JP5246764B2 - Wireless communication device - Google Patents

Description

  The present invention relates to a wireless communication apparatus that performs wireless communication using a coil antenna.

Conventionally, a technique for performing high-speed wireless communication using a loop antenna is known.
In such wireless communication technology, an output circuit that outputs a transmission signal to a loop antenna inputs differential signals to both ends of the loop antenna and generates an alternating magnetic field, thereby transmitting information to the receiving side. doing.
Specifically, the output circuit includes output transistors at both ends of the loop antenna, and the end of the loop antenna is connected to the collector of each output transistor via a matching circuit, and the connection point is And having a configuration connected to a power source via a pull-up coil. The emitter of the output transistor is grounded. Then, by inputting a differential signal (a signal whose phase is shifted by 180 degrees) to each output transistor installed at both ends of the loop antenna, an AC magnetic field is generated in the loop antenna.
As a wireless communication device using such a loop antenna, for example, a technique described in Patent Document 1 is known.
JP-T-2004-527974

However, in the output circuit as described above, among the transistors at both ends of the loop antenna to which the differential signal is input, the transistor that is turned on can pass a current to the loop antenna because the drive current flows. A part of the drive current flows from the collector to the emitter.
Then, the current flowing from the collector to the emitter does not contribute to the generation of the AC magnetic field, and thus becomes a loss current.
Such a situation is common to not only loop antennas but also coil antennas such as planar coil antennas and helical antennas.
That is, it is difficult to perform efficient communication in a conventional wireless communication apparatus using a coil antenna such as a loop antenna.
An object of the present invention is to perform wireless communication using a coil antenna more efficiently.

In order to solve the above problems, a wireless communication device according to a first invention is
An output transistor that switches a conduction state between the input terminal and the output terminal according to a control signal based on a transmission signal input to the control terminal, one end connected to the input terminal of the output transistor, and the other end to a feeding point And a capacitor having one end connected to the connection point on the feeding point side of the coil antenna and the other end grounded (for example, the antenna of FIG. 2). Differential signal generation circuit (for example, differential signal generation circuit 110 in FIG. 2) that outputs system circuit units A and B), a normal transmission signal, and an inverted transmission signal obtained by inverting the normal transmission signal. In each of the first and second antenna system circuit units, the coil antenna functions as an inductor, and forms a series resonant circuit together with the capacitor. A normal transmission signal output by the differential signal generation circuit is input to a control terminal of the output transistor in one antenna system circuit unit, and a control terminal of the output transistor in the second antenna system circuit unit Is characterized in that the inverted transmission signal output by the differential signal generation circuit is input.

With such a configuration, the load existing at the input destination of the forward transmission signal and the reverse transmission signal becomes the first and second antenna system circuit units having the same structure, so that the input impedance is the same and matching is performed. Since it is not necessary to provide a circuit, the circuit scale can be reduced.
In addition, since the normal and inverted transmission signals are input to the first and second antenna system circuit units for wireless transmission, the balanced signal may be converted into a wireless transmission signal without being converted into an unbalanced signal. It is not necessary to provide a balun, and the circuit scale can be further reduced.

In addition, the second invention,
The coil antennas in the first and second antenna system circuit units are arranged to face each other in a direction in which resonance currents flow in the same direction.
With such a configuration, an AC magnetic field in the same direction can be generated in the coil antennas provided in the first and second antenna system circuit units, so that each forward and inversion transmission signal can be efficiently wirelessly transmitted. can do.

In addition, the third invention,
The coil antennas in the first and second antenna system circuit units are arranged to face each other at a predetermined interval determined based on antenna characteristics of each of the coil antennas.
With such a configuration, in the coil antennas provided in the first and second antenna system circuit units, the magnetic field lines in the far field can be increased, and the emission amount of electromagnetic waves can be increased.
In addition, by making the coil antennas face each other at a predetermined interval, the capacitance formed between the two coil antennas can be reduced compared to the case where the coil antennas face each other in close proximity. It is also possible to reduce the loss of flowing current.

Embodiments of the present invention will be described below with reference to the drawings.
First, a reference embodiment will be described.
( Reference embodiment)
The wireless communication apparatus according to the reference embodiment has a configuration in which one end of the loop antenna is connected to the collector of the output transistor and a feeding point is provided at the other end of the loop antenna. Therefore, it is not necessary to connect the pull-up coil and power supply to the collector of the transistor, so that all the drive current of the output transistor flows into the loop antenna without branching in the current path formed by the loop antenna and transistor. Can be made.

FIG. 1 is a diagram illustrating a configuration of a wireless communication device 1 according to a reference embodiment of the present invention.
In FIG. 1, the wireless communication device 1 includes a buffer 10, a transistor 20, a loop antenna 30, capacitors 40 and 60, and an inductor 50.
In FIG. 1, only the main part related to the description of the present invention is shown among the units of the wireless communication device 1. In the wireless communication device 1, the buffer 10, the transistor 20, the loop antenna 30, A portion constituted by the capacitors 40 and 60 and the inductor 50 is hereinafter appropriately referred to as an “antenna system circuit portion”.
The buffer 10 holds a high-level or low-level signal input from the previous signal processing circuit and outputs it to the base of the transistor 20. At this time, the low level signal output from the buffer 20 is lower than the threshold voltage of the transistor 20, and the high level signal is higher than the threshold voltage of the transistor 20.

Note that if the high-level and low-level signals input from the circuit in the previous stage are at a level that matches the threshold voltage of the transistor 20 as described above, a circuit configuration in which the buffer is omitted may be employed.
The transistor 20 is configured by an NPN junction transistor, and has a collector connected to one end of the loop antenna 30 and an emitter grounded. Further, the transistor 20 is turned on when a high level signal is input from the buffer 10, and the current flowing from the antenna 30 flows out from the collector to the emitter.
Note that the transistor 20 may be formed of an N-type MOS transistor.

The loop antenna 30 has a feeding point on the end side opposite to one end to which the transistor 20 is connected. The loop antenna 30 has a function as an inductor, and constitutes a series resonance circuit with a capacitor 40 described later. That is, a resonance current flows in the loop antenna 30 in the direction from the feeding point toward the transistor 20 and in the opposite direction, and an alternating magnetic field is generated in the loop antenna 30 by the resonance current.
One end of the capacitor 40 is connected between the end of the loop antenna 30 on the side where the feeding point is installed and the feeding point, and the other end is grounded. The capacitor 40 has a function of a low-pass filter that suppresses transmission of a high-frequency signal between the feeding point and the loop antenna 30, and a function of a capacitor that forms a series resonance circuit with the loop antenna 30. have.

The antenna 30 and the capacitor 40 have inductance and capacitance so that they resonate with the on / off frequency of the transistor 20.
The inductor 50 is connected between the end of the loop antenna 30 on the side where the feeding point is installed and the feeding point, and removes unnecessary high-frequency signals between the feeding point and the loop antenna 30 (AC separation function). )have.
One end of the capacitor 60 is connected to the connection point of the inductor 50 on the feeding point side, and the other end is grounded. The capacitor 60 functions as a bypass capacitor, and constitutes a low-pass filter that suppresses transmission of a high-frequency signal between the feeding point and the loop antenna 30.

(Operation)
Next, the operation of the wireless communication device 1 will be described.
A periodic signal that swings to a high level and a low level is input from the buffer 10 to the base of the transistor 20.
In addition, although the specific form of the signal input at this time varies depending on the wireless communication system, in the case of communication using a pulse signal such as PWM (Pulse Width Modulation), for example, it represents one pulse. A periodic signal is input to the base of the transistor 20 for a period corresponding to the width of the pulse.
When a high level signal is input to the base of the transistor 20, the transistor 20 is turned on, and the current flowing from the feeding point through the loop antenna 30 flows out from the emitter to the ground.

When a low level signal is input to the base of the transistor 20, the transistor 20 is turned off and the current flowing from the loop antenna 30 is cut off.
The transistor 20 corresponds to the high-level and low-level periodic signals input from the buffer 10 at a predetermined period (for example, 315 MHz) in a set period (for example, a period for outputting one PWM pulse). Repeat the on / off operation.
At this time, the loop antenna 30 and the capacitor 40 constitute a series resonance circuit, and their inductance and capacitance are set to values that resonate with the on / off cycle of the transistor 20.

Therefore, while the transistor 20 is off, a current in the direction opposite to that when the transistor 20 is on flows through the loop antenna 30, and an alternating magnetic field is generated in the loop antenna 30 by this current.
When the receiving-side loop antenna is arranged in the AC magnetic field generated by the loop antenna 30, the number of magnetic fluxes penetrating the receiving-side loop antenna changes according to the change of the AC magnetic field, and the current according to the change rate of the magnetic flux number is changed to the receiving side. Occurs in the loop antenna.
This current becomes a detection signal, and the reception side can receive the transmission signal.
As described above, in the wireless communication device 1 according to the reference embodiment, the loop antenna 30 and the capacitor 40 form a series resonance circuit, and a power is fed to the end of the loop antenna 30 opposite to the connection end of the output transistor. It has a point.

Therefore, it is not necessary to connect the pull-up coil and power supply to the collector of the transistor, so that all the drive current of the output transistor flows into the loop antenna without branching in the current path formed by the loop antenna and transistor. Can be made.
Therefore, high power efficiency can be realized and the number of elements constituting the circuit can be reduced, so that wireless communication using a loop antenna can be performed more efficiently.
Note that the power feeding point in this specification refers to a connection point of a DC power source.

(First Embodiment)
Next, a first embodiment of the present invention will be described.
The wireless communication apparatus according to the present embodiment has a function of transmitting a differentially output signal, and the antenna system circuit unit in the reference embodiment (circuit structure from the transistor 20 including the loop antenna 30 to the feeding point). Are provided in parallel. The wireless communication apparatus according to the present embodiment outputs the forward rotation signal and the inverted signal that are differentially output to the antenna system circuit unit provided in parallel with the loop antenna facing each other, and the forward rotation signal. The antenna system circuit unit is arranged so that the loop antenna to which the signal is inputted and the loop antenna to which the inverted signal is inputted have a current direction that generates a magnetic flux in the same direction at the time of resonance.

FIG. 2 is a diagram illustrating a configuration of the wireless communication device 2 according to the first embodiment of the present invention.
In FIG. 2, the wireless communication device 2 includes a differential signal generation circuit 110, a transmission path 120, and antenna system circuit units A and B in the reference embodiment.
The differential signal generation circuit 110 inputs a signal to be transmitted to the buffer 111 and the inverter 112, respectively, and outputs a normal signal output from the buffer 111 and an inverted signal output from the inverter 112 as a differential signal.
The transmission line 120 is a transmission line that transmits the differential signal output from the differential signal generation circuit 110 at high speed.

The antenna system circuit units A and B have the same configuration as the antenna system circuit unit in the reference embodiment.
Therefore, for each element constituting the antenna system circuit portions A and B, the description in the reference embodiment will be referred to, and here, a different part from the reference embodiment will be described.
Regarding the buffer 10, transistor 20, loop antenna 30, capacitors 40 and 60, and inductor 50 constituting the antenna system circuit portions A and B, the elements constituting the antenna system circuit portion A are denoted by reference numerals at the end. A is attached, and each element constituting the antenna system circuit unit B is added with a reference sign B at the end of the reference sign so as to be identified and represented. In FIG. 2, the buffers 10A and 10B and the capacitors 40A, 40B, 60A, and 60B included in the antenna system circuit portions A and B are not shown.

Of the differential signals output from the differential signal generation circuit 110, the normal signal output from the buffer 111 is input to the base of the transistor 20A in the antenna system circuit portion A.
The inverted signal output from the inverter 112 among the differential signals output from the differential signal generation circuit 110 is input to the base of the transistor 20B in the antenna system circuit portion B.

In the antenna system circuit portions A and B, feed points are independently installed in the loop antennas 30A and 30B.
Therefore, since the antenna system circuit portions A and B each have a unique input / output terminal, mutually independent circuits operate in parallel.
Further, the loop antennas 30A and 30B in the antenna system circuit portions A and B are disposed so as to face each other in an arrangement in which the turns are opposite to each other. Note that the loop antennas 30A and 30B are arranged to face the position where the coil centers overlap when the coil plane is viewed in plan.

FIG. 3 is a schematic diagram showing the arrangement of the antenna system circuit portions A and B. As shown in FIG.
As shown in FIG. 3, when the coil plane of the loop antenna 30A is viewed in plan from one side (the direction of arrow α in FIG. 3), if the direction from the transistor 20A toward the feeding point is clockwise, the loop antenna When the coil plane of 30B is viewed in plan from the same direction, the antenna system circuit portions A and B are arranged so that the direction from the transistor 20B toward the feeding point is counterclockwise.
Therefore, when a differential signal is input to the bases of the transistors 20A and 20B, when the transistor 20A is in a conductive state, the loop antenna 30A has a direction from the feeding point toward the transistor 20A (counterclockwise in the plan view). ) Current. At this time, in the loop antenna 30B, the transistor 20B is in a non-conductive state, and a current flows in a direction from the transistor 20B toward the feeding point due to resonance (counterclockwise in the plan view).

On the other hand, when the transistor 20B is in a conductive state, in the loop antenna 30B, a current flows in a direction from the feeding point toward the transistor 20B (clockwise in the plan view). At this time, in the loop antenna 30A, the transistor 20A is in a non-conductive state, and a current flows in a direction from the transistor 20A toward the feeding point (clockwise in the plan view) due to resonance.
That is, the loop antennas 30A and 30B of the antenna system circuit portions A and B behave such that magnetic fluxes in the same direction are generated when a differential signal is input.
When the loop antennas 30A and 30B are mounted on a circuit board, they can be overlapped with each other through a glass epoxy having a small capacitance.

(Operation)
Next, the operation will be described.
When the wireless communication device 2 transmits a wireless signal, first, an unbalanced transmission signal is input to the differential signal generation circuit 110.
Then, the differential signal generation circuit 110 inputs an unbalanced transmission signal to the buffer 111 and the inverter 112, outputs a normal rotation signal from the buffer 111, and outputs an inverted signal from the inverter 112.
The normal rotation signal output from the buffer 111 is input to the antenna system circuit unit A, and the transistor 20A is turned on and off by the normal rotation signal.

In the antenna system circuit portion A, since the loop antenna 30A and the capacitor 40A constitute a series resonance circuit, an AC magnetic field is generated in the loop antenna 30A by resonating with the on / off operation of the transistor 20A.
On the other hand, the inverted signal output from the inverter 112 is input to the antenna system circuit unit B, and the transistor 20B is turned on / off by the inverted signal.
In the antenna system circuit portion B, since the loop antenna 30B and the capacitor 40B constitute a series resonance circuit, an resonance magnetic field is generated in the loop antenna 30B by resonating with the on / off operation of the transistor 20B.

Here, as shown in FIG. 3, the loop antenna 30A and the loop antenna 30B are overlapped so that the directions from the transistors 20A and 20B toward the feeding point are opposite to each other.
Since the on / off timings of the transistor 20A and the transistor 20B are opposite to each other, the resonance currents of the loop antennas 30A and 30B flow in the same direction, and generate AC magnetic fields in the same direction.
That is, as a result of the balanced transmission signal being input to the differential signal generation circuit 110, an alternating magnetic field in the same direction is generated in the loop antennas 30A and 30B, and an alternating magnetic field generated by the loop antennas 30A and 30B alone is generated. An AC magnetic field (double magnetic flux) having twice the strength is generated.

When the receiving-side loop antenna is arranged in the AC magnetic field generated in this way, the number of magnetic fluxes penetrating the receiving-side loop antenna changes according to the change of the AC magnetic field, and the current according to the change rate of the number of magnetic fluxes is changed to the receiving side. Occurs in the loop antenna.
This current becomes a detection signal, and the reception side can receive the transmission signal.
As described above, the wireless communication device 2 according to the present embodiment includes the two antenna system circuit units in the reference embodiment, and the first non-inverted signal is transmitted among the balanced transmission signals (differential signals). The antenna system circuit part A and the inverted signal are input to the second antenna system circuit part B. The first and second antenna system circuit portions A and B are arranged so that the turns of the loop antennas 30A and 30B are reversed.

Therefore, the on / off timings of the transistors 20A and 20B are opposite to each other, and the resonance current flows in the same direction in the loop antennas 30A and 30B.
Therefore, since alternating current magnetic fields in the same direction can be generated in the loop antennas 30A and 30B, a transmission signal that is a balanced signal can be efficiently transmitted wirelessly.
In addition, since the loads existing at the input destinations of the forward signal and the inverted signal are the antenna system circuit portions A and B having the same structure, the input impedance is the same and it is not necessary to provide a matching circuit. Can be reduced.

Furthermore, each transmission signal input to the antenna as a balanced signal is input to the two antenna system circuits A and B with the loop antennas arranged in the opposite direction for wireless transmission, so that the balanced signal is converted into an unbalanced signal. Without using a balun, and the circuit scale can be further reduced.
In the reference embodiment and the first embodiment, the case where a loop antenna is used has been described as an example. However, the present invention can be applied to a coil antenna such as a planar coil antenna or a helical antenna. Is possible.

(Application 1)
In the first embodiment, the loop antennas 30A and 30B have been described as facing each other. At this time, by making the loop antennas 30A and 30B face each other with a predetermined interval, the electromagnetic waves generated by the loop antennas 30A and 30B can be obtained. Can be increased.
That is, when the loop antennas 30A and 30B generate an alternating magnetic field, part of the magnetic force lines output from the loop antenna returns to the loop antenna again, and the remaining magnetic force lines are released into the air.

The range of the magnetic field generated by the magnetic lines returning to the loop antenna is referred to as a near field, and the range of the magnetic field generated by the magnetic lines emitted to the air without returning to the loop antenna is referred to as a far field.
Near-field magnetic field lines do not release energy into the air, and therefore do not contribute to the radiation of electromagnetic waves from the loop antennas 30A and 30B.
Here, by making the loop antennas 30A and 30B face each other at a predetermined interval, the magnetic field lines of the far field can be increased, and the amount of electromagnetic waves emitted can be increased.

In addition, the space | interval at the time of making loop antenna 30A, 30B oppose can determine an appropriate range based on antenna characteristics, such as the alternating current frequency of loop antenna 30A, 30B, a resonant current amount, and a loop diameter.
In addition, by making the loop antennas 30A and 30B face each other at a predetermined interval in this way, the capacitance formed between the loop antenna 30A and the loop antenna 30B can be reduced as compared with the case where the loop antennas 30A and 30B face each other. It is also possible to reduce the loss of current flowing through the loop antennas 30A and 30B.

(Application example 2)
In the first embodiment, the loop antennas 30A and 30B have been described as being arranged to face the position where the coil centers overlap when the coil plane is viewed in plan, but the loop antennas 30A and 30B can also be arranged by shifting the centers. .
When the coil centers are shifted in this way, the AC magnetic field created by the loop antennas 30A and 30B has an inclination with respect to the coil planes of the loop antennas 30A and 30B, compared to the case where the centers are matched. The directivity direction of the loop antennas 30A and 30B can be changed.

Further, in addition to the case where one loop antenna 30B is arranged with respect to the loop antenna 30A, two or more loop antennas 30B may be arranged at different positions where the coil center is shifted with respect to the loop antenna 30A. .
By arranging the loop antennas in this way, the loop antenna 30B combined with the loop antenna 30A can be switched, and the directivity directions of the loop antennas 30A and 30B can be switched by control.

It is a figure which shows the structure of the radio | wireless communication apparatus 1 which concerns on reference embodiment. It is a figure which shows the structure of the radio | wireless communication apparatus 2 which concerns on 1st Embodiment. It is a schematic diagram which shows arrangement | positioning of the antenna system circuit parts A and B. FIG.

Explanation of symbols

1, 2 Wireless communication device 10, 10A, 10B, 111 buffer, 20, 20A, 20B transistor, 30, 30A, 30B loop antenna, 40, 40A, 40B, 60, 60A, 60B capacitor, 50, 50A, 50B inductor 110 Differential signal generation circuit 112 Inverter 120 Transmission line

Claims (3)

An output transistor that switches a conduction state between the input terminal and the output terminal according to a control signal based on a transmission signal input to the control terminal;
A coil antenna having one end connected to the input terminal of the output transistor and the other end having a feeding point;
A capacitor having one end connected to the connection point on the feeding point side in the coil antenna and the other end grounded;
First and second antenna system circuit units comprising:
A differential signal generation circuit that outputs a normal transmission signal and an inverted transmission signal obtained by inverting the normal transmission signal;
Have
In each of the first and second antenna system circuit units, the coil antenna functions as an inductor, and forms a series resonance circuit together with the capacitor.
The normal transmission signal output by the differential signal generation circuit is input to the control terminal of the output transistor in the first antenna system circuit unit, and the output transistor of the second antenna system circuit unit A radio communication apparatus, wherein an inverted transmission signal output by the differential signal generation circuit is input to a control terminal. Wherein said coil antenna in the first and second antenna circuits unit, the radio communication apparatus according to claim 1, wherein the resonant current is arranged to face the direction of flow in the same direction. Wherein said coil antenna in the first and second antenna circuits unit is according to claim 2, characterized in that it is arranged to face at a predetermined distance determined based on the antenna characteristics of each of the coil antenna Wireless communication device.

Images