JP2002064403A - Non-contact transponder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve power consumption efficiency of a non-contact communication system. SOLUTION: The driving power of a non-contact transponder 2 is obtained by making a rectifying circuit 22 rectify carrier waves which are transmitted from an interrogator 1 and received by an antenna circuit 20. When the non- contact transponder 2 is put on standby, waiting for a query from the interrogator 1, an inner logic circuit 25 controls a capacity switching circuit 21 which varies the antenna circuit 20 in impedance for decreasing the antenna circuit in receiving power efficiency so as to reduce the receiving power volume from the interrogator 1 to an irreducible minimum power just enough for recognizing query data, and when the transponder 2 receives query data for itself, the inner logic circuit 25 controls the capacity switching circuit 21 to vary the antenna circuit 20 in impedance for increasing the antenna circuit 20 in receiving power efficiency so as to increase the receiving power volume from the interrogator 1 to an irreducible minimum power just enough for generating and sending response waves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact communication system comprising an interrogator and a responder for performing power supply and data communication in a non-contact state using electromagnetic induction, and more particularly to an internal circuit according to the communication state. The present invention relates to a non-contact response device capable of improving power transmission efficiency by dynamically changing the characteristics of the non-contact response device.

[0002]

2. Description of the Related Art In recent years, portable electronic data carriers such as IC cards, RF tags, and data carriers have been used as non-contact responders, and electromagnetic induction using a carrier frequency of about 0.1 MHz to several tens of MHz has been utilized. In addition, a non-contact communication system that supplies power to a non-contact response device in a non-contact manner and performs data communication by superimposing data by modulating a carrier wave has been actively studied and commercialized. . In such a non-contact communication system, a plurality of non-contact response devices are simultaneously supplied with power by the electromagnetic field of one interrogation device, and an internal circuit of each non-contact response device can be in an active state in which it can operate, The interrogation device is characterized in that it can communicate with each contactless response device.

However, in such a non-contact communication system, the output characteristics of the electromagnetic field are restricted by laws and regulations such as the Radio Law. Various restrictions are also imposed by self-regulation operating regulations, such as “Self-regulation operation regulations for interfering waves generated from information processing devices and electronic office equipment” established by the association. Due to such a limitation, as a result of setting the transmission output of the interrogation device low, the power that can be received by the contactless response device must be set low, and the data processing function of the contactless response device needs to be suppressed. In addition, since the transmission output of the interrogation device must be suppressed, the fact is that the communication function between the interrogation device and a plurality of non-contact response devices, which is a feature of the non-contact communication system, is impaired.

One of the technical problems behind such a problem is the power consumption characteristics of the contactless response device. In order to perform stable data communication modulation and demodulation while receiving power from the interrogation device by electromagnetic induction, the power supply circuit in the non-contact response device is usually designed with a constant power, and suppresses internal signal noise due to the operation of the entire circuit It is designed to be. When the processing inside the non-contact response device is light, the power supply circuit converts the surplus power into heat by a resistance component. as a result,
The non-contact response device consumes constant power regardless of the state of the internal processing.

If a plurality of such non-contact response devices enter the transmission electromagnetic field of the interrogation device and take an active state, each of them will be electromagnetically coupled irrespective of the communication state with the interrogation device or the internal processing state. Attempts to ensure constant power supply depending on the state. From the viewpoint of the power consumption of the contactless communication system, at a certain time, there is only one device that responds to the interrogation device, and the other non-contact response device is only in a state of waiting for the inquiry, In terms of energy efficiency, the large power consumption of the contactless response device in the standby state has been a problem.

[0006]

As described above, in the conventional non-contact communication system, all the non-contact response devices that enter the transmission electromagnetic field of the interrogation device communicate with the interrogation device and the internal processing. There is a problem that constant power is consumed regardless of the state. The present invention has been made to solve the above problems, and realizes efficient control of the amount of power received from an interrogation device with a simple configuration to improve the efficiency of power consumption in a contactless communication system. It is an object of the present invention to provide a non-contact response device capable of performing the following.

[0007]

In order to solve the above-mentioned problems, the present invention provides an antenna circuit for receiving a carrier wave from an interrogator and transmitting a response wave to the interrogator, A rectifier circuit that obtains the driving power of the own device from the carrier wave obtained, and an internal logic that, when acquiring question data for the own device from the carrier wave, generates response data to the question data and transmits the data as a response wave from the antenna circuit A non-contact response device that receives power from the interrogation device in a non-contact state using electromagnetic induction and performs data communication with the interrogation device, and has a capacitance switching circuit that changes the impedance of the antenna circuit. Then, when the internal logic circuit is in a standby state of waiting for interrogation data from the interrogation device,
When the power received from the interrogation device is reduced to the minimum required power PL for recognizing the interrogation data, the power receiving efficiency of the antenna circuit is reduced, and when the interrogation data for the own device is received,
The capacity switching circuit is controlled so as to increase the power receiving efficiency so that the received power amount becomes the minimum required power amount PH (PL <PH) for generating and transmitting the response wave. As described above, according to the present invention, in the normal transmission mode in which the non-contact response device communicates with the interrogation device while receiving power supply from the interrogation device, the internal logic circuit controls the capacitance switching circuit, so that the non-contact response device When in the standby state, the impedance of the antenna circuit is changed to reduce the power receiving efficiency, and the power received from the interrogation device is reduced to the power PL.
When the contactless answering device receives the inquiry data from the interrogation device and enters the active state, the impedance of the antenna circuit is changed to increase the power receiving efficiency, and the amount of power received from the interrogation device is set to the power amount PH. Therefore, the power consumption of the contactless response device in the standby state can be reduced with a simple configuration.

Further, as one configuration example of the non-contact response device of the present invention, the capacitance switching circuit includes at least one pair of capacitance switches in which a capacitance element and an electronic switch are connected in series, and the capacitance switch is parallel to the antenna circuit. It is connected to the.
Thus, the impedance of the antenna circuit can be changed with a circuit having a simple configuration. Further, as one configuration example of the non-contact response device of the present invention, the non-contact response device further includes a voltage detection circuit that detects an output voltage of the rectifier circuit,
The internal logic circuit includes a plurality of the capacitance switches, and the internal logic circuit is configured to control an open / close state of each electronic switch in the capacitance switching circuit according to an output state of the voltage detection circuit. Thereby, even if the received power fluctuates depending on the output characteristics of the interrogation device and the mutual position and angle of the interrogation device and the non-contact response device, it is possible to appropriately reduce the received power. In one configuration example of the non-contact response device of the present invention, the non-contact response device is an IC card.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention uses a non-contact response device equipped with a capacity switching circuit capable of controlling a switch, dynamically controls impedance in a transmission state, and reduces the power consumption of the non-contact response device. It is characterized by controlling. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a non-contact communication system according to a first embodiment of the present invention. The contactless communication system of FIG. 1 includes a query device 1 and a contactless response device 2. The interrogation device 1 transmits an unmodulated carrier wave even at a time other than data transmission in order to supply power to the non-contact response device 2. When transmitting data, the interrogating device 1 and the contactless response device 2 modulate a carrier wave and superimpose the data.

The interrogator 1 includes a carrier wave generating circuit 10 for generating an unmodulated carrier wave, and a carrier wave generating circuit 1
It has an antenna circuit 11 for transmitting a non-modulated carrier wave or a modulated carrier wave output from 0, and for receiving a response wave transmitted from the non-contact response device 2. The antenna circuit 11 includes a coil L11 operating as an antenna and two capacitance elements C11 and C12. The coil L11 is connected in parallel with one capacitance element C11 and connected in series with the other capacitance element C12. ing. In FIG. 1, a modulation circuit that modulates a carrier wave when transmitting data, a demodulation circuit that receives and demodulates a response wave transmitted from the non-contact response device 2, and generates data to the non-contact response device 2 Circuits such as a control circuit for processing data demodulated by the demodulation circuit are omitted.

The contactless response device 2 includes an antenna circuit 20 for receiving a carrier wave transmitted from the interrogation device 1 and transmitting a response wave, and a capacitance switching circuit 21 for changing the impedance of the antenna circuit 20. And a rectifier circuit 22 for rectifying a carrier wave received by the antenna circuit 20 to obtain power for driving each circuit of the non-contact response device 2, and a constant voltage circuit 23 for converting an output voltage of the rectifier circuit 22 to a constant voltage.
And a demodulation circuit 24 for demodulating the modulated carrier wave received by the antenna circuit 20; and, when acquiring question data for the own device from the carrier wave, generating response data to the inquiry data and responding from the antenna circuit 20. And an internal logic circuit 25 that controls the capacity switching circuit 21 according to the communication state to change the impedance of the antenna circuit 20 and controls the amount of received power of the contactless response device 2. Circuit 26 for modulating a carrier wave with response data output from
And

The antenna circuit 20 includes a coil L21 operating as an antenna and two capacitance elements C21 and C22. The coil L21 is connected in parallel with one capacitance element C21 and connected to the other capacitance element C22. They are connected in series. Here, the inductance of the coil L21 and the capacitances of the two capacitive elements C21 and C22 are set such that the amount of received power of the antenna circuit 20 becomes a power level necessary and sufficient for all operations of the contactless response device 2. I have.

The capacitance switching circuit 21 includes a capacitance element Cv1,
For example, a capacitance switch CS in which an electronic switch S1 composed of a transistor or the like is connected in series is connected to the antenna circuit 20 in parallel. Here, the capacitance element Cv1
When the electronic switch S1 is closed and the capacitive element Cv1 is connected in parallel to the antenna circuit 20, the capacity of the antenna circuit 20 is at least the minimum required for normal reception of the query transmitted by the query device 1. The power level is set so that an appropriate margin is added to the power amount. In addition, a signal line for controlling opening and closing of the electronic switch S1 is connected between the electronic switch S1 and the internal logic circuit 25.

The rectifier circuit 22 is a full-wave rectifier circuit. The input side is connected to both ends of the capacitance switch CS of the capacitance switching circuit 21, and the output side is connected to the input side of the constant voltage circuit 23. The output side of the constant voltage circuit 23 is connected to each circuit that requires driving power. The internal logic circuit 25
It has a CPU 25a, a ROM 25b, a RAM 25c, a non-volatile memory 25d, and a counter 25e.

The power supplied from the interrogation device 1 to the contactless response device 2 is a function of the matching state of both impedances. When the power is matched, power is supplied with high efficiency, so that the reception power of the contactless response device 2 increases. If the matching mismatch occurs, the reflected power increases, and the received power of the contactless response device 2 decreases. Normally, the control of the impedance of the antenna circuit 20 is used for impedance matching for increasing the received power. However, in the present invention, in order to reduce extra power consumption of the non-contact response device 2, control for mismatching the impedance matching is performed. It is also characterized by being used for

Next, the operation of the contactless response device 2 will be described with reference to FIGS. FIG. 2 is a timing chart showing the timing of the inquiry from the interrogation device 1 and the response from the non-contact response device 2 and the received power amount of the non-contact response device 2 in that case in a time-series manner. In FIG. 2, the power level required and sufficient for the contactless response device 2 to perform the command processing is indicated by PH, and the minimum power required for the contactless response device 2 to normally receive the inquiry from the interrogation device 1. The power level obtained by adding an appropriate margin to the amount is indicated by PL. FIG.
5 is a flowchart showing the operation of the internal logic circuit 25 in FIG.

Here, the internal logic circuit 25 switches the capacitance by controlling the capacitance switching circuit 21 to change the impedance of the antenna circuit 20 in order to realize the states of PH and PL. The initial state of the capacity switching circuit 21 may correspond to either the state of PH or PL, but in consideration of performing an initialization process in the activation of the non-contact response device 2, the state of PH is set to the initial state. Is more preferable. In this embodiment, the capacitance switching circuit 21
The description will be made on the assumption that the initial state takes PH.

First, when the non-contact response device 2 is inserted into the region of the electromagnetic field generated by the interrogation device 1, the antenna circuit 20
Receives the carrier wave and feeds it to the rectifier circuit 22. The rectifier circuit 22 rectifies the carrier wave to generate a constant voltage
Supply 3 When the output voltage of the constant voltage circuit 23 exceeds a predetermined threshold value, the internal logic circuit 25 is reset to activate the internal logic circuit 25, and an initialization process is performed (step S11). During this initialization processing, since the capacity switching circuit 21 takes an initial state, the contactless response device 2
Is in the PH state.

When the initialization process is completed, the internal logic circuit 25 transitions to a standby state waiting for a question from the interrogation device 1, and determines whether a question addressed to itself has been received from the interrogation device 1 (step S12). . If the inquiry has not been received, a control signal for turning on the electronic switch S1 is output to the capacity switching circuit 21 (step S13), and the received power amount of the non-contact response device 2 is set to the PL state. Next, the state transits to the standby state, and returns to the reception determination in step S12.

When a question is received, the capacity switching circuit 2
1 to output a control signal for turning off the electronic switch S1 (step S14).
State. Next, a transition is made to the command processing state, and the command processing is executed (step S15). After the command processing, the state transits to the data transmission state and executes data transmission (step S16). When the data transmission is completed, the internal logic circuit 25 transitions to the standby state, and returns to the reception determination in step S12. Immediately after the data transmission is completed, no inquiry has been received, so that the received power of the non-contact response device 2 is controlled to be in the PL state. Non-contact response device 2
After the startup, the interrogation and the response are repeated with the interrogation device 1. By the above-described process, the power reception efficiency is reduced in the standby state, and the power reception efficiency is improved in response to the inquiry.

Here, the non-contact response device detection command, which is usually called polling, transmitted from the interrogation device 1 is, for example, a command transmitted by the interrogation device 1 when another non-contact response device already exists in the same electromagnetic field region. In the case of communication, etc., it is not emitted frequently. For this reason, if the power level is maintained in the PH state, the polling will be awaited for a long time at the PH, and the power efficiency of the entire non-contact communication system will be reduced.
This may hinder communication of other non-contact response devices. Therefore, when the initialization of the internal logic circuit 25 is completed,
Once, it is preferable to reduce the power level from PH to PL. In this embodiment, as described above,
It is determined whether a question addressed to itself has been received from the questioning apparatus 1 immediately after the transition to the standby state, and if no question has been received, the received power amount is set to PL. I have.

The operation of the above-described internal logic circuit 25 is as follows.
This is realized by the CPU 25a and a program for operating the CPU 25a. In this case, when the reset of the internal logic circuit 25 operates, the reset internal logic circuit 2
The CPU 25a controls the contactless response device 2 by reading predetermined data from the nonvolatile memory 25d based on a program stored in the ROM 25b. Also,
The CPU 25a uses the RAM 25c and the counter 25e as work areas for executing programs.

In the contactless response device 2 of this embodiment, when the received power amount is switched between PH and PL, the electronic switch S1 of the capacity switching circuit 21 is turned on in accordance with the operation state of the internal logic circuit 25. Since it is only necessary to turn off and change the impedance of the antenna circuit 20, the circuit configuration is simple, and miniaturization and cost reduction are possible. In the non-contact response device 2 of this embodiment, since the amount of change in impedance is fixed, the mutual
It is preferable to apply when conditions such as an angle are fixed.

In this embodiment, the case where the capacitance switching circuit 21 has one capacitance switch CS has been described, but a plurality of capacitance switches CS may be provided. In this case, the antenna circuit 2 is formed by combining a plurality of capacitance switches CS.
Since a plurality of zero impedances can be set, the combination of the capacitance switches CS to be used is stored in the non-volatile memory 25d, and the CPU 25a controls the capacitance switching circuit 21 so that the combination is used when the received power is switched to PL. Thus, it is possible to cope with the interrogation devices 1 having different output characteristics. In this way, it is not necessary to increase the number of types of the non-contact response device 2, so that a mass production effect can be expected, and costs for production management and inventory management can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram showing a second embodiment of the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals. The difference between the contactless response device 3 of this embodiment and the contactless response device 2 shown in the first embodiment is that the contactless response device 3 further includes a voltage detection circuit 27 for detecting the output voltage of the rectifier circuit 22; The capacitance switching circuit 21 has a plurality of capacitance switches CS1 to CSn, and the internal logic circuit 25 controls each of the electronic switches S1 to S1 of the capacitance switching circuit 21 in accordance with the output state of the voltage detection circuit 27.
n, the connection state of each of the capacitance elements Cv1 to Cvn is changed by a combination of the opening and closing of each of the electronic switches S1 to Sn, and the impedance of the antenna circuit 20 is changed so that the required reception power is minimized in the standby state. That's what we did.

Here, the voltage detection circuit 27 may be based on a known technique.
A device that converts and outputs a DC voltage of 5 V, a device that outputs a measured value as numerical data, a device that turns on at a set voltage or more, and the like are appropriately selected according to the configuration of the internal logic circuit 25, the usage application, the cost, and the like. It may be used. In the capacitance switching circuit 21, a plurality of capacitance switches CS1 to CSn are connected in parallel. Each of the electronic switches S1 to Sn is
One-to-one signal line to control opening and closing so that it can be opened and closed individually
Are connected to the internal logic circuit 25. The nonvolatile memory 25d of the internal logic circuit 25 stores data defining the combination of the output of the voltage detection circuit 27 and the opening and closing of each of the electronic switches S1 to Sn.
When a is in a standby state, the electronic switches S1 to Sn are simultaneously opened and closed in a combination according to the output of the voltage detection circuit 27.

Next, the operation of the non-contact response device 3 will be described with reference to FIGS. FIG. 5 is a flowchart showing the operation of the internal logic circuit 25 of FIG. Note that also in this embodiment, the description will be made on the assumption that the initial state of the capacitance switching circuit 21 is PH. First, when the non-contact response device 3 is inserted into the region of the electromagnetic field generated by the interrogation device 1, the carrier wave is received by the antenna circuit 20 and supplied to the rectifier circuit 22. The rectifier circuit 22 rectifies the carrier wave and supplies it to the constant voltage circuit 23. When the output voltage of the constant voltage circuit 23 exceeds a predetermined threshold, the reset of the internal logic circuit 25 is activated to activate the internal logic circuit 25, and an initialization process is performed (step S21). During this initialization process, since the capacity switching circuit 21 is in the initial state, the received power amount of the non-contact response device 3 is in the PH state.

When the initialization process is completed, the internal logic circuit 25 transitions to a standby state waiting for a question from the interrogation device 1, and determines whether a question addressed to itself has been received from the interrogation device 1 (step S22). . If no question has been received, the output state of the voltage detection circuit 27 is checked (step S23), and the open / close data of each of the electronic switches S1 to Sn corresponding to the output of the voltage detection circuit 27 is stored in the nonvolatile memory 2.
5d (step S24), a control signal for controlling the opening and closing of each of the electronic switches S1 to Sn is output to the capacitance switching circuit 21 based on the opening and closing data to switch the opening and closing state of each of the electronic switches S1 to Sn (step S25). ),
The received power amount of the non-contact response device 3 is set to the PL state. Next, the state transits to the standby state, and returns to the reception determination in step S22.

When a question is received, a control signal for opening all the electronic switches S1 to Sn is sent to the capacitance switching circuit 21.
(Step S26), and the received power amount of the non-contact response device 3 is set to the PH state. Next, a transition is made to the command processing state, and the command processing is executed (step S27).
After the command processing, the state transits to the data transmission state and executes data transmission (step S28). When the data transmission is completed, the internal logic circuit 25 transitions to the standby state, and returns to the reception determination in step S22. Immediately after the completion of the data transmission, since no inquiry has been received, the capacitance switching circuit 21 is controlled based on the output state of the voltage detection circuit 27. After starting, the non-contact response device 3 repeats a query and a response with the interrogation device 1. In the standby state, the non-contact response device 3 lowers the power receiving efficiency based on the output state of the voltage detection circuit 27 and receives a query. Repeat to improve the power receiving efficiency.

The operation of the above-described internal logic circuit 25 is as follows.
CPU 25a and CPU 25a as in the first embodiment.
Is realized by a program that operates. According to this embodiment, information on the received power can be obtained by the voltage detection circuit 27, and the impedance of the antenna circuit 20 can be variously changed by a combination of opening and closing of the electronic switches S1 to Sn in accordance with the information. Therefore, it is possible to more flexibly control the received power. Therefore, it is possible to cope with a change in the received power due to factors other than the input / output impedance of the non-contact response device 3, such as the output characteristics of the interrogation device 1 and the distance and angle between the interrogation device 1 and the non-contact response device 3. Therefore, it is possible to reduce an appropriate margin added to the minimum amount of power required for normally receiving the inquiry from the interrogation device 1 as provided in the first embodiment, and thus the standby state is established. Can be further reduced.

In this embodiment, each electronic switch S1
Although the opening and closing of .about.Sn are performed at the same time, the electronic switches S1 to Sn may be sequentially switched one by one to evaluate the received power and select the combination closest to the predetermined received power. In this case, compared to the case where the electronic switches S1 to Sn are simultaneously opened and closed, the fluctuation in impedance is small, and the operation of the internal logic circuit 25 is less likely to be unstable. It can be carried out.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the contactless response device according to the present invention will be described below. Since the impedance of the antenna circuit of the non-contact response device changes depending on the inductance of the coil L21, the capacitance of the two capacitance elements C21 and C22, the resistance component of the internal circuit, and the like, the capacitance of the capacitance element used in the capacitance switching circuit is generally I can not say. For this reason, it is necessary to first determine the characteristic value of the entire circuit and the PH and PL of the power consumption, and then obtain the capacity required to control the PH and PL. However, generally speaking, usually 10-5
Values between the 00 pF order are appropriate. This is because if the switching is performed at 10 pF or less, the degree of change in impedance is insufficient, and conversely, if the switching exceeds 500 pF, the change is too large.

[Embodiment 1] In Embodiment 1, the non-contact response device described in the first embodiment is applied to a non-contact IC card, and its configuration and operation are the same as those of the first embodiment. The description is omitted because it is the same as the embodiment. Referring to FIG. 1, the contactless IC card includes a capacity switching circuit 21.
Is composed of a capacitor having a capacitance of 100 pF, and the electronic switch S1 is composed of a field effect transistor (FET). This electronic switch S1
The signal to open and close is connected to the gate of the FET,
It is configured to be off (switch open) in the initial state. In the capacitance switching circuit 21, the reception power level is PH when the electronic switch S1 is off, and the power level is PL when the electronic switch S1 is on (switch closed).

When this non-contact IC card is inserted into an electromagnetic field of a reader / writer as the interrogating device 1, a capacitance switching circuit 2
No. 1 can receive PH level power in the initial state, and the internal logic circuit 25 is reset to an idle state. At this stage, the CPU 25a turns on the electronic switch S1 by determining that the CPU 25a is in the standby state for the question. As a result, the impedance of the antenna circuit 20 changes, and the reception power level changes in a time of several μs, and P
It becomes L. When a question is received from the reader / writer (interrogation device 1) while holding in this state, the CPU 25a
Turns off the electronic switch S1. As a result, the impedance of the antenna circuit 20 changes, and the received power level changes in a few μs to PH. After this, this 2
The state is repeated according to the communication state. This non-contact IC card can be used when performing data transmission in a state where the mutual position and angle with the reader / writer as the interrogating device 1 are fixed, and can reduce the amount of received power in the standby state.

[Second Embodiment] In a second embodiment, the non-contact response device described in the second embodiment is applied to a non-contact IC card, and its configuration and operation are the same as those of the second embodiment. The description is omitted because it is the same as the embodiment. Referring to FIG. 4, the contactless IC card includes a voltage detecting circuit 27.
Detects the output voltage of the rectifier circuit 22 and outputs a status to the internal logic circuit 25. Further, the capacitance switching circuit 21
Has a capacitance of 30 pF, 50 pF, and 100 pF.
It has two capacitance switches, and each capacitance switch is connected in parallel. In this case, the capacitance element is a capacitor, and the electronic switch is an FET. A signal for opening and closing each electronic switch is sent from the internal logic circuit 25 on a one-to-one basis to each F.
It is connected to the gate of the ET, and is configured to be off (switch open) in the initial state.

The capacitance switching circuit 21 is configured so that the received power level becomes PH when all the electronic switches are turned off, and the internal logic circuit 25 detects the communication state and the output state of the voltage detection circuit 27 based on the output state. To control each electronic switch. This non-contact IC card is obtained by the CPU 25a of the internal logic circuit 25 combining ON / OFF of three electronic switches according to the output state of the voltage detection circuit 27.
F, 50 pF, 80 pF, 100 pF, 130 pF, 1
Since an appropriate one can be selected and switched from the capacitance values of 50 pF and 180 pF｝, the output characteristics of the reader / writer (interrogation device 1) and the non-contact I / O
Even if the received power fluctuates depending on the mutual position and angle of the C cards, the received power can be appropriately reduced.

[0037]

According to the present invention, a capacitance switching circuit for changing the impedance of an antenna circuit is provided, and when the internal logic circuit enters a standby state of waiting for interrogation data from the interrogation device, the internal logic circuit switches from the interrogation device. The received power amount of the antenna circuit is reduced so that the received power amount of the antenna circuit becomes the minimum required power amount PL for recognizing the interrogation data. When the interrogation data for the own device is received, the received power amount is used to generate and transmit a response wave. With a simple configuration in which the capacity switching circuit is controlled so as to increase the power receiving efficiency of the antenna circuit so that the minimum required power amount PH (PL <PH), the power consumption in the transmission mode of the contactless response device is appropriately adjusted. The power consumption in the non-contact communication system can be improved because the power consumption in the standby state can be reduced and the power consumption in the standby state can be reduced. Door can be. Further, as a result of reducing the power consumption of the non-contact response device in the standby state, heat generation of the non-contact response device can be suppressed.

Further, since the capacitance switching circuit is constituted by a capacitance switch in which a capacitance element and an electronic switch are connected in series, and at least one set of this capacitance switch is provided and connected in parallel with the antenna circuit, a simple configuration is achieved. The impedance of the antenna circuit can be changed by the circuit. In addition, a voltage detection circuit for detecting an output voltage of the rectifier circuit is further provided, the capacitance switching circuit is constituted by a plurality of capacitance switches, and an internal logic circuit is connected to each electronic switch in the capacitance switching circuit according to an output state of the voltage detection circuit. The received power fluctuates depending on the output characteristics of the interrogation device and the mutual position and angle of the interrogation device and the non-contact response device, so that the received power is appropriately reduced. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a non-contact communication system according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing in chronological order the timing of the inquiry from the interrogation device and the response from the non-contact response device, and the received power amount of the non-contact response device at that time.

FIG. 3 is a flowchart showing an operation of the internal logic circuit of FIG. 1;

FIG. 4 is a block diagram illustrating a configuration of a contactless communication system according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing an operation of the internal logic circuit of FIG. 4;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Interrogation device, 2, 3 ... Non-contact response device, 10 ... Carrier wave generation circuit, 11, 20 ... Antenna circuit, 21 ... Capacitance switching circuit, 22 ... Rectification circuit, 23 ... Constant voltage circuit, 24 ...
Demodulation circuit, 25: internal logic circuit, 26: modulation circuit,
27: voltage detection circuit, 25a: CPU, 25b: RO
M, 25c RAM, 25d nonvolatile memory, 25e
Counter, C11, C12, C21, C22, Cv1
Cvn: capacitance element, CS, CS1 to CSn: capacitance switch, L11, L21: coil, S1 to Sn: electronic switch.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Yoshizawa 2-3-1 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor Tadao Takeda 2-3-3 Otemachi, Chiyoda-ku, Tokyo No. 1 Nippon Telegraph and Telephone Corporation F-term (reference) 2C005 MA29 MA31 NA09 TA22 5B035 CA13 CA23 5B058 CA17

Claims (4)

[Claims] An antenna circuit for receiving a carrier wave from an interrogation device and transmitting a response wave to the interrogation device, a rectifier circuit for obtaining driving power of the own device from the carrier wave received by the antenna circuit. An internal logic circuit that generates response data to the inquiry data when the interrogation data for the own device is obtained from the carrier wave, and transmits the response data as a response wave from the antenna circuit. A non-contact response device that receives power supply from the interrogation device and performs data communication with the interrogation device, further comprising: a capacitance switching circuit that changes an impedance of the antenna circuit; Is in a standby state waiting for interrogation data from the interrogation device, when the amount of power received from the interrogation device When the power receiving efficiency of the antenna circuit is reduced so that the power amount PL required for data recognition becomes the minimum, and the interrogation data for the own device is received, the received power amount is at least a minimum for generating and transmitting the response wave. A non-contact response device that controls the capacity switching circuit so as to increase the power receiving efficiency so that a required power amount PH (PL <PH) is satisfied. 2. The non-contact response device according to claim 1, wherein the capacitance switching circuit includes at least one set of a capacitance switch in which a capacitance element and an electronic switch are connected in series, and wherein the capacitance switch is connected to the antenna circuit. A non-contact response device which is connected in parallel. 3. The non-contact response device according to claim 2, further comprising: a voltage detection circuit that detects an output voltage of the rectifier circuit; wherein the capacitance switching circuit has a plurality of the capacitance switches; A non-contact response device, wherein the circuit is configured to control an open / close state of each electronic switch in the capacitance switching circuit according to an output state of the voltage detection circuit. 4. The non-contact response device according to claim 1, wherein the non-contact response device is an IC card.