JP2012059220A - Communication mode setting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication mode setting apparatus capable of extending a communication distance of wireless personal area communication and also executing actual communication without problems.SOLUTION: When confirming whether or not an electronic key 2 approaches a reader/writer 10, an RF circuit impedance is set low (a Q factor of an antenna 14 is set high), thereby setting an operation mode of the reader/writer 10 to a detection mode. Therefore, the approach of the electronic key 2 can be detected remotely. Furthermore, when the approach of the electronic key 2 is detected under the detection mode, the RF circuit impedance is set high (the Q factor of the antenna 14 is set low), thereby setting the operation mode of the reader/writer 10 to a communication mode. Therefore, after the approach of the electronic key 2, communication with the electronic key 2 can be established without problems.

Description

  The present invention relates to a communication mode setting device for setting an operation mode of a communication master.

  Conventionally, for example, NFC (Near Field Communication) has been widely used as wireless communication between two parties (see, for example, Patent Document 1). NFC includes, for example, Mifare and Felica (both are registered trademarks). In NFC, a reader / writer is installed in a communication master. When a tag is placed over the reader / writer, bidirectional communication is started. Specifically, the tag is activated by the driving radio wave transmitted from the reader / writer, and the tag returns data to the reader / writer. The tag consists of a very small IC chip.

Japanese Patent Laid-Open No. 10-266651

  By the way, the communication distance of this type of NFC is very short, for example, 10 cm or less in order to satisfy the Radio Law and ISO standards. However, there is a need to extend the communication distance and capture the electronic key from a distance. In this case, in order to extend the communication distance of the reader / writer, simply switching the characteristic value of the circuit element does not conform to the communication standard and regulations, and communication is not established. .

  An object of the present invention is to provide a communication mode setting device that can extend the communication distance of short-range wireless communication and can perform actual communication without any problem.

  In order to solve the above problems, in the present invention, in a communication mode setting device in which a communication master and its communication terminal communicate via short-range wireless communication using a magnetic field as a radio wave, the communication terminal serves as the communication master. A distance detecting means for detecting an approaching distance when approaching, a variable impedance setting element serving as an element for determining an impedance on the antenna side of the communication master, and the impedance when monitoring the approach of the communication terminal By setting the operation mode of the communication master to a first mode in which communication is not established but the transmission magnetic field intensity of radio waves is high, and the approach of the communication terminal is detected in the first mode, the impedance is By increasing the operating mode of the communication master, the transmission magnetic field strength is lower than that of the first mode, but communication can be executed. And summarized in that and a mode switching means for switching to the second mode.

  According to this configuration, when the communication master monitors the approach of the communication terminal, the Q value (resonance sharpness) of the antenna of the communication master is increased by lowering the impedance on the antenna side of the communication master (first mode). . As a result, although actual communication is not established, the transmission magnetic field strength of the communication master is increased, so that the communication area of the communication master can be widened. Therefore, the communication master can capture the communication terminal from a far position. At this time, since it is only necessary to detect whether or not the communication terminal is approaching, there is no problem even if actual communication is not established.

  When the communication master detects the approach of the communication terminal in the first mode, the Q value of the communication master is lowered (second mode) by increasing the impedance on the antenna side of the communication master. Therefore, since actual communication is possible if the Q value of the antenna is kept low, the communication master can establish communication with a communication terminal that is close without any problem. For this reason, the approach of the communication terminal can be monitored in a wide range, and actual communication can be executed without any problem.

  In the present invention, based on a variable transmission intensity setting element as one element when determining the transmission magnetic field intensity of the antenna of the communication master, and when the communication master is in the second mode, the detection value of the distance detection means is used. Further, the present invention includes an area setting unit that sets the transmission magnetic field strength of the communication master by adjusting the transmission strength setting element.

  According to this configuration, when the communication terminal approaches the communication master after the communication master enters the second mode, for example, when the approach distance is shortened, the transmission magnetic field strength of the communication master is switched to a low value. That is, when the communication terminal suddenly approaches the communication master under the second mode, the communication area is switched to a narrow range. For this reason, since it becomes difficult to apply an excessive voltage to a communication terminal, it becomes possible to make it difficult to produce a breakdown in the circuit of a communication terminal.

In the present invention, the impedance setting element is a variable capacitance component provided in a matching circuit of the communication master, and the mode switching means adjusts the variable capacitance component to adjust the communication The gist is to switch the operation mode of the master.
According to this configuration, the impedance on the antenna side of the communication master can be switched using the electrostatic capacitance component of the matching circuit provided in the communication master.

  In the present invention, the transmission strength setting element includes a variable capacitance component used also as the impedance setting element provided in the matching circuit of the communication master, and a variable dump resistor provided in the antenna of the communication master. The area setting means sets the transmission magnetic field strength of the communication master by adjusting the variable capacitance component and the variable dump resistor.

  According to this configuration, it is possible to adjust the transmission magnetic field strength of the communication master using both the variable capacitance component and the variable dump resistor, so that the transmission magnetic field strength can be efficiently and efficiently over a wide range. Can be switched.

The gist of the present invention is that the second mode is set to a mode in which communication is always performed.
According to this configuration, in the second mode, since the communication master always tries to communicate with the communication terminal, short-range wireless communication is immediately started when the communication terminal enters the communication area of the communication master. Therefore, the boundary line of the communication area of the communication master is exactly the boundary of whether communication is possible or not, so that it is possible to apparently extend the communication area of short-range wireless communication.

  According to the present invention, the communication distance of near field communication can be extended, and actual communication can be executed without any problem.

The block diagram of the communication area setting apparatus of one Embodiment. The conceptual diagram which shows the example of the arrangement position of a reader / writer, and a communication area. (A), (b) is explanatory drawing which shows the modulation waveform and spectrum which are transmitted from an antenna. The time chart which shows the communication sequence of NFC. The graph which shows correlation with approach distance and antenna current. (A)-(c) is explanatory drawing which shows the transition of the area change of a reader / writer. The graph which shows the correlation with the approach distance and antenna current in each mode. The graph which shows correlation with RF circuit impedance and communication distance. Explanatory drawing which shows the communication aspect of polling type NFC. The block diagram of the communication area setting apparatus in another example. The block diagram of the communication area setting apparatus in another example. The circuit diagram of the reader / writer in another example. The circuit diagram of the reader / writer in another example.

Hereinafter, an embodiment of a communication mode setting device embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1, the vehicle 1 is provided with an electronic key system 3 that executes ID verification by short-range wireless communication with the electronic key 2. The near field communication is so-called NFC (Near Field Communication), and for example, Mifare, Felica (both are registered trademarks) and the like are used. In this electronic key system 3, door lock / unlock is permitted or executed when ID verification (external vehicle verification) is established outside the vehicle, and engine start is permitted when ID verification (in-vehicle verification) is established inside the vehicle. The electronic key 2 corresponds to a communication terminal.

  In this case, the vehicle 1 includes a key verification device 4 for verifying the ID code of the electronic key 2, a door lock device 5 for managing the locking / unlocking operation of the vehicle door, and an engine starter 6 for managing the operation of the engine. Provided, and these are connected via an in-vehicle bus 7. Among these, the key collating device 4 is provided with a collation ECU 8 that performs a collation operation of the ID code. The engine starter 6 is connected to a push momentary engine switch 9 that is operated when the power state of the vehicle 1 is switched.

  A reader / writer 10 is connected to the verification ECU 8 as a communication device on the vehicle 1 side of the electronic key system 3. The reader / writer 10 writes and reads various data to and from the electronic key 2 that is a communication partner. Note that the reader / writer 10 is provided outside the vehicle and inside the vehicle in order to perform the vehicle exterior verification and the vehicle interior verification, but in the case of this example, these are illustrated as one reader / writer 10 for convenience. The reader / writer 10 corresponds to a communication master.

  The reader / writer 10 is provided with a reader / writer control ECU 11 that manages short-range wireless communication with the electronic key 2. An antenna 14 for near field communication is connected to the reader / writer control ECU 11 via a communication circuit 12 and a filter 13. The antenna 14 is a magnetic field antenna that transmits and receives a magnetic field as radio waves. For example, a loop antenna is used. The antenna 14 transmits and receives radio waves in, for example, an HF (High Frequency: 13.56 MHz) band.

  The antenna 14 is provided with a matching circuit 15 having a plurality of electrostatic capacitance components, a dump resistor 16 that suppresses the Q value (resonance sharpness) of the signal waveform, and an antenna coil 17 having an inductance component. The antenna 14 is composed of a resonance circuit of L of the antenna coil 17, C of the matching circuit 15, and R of the dump resistor 16. Since the antenna 14 is a magnetic field antenna in the HF band, as shown in FIG. 2, a substantially circular communication area E is formed in plan view. The matching circuit 15 and the dump resistor 16 constitute a transmission intensity setting element.

The Q value is calculated by the following equation, where f is the resonance frequency, L is the inductance of the antenna coil 17, and R is the copper loss of the dump resistor 16 and the antenna coil 17.
Q = (2πfL) / R
Therefore, it can be seen that if the resistance value of the dump resistor 16 is set to a large value, the Q value can be kept low. By the way, as shown in FIG. 3A, if the Q value is high, the modulation waveform of the transmission radio wave is distorted and takes a waveform like a triangular wave, leading to the possibility that the radio wave bit cannot be accurately determined. However, as shown in FIG. 3B, if the Q value is suppressed to a low value, the transmission band is widened, and as a result, the modulation waveform of the transmission radio wave approaches a rectangular wave. Therefore, in order to ensure accurate bit determination, the dump resistor 16 is connected to the antenna 14 to lower the Q value.

  However, the resistance value of the dump resistor 16 is not simply increased. If the resistance value is increased more than necessary, the loss due to the resistance increases and the magnetic field strength decreases. Further, there is a suitable target value also from the relationship with the matching condition with the output impedance of the communication circuit 12.

The communication circuit 12 illustrated in FIG. 1 modulates a radio wave transmitted from the antenna 14 or demodulates a radio wave received by the antenna 14.
The filter 13 is composed of, for example, a band-pass filter or a low-pass filter, and cuts components other than a sine wave, that is, harmonic components from the signal.

  The electronic key 2 is a so-called IC tag that performs near field communication with the reader / writer 10. The electronic key 2 is not limited to what is apparently a key, and includes, for example, a mobile phone and an IC card. The electronic key 2 is provided with a communication control circuit 18 that manages the operation of the electronic key 2. In the communication control circuit 18, the ID code of the electronic key 2 is registered.

  An antenna 19 for near field communication is connected to the communication control circuit 18. For example, a loop antenna is used as the antenna 19 as a kind of magnetic field antenna. The antenna 19 is composed of a parallel resonance circuit including an antenna coil 20 and a resonance capacitor 21. Since the electronic key 2 operates to maximize the voltage generated by electromagnetic induction, the electronic key 2 takes parallel resonance. The antenna 19 is a transmission / reception antenna, and transmits and receives HF band radio waves, for example.

  For example, when the vehicle 1 is in a parked state or when the user gets on the reader / writer 10, as shown in FIG. 4, the reader / writer 10 enters a transmission operation using the antenna 14 as a transmission antenna, Transmit intermittently at polling intervals. The drive radio wave Sv includes a power radio wave Vpw serving as a power source for the electronic key 2 and a request signal Srq as a key ID return request.

  The drive radio wave Sv in this example is composed of one frame of Vpw + Srq + Vpw, and this frame is transmitted intermittently. In the communication of the reader / writer 10, the electronic key 2 is activated by the first power radio wave Vpw, an ID reply is requested by the subsequent request signal Srq, and the ID code is returned to the electronic key 2 by the last power radio wave Vpw.

  The reader / writer control ECU 11 transmits the driving radio wave Sv from the antenna 14 and operates the receiving circuit to wait for a response from the electronic key 2. Then, the reader / writer control ECU 11 repeatedly performs the transmission and reception operations at predetermined time intervals until radio waves are received from the electronic key 2.

  When the electronic key 2 enters the communication area E of the drive radio wave Sv and receives the drive radio wave Sv, the electronic key 2 is activated using the power radio wave Vpw as a power source and transmits the ID signal Sid from the antenna 19 in response to the request signal Srq. . The ID signal Sid includes the ID code of the electronic key 2. Since the reader / writer 10 communicates with the electronic key 2 by a magnetic field coupling method, the reader / writer 10 receives a radio wave from the electronic key 2 with a change in transmission waveform. When the reader / writer control ECU 11 receives the ID signal Sid by the antenna 14, the reader / writer control ECU 11 transfers the ID code in the ID signal Sid to the verification ECU 8. When the ID code is input from the reader / writer control ECU 11, the verification ECU 8 performs ID verification, and if ID verification is established, permits or executes door lock locking / unlocking and engine start.

  The electronic key system 3 is provided with a communication area setting device 22 that sets the communication area E of the reader / writer 10 (antenna 14) according to the distance from the electronic key 2 (referred to as an approach distance r). When the approach distance r is reduced, the communication area setting device 22 of this example sets the transmission magnetic field strength of the reader / writer 10 to be low and switches the communication area E (see FIG. 2) of the reader / writer 10 to a small range. This is to prevent an excessive voltage from being induced in 2.

  A high impedance resistor 23 for detecting the antenna current Ia is connected to the dump resistor 16 in parallel. Incidentally, as shown in FIG. 5, there is a correlation between the approach distance r and the antenna current Ia in which the antenna current Ia decreases as the approach distance r decreases. This is because the power of the antenna 14 is transmitted to the electronic key 2 by the approach of the electronic key 2, and the antenna current Ia that is the source of the magnetic field energy that the antenna 14 has decreases. In other words, the magnetic field energy of the antenna 14 moves to the electronic key 2 and an induced current flows in the reverse direction through the resonance circuit of the antenna 14, so that the energy acts in the direction of losing the magnetic field. The Hi impedance resistor 23 detects the antenna current Ia by detecting the induced voltage Vs (see FIG. 1) between the terminals of the dump resistor 16. Note that the Hi impedance resistor 23 constitutes a distance calculating means.

  As shown in FIG. 1, the vehicle 1 is provided with an area setting circuit 24 that sets a communication area E of the reader / writer 10. The area setting circuit 24 is composed of, for example, a one-chip IC independent of the reader / writer control ECU 11. The area setting circuit 24 may be formed in the reader / writer control ECU 11.

  The area setting circuit 24 is provided with an approach distance calculation unit 25 that calculates an approach distance r to the electronic key 2 based on the antenna current Ia flowing through the Hi impedance resistor 23. The approach distance calculation unit 25 calculates the approach distance r to the electronic key 2 based on the induced voltage Vs obtained by the Hi impedance resistor 23. The approach distance calculation unit 25 constitutes a distance calculation unit.

  The area setting circuit 24 is provided with a mode switching unit 26 for switching the operation mode of the reader / writer 10 based on the approach distance calculated by the approach distance calculating unit 25 based on r. The mode switching unit 26 of the present example initially sets the operation mode of the reader / writer 10 to a mode (detection of a wide area (Ea shown in FIG. 6A)) in which communication cannot be performed but the approach of the electronic key 2 can be determined. Mode) and the presence or absence of the electronic key 2 is monitored. When the approach of the electronic key 2 is detected in the detection mode, the operation mode of the reader / writer 10 is set to a mode (communication mode) of a small area (Eb shown in FIG. 6B) that can perform communication. Try to execute the actual communication. The mode switching unit 26 corresponds to mode switching means.

  As shown in FIG. 1, the capacitors C1 and C2 of the matching circuit 15 are T-shaped and employ a variable type capable of switching the capacitance value. For these capacitors C1 and C2, variable capacitance diodes such as varicap diodes and varactor diodes are used. The capacitance values of the capacitors C1 and C2 are controlled by the mode switching unit 26. Capacitors C1 and C2 constitute an impedance setting element, a transmission intensity setting element, and a variable capacitance component.

  The mode switching unit 26 sets the operation mode of the reader / writer 10 to one of the detection mode and the communication mode by controlling the capacitors C1 and C2 based on the approach distance r calculated by the approach distance calculation unit 25. . In other words, when monitoring whether the electronic key 2 is approaching, the mode switching unit 26 lowers the value of the capacitor C1 and increases the value of the capacitor C2, thereby increasing the impedance on the antenna side (hereinafter referred to as the communication circuit 12). , RF circuit impedance) is lowered, and the operation mode of the reader / writer 10 is set to the detection mode. When the RF circuit impedance is lowered, the RF circuit impedance approaches the output impedance of the communication circuit 12 (hereinafter referred to as IC circuit impedance), and the antenna current Ia easily flows. For this reason, the transmission magnetic field intensity of the antenna 14 becomes high, and as a result, the communication area E of the reader / writer 10 becomes wide.

  In the detection mode, since the Q value of the antenna 14 becomes high, the modulation waveform becomes a triangular wave, and actual communication cannot be performed. However, on the contrary, as shown in FIG. 7, since the change in the electrical characteristics due to the approach of the electronic key 2, that is, the antenna current Ia is increased, the presence / absence of the approach of the electronic key 2 can be detected more sensitively. .

  When the mode switching unit 26 detects the approach of the electronic key 2 in the detection mode, the value of the capacitor C1 is increased and the value of the capacitor C2 is decreased, thereby increasing the RF circuit impedance and the operation of the reader / writer 10. Set the mode to communication mode. When the reader / writer 10 is in the communication mode, since the RF circuit impedance is larger than the IC circuit impedance, the Q value of the antenna 14 is lowered. Therefore, the signal waveform takes a rectangular wave, and actual signal decoding is possible.

  As the dump resistor 16, a variable type capable of switching the resistance value is used. Since the variable dump resistor 16 is an element of the resonance circuit, the variable dump resistor 16 is also an element related to the transmission magnetic field strength of the antenna 14, that is, the communication area E of the reader / writer 10. Therefore, when the resistance value of the variable dump resistor 16 is switched, the current flowing through the antenna 14 (hereinafter referred to as the antenna current Ia) changes, and the transmission magnetic field of the reader / writer 10 also changes. When the variable dump resistor 16 is set low, the communication area E is widened, and when the variable dump resistor 16 is set high, the communication area E is narrowed.

  The area setting circuit 24 is provided with an area setting unit 27 for setting the communication area E of the reader / writer 10 based on the approach distance r calculated by the approach distance calculating unit 25 when the reader / writer 10 is in the communication mode. . The area setting unit 27 switches the value of the antenna current Ia by adjusting the values of the variable dump resistor 16 and the capacitors C1 and C2 based on the approach distance r when the reader / writer 10 is in the communication mode. 10 transmission magnetic field strengths, that is, the communication area E of the reader / writer 10 is set. The area setting unit 27 corresponds to area setting means.

  When the reader / writer 10 monitors whether the electronic key 2 is approaching, the mode switching unit 26 lowers the capacitor C1 of the matching circuit 15 and raises the capacitor C2 while minimizing the variable dump resistor 16. Thus, the operation mode of the reader / writer 10 is set to the detection mode. At this time, since the RF circuit impedance is low, the antenna current Ia easily flows through the circuit. Therefore, the communication area E of the reader / writer 10 becomes a wide range Ea shown in FIG. 6A, and the approach of the electronic key 2 can be monitored over a wide range.

  The reader / writer 10 monitors the approach of the electronic key 2 at a predetermined polling interval in the detection mode. That is, the reader / writer 10 repeatedly performs the operation of transmitting the driving radio wave Sv from the antenna 14 and waiting for the radio wave by receiving rotation at predetermined intervals.

  At this time, the approach distance calculation unit 25 monitors whether the electronic key 2 is approaching based on the induced voltage Vs of the Hi impedance resistor 23. When the reader / writer 10 is in the detection mode, when the electronic key 2 enters the communication area Ea, the antenna current Ia decreases and the approach distance calculation unit 25 recognizes the approach of the electronic key 2. When the approach distance calculation unit 25 detects the approach of the electronic key 2 in the detection mode, the approach distance calculation unit 25 outputs a key approach notification to the mode switching unit 26. FIG. 6 shows two examples of the case where the electronic key 2 enters the communication area Ea from the side and the case where the electronic key 2 enters from the opposite side.

  When a key approach notification is input in the detection mode, the mode switching unit 26 switches the operation mode of the reader / writer 10 from the detection mode to the communication mode. That is, the mode switching unit 26 switches the operation mode of the reader / writer 10 to the communication mode by setting the variable dump resistor 16 to the minimum value and increasing the capacitor C1 of the matching circuit 15 and decreasing the capacitor C2. . At this time, since the RF circuit impedance becomes high, it becomes difficult for the antenna current Ia to flow through the circuit. Therefore, the communication area E of the reader / writer 10 is reduced to a narrow range Eb shown in FIG.

  In the communication mode, since the RF circuit impedance is set high, the Q value of the antenna 14 takes a low value. Therefore, since the communication band of the antenna 14 is ensured, actual communication can be executed. For this reason, when the electronic key 2 enters the communication area Eb, communication is established.

  Further, the reader / writer 10 always activates the antenna 14 in the communication mode and tries to communicate with the electronic key 2. That is, the reader / writer 10 repeatedly performs the transmission operation and the reception operation with the antenna 14 in the communication mode.

  When the reader / writer 10 is in the communication mode, the area setting unit 27 sets the communication area E in a range corresponding to the approach distance r. That is, as shown in FIG. 6C, the area setting unit 27 suppresses the antenna current Ia by adjusting the variable dump resistor 16 and the capacitors C1 and C2 to a value corresponding to the approach distance r. The transmission magnetic field strength (communication area E) of the antenna 14 is reduced. At this time, the communication area E is narrowed by increasing the variable dump resistor 16, increasing the capacitor C1, and further decreasing the capacitor C2.

  By the way, as shown in FIG. 6C, when the electronic key 2 suddenly approaches the reader / writer 10 from the side, an excessive voltage is suddenly applied to the electronic key 2, and this causes a circuit breakdown of the electronic key 2. May lead to However, in the case of this example, the transmission magnetic field strength of the reader / writer 10 is kept low according to the approach distance r of the electronic key 2, so even if the electronic key 2 suddenly approaches the reader / writer 10 from the side, Excessive voltage is not induced. Therefore, circuit breakdown is unlikely to occur in the electronic key 2.

  Here, the standard for short-range wireless communication includes the ISO standard in which the magnetic field strength applied to the electronic key 2 in communication must be suppressed to a constant value. This means that the induced voltage is suppressed below a certain value. In the case of this example, the driving radio wave Sv is transmitted from the antenna 14 with a strong transmission magnetic field intensity in the approach detection of the electronic key 2, but even if the electronic key 2 receives the driving radio wave Sv in this situation, the communication start initial stage At that time, since the distance from the antenna 14 to the electronic key 2 is long, the voltage actually applied to the electronic key 2 falls within a low value. Therefore, even if the driving radio wave Sv is transmitted with a strong magnetic field strength for detecting the approach of the electronic key 2, there is no conflict with the standard.

  Since the transmission magnetic field strength of the reader / writer 10 that must be satisfied by the radio wave method is a very high value, even if the transmission magnetic field strength of the reader / writer 10 is increased to extend the communication distance in this example, this radio wave method is used. The value is within the range of. Therefore, in this example, the Radio Law complies with no problem.

  FIG. 8 shows the correlation between the RF circuit impedance and the communication distance. As shown in the figure, when the operation mode of the reader / writer 10 is switched from the detection mode to the communication mode by increasing the RF circuit impedance, it can be seen that communication is possible although the communication distance is shortened (black from the white point). To the point of fill).

  In addition to changing the impedance only with the capacitors C1 and C2, for example, if the dump resistor 16 is increased, the curve can be translated as shown by the alternate long and short dash line shown in FIG. . In this way, the communication distance can be changed dramatically, so that the communication mode can be switched to various modes by the combination of the capacitors C1 and C2 and the variable dump resistor 16.

  As described above, in this example, when the approach of the electronic key 2 is detected (detection mode), the RF circuit impedance is lowered to increase the Q value of the antenna 14 to increase the sensitivity. When communicating (communication mode), the communication circuit band is secured by lowering the Q value of the antenna 14 by increasing the RF circuit impedance. Therefore, while monitoring the presence / absence of the electronic key 2 in a wide area, during actual communication, the Q value is lowered to secure a communication band, so that the actual communication is a problem while extending the detection distance of the electronic key 2. It becomes possible to execute without.

  In the case of this example, when the approach of the electronic key 2 is detected, the communication mode is immediately entered to establish communication with the electronic key 2. Therefore, as shown in FIG. 9, what has been established only at the polling interval until now becomes established when the electronic key 2 enters the communication area Eb in this example. Therefore, the communication area E of the reader / writer 10 can be apparently extended.

  Furthermore, when the reader / writer 10 is in the communication mode, the transmission magnetic field strength of the antenna 14 is suppressed to a low level according to the approach distance r. Therefore, as shown in FIG. 6C, even when the electronic key 2 suddenly moves from the side into the communication area Eb of the reader / writer 10, the transmission magnetic field strength of the antenna 14 corresponds to the approach distance r. Since the value is lowered, an excessive voltage is not applied to the circuit of the electronic key 2, and it is possible to prevent the electronic key 2 circuit from being broken.

According to the configuration of the present embodiment, the following effects can be obtained.
(1) When checking whether or not the electronic key 2 is close to the reader / writer 10, the operation mode of the reader / writer 10 is detected by setting the RF circuit impedance low (increasing the Q value of the antenna 14). Set to mode. For this reason, since the transmission magnetic field intensity of the antenna 14 becomes strong, the approach of the electronic key 2 can be detected from a distance. When the approach of the electronic key 2 is detected in the detection mode, the operation mode of the reader / writer 10 is set to the communication mode by setting the RF circuit impedance high (decreasing the Q value of the antenna 14). Therefore, even if the reader / writer 10 cannot be communicated but is set to a detection mode in which the approach of the electronic key 2 can be detected so that the electronic key 2 can be detected from a distance at the beginning, Communication with the key 2 can be established without any problem.

  (2) When the reader / writer 10 is in the detection mode, since the Q value of the antenna 14 is high, a change in electrical characteristics due to the approach of the electronic key 2, that is, a change in the antenna current Ia becomes large. Therefore, since the reader / writer 10 can be said to have high sensitivity in the detection mode, the electronic key 2 can be detected with high sensitivity.

  (3) Even when the reader / writer 10 is in the communication mode, the transmission magnetic field strength (communication area E) of the reader / writer 10 is adjusted to a value corresponding to the approach distance r between the electronic key 2 and the reader / writer 10. That is, when the reader / writer 10 is in the communication mode, when the electronic key 2 approaches the reader / writer 10, the transmission magnetic field strength of the reader / writer 10 is switched to a low value accordingly. For this reason, it is difficult to apply an excessive voltage to the electronic key 2, so that the circuit of the electronic key 2 can be hardly damaged.

  (4) Both the dump resistor 16 and the capacitors C1 and C2 are made variable, and the transmission magnetic field strength of the reader / writer 10 is switched by adjusting both the variable dump resistor 16 and the capacitors C1 and C2. Therefore, the transmission magnetic field strength of the reader / writer 10 can be efficiently switched over a wider range.

  (5) For example, when the transmission magnetic field strength of the reader / writer 10 is lowered only with the variable dump resistor 16, when the resistance value of the variable dump resistor 16 is increased, the RF circuit impedance decreases so as to approach the IC circuit impedance. Therefore, as a result, impedances are matched, leading to a problem that the current flowing through the antenna 14 increases. However, in the case of this example, when the transmission magnetic field strength of the reader / writer 10 is lowered, the impedance is increased by the capacitors C 1 and C 2 of the matching circuit 15. Is compensated by capacitors C1 and C2. Therefore, even if the variable dump resistor 16 is increased to reduce the transmission magnetic field strength of the reader / writer 10, it is possible to make it difficult to match the RF circuit impedance and the IC circuit impedance, so that the current consumption is also kept low. Can do.

  (6) When the reader / writer 10 enters the communication mode, the reader / writer 10 does not operate at a polling interval, but always attempts to establish communication, so the electronic key 2 enters the communication area E of the reader / writer 10. At that time, communication is started immediately. Therefore, since the boundary line of the communication area E of the reader / writer 10 becomes the boundary of whether communication is possible or not, the NFC communication range can be extended apparently.

Note that the embodiment is not limited to the configuration described so far, and may be modified as follows.
The distance detecting means is not limited to the Hi impedance resistor 23. By the way, the RF circuit impedance has a value that changes depending on the approach distance of the electronic key 2. Therefore, as shown in FIG. 10, an impedance detection unit 31 may be provided in the area setting circuit 24, and the approach distance r may be calculated based on the RF circuit impedance detected by the impedance detection unit 31. In this case, the impedance detector 31 constitutes a distance detector.

  The distance detection means is not limited to the Hi impedance resistor 23 or the impedance detection unit 31. Here, the current (consumption current Ib) supplied from the reader / writer control ECU 11 to the antenna 14 changes according to the approach distance r of the electronic key 2. Therefore, as shown in FIG. 11, a current detection unit 41 may be provided between the reader / writer control ECU 11 and the communication circuit 12, and the approach distance r may be calculated from the consumption current Ib detected by the current detection unit 41. . In this case, the current detection unit 41 constitutes a distance detection unit.

  As shown in FIG. 12, a Hi impedance resistor 23 may be connected in parallel with the resonance circuit of the antenna 14, and the antenna current Ia may be detected by the induced voltage Vs of the Hi impedance resistor 23.

  As shown in FIG. 13, by setting the dump resistor 16 as a fixed value resistor, connecting the shunt resistor 51 capable of adjusting the antenna current Ia in parallel to the resonance circuit of the antenna 14, and adjusting the value of the shunt resistor 51, The transmission magnetic field strength of the antenna 14 may be changed.

The distance detection means may be a proximity sensor provided separately in the reader / writer 10.
The detection of the antenna current Ia is not limited to the method of viewing the voltage across the dump resistor 16. For example, an ammeter may be provided in the resonance circuit, and the antenna current Ia may be detected directly from the value of the ammeter.

  The impedance setting element is not limited to the capacitors C1 and C2 of the matching circuit 15, and other elements may be adopted. Further, an electronic component other than the matching circuit 15 may be used as the impedance setting element.

The first mode may be anything as long as the electronic key 2 can be detected from a distance. The second mode only needs to be a mode in which the electronic key 2 can be actually communicated.
The adjustment of the transmission magnetic field strength of the reader / writer 10 in the communication mode is not limited to the adjustment by adjusting both the variable dump resistor 16 and the capacitors C1 and C2. For example, only one of these two parties may be adjusted.

The driving radio wave Sv is not limited to being transmitted with only one frame, and may be transmitted with a plurality of frames.
In the communication mode, the transmission magnetic field strength of the reader / writer 10 is not limited to being variable according to the approach distance r, and may be fixed.

  The electronic key system 3 may employ either a polling type or a trigger type. In the polling method, the drive radio wave Sv is constantly intermittently transmitted to search for the presence or absence of the electronic key 2. The trigger type starts transmission of the drive radio wave Sv using a predetermined operation such as a touch operation on a door handle outside the vehicle as a trigger.

Short-range wireless communication is not limited to NFC, and any communication format may be adopted as long as it uses a magnetic field as a radio wave.
The frequency of short-range wireless communication is not limited to HF, and other bands such as LF (Low Frequency) and UHF (Ultra High Frequency) may be employed.

The transmission intensity setting element is not limited to the dump resistor 16 and the shunt resistor 51, and other elements can be used.
The change of the communication area is not limited to the change of the range but may be the directivity of the antenna 14.

The arrangement place of the reader / writer 10 may be, for example, a vehicle exterior door mirror.
In addition to the NFC electronic key system 3, the vehicle 1 may be provided with a key operation free system or a wireless key system. The key operation free system has a wider communication area than NFC, for example, a system using LF or UHF as a frequency. The wireless key system is a system that performs collation by using communication from the electronic key 2 as a trigger.

The communication area setting device 22 is not limited to being used for the vehicle 1 and may be applied to other devices and apparatuses.
Next, technical ideas that can be grasped from the above-described embodiment and other examples will be described below together with their effects.

  (A) In any one of claims 1 to 5, the communication master uses one antenna as a transmission / reception antenna. According to this configuration, the number of antennas can be reduced.

  (B) In any one of claims 1 to 5 and the technical idea (a), the communication master transmits an inquiry from an antenna to the communication terminal, waits for a response of the communication terminal to the inquiry, and performs this transmission / reception The above operation is repeated until the response is received from the communication terminal. According to this configuration, it is possible to monitor whether the communication terminal is approaching at a polling interval.

  2 ... an electronic key as a communication terminal, 10 ... a reader / writer as a communication master, 14 ... an antenna, 15 ... a matching circuit, 16 ... a variable dump resistor constituting a transmission intensity setting element, 23 ... a Hi constituting a distance calculation means Impedance resistance, 25... Proximity distance calculation unit constituting distance calculation means, 26... Mode switching part as mode switching means, 27... Area setting part as area setting means, r .. approach distance, C1, C2. , A capacitor constituting a transmission intensity setting element and a variable capacitance component.

Claims (5)

In a communication mode setting device in which a communication master and its communication terminal communicate via short-range wireless communication using a magnetic field as a radio wave,
Distance detecting means for detecting an approach distance when the communication terminal approaches the communication master;
A variable impedance setting element that becomes one element when determining the impedance of the antenna side of the communication master;
When monitoring the approach of the communication terminal, by setting the impedance low, the operation mode of the communication master is set to a first mode in which radio wave transmission magnetic field strength is high although communication is not established, Mode switching means for switching the operation mode of the communication master to a second mode in which the transmission magnetic field strength is lower than that in the first mode but communication can be performed by detecting the approach of the communication terminal by increasing the impedance; A communication mode setting device comprising: A variable transmission intensity setting element that is one element when determining the transmission magnetic field intensity of the antenna of the communication master;
When the communication master is in the second mode, there is provided area setting means for setting the transmission magnetic field strength of the communication master by adjusting the transmission strength setting element based on the detection value of the distance detection means. The communication mode setting device according to claim 1, wherein: The impedance setting element is a variable capacitance component provided in the matching circuit of the communication master,
The communication mode setting device according to claim 1, wherein the mode switching unit switches an operation mode of the communication master by adjusting the variable capacitance component. The transmission intensity setting element is a variable capacitance component used also as the impedance setting element provided in the matching circuit of the communication master, and a variable dump resistor provided in the antenna of the communication master,
The communication mode according to claim 2 or 3, wherein the area setting means sets a transmission magnetic field strength of the communication master by adjusting the variable capacitance component and the variable dump resistor. Setting device. The communication mode setting device according to any one of claims 1 to 4, wherein the second mode is set to a mode in which communication is always performed.

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