JP4831016B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device for an in-vehicle device used for a communication system that performs communication between an in-vehicle device mounted on a vehicle and a portable device carried by a user to unlock / lock a vehicle door, and more particularly to an antenna. The present invention relates to the formation of a transmission request signal reachable range (hereinafter referred to as a communication range) that is transmitted by the device to detect the presence of a portable device.

  In recent years, a so-called smart entry system in which a user carries a portable device and unlocks / locks a vehicle door only by approaching or leaving the vehicle is becoming widespread. This system can be unlocked / locked on the vehicle door without a mechanical key and is very convenient.

  In this system, a vehicle-mounted device mounted on a vehicle outputs a transmission request signal via an antenna device. The portable device that has received this transmission request signal returns a response signal. The vehicle-mounted device that has received the response signal controls the door actuator to unlock / lock the vehicle door.

  The in-vehicle device includes a plurality of antenna devices. Each antenna device is formed by providing a transmission unit and, for example, a transmission antenna for the outside of the vehicle arranged in the door handle of each vehicle door, and a transmission unit and a transmission antenna for the inside of the vehicle arranged in the vicinity of the instrument panel, for example. Has been.

  The antenna device is configured such that the transmission unit is driven by the control unit of the in-vehicle device and a transmission request signal is output to a desired communication range via the transmission antenna under the control of the transmission unit.

  The formation of the communication range of the conventional antenna device used in this system will be described with reference to FIGS.

  4 is a circuit diagram of a conventional antenna device, and FIG. 5 is a diagram for explaining the operation. In FIG. 4, 52 is a modulation circuit, and the modulation circuit 52 formed by an AND circuit is a control unit of an in-vehicle device (not shown). 5A is supplied with a binary signal a having a duty of 50% for repeating H / L in FIG. 5A and a pulsed carrier wave b in FIG. 5B, and the binary signal a is modulated with the carrier wave b. The modulation signal f shown in (c) is output.

  Reference numeral 54 denotes a drive circuit. The drive circuit 54 is formed by connecting a pair of power transistors in series between a power supply Vd and GND. Here, the first power transistor 121 on the power supply Vd side is a P-channel FET, and the second power transistor 122 on the GND side is an N-channel FET. Each power transistor includes parasitic diodes 121a and 122a in parallel.

  Further, the modulation signal f from the modulation circuit 52 is inputted in parallel to each power transistor of the drive circuit 54, so that the transmission unit 51 is formed.

  Next, reference numeral 55 denotes a transmission antenna. In the transmission antenna 55, a coil L and a capacitor C are connected in series via a resistor R, a terminal M1 and a wiring N1 arranged from the middle point of the pair of power transistors 121 and 122 to the circuit side. And is connected to GND on the circuit side through the wiring N2 and the terminal M2. That is, the transmission antenna 55 is connected to the second power transistor 122 in parallel.

  Note that R, L, and C are referred to as antenna constants. The transmission antenna 55 has a Q indicating a predetermined resonance strength determined by an antenna constant. This Q value is proportional to L / R of the antenna constant, and when the value of L is constant, the Q value becomes Q∝1 / R. The Q value is generally formed by reducing the number of turns of the coil in order to reduce the cost of the transmission antenna 55, and the Q value of the conventional transmission antenna 55 is, for example, relatively small Q≈10. .

  The antenna device 50 is configured by connecting the transmission antenna 55 to the transmission unit 51 described above.

  In the above configuration, in the antenna device 50, the modulation circuit 52 performs on / off control of the drive circuit 54 with the modulation signal f. As a result, the antenna current Ig shown in FIG. 5D flows through the transmission antenna 55, a transmission request signal having a strength corresponding to the current Ig is transmitted, and a communication range substantially proportional to the magnitude of the current Ig. Form.

  Since this antenna current Ig has a Q value of the transmission antenna 55 that is relatively small Q≈10, the binary signal a is H, as shown in the positive-side envelope waveform of FIG. During a t-on period (when energization) in which f repeats H / L, the modulation circuit 52 alternately turns on / off the pair of power transistors 121 and 122 so that the transmitting antenna 55 is energized, and the maximum current immediately after rising It becomes an energizing current j that saturates to.

  Further, the antenna current Ig is transmitted by the transmitting antenna 55 by controlling only the power transistor 122 to be in the ON state during the t-off period (when power is cut off) when the binary signal a is L and the modulation signal f is also L only. Is in a power disconnection state. At this time, the antenna current Ig becomes a breaking current k that is consumed by the resistor R and converges to zero immediately after falling.

  As described above, the antenna current Ig of the transmission antenna 55 has a characteristic of quickly saturating or converging because the Q value of the transmission antenna 55 is small in both the energization current j and the disconnection current k. The antenna device 50 changes the energization current j by changing the resistance R of the antenna constant, and forms a communication range that is substantially proportional to the maximum value.

  That is, as shown in FIG. 5E, the antenna device 50 changes the maximum value of the energization current j flowing through the transmission antenna 55 by the resistance R of the antenna constant, and when R is small, the large energization currents j1 and R When it is large, a small energizing current j2 is passed. As a result, for example, via the transmission antenna 55 disposed in the door handle or in the vicinity of the instrument panel, the desired communication can be performed outside or inside the vehicle in proportion to the magnitude of the energization current j flowing through each transmission antenna 55. Forming a range.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP 2002-47835 A

  However, in the above conventional antenna device, since the communication range is formed by changing the resistance R of the antenna constant, individual communication ranges that differ depending on the arrangement position of the transmission antenna, the vehicle type, etc. are different for each antenna device. It is necessary to set by changing the resistance R.

  The work of setting the communication range by changing the resistance R is complicated. That is, when actually measuring the communication range using a test vehicle or the like, it involves an operation of changing the resistance R with a soldering iron each time. Furthermore, if the location of the transmission antenna, the vehicle design, etc. are changed between the test vehicle and the completed vehicle, the communication range will change, so the same work must be performed each time.

  The resistor R is generally a general-purpose resistor. The resistance value is, for example, in a range of 5Ω to 12Ω, and this range is determined as a stepwise change value such as 4.9Ω, 5.6Ω, 6.8Ω, etc. according to JIS standards. For this reason, there has been a problem that it is difficult to form a communication range when 5.3Ω or the like that is not included in the standard is required, that is, a highly accurate communication range.

  An object of the present invention is to solve such a conventional problem. An antenna that can perform a communication range formed by an antenna device without changing the resistance R of an antenna constant, can improve accuracy, and can obtain a desired communication range. An object is to provide an apparatus.

  In order to achieve the above object, an antenna device of the present invention has the following configuration.

According to the first aspect of the present invention, the transmission unit includes a drive circuit that supplies an antenna current to the transmission antenna based on a carrier wave signal input from the control unit of the in-vehicle device to the transmission unit, and a control unit of the in-vehicle device. A duty control circuit for outputting a duty signal by controlling a binary signal input from the transmitter to the transmission unit to be a duty signal having a predetermined duty, and a transmission antenna based on the predetermined duty when the duty signal is input And the switching circuit for switching on / off of the antenna current flowing through the antenna device.

  The antenna device having such a configuration uses the rising characteristic of the energization current flowing through the transmission antenna to form the communication range, and changes the maximum value of the current by the duty of the duty signal, thereby reducing the resistance R of the antenna constant. It is possible to obtain an antenna device that can be performed without change and that can improve the accuracy and form a desired communication range by finely setting the duty of the duty signal.

In the invention according to claim 2, in the invention according to claim 1, the Q value of the transmitting antenna is 40 to 220, and the rising characteristic of the antenna current that is uniquely determined by the Q value can be formed in a useful range. Has an effect.

  According to a third aspect of the present invention, in the first aspect of the invention, the duty control circuit includes a storage unit that stores a plurality of pieces of duty information in advance, and the duty signal based on the duty information selected from the storage unit. In the case of an antenna device that forms a communication range by changing the conventional resistance R, it is necessary to change the resistance R depending on the arrangement position of the transmission antenna, etc. The antenna device of the present invention has an effect that the resistance R can be made the same.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, an attenuation circuit for attenuating a disconnection current when the transmission antenna is disconnected is connected in parallel to the transmission antenna. It has the effect that the current can be reduced to zero in a short time.

The invention of claim 5 is the invention of claim 1, further provided with a current detection circuit for detecting the electric current flowing through the transmitting antenna to the transmission section, the duty control circuit based on the detection known signal of the current sensing circuit This is to change a predetermined duty of the duty signal, and has an effect of suppressing a variation in energization current caused by circuit characteristics, temperature characteristics, etc., that is, a variation in communication range.

  As described above, according to the present invention, there is an advantageous effect that an antenna device that forms a desired communication range can be obtained without changing the resistance R of the antenna constant.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

(Embodiment 1)
The first to fourth aspects of the present invention will be described with reference to the first embodiment.

  FIG. 1 is a circuit diagram of an antenna device according to Embodiment 1 of the present invention. FIG. 2 is a diagram for explaining the operation. In FIG. 1, 1 is a duty control circuit, and the duty control circuit 1 has a plurality of pieces of duty information in advance. Based on the stored storage unit 1b and the duty information selected from the storage unit 1b, the binary signal a having a duty of 50% shown in FIG. ) And a duty control unit 1a that controls to a predetermined duty signal a1.

  Here, the binary signal a is a signal having a period T with a duty of 50%, in which the respective periods t0 of H / L are equal. On the other hand, the duty signal a1 is formed based on the duty information and is a signal having a period T having a predetermined duty determined by the ratio of the H / L periods t1 and t2.

  Reference numeral 4 denotes a drive circuit, and the drive circuit 4 is formed of power transistors 21 and 22 which are a pair of switching means connected in series between the power supply Vd and GND. Here, the first power transistor 21 on the power supply Vd side is a P-channel FET, and the second power transistor 22 on the GND side is an N-channel FET. Each power transistor includes parasitic diodes 21a and 22a in parallel.

  The pulsed carrier wave b shown in FIG. 2C is input in parallel to the first and second power transistors 21 and 22 of the drive circuit 4 from a control unit of an in-vehicle device (not shown), and on / off control is performed by this signal. Is done.

  Reference numeral 7 denotes a switching circuit, and the switching circuit 7 is formed by a single power transistor 23. The third power transistor 23 is an N-channel FET and includes a parasitic diode 23a in parallel. The duty signal a1 shown in FIG. 2B is input from the duty control circuit 1 to the third power transistor 23, and ON / OFF control is performed by this signal.

  Further, reference numeral 5 denotes a transmission antenna, and one end of the transmission antenna 5 is connected to the midpoint of the pair of power transistors 21 and 22 via a resistor R, a terminal M1 and a wiring N1 arranged on the circuit side from this connection point. A coil L and a capacitor C are formed in series, and the other end is connected to the third power transistor 23 on the circuit side via the wiring N2 and the terminal M2, and is dropped to GND via the third power transistor 23. That is, the transmission antenna 5 is connected between the drive circuit 4 and the switching circuit 7.

  Here, R, L, and C are referred to as antenna constants. The transmitting antenna 5 has a Q indicating a predetermined resonance strength determined by an antenna constant. In order to obtain a predetermined Q value, the transmission antenna 5 is formed by increasing the number of turns of the coil from the relational expression of Q∝L / R. For this reason, the Q value is a relatively large Q = 40 to 220. It is a range.

  Reference numeral 6 denotes a resistor that forms an attenuation circuit. The resistor 6 is connected in parallel between the midpoint of the pair of power transistors 21 and 22 and the third power transistor 23, that is, connected in parallel to the transmitting antenna 5 including the resistor R. Has been. The resistor 6 may be connected in parallel between the coil L and the capacitor C.

  As described above, the antenna device 10 is configured by connecting the transmission antenna 5 to the transmission unit 12 formed on the circuit side.

  In the above-described configuration, in the antenna device 10, the duty control circuit 1 controls the switching circuit 7 on / off with the duty signal a1, and the control unit of the vehicle-mounted device (not shown) controls the driving circuit 4 on / off with the carrier wave b. . As a result, the antenna current Ie shown in FIG. 2D flows through the transmitting antenna 5 having a predetermined Q value. The antenna device 10 forms a communication range that is substantially proportional to the magnitude of the current by transmitting a transmission request signal having a strength corresponding to the current.

  Since this antenna current Ie is in the range of Q = 40 to 220 where the Q value of the transmitting antenna 5 is relatively large, the duty signal a1 is H as shown in the positive-side envelope waveform of FIG. During the on period (when energized) in which the carrier wave b repeats H / L, the duty control circuit 1 controls the third power transistor 23 to be turned on, while the carrier transistor b turns on the pair of power transistors 21 and 22 alternately. By performing the / off control, the transmitting antenna 5 is energized, and becomes an energized current m in an energized state that draws a substantially linear shape from a substantially parabola without being saturated immediately after rising.

  Further, the antenna current Ie does not depend on the on / off control of the pair of power transistors 21 and 22 alternately during the t-off period (when power is cut off) when the duty signal a1 is L and the carrier wave b repeats H / L. Since the duty control circuit 1 controls the third power transistor 23 to be in the OFF state, the transmission antenna 5 is in a power-off state, and the power-off current n is in a power-off state that converges to zero immediately after the fall.

  The flow path of the disconnection current n is formed in a loop shape by the transmission antenna 5 and the resistor 6 of the attenuation circuit connected in parallel to the transmission antenna 5, and the disconnection current n is sufficiently larger than the resistance R. It is consumed by the resistor 6 and attenuates and converges rapidly to zero.

  As described above, the antenna current Ie of the transmission antenna 5 has a characteristic that draws a substantially straight line from a substantially parabola without the saturation of the rising of the conduction current m immediately since the Q value of the transmission antenna 5 is relatively large.

  Then, the antenna device 10 changes the maximum value of the energized current by changing the duty of the duty signal a1 using the rising characteristic of the energized current m during the t-on period (when energized) when the duty signal a1 is H. The transmission request signal having a strength proportional to the energization current m is transmitted. As a result, the antenna device 10 can be connected to the outside of the vehicle in proportion to the magnitude of the energization current m flowing through each transmission antenna 5 via, for example, the transmission antenna 5 disposed in the door handle or in the vicinity of the instrument panel. A desired communication range is formed in the vehicle.

  For example, when the transmission antenna 5 has a Q value of 40 and the duty control circuit 1 selects the duty information “60” in the storage unit 1b, the communication range of the antenna device 10 is formed. As shown in FIG. 2E, the positive-side envelope of m has a characteristic of drawing a substantially parabola without saturation at the rising edge.

  Further, when the Q value is further increased, for example, approximately 220, and the duty control circuit 1 selects the duty information “60” in the storage unit 1b to form a communication range, the positive side of the energization current m of the antenna current Ie As shown in FIG. 2 (e), the envelope has a substantially linear characteristic that is proportional to the duty of the duty signal a1 while the slope θ becomes smaller in inverse proportion to the Q value.

  Therefore, as is apparent from FIG. 2 (e), the antenna device 10 can set the maximum value of the energization current m to the current Ix when the Q value of the transmission antenna 5 is 40 and the duty of the duty signal a1 is 60%. The current Iy can be set at a value and a duty of 40%.

  On the other hand, the antenna device 10 can set the maximum value of the energizing current m to the current Ix when the Q value of the transmitting antenna 5 is 220 and the duty of the duty signal a1 is 60%, and the current Iy can be set at the Q value and the duty of 50%. it can.

  In this way, the duty control circuit 1 changes the maximum value of the energization current m of the transmission antenna 5 by changing the duty of the duty signal a1, and transmits a transmission request signal having a strength based on the energization current m. A desired communication range is formed approximately in proportion to the current.

  Further, the antenna device 10 stores the duty information in a fine value such as 53% or 53.5% in the storage unit 1b, and the duty control circuit 1 appropriately fines it by, for example, the program processing of the duty control unit 1a. By selecting the duty information of the storage unit 1b, it is possible to finely change the maximum value of the energization current m of the transmission antenna 5 and form a highly accurate communication range.

  The practical duty of the duty signal a1 is preferably set in the range of 40% to 60% because it is necessary to secure the transmission time of the transmission request signal.

  The Q value of the transmission antenna 5 is preferably in the range of 40 to 220. When the Q value is set to a value smaller than 40, the rising characteristic of the conduction current m approaches the conduction current j of the prior art shown in FIG. It is difficult to use.

  On the other hand, when the Q value is set to a value larger than 220, the rising characteristic of the energizing current m is practical because the inclination θ becomes smaller and the linear inclination characteristic becomes gentler. It is necessary to further increase the number of coil turns from the L / R relational expression. Further, there is a limit to further reducing the resistance R having a value of several Ω due to the influence of the wiring resistances such as the wirings N1, N2, and it is difficult to put them into practical use.

  As described above, according to the present embodiment, the transmission antenna 5 having a predetermined Q value is used, and the maximum value of the energization current m flowing through the transmission antenna 5 is set to the duty of the duty signal a1 formed by the duty control circuit 1. It is possible to obtain the antenna device 10 that can form a desired communication range by changing the frequency, and can form a highly accurate communication range by the duty control circuit 1 finely setting the duty of the duty signal a1.

  Further, by setting the Q value of the transmission antenna 5 in the range of approximately 40 to 220, the range in which the rising characteristic of the energization current m is useful, that is, the maximum value of the energization current m is effectively changed by the duty of the duty signal a1. To the extent possible.

  The duty control circuit 1 includes a storage unit 1b that stores a plurality of pieces of duty information in advance, and a duty control unit 1a that determines the duty of the duty signal a1 based on the duty information selected from the storage unit 1b. The antenna device 50 described in the background art changes the resistance R in accordance with the arrangement position of the transmission antenna 55, that is, the antenna device 50 has many types and becomes complicated to manage, but the antenna device 10 of the present invention is complicated. Can be handled with one type since there is no need to change the resistance R.

  Furthermore, by providing an attenuation circuit that attenuates the disconnection current n of the transmission antenna 5, the disconnection current n can be made zero in a short time. As a result, communication performance can be maintained without changing the transmission rate of the transmission request signal. This attenuation circuit can be formed at a low cost by being formed by the resistor 6.

(Embodiment 2)
The invention according to claim 5 of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the part of the same structure as Embodiment 1, and detailed description is simplified.

  FIG. 3 is a circuit diagram of the antenna device according to the second embodiment of the present invention. In the first embodiment, the transmitter 31 is formed by further providing a current detection circuit 32 for detecting the antenna current Ie.

  The current detection circuit 32 smoothes the resistor Ra inserted between the third power transistor 23 and GND, the amplifier Ap that amplifies the voltage generated in the resistor Ra when the antenna current Ie flows, and the output signal of the amplifier Ap. The antenna device 30 is configured such that an analog detection signal Si formed by the low-pass filter Fa and changing according to the antenna current Ie is fed back to the duty control circuit 11.

  In the above configuration, the duty control circuit 11 is configured such that the duty control unit 11a converts the detection signal Si proportional to the antenna current Ie into a digital signal by AD conversion and recognizes the current reference value Is stored in advance in the storage unit 11b. And the duty of the duty signal a1 is controlled so that the antenna current Ie is equal to the current reference value Is.

  That is, the antenna device 30 forms a desired communication range by appropriately selecting the current reference value Is and performs feedback control so that the antenna current Ie and the current reference value Is are always the same.

  As an example of the feedback control, the duty control circuit 11 operates the transmission antenna 5 a predetermined number of times by changing the duty of the duty signal a1 at regular intervals. The duty having the smallest difference from the current reference value Is is selected and determined from among the plurality of detection signals Si thus obtained. Since the antenna current Ie flowing through the transmission antenna 5 is controlled by the duty signal a1 having the selected duty, it is possible to always ensure a constant antenna current Ie and maintain a constant communication range.

  As described above, according to the present embodiment, the current detection circuit 32 is provided, and the duty control circuit 11 feeds back the detection signal Si so that the antenna current Ie and the current reference value Is are equal to each other. Ie is controlled. As a result, in addition to the effects of the first embodiment, the antenna device 30 can stably stabilize the communication range that is affected by circuit characteristics, parameter variations of the transmission antenna 5, aging, temperature changes, and the like. Can be obtained.

  In the present embodiment, the current reference value Is is stored in the storage unit 11b. However, instead of the current reference value Is, the conversion data information between the detection signal Si and the duty detected in advance is used. Is possible.

  In any of the embodiments, in the description, the duty control circuits 1 and 11 and the current detection circuit 32 are described as examples of hardware formed by combining a plurality of electronic components. Instead, it may be formed by a single microcomputer.

  The antenna device according to the present invention can be performed without changing the resistance R of the antenna constant, has the effect of improving accuracy and forming a desired communication range, and is a communication system that can unlock / lock a vehicle door. This is useful for the antenna device used.

1 is a circuit diagram of an antenna device according to a first embodiment of the present invention. Operation explanation diagram Circuit diagram of antenna apparatus according to embodiment 2 of the present invention Circuit diagram of conventional antenna device Operation explanation diagram

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Duty control circuit 1a Duty control part 1b Memory | storage part 4 Drive circuit 5 Transmitting antenna 6 Resistor (attenuation circuit)
7 Switching Circuit 10 Antenna Device 12 Transmitting Unit 21, 22, 23 Power Transistor (Switching Means)
21a, 22a, 23a Parasitic diode a Binary signal a1 Duty signal b Carrier Ie Antenna current

Claims (5)

A transmission unit connected to the control unit of the in-vehicle device, and a transmission antenna connected to the transmission unit, the transmission unit,
A drive circuit for supplying an antenna current to the transmission antenna based on a carrier wave signal input from the control unit of the in-vehicle device to the transmission unit;
A duty control circuit for controlling the binary signal input from the control unit of the in-vehicle device to the transmission unit to be a duty signal having a predetermined duty, and outputting the duty signal;
A switching circuit configured to switch on / off of an antenna current flowing in the transmission antenna based on the predetermined duty when the duty signal is input ; The antenna device according to claim 1 , wherein a Q value of the transmitting antenna is 40 to 220. 2. The antenna according to claim 1, wherein the duty control circuit includes a storage unit that stores a plurality of pieces of duty information in advance, and a duty control unit that determines a duty of the duty signal based on the duty information selected from the storage unit. apparatus. The antenna device according to claim 1, wherein an attenuator circuit for attenuating a disconnection current when the transmit antenna is disconnected is connected in parallel with the transmit antenna. The transmitter further includes a current detection circuit that detects an antenna current of the transmission antenna and outputs a detection signal to the duty control circuit, and the duty control circuit based on the detection signal of the current detection circuit, The antenna device according to claim 1, wherein the predetermined duty of the duty signal is changed.

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