JP4466678B2 - RFID tag and method for adjusting resonance frequency in RFID tag - Google Patents

Description

  The present invention relates to an RFID tag and a method for adjusting a resonance frequency in the RFID tag.

  FIG. 1 shows a system overview of an RFID tag and an RFID interrogator using the RFID tag. In FIG. 1, reference numeral 1 denotes an RFID tag. The interrogator (reader / writer) 2 has a detection area 3 having a predetermined spread. That is, in this system, there may be a plurality of RFID tags, 1.

  When the RFID tag 1 is mounted on a book, envelope, casino chip, etc., if the RFID tags 1 overlap with each other, the communication performance is remarkably lowered, and the interrogator (reader / writer) 2 cannot be accessed successfully. There's a problem. In these applications, there are cases where the RFID tags 1 are stacked or the interval between the RFID tags 1 and 1 is set very close.

  In this state, L (resonance coil inductance) of both RFID tags 1 is mutually coupled to form mutual inductance, and the inherent inductance of the RFID tag 1 tends to increase in conjunction with the mutual inductance. .

  This is because the resonance capacitor existing in the RFID tag 1 has a constant value, so that the resonance frequency is in a state where there is no mutual coupling (the expected resonance frequency and the frequency specified by the interrogator). It means lower than that.

  On the other hand, the interrogator (reader / writer) 2 oscillates at the same frequency as the resonance frequency (expected resonance frequency) of the RFID tag 1. This means that when viewed from the RFID tag 1 whose resonance point is lowered due to the overlap of the RFID tag 1 or the like, a magnetic field whose resonance is shifted is provided from the interrogator (reader / writer) 2 side antenna. The supplied energy will be reduced. As a result, the communication distance is reduced.

  In order to eliminate the decrease in communication distance due to the overlapping of the RFID tags 1, Japanese Unexamined Patent Publication No. 2000-151480 discloses an identification method when a plurality of tags are superimposed. Here, a configuration is described in which the resonance frequency can be changed by switching the capacitor built in the tag, but the desired capacitor can be switched by switching the built-in capacitor for each tag among a plurality of superimposed tags. Describes how to adjust to match the frequency. The resonance frequency of other tags is changed sequentially after the communication with one tag is completed.

  In the case of this method, it is possible to match the resonance frequency of one tag with the resonance frequency emitted by the interrogator, but the resonance frequency of the other tag deviates from the resonance frequency emitted by the interrogator. Therefore, a general collision prevention procedure (for example, JIS6323-3 ISO / IEC 15693-3) is not used, and the interrogator and the tag perform one-to-one communication.

  In addition, there is no method for determining the order between multiple tags (from which tag the resonance frequency is adjusted), and it is difficult to ensure stable operation as a realistic system, and difficult to realize. There is a problem.

  The present invention has been made to solve such a problem, and an object thereof is to effectively use a collision prevention-related function called anti-collision, which has a simple configuration and can realize a stable system operation. An object of the present invention is to provide a method for adjusting a resonance frequency in an RFID tag.

  The following is a brief description of problems that occur with the superposition of RFID tags. That is, the coil tag inductance L of the RFID tag causes mutual inductance due to the overlap with other tags, and the L value is increased accordingly. Therefore, by reducing the value of C for resonance corresponding to the increment of L, the resonance frequency is always kept constant, thereby solving problems such as insufficient rise in power supply voltage. In addition, the configuration consists of a plurality of resonance capacitors, and by separating this resonance capacitor configured under certain conditions, the capacitor value is reduced, and the decrease in resonance frequency caused by the increase in mutual inductance is corrected. To do.

  In order to solve the above-mentioned problems, an RFID tag according to the present invention is an RFID tag, and is a switch circuit for performing on / off connection of at least one of an inductance and a plurality of resonance capacitors or a plurality of resonance capacitors forming a resonance circuit. A constant voltage circuit that outputs a constant voltage by smoothing a power signal applied from the interrogator (reader / writer) via the resonance circuit, voltage detection means for detecting the smoothed voltage, and Voltage monitoring means for monitoring the degree of rise of the smoothed voltage; and resonance capacity switching command means for commanding on / off of the switching circuit in response to an output of the voltage monitoring means when a predetermined increase cannot be obtained. And the voltage monitoring means outputs a detection output when the output from the constant voltage circuit reaches the first voltage. A timer circuit that receives the output of the first voltage detection circuit and outputs a timer signal for a predetermined period; and a detection output when the output of the constant voltage circuit reaches a second voltage higher than the first voltage. A second voltage detection circuit for outputting, and while the timer circuit outputs a timer signal, when the output from the second voltage detection circuit is not obtained, the switching circuit is driven to output the resonance capacitor When the output from the second voltage detection circuit is not obtained before the output of the timer signal passes the predetermined period, the timer signal is output again from the timer circuit. After a predetermined period of time elapses, the resonance circuit is returned to the initial state by the operation of the switching circuit.

According to another aspect of the present invention, there is provided a method for adjusting a resonance frequency in an RFID tag, wherein a switching circuit is used to turn on and off at least one connection of an inductance forming a resonance circuit and a plurality of resonance capacitors or the plurality of resonance capacitors. The power signal supplied from the reader / writer via the resonance circuit is smoothed and a constant voltage is output from the constant voltage circuit. The smoothed voltage is detected by the voltage detection means, and the degree of increase in the smoothed voltage is detected. Is monitored by voltage monitoring means,
When a predetermined increase cannot be obtained, the switching circuit is instructed to turn on / off by the resonance capacitance switching command unit in response to the output of the voltage monitoring unit, and the output from the constant voltage circuit is the first in the voltage monitoring unit. When the voltage reaches the first voltage detection circuit, the first voltage detection circuit outputs a detection output. Upon receiving the output of the first voltage detection circuit, the timer circuit outputs a timer signal for a predetermined period. When a second voltage higher than the first voltage is reached, a detection output is output by the second voltage detection circuit, and an output from the second voltage detection circuit while the timer circuit outputs a timer signal. Is not obtained, the switching circuit is driven to reduce the capacitance value of the resonance capacitor, while the output of the timer signal passes from the second voltage detection circuit until the predetermined period elapses. When the output is not obtained, the timer circuit outputs a timer signal again, and after the predetermined period of time elapses, the switching circuit operates to return the resonance circuit to the initial state. It is characterized by that.

  According to this invention, the RFID tag is equipped with an anti-collision function and a switching circuit for switching on and off the resonance capacitor. For this reason, if a certain level of power supply voltage / operating voltage on the RFID tag side is obtained, identification of each RFID tag can be surely performed by the anti-collision function. For this reason, even if the change of the resonance frequency is set relatively rough, stable operation can be ensured, and the practicality that the reliability of the entire system can be easily improved is very high. For example, when the RFID tag is initially intruded into the communication area of the interrogator, and the distance between the RFID tag and the interrogator is far, the output of the second voltage detection circuit can be selected by selecting the resonance capacitance. When the distance between the RFID tag and the interrogator becomes close, the predetermined resonance of the RFID tag due to the reduction of the resonant capacity is restored by returning the resonant capacity of the resonant circuit to the initial state. The frequency can be prevented from greatly deviating.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. 2 is a block diagram of the main part of one embodiment of the RFID tag according to the present invention, FIG. 3 is a waveform diagram of the RFID tag according to the present invention, FIG. 4 is another waveform diagram of the RFID tag according to the present invention, FIG. FIG. 2 is an operation flowchart of one embodiment of an RFID tag according to the present invention. In FIG. 2, voltage detection circuits 8 and 11 are voltage monitoring means, latch circuit 15 is resonance capacitance switch command means, control circuit 12, UID storage means 16 and data modulator / demodulator 17 are anti-collision information output means. Constitute.

  The RFID tag 1 includes a parallel resonance circuit 4 including a coil L, a resonance capacitor C1, and an adjustment capacitor C2. Since the initial state of the switching circuit SW1 made of a semiconductor such as a CMOS-FET is ON, the adjustment capacitor C2 and the resonance capacitor C1 are connected in parallel and included in the resonance circuit 4 in the initial state. The resonance circuit 4 resonates when entering a high-frequency magnetic field (corresponding to the detection area 3 in FIG. 1) provided by the antenna of the interrogator (reader / writer) 2, and the resonance output is applied to the rectifier circuit 5.

  As a result, the rectifying circuit 5 outputs a direct current component (rectification result) corresponding to the degree of coupling between the RFID tag 1 and the interrogator (reader / writer) 2 antenna. This DC component is smoothed by the smoothing capacitor 6 and stabilized by the constant voltage circuit 7. However, the output of the constant voltage circuit 7 is stabilized after a predetermined time has elapsed since the RFID tag 1 entered the detection area 3, and the output Vcc of the constant voltage circuit 7 at the beginning of the entry is not stable. This is important for the present invention and will be described in detail below.

  On the other hand, various commands received from the interrogator (reader / writer) 2 via the coil L are demodulated by the data modulator / demodulator 17, and the demodulated commands are supplied to the control circuit 12 for processing. The control circuit 12 collates the UID included in the command with the UID of the UID storage means 16, and outputs the UID to the data modulator / demodulator 17 if they match, and the data modulator / demodulator 17 modulates the UID. The UID is transmitted to the interrogator (reader / writer) 2 through the coil L.

  When the control circuit 12 receives the data call request or data write request received from the interrogator (reader / writer) 2 via the coil L → data modulator / demodulator 17, it reads the requested data from the UID storage means 16. Output or write the requested data to the UID storage means 16.

  When receiving a command response prohibition request from the interrogator (reader / writer) 2, the control circuit 12 sets the prohibit mode and prohibits the response to the command as long as power is supplied thereafter.

  If it demonstrates using the waveform of FIG. 3, the constant voltage output Vcc will be 0 initially. As the RFID tag 1 enters the detection area 3, Vcc increases. When the voltage V1 is reached, the voltage V1 is detected by the first voltage detection circuit 8, and the voltage detection circuit 8 raises the detection output A.

  This detection output A is applied to the timer circuit 10 via an exclusive OR circuit 9. This timer circuit 10 is triggered by the rising or falling of its input. In this case, as shown by the signal waveform B in FIG. 3, the timer circuit 10 outputs a timed signal B for a predetermined timer time t1.

  When the constant voltage output Vcc reaches a higher voltage V2 during the timer time t1, the voltage V2 is detected by the second voltage detection circuit 11, and the detection output C rises. This detection output C is applied to the reset terminal 13 of the control circuit 12. When the detection output C applied to the reset terminal 13 rises, the control circuit 12 can perform an original operation such as access to the interrogator (reader / writer) 2 or the like. In other words, when the detection output C is at a low level, the control circuit 12 is held in a reset state, and at least its output section is immobilized so that an unnecessary signal is not output. The above shows the case where the RFID tag 1 enters the detection area 3 of the interrogator (reader / writer) 2 and operates normally.

  Next, the case where it cannot be said that it is normal compared with FIG. 3 is demonstrated using the waveform of FIG. The power supply voltage Vcc in FIG. 4 does not rise smoothly compared to the waveform diagram 3. As described above, as described above, there are various cases where a plurality of RFID tags 1 are overlapped with each other and are located relatively far from the interrogator (reader / writer) 2.

  This abnormal state is shown in FIG. 4, and corresponds to the steps after step S5 in the operation flow diagram of FIG. That is, when the RFID tags 1 overlap each other, the power supply voltage Vcc cannot reach the voltage V2 even after the timer time t1 has elapsed after reaching the voltage V1. That is, the detection output C of the voltage detection circuit 11 that detects the voltage V2 remains at a low level.

  On the other hand, when the timer time t1 elapses in this state, the signal waveform B output from the timer circuit 10 falls, and this fall is applied to the clock terminal CK of the latch circuit 15 via the OR circuit 14, and the latch circuit 15 The output D is inverted. Thus, when the output of the latch circuit 15 is inverted, the output (inverted D) connected to the switching circuit SW1 is inverted from high to low, and the switching circuit SW1 is turned off.

  As a result, the adjustment capacitor C2 is disconnected from the resonance circuit 4, the resonance frequency of the resonance circuit 4 increases, and approaches the resonance frequency defined by the interrogator (reader / writer) 2. As a result, the power supply voltage Vcc rises as shown in FIG. When the power supply voltage Vcc reaches the operating voltage V2 of the circuit, the detection output C of the voltage detecting circuit 11 changes from low to high as described in the previous example, and the control circuit 12 enters the operating state. As a result, the corresponding RFID tag 1 can be accessed with the interrogator (reader / writer) 2.

  The above is an effective compensation operation in the case where the RFID tag 1 is superimposed and there is mutual interference. However, this compensation operation sometimes becomes a problem. That is, in the case of an application in which the RFID tag 1 moves and enters the detection area 3, even when the RFID tag 1 is alone, the operation is performed when the distance from the interrogator (reader / writer) 2 is long. It does not reach the level of the possible voltage V2, but reaches the voltage V1 that triggers the timer circuit 10.

  In this case, when the adjustment capacitor C2 is switched, the above-described compensation operation causes the resonance frequency of the RFID tag 1 to deviate from the desired resonance frequency, greatly reducing the communication distance of the corresponding single RFID tag 1. It will be.

  To improve this, the operation when the timer circuit 10 times up again is shown in the signal B of the waveform in FIG. That is, when the power supply voltage Vcc does not reach the voltage V2 at the second timer time t1, the signal waveform B output from the timer circuit 10 falls, while the detection output C of the voltage detection circuit 11 is the same as the previous example. Unlike in the low level. For this reason, the output of the OR circuit 14 falls. As a result, the state of the latch circuit 15 in which the output of the OR circuit 14 is applied to the clock terminal CK is inverted again, the switching circuit SW1 is turned on, the adjustment capacitor C2 is connected, and the resonance circuit 4 Return to state.

  As a result, the RFID tag 1 whose power supply voltage Vcc could not reach the operating voltage V2 because the distance to the interrogator (reader / writer) 2 was initially long is also moved by the interrogator (reader / writer). ) As the value approaches 2, the power supply voltage Vcc increases. When the power supply voltage Vcc rises and reaches the voltage V2, the voltage V2 is detected by the voltage detection circuit 11, and the control circuit 12 is set to an accessible state in which communication with the interrogator (reader / writer) 2 is possible.

  Thus, for example, as shown in a part of FIG. 1, even when the RFID tags 1 and 1 are overlapped and superimposed, each resonance frequency is defined by the interrogator (reader / writer) 2. The access state can be set close to the frequency, the power supply voltage Vcc is secured, and signals can be transmitted and received between each RFID tag 1 and the interrogator (reader / writer) 2 relatively easily. Can do.

  Next, an anti-collision (multiple responder recognition) technique for distinguishing each RFID tag will be described. Here, an embodiment will be described based on Japanese Industrial Standard (JIS) X6323-3 (ISO / IEC 15693-3) “IC Card without External Terminal—Nearby Type—Part 3: Collision Prevention and Transmission Protocol”. Therefore, in order to further understand this embodiment, the above-mentioned standard published by the Japanese Standards Association is helpful.

  In the anti-collision algorithm employed here, an inventory of a plurality of responders (RFID tags 1, 1, 1,...) Existing in the detection area 3 of the interrogator (reader / writer) 2 is used as the UID. It is extracted based on (tag unique number).

  It is the interrogator (reader / writer) 2 that can detect the presence of a plurality of responders (RFID tags) (the RFID tag itself as the responder is separated only by information from the interrogator (reader / writer) 2). The interrogator (reader / writer) 2 is the main subject of executing the algorithm.

  FIG. 6 shows a UID (tag unique number) that is information for identifying each RFID tag. In this embodiment, the UID is composed of 64 bits as shown in FIG. 6, and the binary display character length of the number of time slots is set as an area. Here, since the number of time slots is 16, the area is divided in units of 4 bits, and the UID is divided into 16 areas. This UID uniquely sets each RFID tag by 14 areas and 56 bits of the IC manufacturer code 4 area and the serial number 10 area in areas A, B, C, and D. The UID of the control circuit 12 of the RFID tag 1 Written and kept inside.

  Next, the anti-collision sequence will be described with reference to the operation flowchart shown in FIG. The operation flowchart shown in FIG. 7 shows the contents of a program stored and executed in the interrogator (reader / writer) 2. Here, a typical anti-collision sequence when the number of time slots is 16 will be described.

  First, in step S11, an area (mask data area) that stores interrogator mask-related data is initialized. In this initialization, the mask length data is set to 0, the mask value data is set to a predetermined value, and the area position data indicating the position where the UID (unique data) stored in the RFID tag is operated is also set to 0.

  When preparation for issuing a command is completed in this way, the interrogator (reader / writer) 2 transmits an inventory command in step S12. As a result, an inventory command is transmitted to the plurality of RFID tags 1. Since each RFID tag 1 has a mask length of 0, a response is independently returned to the interrogator (reader / writer) 2 at its own time slot timing determined by the area 0 of the UID. Therefore, in many cases, each UID returns a response alone to the interrogator (reader / writer) 2 due to the access between the two, but the response may collide with some of the RFID tags 1.

  Correspondingly, in step S13, the RFID tag 1 side signal in response to the inventory command is detected to detect the colliding time slot position. The detected time slot position is stored in the collision slot buffer 18 shown in FIG. This is to distinguish the RFID tag 1 that has collided, as will be described later. The collision slot buffer 18 is formed in the interrogator (reader / writer) 2.

  If there is no collision, when the presence of the tag is detected normally in the next step S14, the UID data of the corresponding RFID tag 1 is stored and held in the detection UID buffer 19 shown in FIG. This detection UID buffer 19 is also formed in the interrogator (reader / writer) 2. In this way, the time slot data and the UID data that have collided are accumulated in the buffers 18 and 19 of the interrogator (reader / writer) 2.

  Next, if there is a normally detected tag, this is confirmed in step S15, and the next control is executed in step S16. In step S16, referring to the contents of the detection UID buffer 19, the interrogator (reader / writer) 2 specifies the corresponding (having UID) tag by specifying the UID, and accesses the tag. That is, necessary data / information exchange is completed.

  After this access is completed, in step S17, a command for setting a response not returned to the inventory command called the STAY QUIET command is transmitted to the corresponding RFID tag 1, and the operation as a tag is stopped. (However, when the power is reset, the state returns to a response state.) This terminates the access to the corresponding RFID tag 1 at this timing, and is equivalent to the fact that the corresponding RFID tag 1 does not exist (is not in stock). Transition to the state.

  Next, in step S18, it is searched whether there is any other RFID tag 1 detected. If another RFID tag 1 is detected in step S15, the above-described step S16 and subsequent steps are repeated, and the corresponding RFID tag is repeated. Processing corresponding to each one is performed. When the processing of the normally detected RFID tag 1 is completed, the determination result in Step S15 is No, and the control is moved to Step S20.

  In step S <b> 20, whether or not there is a collided RFID tag 1 is determined by looking at the contents of the collision slot buffer 18. When it is detected that there is a collision, the determination in step S20 is Yes, and in step S21 and subsequent steps, a process of distinguishing the collided tags using the UID is executed.

  That is, first, in step S21, the first time slot position data among the time slots in which a collision has occurred is taken in as mask related data. In this embodiment, as described above, there are 16 time slots. Now, it is assumed that a collision has occurred at two locations of time slot 1 and time slot 4. In this example, “1”, that is, binary data (0001) is stored as the first time slot position data. In addition, (0001) is stored / stored as mask value data.

  In the subsequent step S22, +4 is added to the mask length whose initial value is 0 (see step S11). As a result, the mask length is set to 4 bits. Also, +1 is added to the area position, and as a result, UID area 1 (see FIG. 6) is selected as position data for designating the next time slot.

  In this way, when the condition for executing the next inventory command is established, control is transferred to step S12. The inventory command to be executed next is different from the previous contents, and is updated with “mask length is 4”, “mask value is 0001”, and “UID area position is 1”. In this way, the updated inventory command is executed. In this case, where there is a tag that has collided, the value (0001) once collided is entered as a mask, so there are always a plurality of RFID tags 1. However, since the “UID area position” that specifies the timing at which the RFID tag 1 returns a response is different from the previous time, the possibility of collision again becomes low. However, it cannot be said that there is nothing in principle.

  Anyway, when the inventory command is performed again like this, steps S15, 16, 17, and 18 are repeated as in the previous case. As a result, access to the interrogator (reader / writer) 2 is completed for the RFID tags 1 that are normally detected, and the number of RFID tags 1 that cannot be accessed due to a collision state decreases gradually. However, in principle, it is not completely eliminated. Therefore, if a collision tag remains even after the second execution of the inventory command, control is transferred to step S20 again, and the determination result is Yes. Subsequently, the process of updating the inventory command in steps S21 and S22 is executed again, and in response to this, the third inventory command is executed in step S12.

  Thereafter, when this process of updating the mask position is repeated and there is no colliding slot, the determination result determined in step S20 is No, and the control is moved to step S23 this time. As a result, this time, the process of returning the area position is performed by repeating steps S24 and S25 and step S19. This is to cover a dropout when a collision occurs in a plurality of slots at the same area position. A series of processing is performed, and when the area position returns to 0, the anti-collision sequence is completed. By repeating the process in this manner, it is possible to substantially eliminate the remaining RFID tag 1 that cannot be accessed due to a collision.

  Next, the simple collision handling algorithm shown in FIG. 10 will be described. The operation flowchart shown in FIG. 10 is a simplified version of the anti-collision algorithm shown in FIG. 7, and a read command with a simple collision prevention function is executed in step S31. In this case, a command having a code indicating the order of the unique ID of the tag to start the collision prevention slot and a code indicating the location of data to be read from the tag is issued as the command. As a result, as shown in steps S12 and S13, the collided time slot, the normally detected UID, and the desired read data are stored and held.

  If there is a collision, the determination result in step S35 is Yes, and the read command with a simple collision prevention function in step S31 is executed again. In this case, in step S31, the fine command shown in the flowchart of FIG. 7 is not executed, but the next command is executed with a simple algorithm. That is, the next command is executed by simply moving the slot start position to the next position.

  In this way, when the slot start position is simply moved, it is not possible to completely eliminate the occurrence of a collision with the same RFID tag 1 again. However, as described above, each RFID tag 1 is given a unique UID at least with 56 bits of the IC manufacturer code and serial number, and as described above, the slot start position is simply and easily moved. Even if the executed command is executed, each RFID tag 1 can be almost identified by repeating it several times from the second time, and there is no problem or malfunction in a normal application.

  This has been confirmed by experiments and experiences of the inventors. The advantage of adopting such a simple collision prevention algorithm is that the system configuration is simplified and maintenance is facilitated, and the access speed between the RFID tag 1 and the interrogator (reader / writer) 2 is increased. As a result, in an application in which the RFID tag 1 and the interrogator (reader / writer) 2 move relatively, the reliability of signal exchange is improved, which is advantageous in ensuring the reliability of the system. . In such a case, the simplified collision prevention algorithm can be positively adopted by selecting application conditions.

  In the above-described embodiment, as shown in the circuit diagram of FIG. 2, there is one adjustment capacitor C2. By providing a plurality of adjustment capacitors C2, finer adjustment is possible. However, as a result of various experiments conducted by the inventors, a single adjustment capacitor is almost sufficient when the anti-collision function is used.

  In the present invention, an anti-collision function is mounted on the RFID tag, and a switching circuit for switching on and off the resonance capacitor is provided. For this reason, if a certain level of power supply voltage / operating voltage on the RFID tag side is obtained, identification of each RFID tag can be surely performed by the anti-collision function. For this reason, even if the change in the resonance frequency is set relatively rough, a stable operation can be ensured, and the reliability of the entire system can be easily improved. In addition, for example, when the RFID tag is initially invaded into the communication area of the interrogator, when the distance between the RFID tag and the interrogator is long, the second voltage detection circuit can be selected by selecting the resonance capacitance. When the distance between the RFID tag and the interrogator becomes short, the resonance capacity of the RFID tag is reduced by returning the resonance capacity of the resonance circuit to the initial state. The predetermined resonance frequency can be prevented from greatly deviating. As a result, even if the change in the resonance frequency is set to be relatively rough, stable operation can be ensured, and the practicality that the reliability of the entire system can be easily improved is extremely high. In addition, it can be said that it is suitable as a method for adjusting the resonance frequency in the RFID tag.

1 is a system overview of an RFID interrogator that uses an RFID tag. 1 is a block diagram of a main part of an embodiment of an RFID tag according to the present invention. It is a waveform diagram of the RFID tag according to the present invention. It is another waveform diagram of the RFID tag according to the present invention. It is an operation | movement flowchart of one Embodiment of the RFID tag which concerns on this invention. It is a UID (tag unique number) information diagram for identifying the RFID tag according to the present invention. It is an operation | movement flowchart of the anti-collision sequence which concerns on this invention. It is an area storage figure of the collision slot buffer based on this invention. It is a UID data storage figure of the detection UID buffer based on this invention. It is an operation | movement flowchart of the simple collision corresponding | compatible algorithm which concerns on this invention.

Explanation of symbols

1 RFID tag 2 Interrogator (reader / writer)
DESCRIPTION OF SYMBOLS 3 Detection area 4 Resonance circuit 5 Rectifier circuit 6 Smoothing capacitor 7 Constant voltage circuit 8,11 Voltage detection circuit 9 Exclusive OR (Exclusive OR) circuit 10 Timer circuit 12 Control circuit 13 Reset terminal 14 OR circuit 15 Latch circuit 16 UID memory | storage Means 17 Data modulator / demodulator 18 Collision slot buffer 19 Detection UID buffer C1 Resonance capacitor C2 Adjustment capacitor SW1 Switching circuit

Claims (2)

An RFID tag,
A switch circuit for turning on and off at least one of the plurality of resonance capacitors or the inductance forming the resonance circuit and the plurality of resonance capacitors;
A constant voltage circuit for smoothing a power signal supplied from the interrogator (reader / writer) via the resonance circuit and outputting a constant voltage;
Voltage detecting means for detecting the smoothed voltage;
Voltage monitoring means for monitoring the degree of rise of the smoothed voltage;
A resonance capacitance switching command means for commanding on / off of the switching circuit in response to an output of the voltage monitoring means when a predetermined increase cannot be obtained;
The voltage monitoring means is
A first voltage detection circuit that outputs a detection output when the output from the constant voltage circuit reaches a first voltage;
A timer circuit that receives the output of the first voltage detection circuit and outputs a timer signal for a predetermined period;
A second voltage detection circuit for outputting a detection output when the output of the constant voltage circuit reaches a second voltage higher than the first voltage;
While the timer circuit outputs the timer signal, when the output from the second voltage detection circuit cannot be obtained, the switching circuit is driven to reduce the capacitance value of the resonance capacitor, and the output of the timer signal is If the output from the second voltage detection circuit is not obtained before the predetermined period elapses, a timer signal is output again from the timer circuit, and after the predetermined period elapses, the switching of the timer signal is performed. An RFID tag configured to return the resonance circuit to an initial state by an operation of the circuit. A switching circuit is used to turn on and off at least one of the plurality of resonance capacitors or the inductance forming the resonance circuit and the plurality of resonance capacitors,
The constant voltage circuit outputs a constant voltage by smoothing the power signal given from the interrogator (reader / writer) via the resonance circuit,
A voltage detection means detects the smoothed voltage,
The voltage monitoring means monitors the degree of increase in the smoothed voltage,
When the predetermined increase cannot be obtained, the switching of the switching circuit is commanded by the resonance capacitance switching command means in response to the output of the voltage monitoring means,
In the voltage monitoring means, when the output from the constant voltage circuit reaches the first voltage, the first voltage detection circuit outputs a detection output, and the timer circuit receives the output of the first voltage detection circuit. A timer signal for a predetermined period is output, and when the output of the constant voltage circuit reaches a second voltage higher than the first voltage, the detection output is output by the second voltage detection circuit, and the timer circuit outputs the timer signal. When the output from the second voltage detection circuit is not obtained during output, the switching circuit is driven to reduce the capacitance value of the resonance capacitor, while the output of the timer signal is set to the predetermined period. If the output from the second voltage detection circuit cannot be obtained by the time elapsed, the timer circuit outputs a timer signal again, and the operation of the switching circuit is performed after the output of the timer signal has passed a predetermined period. In Ri, method of adjusting the resonant frequency in the RFID tag, characterized in that said resonant circuit is configured to return to the initial state.

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