JP4905042B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device of an in-vehicle device used in a communication system that performs communication between an in-vehicle device mounted on a vehicle and a portable device and performs unlocking / locking of a vehicle door, and the like. The present invention relates to the formation of a transmission request signal reachable range (hereinafter referred to as a communication range) to be transmitted to detect the presence.

  In recent years, a so-called smart entry system in which a user unlocks / locks a vehicle door simply by carrying a portable device and approaching / 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 a transmission antenna for outside the vehicle arranged in the door handle of each vehicle door, and a transmission antenna for the inside of the vehicle arranged in the vicinity of the transmission unit and the instrument panel. Yes.

  In the antenna device, the transmission unit is driven by the control unit of the in-vehicle device, and a transmission request signal is output from the transmission antenna to form a desired communication range.

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

  FIG. 5 is a circuit diagram of a conventional antenna device, and FIG. 6 is an operation explanatory diagram. In FIG. 5, 52 is a modulation circuit, and the modulation circuit 52 formed by an AND circuit is from a control unit of an in-vehicle device (not shown). A binary signal a having a duty of 50% that repeats H / L in FIG. 6A and a pulsed carrier wave b in FIG. 6B are supplied, and the binary signal a is modulated by the carrier wave b, and FIG. The modulated signal f of c) is output.

  Reference numeral 54 denotes a drive circuit, and the drive circuit 54 is formed by connecting a pair of power transistors in series between a power source 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 is provided with parasitic diodes 121a and 122a in parallel.

  The transmitter 51 is formed by connecting the modulation signal f from the modulation circuit 52 to each power transistor of the drive circuit 54.

  Next, reference numeral 55 denotes a transmission antenna. In the transmission antenna 55, a coil L and a capacitor C are connected in series from a midpoint of a pair of power transistors 121 and 122 via a resistor R on the circuit side via a terminal M1 and a wiring N1. The antenna device 50 is configured by being connected to the circuit side GND via the wiring N2 and the terminal M2.

  Note that R, L, and C are referred to as antenna constants.

  Here, the transmission antenna 55 has a predetermined resonance strength Q 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 transmission antenna 55 is formed by reducing the number of turns of the coil in order to reduce the price, and the Q value thereof is, for example, relatively small Q = 10.

  In the configuration described above, the antenna device 50 is controlled to be turned on / off by the modulation signal f of the modulation circuit 52, whereby the antenna current Ig shown in FIG. A current is transmitted as a transmission request signal, and a communication range substantially proportional to the magnitude of this current is formed.

  Since the antenna current Ig has a relatively small Q value of the transmission antenna 55 of Q = 10, as shown in the positive-side envelope waveform of FIG. The energizing current j at the time of energization saturates to the maximum current immediately after the rising, and the breaking current k during the t-off period (at the time of the energization) of the binary signal a is saturated to zero immediately after the falling. Become.

  That is, since the Q value is small, the energization current j and the disconnection current k of the transmitting antenna 55 are saturated quickly.

  A communication range is formed approximately in proportion to the maximum value of the energization current j.

  That is, as shown in FIG. 6E, the antenna device 50 changes the maximum value of the energization current j by changing the resistance R of the antenna constant. When R is small, the large energization current j1 and R are large. As a small energization current j2, for example, a transmission antenna is disposed in the door handle or in the vicinity of the instrument panel to form a communication range proportional to the magnitude of the energization current.

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, the communication range is formed by changing the resistance R of the antenna constant. Therefore, the formation of the communication range that differs depending on the arrangement position of the transmission antenna, the vehicle type, etc. It is necessary to set the resistance R in the same way.

  The work of setting the communication range by changing the resistance R is complicated. That is, when actually measuring the communication range using an experimental vehicle, it involves an operation of replacing the resistance R with a soldering iron each time.

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

  The present invention solves such a conventional problem, and an antenna device capable of forming a communication range of an antenna device without changing the resistance R of the antenna constant and obtaining a highly accurate desired communication range. The purpose is to provide.

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

Invention of Claim 1 of this invention is equipped with the transmission part connected to the control part of vehicle equipment, and the transmission antenna connected to the said transmission part, The said transmission part is a binary value from the said control part. A duty control circuit that generates a signal with a predetermined duty signal; a modulation circuit that modulates the duty signal with a carrier wave from the control unit to output a modulation signal; and a synthesized signal that combines the modulation signal and the duty signal. Is formed from a signal combining circuit that outputs the modulation signal and the combined signal, and a power supply is controlled to be turned on / off and the transmission antenna is energized, and the duty control circuit includes the binary signal By changing the duty of the duty signal generated from the input signal and changing the current flowing to the transmission antenna, the desired signal is transmitted through the transmission antenna. Forming a range is obtained by forming an antenna device.

  The formation of the communication range of the antenna device configured as described above can be performed without changing the resistance R of the antenna constant because the maximum value is changed by the duty of the duty signal by using the rising characteristic of the conduction current of the transmitting antenna. By setting the signal duty finely, the desired communication range with high accuracy can be formed.

  The invention according to claim 2 is the invention according to claim 1, in which the Q value of the transmitting antenna is approximately 40 to 220, and has an effect that the rising characteristic of the antenna current can be formed in a useful range.

  According to a third 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.

  According to a fourth aspect of the present invention, in the third aspect of the invention, the attenuating circuit alternately passes through the parasitic diodes of the energizing elements provided in parallel to each of the pair of switching means, and the parasitic diodes are used. This has the effect of not requiring a separate part for forming the flow path.

  According to a fifth aspect of the present invention, in the first aspect of the invention, a current detection circuit for detecting an energization current flowing through the transmission antenna is provided, and the duty control circuit changes the duty of the duty signal based on the detection signal of the current detection circuit. Therefore, it is possible to suppress a variation in energization current caused by circuit characteristics, temperature characteristics, and the like, 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, and FIG. 2 is an operation explanatory diagram. In FIG. 1, 1 is a duty control circuit, and duty control circuit 1 stores duty information in advance. A binary signal a having a duty of 50% in FIG. 2A input from a storage unit 1b and a control unit of an external vehicle device (not shown) based on the duty information to a predetermined duty signal a1 in FIG. 2B. And a duty control unit 1a that outputs

  Here, the binary signal “a” is equal in period T0 of H / L in the cycle T, and its duty is 50% of T / 2. On the other hand, the duty signal a1 has a predetermined duty determined by the ratio of the H / L periods t1 and t2 with the period T.

  Next, reference numeral 2 denotes a modulation circuit. In the modulation circuit 2 formed by an AND circuit, the duty signal a1 is input to one terminal, and the carrier wave b in FIG. Then, the modulated signal c shown in FIG. 2D is output from these two signals.

  Here, the carrier wave b is a pulse signal having a carrier frequency f0. Further, the modulation signal c has the same duty as the duty signal a1.

  Further, 3 is a signal synthesis circuit, and the signal synthesis circuit 3 is formed by an inverter and an OR logic circuit, and outputs the synthesis signal c1 of FIG. 2 (e) from the modulation signal c and the duty signal a1. The synthesized signal c1 has the same duty as the duty signal a1.

  Reference numeral 4 denotes a drive circuit. The drive circuit 4 is formed by connecting power transistors as a pair of switching means in series between a power supply Vd and GND. Generally, such a circuit is called a half bridge.

  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 is provided with parasitic diodes 21a and 22a as energization elements forming an attenuation circuit in parallel.

  The drive circuit 4 is formed such that the composite signal c1 is input to the first power transistor 21 and the modulation signal c is input to the second power transistor 22, and the on / off control is performed by these two signals.

  Reference numeral 5 denotes a transmission antenna. The transmission antenna 5 having a predetermined Q value has a coil L and a capacitor via a terminal M1 and a wiring N1 from a middle point of the pair of power transistors 21 and 22 through a resistor R on the circuit side. The antenna device 10 is configured such that C is connected in series and connected to GND on the circuit side via the wiring N2 and the terminal M2.

  Note that R, L, and C are referred to as antenna constants.

  Here, the transmission antenna 5 has a predetermined resonance strength Q determined by an antenna constant. Therefore, the transmission antenna 5 is formed by increasing the number of turns of the coil, and the Q value is in a relatively large range of Q = 40 to 220.

  In the above configuration, the antenna device 10 uses the transmission antenna 5 having a predetermined Q value and uses the rising characteristic of the conduction current of the transmission antenna 5 determined by the Q value.

  That is, the duty control circuit 1 changes the duty signal a1 and changes the maximum value of the energization current, thereby outputting this current as a transmission request signal and forming a communication range substantially proportional to the magnitude of this current.

  For example, an example will be described in which the duty control circuit 1 selects the duty information “60” in the storage unit 1b and outputs a duty signal a1 having a duty of 60% from a binary signal a having a duty of 50% to form a communication range. To do.

  First, when the duty control circuit 1 selects the duty information “60”, the synthesized signal c1 input to the first power transistor 21 and the modulation signal c input to the second power transistor 22 have a period T of t1 period. (T on), t2 period (t off), and t1 / T is formed into a signal with a duty of 60%.

  The first power transistor 21 is a composite signal c1 in FIG. 2E, and the second power transistor 22 is ON / OFF controlled by a modulation signal c in FIG. The antenna current Ie shown in FIG. 2 (f) flows.

  When the composite signal c1 and the modulation signal c are L, the first power transistor 21 is controlled to be on and the second power transistor 22 is controlled to be off. On the other hand, when the composite signal c1 and the modulation signal c are H, the first power transistor 21 is controlled to be off and the second power transistor 22 is controlled to be on.

  Therefore, during the t-on period when the combined signal c1 and the modulation signal c repeat H / L, the first and second power transistors 21 and 22 are alternately turned on / off, and the transmitting antenna 5 is energized. Flows.

  On the other hand, during the t-off period in which the composite signal c1 is H and the modulation signal c is L, both the first and second power transistors 21 and 22 are controlled to be off, and the disconnection current n in the disconnection state flows through the transmission antenna 5.

  The antenna current Ie is an alternating current of the energization current m and the disconnection current n.

  Here, when the Q value of the transmitting antenna 5 is formed to be approximately 40, for example, the positive-side envelope of the energization current m of the antenna current Ie has a substantially parabola without saturation as shown in FIG. It becomes the characteristic to draw.

  Further, the rising characteristic of the energization current m is such that when the Q value of the transmitting antenna 5 is further increased, for example, approximately 220, the rising slope θ decreases substantially inversely proportional to the Q value and a substantially straight line is drawn.

  Therefore, when the Q value of the transmission antenna 5 is 40 and the duty signal a1 is 60% duty, the maximum value of the conduction current m flowing through the transmission antenna 5 in the t-on period t1 can be set to the current Ix. Similarly, the maximum value of the energization current m when the duty of the duty signal a1 is 40%, that is, the t-on period is t11, can be set to the current Iy.

  Further, when the Q value of the transmission antenna 5 is 220 and the duty signal a1 is 60% duty, the maximum value of the energization current m flowing through the transmission antenna 5 in the t-on period t1 can be set to the current Ix. Similarly, the maximum value of the energization current m when the duty of the duty signal a1 is 50% can be set to the current Iy.

  That is, when the Q value is 40, the energization current m can be set to the current Ix with a duty of 60% and the current Iy with a duty of 40%. Further, when the Q value is 220, the energization current m can be set to the current Ix with a duty of 60% and the current Iy with a duty of 50%.

  Thus, 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 forms a desired communication range substantially proportional to this current.

  Therefore, the communication range can be finely adjusted by storing and selecting fine duty information such as a duty of 53% in the storage unit 1b.

  The practical duty of the duty signal a1 is preferably set to 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 40 or less, the rising characteristic of the conduction current m becomes a characteristic that saturates immediately, similar to the conduction current j of the prior art shown in FIG. 6, and the change in the antenna current is small and practical even if the duty is slightly changed. It is difficult to serve.

  On the other hand, when Q = 220 or more, the rising characteristic of the energization current m is advantageous because the slope θ is further reduced, but in order to further increase Q, the number of coil turns is further increased from the relational expression of Q∝L / R. It is necessary to increase the resistance R, and reducing the resistance R is limited by the influence of the wiring resistances such as the wirings N1, N2, and is difficult to be put to practical use.

  Next, the positive-side envelope waveform of the disconnecting current n of the antenna current Ie in the t-off period has a reverse characteristic opposite to the rising of the energizing current m, that is, a one-dot chain line having a gentle slope shown in FIG. Since the characteristics are Vn and the current cannot be made zero within the predetermined period T as it is, it is necessary to lengthen the period T. As a result of increasing the period T, the transmission speed of the transmission request signal is lowered and cannot be put to practical use.

  For this reason, it is necessary to shorten the fall time of the disconnection current n in the t-off period. Next, the operation of the signal synthesis circuit 3 that performs this will be described.

  During the t-off period, the combined signal c1 input to the first power transistor 21 can be formed H and the modulated signal c input to the second power transistor 22 can be formed L by the operation of the signal combining circuit 3. As a result, both the first and second power transistors 21 and 22 are controlled to be off.

  Thus, the flow path of the disconnection current n in the t-off period is such that when the disconnection current n is positive, that is, Ie in the direction of the arrow shown in FIG. The attenuation circuit returns to the transmitting antenna 5 again via the diode 22a. On the other hand, when the disconnecting current n is on the negative electrode side, the current flows through the attenuation circuit that connects the power source Vd from GND through the transmission antenna 5 and the parasitic diode 21a of the first power transistor 21.

  The flow path of the disconnecting current n is defined as connecting the attenuation circuit in parallel to the transmission antenna 5 for the sake of convenience of using the attenuation circuit of the positive electrode side and the negative electrode side as a flow path.

  With this operation of the signal synthesis circuit 3, the disconnecting current n during the t-off period can be formed through the parasitic diodes 21a and 22a of the attenuation circuit in both the positive and negative flow paths, so that the current is consumed by the parasitic diodes 21a and 22a. As shown in FIG. 2 (g), the characteristics of the current Wn that rapidly attenuates and becomes zero are obtained.

  Therefore, the interruption current n can be made zero within the predetermined period T, and the period T can be used as it is. That is, since it is not necessary to lengthen the period T, the transmission speed of the transmission request signal can be reduced. No.

  As described above, according to the present embodiment, the antenna apparatus 10 changes the duty of the duty signal a1 formed by the duty control circuit 1 to change the maximum value of the energization current m flowing through the transmission antenna 5 having a predetermined Q value. To form a desired communication range.

  Therefore, the antenna device 10 that can form a highly accurate communication range can be obtained by finely setting the duty of the duty signal a1.

  Further, by setting the Q value of the transmission antenna 5 to about 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 can be effectively changed by the duty of the duty signal a1. It can be formed to the extent possible.

  Further, by providing an attenuation circuit that attenuates the disconnection current n of the transmission antenna 5, even if the Q value of the transmission antenna 5 is increased, the disconnection current n can be reduced to zero in a short time. Communication performance can be maintained without changing the transmission rate of the request signal.

  Further, the attenuation circuit passes through the parasitic diodes 21a and 22a, and can be made inexpensive without requiring a separate part. As can be seen from the name, this parasitic diode is inevitably formed in the structure of the FET, and is not a separate component from the FET.

  In the present embodiment, the flow path of the disconnecting current n of the transmission antenna 5 has been described as passing through the parasitic diodes 21a and 22a. However, the present invention is not limited to this, and for example, the transmission antenna 5 of FIG. It is also possible to implement a flow path in which a separate resistor is connected in parallel to each other and the disconnecting current of the transmitting antenna passes through the resistor.

  Although the drive circuit 4 is a half bridge, the present invention is not limited to this, and a drive circuit 4a is provided in parallel with the drive circuit 4 as shown in FIG. 3, and a full bridge is configured by these four power transistors. The antenna device 30 may be configured by connecting the transmission antenna 5 between the midpoints of each pair of power transistors.

  As shown in FIG. 3, the third power transistor 23 of the drive circuit 4a is supplied with the second modulation signal d obtained by inverting the modulation signal c with the inverter circuit 32, and the fourth power transistor 24 is supplied with the second modulation signal d with the duty signal a1. The second synthesized signal d1 synthesized by the second signal synthesis circuit 3a is inputted.

  As a result, the first power transistor 21 is turned on / off by the combined signal c1, the second power transistor 22 by the modulated signal c, the third power transistor 23 by the second modulated signal d, and the fourth power transistor 24 by the second combined signal d1. By being turned off, the antenna current Ie flows through the transmission antenna 5.

  Also in this embodiment, by forming the transmission antenna 5 to a predetermined Q value, the characteristics of the antenna current Ie can be formed in the same manner as that of the half bridge. Therefore, the maximum value of the energization current m is changed by the duty of the duty signal a1, and the transmission Since the output power of the antenna 5 can be controlled, the antenna device 30 can form a desired communication range.

  The full bridge can be used for higher power than a half bridge. In other words, in the case of the same power supply Vd as that of the half bridge, the energization current m of the transmission antenna 5 can be increased, so that a wider communication range can be easily formed.

(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. 4 is a circuit diagram of an antenna device according to the second embodiment of the present invention. In FIG. 1 of the first embodiment, a current detection circuit 42 for detecting the antenna current Ie is provided, and a transmitter 41 is formed. is there.

  The current detection circuit 42 includes a resistor Ra inserted between the transmission antenna 5 and GND, an antenna current Ie flowing through the resistor Ra, an amplifier Ap that amplifies the generated voltage, and a low-pass that smoothes the output of the amplifier Ap. The antenna device 40 is configured such that an analog current detection signal Si formed by the 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 becomes equal to the current reference value Is.

  Therefore, the antenna device 40 forms a desired communication range by appropriately selecting the current reference value Is and performs feedback control so that the antenna current Ie becomes the same as the current reference value Is.

  As an example of the feedback control, the duty control circuit 11 changes the duty of the duty signal a1 at regular time intervals and performs the operation of driving the transmission antenna 5 a predetermined number of times to obtain a plurality of detection signals Si and the current reference value Is. Select the duty with the smallest difference. Since the transmission antenna 5 is controlled by this duty, a communication range formed by a constant antenna current Ie can always be maintained.

  As described above, according to the present embodiment, the current detection circuit 42 is provided, and feedback control is performed so that the antenna current Ie becomes equal to the current reference value Is. In addition to the effects of the first embodiment, the parameters of the transmission antenna 5 It is possible to obtain the antenna device 40 that can make the communication range that varies with variations, aging, temperature changes, and the like stable with little variation.

  In the above embodiment, the current reference value Is is stored in the storage unit 11b. However, instead of the current reference value Is, conversion data information of the detection signal Si and the duty may be used.

  In any of the embodiments, the description has been given of the example in which the duty control circuit 1 or 11, the modulation circuit 2, the signal synthesis circuit 3, and the like are configured by hardware in which a plurality of electronic components are combined. However, the present invention can also be implemented as a single microcomputer instead of hardware.

  The antenna device according to the present invention can be used without changing the resistance R of the antenna constant, has an effect of forming a desired communication range with high accuracy, and is used in a system that can unlock / lock a vehicle door. Useful for devices and the like.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Duty control circuit 1a Duty control part 1b Memory | storage part 2 Modulation circuit 3 Signal synthesis circuit 4 Drive circuit 5 Transmitting antenna 10 Antenna apparatus 12 Transmitting part 21, 22 Power transistor (switching means)
21a, 22a Parasitic diode (energizing element)
a binary signal a1 duty signal b carrier wave c modulation signal c1 composite signal Ie antenna current

Claims (5)

A duty control circuit including a transmission unit connected to a control unit of an in-vehicle device and a transmission antenna connected to the transmission unit, wherein the transmission unit generates a binary signal from the control unit as a predetermined duty signal A modulation circuit that modulates the duty signal with a carrier wave from the control unit and outputs a modulation signal, a signal synthesis circuit that synthesizes the modulation signal and the duty signal and outputs a synthesis signal, and the modulation signal and the combined signal is input power is turned on / off control, is formed a drive circuit for energizing the transmitting antenna, the duty control circuit, by changing the duty of the duty signal generated from the binary signal , by changing the current supplied to the transmitting antenna, the antenna device to form a desired communication range via the transmitting antenna. The antenna device according to claim 1, wherein a Q value of the transmission antenna is approximately 40 to 220. The transmission in parallel with the antenna, the transmitting antenna antenna device according to claim 1, wherein the cross-sectional electric current when deenergized to connect an attenuation circuit for attenuating the. 4. The antenna device according to claim 3, wherein the attenuation circuit is formed by including a current-carrying element provided in parallel with the switching means, wherein the driving circuit is formed by connecting a pair of switching means in series. The antenna device according to claim 1, further comprising: a current detection circuit that detects an energization current of the transmission antenna, wherein the duty control circuit changes a duty of the duty signal based on a detection signal of the current detection circuit.

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