JP2005151075A - Asynchronous communication system by pulse gap signal in rfid communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an asynchronous communication system by a pulse gap signal in an RFID communication, which is capable of dealing with a change in carrier frequency and shortening a communication time without increasing a baud rate. <P>SOLUTION: Load modulation is performed by a VPM coding system in which a negative logical pulse signal is outputted for a Tg time as a pulse gap signal for the head of each data indicative of "1" and "0", an H level signal is outputted for a T1 time after the pulse gap signal in the case of "1" data, and the H level signal is outputted for a T0 time after the pulse gap signal in the case of "0" data. Also, in the interrogator side, this load modulation wave is demodulated to detect the VPM code, a signal subsequent to the pulse gap signal is read using the rise edge or the fall edge of the pulse gap signal of each VPM signal as a trigger, and the reference time, the T1 time and the T0 time are compared to detect the "1" data and the "0" data. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention follows a plurality of carrier frequencies in RFID (Radio Frequency Identification) communication for data transmission between a reader called interrogator and a transponder called transponder in a contactless IC card or wireless ID tag system. The present invention relates to an asynchronous communication method using a pulse gap signal in RFID communication, which can be used as a system capable of transmitting data and compatible with a carrier frequency, and can reduce the communication time without increasing the baud rate.

  In recent years, automatic recognition by individual ID identification has been widely used in many fields such as service industry, manufacturing industry, distribution industry, sales industry, and logistics. As a means for identifying the ID, a bar code system has been generally used. However, in order to solve the disadvantage that the information storage capacity is low and the information cannot be rewritten, attention is paid to a non-contact IC card and a wireless ID tag system. It is becoming popular.

  The non-contact IC card and the wireless ID tag system perform data transmission by non-contact communication by magnetic field or inductive coupling of electromagnetic fields, that is, RFID communication, and a close contact type (international standard is ISO / IEC 10536). ), A proximity type of about several cm to 10 cm (international standard is ISO / IEC14443), and a proximity type of about 50 cm to 1 m (international standard is ISO / IEC15693). The carrier frequency is generally 4.915 MHz for the contact type and 13.56 MHz for the proximity type and the proximity type.

  FIG. 2 is a configuration block diagram for explaining the communication principle in RFID communication. The interrogator 1 and the responder 5 in the non-contact IC card or the wireless ID tag system can transmit data by inductive coupling at a frequency lower than the microwave. Has been done. Here, the responder 5 receives power supply from the interrogator 1 as a passive element, and operates the RFID chip 6. That is, in RFID communication using a carrier frequency such as 4.915 MHz or 13.56 MHz, the carrier wave transmitted from the antenna 4 on the interrogator 1 side is received by the antenna 8 on the responder 5 side, and the magnetic field or the electromagnetic field 9 is induced. Since the electromotive force generated in the antenna 8 due to the coupling is rectified and smoothed to obtain a circuit power supply, the responder 5 can operate without a battery. In the figure, when the magnetic field or electromagnetic field 9 output from the antenna 4 connected to the interrogator 1 penetrates the loop of the antenna 8 connected to the responder 5, an electromotive force is generated in the antenna 8 by inductive coupling. At this time, the tuning capacitor 3 is connected in parallel to the antenna 4 of the interrogator 1 to form a resonance circuit having a resonance frequency that matches the carrier frequency output from the oscillator 2. Further, a tuning capacitor 7 is connected in parallel to the antenna 8 of the responder 5, and a resonance circuit adjusted to resonate with the carrier frequency output from the interrogator 1 is configured. Communication and power supply are performed. That is, it is considered that the inductive coupling by the interrogator 1 and the responder 5 constitutes a transformer through a space.

  FIG. 3 shows an example of a PPM (Pulse Position Modulation) modulation waveform transmitted from the interrogator side in RFID communication. (A) shows a carrier waveform of one data length, and (b) shows a hexadecimal code “9”. 1 shows a modulation waveform of one data length when transmitting. In the PPM modulation, hexadecimal data “0” to “F” is represented by the position of the L level signal. Therefore, when transmitting “9” of the hexadecimal code from the interrogator 1, one data length is divided into 16 pieces. Further, in each data area, the data area corresponding to the tenth “9” from the left is modulated to L level, so that the responder 5 detects the position of the L level signal and identifies it as “9”. Can do. The PPM modulation method is generally used as a modulation means for transmitting data from the interrogator 1 to the responder 5.

Next, FIG. 4 is an example of a modulated waveform in which carrier wave is load-modulated from the responder side by Manchester code in RFID communication, and (a) shows a carrier waveform at the normal time, that is, when data is not transmitted from the interrogator 1. (B) shows "9" of the hexadecimal code by the Manchester code, that is, "1001" of the 4-bit code, and (c) shows a modulation waveform when the carrier wave is load-modulated by "9" of the Manchester code. In the load modulation using the Manchester code, “1” is expressed as negatively inverted (falling) and “0” is inverted positively (rising) at the center of the bit, so that the L level signal and the H level signal are expressed in hexadecimal code. This period is ½ each. The modulation method using the Manchester code is generally used as a load modulation method for changing the level of the carrier wave by short-circuiting the antenna circuit and removing the tuning when transmitting data from the responder 5 to the interrogator 1.
RFID handbook, written by Klaus Finkenzeller, translated by Institute of Software Engineering, published by Nikkan Kogyo Shimbun

  As described above, in the load modulation method in which data is transmitted to the interrogator by changing the carrier level by short-circuiting the antenna circuit on the responder side and removing the tuning, the conventional Manchester code, NRZ code, and single pole Coding methods such as RZ code and Miller code have the advantage that the signal time of “1” data and “0” data is the same, so that demodulation of data by the synchronous clock method or the frame synchronous method is easy. . Modulation by the encoding method is effective for long-distance data communication in which the transmission path has a distributed capacity and external noise is likely to be superimposed, but the communication distance is short as in RFID communication, and the influence of the distributed capacity and external noise is small. There is a problem that it is not always an effective encoding method for a small amount of data communication. Further, the carrier frequency is operated at a frequency defined in advance in the system, and there is a problem that it cannot be operated in a system having another different frequency. Further, in the conventional coded modulation system, in order to shorten the communication time, it is necessary to shorten the signal time of “1” data and “0” data, that is, to increase the baud rate. There has been a demand for a new coded modulation method that can shorten the time.

  The present invention has been made to solve the above-mentioned problems and needs. In RFID communication in a non-contact IC card or a wireless ID tag system, data transmission can be performed following a plurality of carrier frequencies. An object is to provide an asynchronous communication method using a pulse gap signal in RFID communication that can be used as a compatible system and can perform high-speed RFID communication by reducing communication time without increasing the baud rate. And

  In order to solve the above-mentioned problem, in the asynchronous communication method using the pulse gap signal in the RFID communication of the present invention, in the RFID communication that performs data transmission between the interrogator and the responder in the non-contact IC card or the wireless ID tag system, the responder As a load modulation method for transmitting data to the interrogator by short-circuiting the antenna circuit on the side, a negative logic pulse signal is output as a pulse gap signal at the beginning of each data representing “1” and “0” for Tg time, VPM (Variable Phase Modulation) code that outputs H level signal for T1 time after pulse gap signal for “1” data, and outputs H level signal for T0 time after pulse gap signal for “0” data Load modulation is performed according to the conversion method. On the interrogator side, the load modulation wave is demodulated to detect the VPM code, and the signal following the pulse gap signal is read using the falling edge or rising edge of the pulse gap signal of each VPM code as a trigger, and the reference time and By comparing the T1 time or the T0 time, “1” data or “0” data is detected. Here, the Tg time is much shorter than the T1 time and the T0 time, the T1 time is longer than the T0 time, and the Tg, T1, and T0 times can be arbitrarily set.

  According to the asynchronous communication method using the pulse gap signal in the RFID communication of the present invention, the reference time for detecting “1” data or “0” data is changed following the carrier frequency as compared with the T1 time or T0 time. By doing so, there is an effect that operation in systems with different carrier frequencies becomes possible. Further, since the time of “0” data is shorter than the time of “1” data at the baud rate in which the time of 1 bit length of the conventional coding method and the time of “1” data of the VPM coding method are the same, the baud rate is Even if it is not increased, the communication time is shortened and the RFID communication can be performed at high speed.

  The best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a modulation waveform example in which a carrier wave is load-modulated from a responder side by a VPM code in order to realize an asynchronous communication method using a pulse gap signal in RFID communication of the present invention. “9”, that is, “1001” of a 4-bit code, shows a modulation waveform when a carrier wave is load-modulated with “9” of the VPM code. In the load modulation by the VPM code, “1” data is output as a pulse gap signal after a negative logic pulse signal of Tg time, and an H level signal of T1 time is output, and “0” data is a pulse gap signal as a negative logic pulse of Tg time. The carrier wave is load-modulated by a VPM code expressed by outputting an H level signal at time T0 after the signal. Here, the Tg time is very short compared to the T1 time and the T0 time, and the T1 time is longer than the T0 time. On the interrogator 1 side, after detecting the envelope of the modulated wave by the demodulator, the signal time following the pulse gap signal is detected, and the reference time defined in advance is compared with the signal time following the pulse gap signal. If it is determined that the time T1 is longer than the reference time, the data is “1”, and if it is determined that the time T0 is shorter than the reference time, the data is read as “0” data. This communication method requires a preamble indicating the start of communication, but is asynchronous communication because subsequent data is an edge trigger method that reads the rising edge or falling edge of the pulse gap signal as a trigger.

  FIG. 5 is a circuit block diagram on the responder side for implementing the asynchronous communication method using the pulse gap signal in the RFID communication of the present invention, and a method for generating a VPM modulated wave by hardware means will be described.

  As shown in FIGS. 5 and 2, the responder 5 includes an antenna 8 for receiving a magnetic wave transmitted from the antenna 4 on the interrogator 1 side or a modulated wave due to the electromagnetic field 9, and the antenna 8 resonates with the maximum. A tuning capacitor 7 for performing efficient RFID communication and power supply, a rectifier circuit 10 for obtaining a circuit power supply from a modulated wave induced in the resonance circuit, and a voltage detection circuit 11 for detecting a power-on voltage And a modulation circuit for detecting the envelope of the modulated wave to extract a data signal, a clock generation circuit 13 for generating a system clock, and a resonance circuit composed of an antenna 8 and a tuning capacitor 7 are load-modulated. For receiving the signals from the VPM modulation circuit 16 and the switching element 17, the voltage detection circuit 11, the demodulation circuit 12, and the clock generation circuit 13. A logic circuit 14 for performing generation and communication control over data, constituting at such a memory circuit 15 to fulfill the storage or register function input data obtained from said demodulating circuit 12.

  When RFID communication is performed between the responder 5 and the interrogator 1 configured by the circuit blocks, the interrogator 1 controls the oscillator 2 and transmits data by the PPM modulation described with reference to FIG. The data penetrates the antenna 8 on the responder 5 side as a magnetic field or electromagnetic field 9 from the antenna 4, and an electromotive force is generated in the antenna 8 by inductive coupling. A tuning capacitor 7 is connected in parallel to the antenna 8 of the responder 5 to form a resonance circuit that is adjusted to resonate with the carrier frequency output from the interrogator 1. Power is supplied.

  The modulated wave induced in the antenna 8 is rectified by the rectifier circuit 10 and charged to a smoothing capacitor (not shown) as DC power. Further, the envelope of the modulated wave is detected by the demodulating circuit 12 and input to the logic circuit 14 as a data signal by the PPM code, and the carrier wave component of the modulated wave is shaped and frequency-divided by the clock generating circuit 13 to be used as the system clock. 14 Further, a power-on signal for resetting the logic circuit 14 is detected by the voltage detection circuit 11 and input.

  When the command transmitted from the interrogator 1 by the above operation is analyzed by the responder 5 and necessary data is transmitted to the interrogator 1, the VPM modulation circuit 16 converts the command into a VPM code as shown in FIG. The switching element 17 connected in parallel to the antenna 8 is driven. The switching element 17 is preferably an FET. When a pulse gap signal, that is, an L level signal is output, the antenna circuit is short-circuited by turning on the gate of the switching element 17, and when an H level signal is output, the gate of the switching element 17 is turned off. Is released and load modulation of the carrier wave is performed. If the logic of the control input of the switching element 17 is reversed, the logic of the VPM code as shown in FIG.

  In the load modulation by the VPM code, “1” data is output as a pulse gap signal after a negative logic pulse signal of Tg time, followed by an H level signal of T1 time, and “0” data is a pulse gap signal as a negative logic pulse of Tg time. The carrier wave is load-modulated by a VPM code expressed by outputting an H level signal at time T0 after the signal. Here, the Tg time is very short compared to the T1 time and the T0 time, and the T1 time is longer than the T0 time. On the interrogator 1 side, the envelope of the modulated wave is detected by the demodulator, the signal time following the pulse gap signal is detected, and the reference time defined in advance is compared with the signal time following the pulse gap signal. If it is determined that the time T1 is longer than the reference time, the data is “1”, and if it is determined that the time T0 is shorter than the reference time, the data is read as “0” data. Here, when the system is operated with another carrier frequency, the reference time for detecting “1” data or “0” data compared to the T1 time or T0 time is set to the carrier frequency by remote operation or the like. If the corresponding change is made, the sequence for comparing the time of the “1” data or “0” data changed corresponding to the carrier frequency and the reference time does not change, and the operation becomes possible.

  FIG. 6 is a comparison diagram showing a difference in transmission time between the conventional Manchester code and the VPM code used in the present invention, where (a) is a Manchester code and (b) is a hexadecimal code “9” of the VPM code. "In other words," 1001 "of a 4-bit code is indicated. Here, at a baud rate in which the time of 1-bit length of the Manchester code and the time of “1” data of the VPM encoding method are the same, if T1≈2 * T0, the VPM code is shorter by Ts≈T1 + Tg time. It has become. Accordingly, the communication time can be shortened and RFID communication can be performed at high speed without increasing the baud rate. In addition, the VPM modulation method can be used as a kind of encryption method because the VPM modulation method has a different length each time depending on the data content, as compared with a modulation method with a constant 1-bit length, such as a conventional Manchester code modulation method. Become.

It is an example of a modulated waveform in which a carrier wave is load-modulated from the responder side by a VPM code in order to realize an asynchronous communication method using a pulse gap signal in RFID communication of the present invention. It is a block diagram for explaining a communication principle in RFID communication. It is an example of a PPM modulation waveform transmitted from the interrogator side in RFID communication. It is an example of a modulated waveform in which a carrier wave is load-modulated from the responder side by a Manchester code in RFID communication. It is a circuit block diagram by the side of the responder for implementing the asynchronous communication system by the pulse gap signal in RFID communication of this invention. It is the comparison figure which showed the difference in the transmission time by the conventional Manchester code | cord | chord and the VPM code | cord | chord used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Interrogator 2 Oscillator 3 Tuning capacitor 4 Antenna 5 Responder 6 RFID chip 7 Tuning capacitor 8 Antenna 9 Magnetic field or electromagnetic field 10 Rectifier circuit 11 Voltage detection circuit 12 Demodulation circuit 13 Clock generation circuit 14 Logic circuit 15 Memory circuit 16 VPM modulation circuit 17 Switching element

Claims (2)

Interrogator (1) by short-circuiting the antenna circuit on the responder (5) side in RFID communication for data transmission between the interrogator (1) and the responder (5) in the non-contact IC card or wireless ID tag system As a load modulation method for transmitting data to the side, a negative logic pulse signal is output as a pulse gap signal for Tg time at the beginning of each data representing “1” and “0”, and in the case of “1” data, a pulse gap signal is output. After that, the H level signal is output for T1 time, and in the case of “0” data, load modulation is performed by the VPM encoding method that outputs the H level signal after the pulse gap signal for T0 time,
On the interrogator (1) side, the load modulation wave is demodulated to detect the VPM code, and the signal following the pulse gap signal is read using the falling edge or rising edge of the pulse gap signal of each VPM code as a trigger, Recognize "1" data or "0" data by comparing the reference time with T1 time or T0 time,
By changing the reference time by remote control, etc., a means that can be used as a carrier frequency compatible system that can perform data transmission following multiple carrier frequencies and that can shorten the communication time without increasing the baud rate. An asynchronous communication method using a pulse gap signal in RFID communication, characterized by having   The Tg time is much shorter than the T1 time and the T0 time, the T1 time is longer than the T0 time, and the Tg, T1, and T0 times can be arbitrarily set. 2. An asynchronous communication method using a pulse gap signal in RFID communication according to 1.

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