FSK communication method is performed in the ASK communication method. In the ASK communication system, a signal obtained by removing a carrier from a signal received from the recording medium 11 is composed of subcarrier A and a section without subcarrier A. In this case, the register 23 is set in advance so that the period of the subcarrier A is determined as the data value “1”. As a result, the rising edge due to subcarrier A is output to the subsequent waveform shaping circuit 22 as the rising edge to be determined as the data value “1”.
Here, when the period of the subcarrier A is the same in the ASK communication method and the FSK communication method, the CPU 24 does not need to change the setting depending on the communication method, and can support both communication methods with the same circuit configuration.

  That is, the CPU 24, strictly speaking, software that controls the CPU 24 does not need to be aware of the communication method. In addition, although the subcarrier A and the subcarrier B are separated from the frequency measurement result by setting in the register 23, it is not strictly determined, but for example, some error is expected with respect to the period of the subcarrier A. Enable judgment. This allows for an increase or decrease in the period due to noise or other factors. Needless to say, it is necessary that the allowable error does not include both subcarriers A and B periods. This also means that pulses having a period longer than or less than the allowable error are removed, that is, pulses other than subcarriers due to noise or the like can be removed.

  The present invention is effective for all standards that employ the ASK or FSK communication system as the communication system with the recording medium, and is not limited to the ISO15693 standard. It is desirable to set a flexible value corresponding to a wide range of standards for the register 23.

  As described above, the receiving apparatus according to the first embodiment performs A / D conversion on a signal obtained by removing the carrier, noise, and the like from the signal received via the antenna 2 from the recording medium 11 that employs the ASK or FSK communication method. Then, binarization is performed, and a signal having a subcarrier period set in the register 23 is extracted from the binarized signal, and from the rising edge signal of the extracted signal, the recording medium 11 responds to a request from the PC 10. I got a reply. Therefore, since the detected subcarrier can be demodulated using a digital circuit, power consumption and performance can be improved, and circuit integration can be facilitated. Cost reduction can be achieved.

It is the figure which showed the structural example of the receiver in the 1st Embodiment of this invention. It is the figure which showed the example of an internal structure of LSI5 of FIG. It is the figure which showed the example of the conventional reader / writer.

Explanation of symbols

1 Reader / Writer 2 Antenna 3 Subcarrier Detection Circuit 4 A / D Conversion Circuit 5 LSI
10 PC
11 Recording Medium 21 Period Measurement Circuit 22 Waveform Shaping Circuit 23 Register 24 CPU
31 Rising edge detection circuit 32 Period measurement count circuit

Claims (5)

In a receiving apparatus for receiving a signal from a medium equipped with an IC using a frequency shift keying communication method or an amplitude shift keying communication method via an antenna,
A subcarrier detection circuit unit that detects and outputs a subcarrier that is a carrier of a specific frequency from a signal received from the medium via the antenna;
An A / D conversion circuit unit that performs A / D conversion on the signal output from the subcarrier detection circuit unit; and
Extracting a signal having a preset period from the output signal of the A / D conversion circuit unit, and outputting a variation edge of a signal level in the extracted signal,
A waveform shaping circuit unit that generates and outputs a pulse signal of a predetermined signal level for a time corresponding to the period of the subcarrier when the variant edge is output from the variant edge detection circuit unit;
A data extraction circuit unit that analyzes an output signal of the waveform shaping circuit unit and extracts data output from the medium;
A receiving apparatus comprising:   The receiving apparatus according to claim 1, wherein the waveform shaping circuit unit performs correction for advancing a terminal edge of each pulse of the generated pulse signal by a predetermined time and outputs the corrected signal to the data extraction circuit unit.   3. The receiving apparatus according to claim 1, wherein the variant edge detection circuit unit, the waveform shaping circuit unit, and the data extraction circuit unit are integrated in one IC. In a data demodulation method for a signal received from a medium equipped with an IC using a frequency shift keying communication method or an amplitude shift keying communication method,
Detecting a subcarrier which is a carrier of a specific frequency from a signal received from the medium;
A / D conversion of the detected subcarrier,
Extracting a signal with a preset period from the A / D converted signal,
Detection of a signal level variation edge in the extracted signal,
When the mutated edge is detected, a pulse signal having a predetermined signal level is generated for a time corresponding to the period of the subcarrier,
A data demodulation method characterized in that data from the medium is obtained from the generated pulse signal. 5. The data demodulating method according to claim 4, wherein correction is performed so that the end edge of each pulse of the generated pulse signal is advanced by a predetermined time, and data from the medium is obtained from the signal obtained by the correction. .

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