Communication device and communication system

Abstract

To improve communication efficiency in a wireless communication system that performs communication by electromagnetic coupling using a transmission line.SOLUTION: A communication device according to the present invention communicates with another communication device by electromagnetic field coupling, and includes a first conductor that transmits or receives a signal by the electromagnetic field coupling, a metal member that functions as a ground for the first conductor, a second conductor connected to the first conductor, and an electrode, one of which is connected to the second conductor, and the other of which is supplied with the signal or to which a termination resistor is connected.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a communication device and a communication system for wirelessly transmitting signals. [Background technology]

[0002] In recent years, close-proximity wireless communication systems that wirelessly communicate using electromagnetic coupling between nearby devices have been researched and developed. Patent Document 1 describes a configuration in which a transmission line is configured by forming a differential signal line 101 as shown in Fig. 12 on a flexible substrate 107 and making a metal member 106 function as a ground, and efficient communication is achieved between the transmission line and another transmission line that is electromagnetically coupled to the above transmission line. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-48068 A Summary of the Invention [Problem to be solved by the invention]

[0004] 2. Description of the Related Art In wireless communication systems that perform communication by electromagnetic coupling using a transmission line, such as the technique described in Patent Document 1, there is a demand for further improvement in communication efficiency.

[0005] In order to further improve communication efficiency, noise reduction is necessary. For example, mismatch between the characteristic impedance of a transmission line and the impedance of a power feeder / termination unit may cause reflected waves from the power feeder / termination unit, resulting in noise. This may result in degradation of signal quality and communication efficiency. In view of the above problems, the present invention aims to improve communication efficiency in a wireless communication system that communicates by electromagnetic coupling using a transmission line. [Means for solving the problem]

[0006] The communication device of the present invention comprises: A communication device that communicates with another communication device by electromagnetic coupling, a first conductor for transmitting or receiving a signal by the electromagnetic coupling; a metal member that functions as a ground for the first conductor; a second conductor connected to the first conductor; One end is connected to the second conductor, The other electrode is an electrode to which the signal is supplied or to which a termination resistor is connected; The present invention is characterized by having the following. Effect of the Invention

[0007] According to the present invention, it is possible to improve the efficiency of communication in a wireless communication system that performs communication by electromagnetic field coupling using a transmission line. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a configuration diagram of a transmission line according to the present invention. [Diagram 2] 1 is a schematic diagram of an electric board inserted between a flexible board and a metal member. [Diagram 3] Reflection characteristics when a substrate 200 made of fluororesin is inserted into the power supply section or terminal section of a differential transmission line. [Figure 4] 6 shows time waveforms at the power supply section and the termination section of a differential transmission line when a substrate 200 made of a fluororesin material is inserted into the power supply section and the termination section. [Diagram 5] Reflection characteristics when a board 200 made of FR-4 material is inserted into the power supply section or termination section of a differential transmission line. [Figure 6] 13 shows time waveforms at the power supply section and the termination section of a differential transmission line when a board 200 made of FR-4 material is inserted into the power supply section and the termination section. [Figure 7] FIG. 13 is a configuration diagram of another differential transmission line according to the present invention. [Figure 8] FIG. 13 is a configuration diagram of still another differential transmission line according to the present invention. [Figure 9]Reflection characteristics when a board 200 made of FR-4 with d=3.0 mm is inserted into the power supply section or termination section of a differential transmission line. [Figure 10] 13 shows time waveforms at the power supply point and termination point of a differential transmission line when a board 200 made of FR-4 with board material d=3.0 mm is inserted into the power supply point or termination point. [Figure 11] 1 is a configuration diagram of a wireless communication system according to the present invention. [Figure 12] FIG. 1 shows a transmission line using a flexible substrate. [Figure 13] FIG. 13 is a diagram showing a method of feeding or terminating a transmission line using a flexible substrate. [Figure 14] 14 is a graph showing reflection characteristics in the power supply or termination method of FIG. 13. [Figure 15] FIG. 13 illustrates another method of feeding or terminating a transmission line using a flexible substrate. [Figure 16] 16 is a graph showing reflection characteristics in the power supply or termination method of FIG. 15. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Issues at the power supply / termination sections of transmission lines> Before describing the embodiments of the present invention, the problem with the transmission line in FIG. 12 will be further described.

[0010] As shown in Fig. 12, differential signal lines 101 for transmitting signals are provided on a flexible substrate (hereinafter, referred to as a flex substrate) 107, and a transmission line is formed with the metal surface of a metal member 106 that is approximately parallel to the flex substrate 107 as the ground surface. In this configuration, an air space is formed between the differential signal lines 101 for transmitting signals and the ground surface. Since air has a relative dielectric constant of 1 and no dielectric loss, it is possible to configure a transmission line with little loss even when it is long. However, since the differential signal lines 101 and the ground surface are located at a distance from each other, it is difficult to implement a commonly used coaxial connector or coaxial cable.

[0011] Simulation results will be shown and explained below.

[0012] FIG. 13 shows a simulation model in which differential signal lines 101 are formed on a flexible board, and wiring 108 is extended from the differential signal lines toward the metal member 106 to which the flexible board is fixed, in a transmission line in which the metal member 106 to which the flexible board is fixed serves as the ground plane. FIG. 14 is a graph showing the reflection characteristics at the termination of FIG. 13. In FIG. 14, the reflection is -10 dB or more above 2.2 GHz. This large reflection indicates that impedance mismatch occurs at the termination. FIG. 15 shows a model in which the termination of a transmission line similar to that of FIG. 13 is connected to a pattern for a surface-mounted small coaxial connector, and FIG. 16 shows the reflection characteristics of FIG. 15. In FIG. 16, the reflection characteristics are slightly improved compared to FIG. 14, but the reflection is -10 dB or more above 3.2 GHz, indicating that impedance mismatch occurs.

[0013] Generally, if the reflection characteristic is -10 dB or less up to twice the fundamental frequency of the signal being transmitted, there will be less signal distortion and fewer errors. In the following, the present invention will be explained using a 10 Gbps signal as an example. Therefore, it is desirable for the reflection to be -10 dB or less up to 10 GHz.

[0014] <Example> As a configuration for solving the above problem, FIG. 1(1) shows a configuration diagram of a transmission line according to the present invention, and FIG. 1(2) shows a cross-sectional view. The transmission line is composed of differential signal lines 101 formed on a flexible substrate 107, and a metal member 106 that fixes the flexible substrate 107 and serves as a reference potential for the differential signal lines 101. A groove is formed in the metal member 106 directly below the differential signal lines 101, and the depth of the groove is adjusted so that the transmission line width of the differential signal lines 101 and the impedance between the differential signal lines are desired. In this way, a differential microstrip line is formed at the ground of the differential signal lines 101 and the metal member 106. 200 is an electric substrate of the present invention for feeding power to the transmission line formed by the differential signal lines 101 and the metal member 106 on the flexible substrate, or for terminating the transmission line. In the substrate 200, 201 is a differential signal line composed of a flat conductor that is connected to the differential signal lines 101 of the flexible substrate 107 by soldering or the like. Reference numeral 202 denotes an extraction electrode, which is connected to differential signal line 201 through via 203. Substrate 200 is inserted between flexible substrate 107 and metal member 106 at the power supply portion or end portion of flexible substrate 107. Here, metal member 106 is notched so as to avoid contact with extraction electrode 202 of substrate 200.

[0015] In FIG. 1(2), 204 is solder that connects the differential signal line 101 of the flexible board 107 and the differential signal line 201 of the board 200. 206 is a ground metal that acts as a reference potential of the differential signal line 201, and when the board 200 is fixed, it comes into contact with the metal member 106 and is electrically connected. As a result, the metal member 106 and the ground conductor 206 have approximately the same potential. Here, the ground conductor 206 of the board 200 and the metal member 106 may be electrically connected by a conductive adhesive or the like, and the conductive means is not particularly limited as long as it acts as a reference potential. In addition, the method of fixing the flexible board 107 and the board 200 is not particularly limited, and may be screwed or bonded with an adhesive. In addition, the flexible board 107 is long enough to cover the board 200, but may be designed to cover the entire electric board 200.

[0016] 2 shows a schematic diagram of the substrate 200. This diagram is seen from the surface on which the extraction electrodes 202 and the ground conductor 206 are formed. The substrate 200 is provided with differential signal lines 201 that are connected to the differential signal lines 101 on the flexible substrate 107, and ground conductors 206 that are in contact with and electrically connected to the ground surface of the metal member 106. Here, a differential microstrip line is also formed on the substrate 200 by the differential signal lines 201 and the ground of the conductors 206.

[0017] Here, the differential signal line 101 of the flexible board and the differential signal line 201 of the board 200 are made of planar conductors and are connected by soldering or a conductive adhesive. Also, the ground conductor 206 which is the reference potential of the differential signal line 201 is connected to the metal member 106 by pressure bonding with a screw or the like (not shown), an anisotropic conductive film (ACF), a conductive adhesive, or the like.

[0018] Here, if the differential characteristic impedance of the differential signal lines 101 on the flexible substrate 107 is 100Ω and the spacing between the centers of the differential signal lines is 4 mm, the line width of the differential signal lines 101 is 3.58 mm and the spacing is 0.42 mm.

[0019] First, the case where the substrate 200 is a fluororesin substrate with a thickness of 1.6 mm is shown. When the center interval of the differential signal lines 201 is set to be the same as that of the differential signal lines 101 of the flexible substrate 107, the line width of the differential signal lines 201 is 2.83 mm, and the line spacing is 1.17 mm. At this time, the differential characteristic impedance is 100 Ω, and impedance matching can be achieved. FIG. 3 shows the reflection characteristics when the substrate 200 made of a fluororesin substrate material is inserted into the termination of the differential transmission line in FIG. 1. The solid line shows the case where the line width and line spacing of the differential signal lines 201 are set to match the characteristic impedance of the substrate 200 with that of the flexible substrate (line width: 2.83 mm, line spacing: 1.17 mm). On the other hand, the dotted line shows the characteristics when the line width and line spacing of the differential signal lines 201 of the substrate 200 are set to the line width and line spacing of the differential signal lines 101 of the flexible substrate (line width: 3.58 mm, line spacing: 0.42 mm). It can be seen that the solid line has better reflection characteristics in almost all frequency bands than the dotted line. Therefore, by matching the characteristic impedance of the fluororesin board to the characteristic impedance of the flexible board, mismatch can be reduced.

[0020] FIG. 4 shows a fluororesin substrate 200 inserted into the termination of the differential transmission line in FIG. 1, and a 10 Gbps signal is input via the extraction electrode 202 of the substrate 200. It is a diagram showing the time waveforms of the power feed section and the termination section when the substrate 200 of the same structure is terminated. In the figure, (1) is the waveform at the power feed section of the extraction electrode 202, and (2) is the waveform at the termination section. The solid line shows the case where the line width and line spacing of the differential signal line 201 are set so that the characteristic impedance of the substrate 200 matches the characteristic impedance of the flexible substrate. On the other hand, the dotted line shows the characteristics when the line width and line spacing of the differential signal line 201 of the substrate 200 match the line width and line spacing of the differential signal line 101 of the flexible substrate. When the line width and line spacing of the differential signal line 201 are matched to the characteristic impedance of the flexible substrate 107, the waveform disturbance due to reflection, especially at the input section, is very small. Even when the line width and line spacing of differential signal line 201 are matched to those of differential signal line 101, although there is some disturbance in the waveform at the input section, the disturbance in the waveform is small.

[0021] Next, the case where the board 200 is an FR-4 board with a thickness of 1.6 mm is shown. When the center interval of the differential signal lines 201 is set to be the same as that of the differential signal lines 101 of the flexible board 107, the line width of the differential signal lines 201 is 2.02 mm and the line spacing is 1.98 mm, which is narrower and wider than that of fluororesin. FIG. 5 shows the reflection characteristics when the board 200 is inserted into the termination of the differential transmission line when the board material is FR-4. In the figure, the solid line shows the case where the line width and line spacing of the differential signal lines 201 are set to match the characteristic impedance of the board 200 with the characteristic impedance of the flexible board (line width: 2.02 mm, line spacing: 1.98 mm). On the other hand, the dotted line shows the characteristics when the line width and line spacing of the differential signal lines 201 of the board 200 are set to the line width and line spacing of the differential signal lines 101 of the flexible board (line width: 3.58 mm, line spacing: 0.42 mm).

[0022] 6 shows the time waveforms at the power feed point and the termination point when a board 200 made of FR-4 material is inserted into the termination point of the differential transmission line in FIG. 1, a 10 Gbps signal is fed through the extraction electrode 202 of the board 200, and a similar electric board is terminated. In the figure, (1) is the waveform at the power feed point of the extraction electrode 202, and (2) is the waveform at the termination point, and the solid line is the case when the line width and line spacing of the differential signal line 201 are set so that the characteristic impedance of the board 200 matches the characteristic impedance of the flexible board. On the other hand, the dotted line is the characteristic when the line width and line spacing of the differential signal line 201 of the board 200 are set to the line width and line spacing of the differential signal line 101 of the flexible board. When the line width and line spacing of the differential signal line 201 are set so that the characteristic impedance matches that of the flexible board 107, the waveform disturbance due to reflection is very small. On the other hand, when the line width and space of differential signal line 201 are set to the same as those of differential signal line 101, the waveform is significantly distorted.

[0023] As can be seen from the results of Figures 3 to 6, when comparing the case where the substrate 200 is a fluororesin substrate with the case where it is an FR-4 substrate, it is found that the fluororesin substrate has better characteristics. This is because the relative dielectric constant of fluororesin is approximately 2.2, while the relative dielectric constant of FR-4 is approximately 4.4, so the line width and spacing of the flexible substrate can be made close to these values. This makes it possible to reduce the occurrence of impedance mismatch.

[0024] 3 to 6 show the characteristics when inserting a board 200 with a board thickness that matches the distance of 1.6 mm between flexible board 107 and metal member 106. Note that the thickness of board 200 does not need to match the distance between flexible board 107 and metal member 106, and a combination in which the thickness of board 200 and the distance between flexible board 107 and member 106 are different is also possible, as shown in FIG.

[0025] 8, the substrate 200 may be a multi-layer substrate, and the metal portion 207 in contact with the metal member 106 and the ground conductor 206 serving as the ground plane for the differential signal line 201 of the substrate 200 may be in different layers. It is desirable that the metal portion 207 in contact with the metal member 106 and the ground conductor 206 are connected to each other with as low impedance as possible by a plurality of vias or the like provided in the substrate.

[0026] Here, in the substrate 200, the material between the ground conductor 206 and the metal portion 207 and the material between the differential signal line 201 and the metal surface 206 may be different substrates, or may be a laminate of a dielectric material and FR-4 or the like. In particular, if the material between the differential signal line 201 and the ground conductor 206 is a dielectric material with a low dielectric constant, the line width and the distance between the lines will be closer in the portion of the differential signal line 101 where the substrate 200 is not inserted and the portion where the substrate 200 is inserted, and loss due to reflection can be reduced.

[0027] <Modification> Next, the configuration when the board thickness is increased is shown. FIG. 9 shows the reflection characteristics when the board 200 is an FR-4 board at the termination of the differential transmission line in FIG. 1 and the board thickness is 3.0 mm. In the figure, the solid line shows the characteristics when the line width and line spacing of the differential signal line 201 are set to match the characteristic impedance of the board 200 to the characteristic impedance of the flexible board (line width: 2.63 mm, line spacing: 1.37 mm). On the other hand, the dotted line shows the characteristics when the line width and line spacing of the differential signal line 201 of the board 200 are set to the line width and line spacing of the differential signal line 101 of the flexible board (line width: 3.58 mm, line spacing: 0.42 mm). It can be seen that the solid line has better reflection characteristics in almost all frequency bands than the dotted line. Therefore, in this case too, mismatching is reduced by matching the characteristic impedance to the characteristic impedance of the flexible board.

[0028] FIG. 10 shows the time waveforms of the power supply section and the termination section when a 10 Gbps signal is fed through the extraction electrode 202 of the above-mentioned substrate 200 and terminated by a similar electric substrate. In the figure, the solid line shows the case where the line width and line spacing of the differential signal line 201 are set to match the characteristic impedance of the substrate 200 to the characteristic impedance of the flexible substrate. On the other hand, the dotted line shows the characteristics when the line width and line spacing of the differential signal line 201 of the substrate 200 are matched to the line width and line spacing of the differential signal line 101 of the flexible substrate. Even in the case of a substrate thickness of 3.0 mm, when the characteristic impedance of the differential signal line 201 is matched to the flexible substrate 107, the waveform disturbance due to reflection is very small, and the waveform disturbance can be reduced. On the other hand, when the line width and line spacing of the differential signal line 201 are matched to the line width and line spacing of the differential signal line 101, the waveform is disturbed, and it is clear that reflection occurs.

[0029] As described above, in a transmission line in which a board provided with differential signal lines and a metal surface of a member or the like are used as a reference potential, a stable power supply section or a termination section, or both, with little reflection can be provided by inserting an electric board as described above. The board material, board thickness, signal line width, line spacing, and the like described here are specified for the purpose of explanation and are not limited thereto. The electric board also includes one in which a metal pattern is drawn on a dielectric material, and in this case, the connection section connecting the differential signal line 201 and the extraction electrode is not limited to a via, and the material and shape are not particularly limited as long as it is a conductive material passed through a hole in the dielectric material. Also, the extraction electrode only needs to be connected to a connection section such as a via, and may also be used as a pattern connected to an electric circuit component as it is, or as a foot pattern of a cable connector or other components.

[0030] In addition, when using an FR-4 board with a board thickness of 3.0 mm, the line width is 2.63 mm, which is wider than the line width of 2.02 mm when the board thickness is 1.6 mm. This makes it possible to strengthen the electromagnetic coupling with the opposing coupler, which will be explained in the next chapter, and improve the signal level.

[0031] <Wireless communication system configuration> FIG. 11(1) shows an example of the configuration of a wireless communication system using a transmission line. In the figure, the first transmission line 100 is the same as in FIG. 1, and will be referred to as the first coupler hereafter. The first coupler 100 and the second coupler 110 face each other and transmit data by electromagnetically coupling. The second coupler is placed at a location with a predetermined distance from the first coupler, and moves in the longitudinal direction of the first coupler while maintaining that distance. Also, the second coupler is placed so that at least a part of it overlaps when viewed from the vertical direction. Furthermore, the length of the second coupler is configured to be shorter than the length of the first coupler. The second coupler 110 is composed of at least a differential signal line 111.

[0032] Fig. 11(2) is a simplified diagram of the board 200 when the first coupler operates as a transmitting coupler and inputs a signal. In Fig. 11(2), 1101 denotes a high-frequency connector, and 104 denotes a transmitting buffer consisting of a high-frequency amplifier with a differential output. Fig. 11(3) is a simplified diagram of the board 200 when the first coupler operates as a receiving coupler and outputs a signal. In Fig. 11(3), 113 denotes a high-frequency amplifier with a differential input, or a comparator with hysteresis. When the high-frequency circuit is mounted on the board as in the figure, it is easy to make the patterns of the differential signals the same length, and the skew between the differential signals can be made very small.

[0033] Furthermore, Fig. 11(4) is a diagram showing the termination of the lead-out electrodes 202' of the termination board 200'. In this figure, the lead-out electrodes connected to the differential signal lines are individually terminated to metal 206', which serves as ground at the termination resistors 102, 102'. Here, it is also possible to terminate between both lead-out electrodes 202' using the differential characteristic impedance without going through ground. In this case, the termination may be performed on the flexible board without inserting the board 200'.

[0034] If the board 200 is a multi-layer board as shown in Fig. 8, it is possible to insert a ground layer between the first surface layer on which the differential signal lines 201 are printed and the second surface layer on which the high-frequency circuit section that inputs and outputs high-frequency signals is mounted. This ground layer serves as a common reference potential for the differential signal lines 201 and the high-frequency circuit section. Since the distance between the high-frequency circuit and the differential signal lines is short and fixed, the high-frequency signal is very stable when being input to and output from the differential signal lines 201 and further to the differential signal lines 101 connected thereto.

[0035] In addition, the differential signal line 111 may be in the form of an inductive coupler in which both differential signal lines are directly or indirectly connected and a current change occurring between the differential signal lines 111 is detected, or in the form of a capacitive coupler in which both signal lines are separated and a voltage difference between the signal lines is detected.

[0036] Also, a metal 114 serving as a reference potential may be disposed on the substrate surface opposite to the differential signal line 111. In this case, a directional coupler of a microstrip line in which one end is shorted and a signal is detected from the other end may be used. Furthermore, as a directional coupler system, the differential signal line 111 may be in the form of a coplanar line having a ground potential on both sides of the same surface as the differential signal line 111. An extraction electrode 212 is connected to the second transmission line 110, and differential signals are input and output.

[0037] Although the case where a high-frequency circuit board is mounted on an electric board 202 on a board has been described using the examples of Figures 11(1), (2), and (3), a cable may be connected to the extraction electrode 202 and signal processing may be performed on a separate board. [Explanation of symbols]

[0038] 100 First transmission line (coupler) 101 Differential signal line of the first transmission line 102 Termination resistor 103 Signal source 104 Send Buffer 106 Metallic parts 107 Flexible PCB 110 Second Transmission Line (Coupler) 111 Differential signal line of the second transmission line 112 Termination resistor 113 Comparator 200 First transmission line and electric board for inputting and outputting signals 201 Differential signal lines on an electrical board 202 Extraction electrode 203 Via and other connections 206 Ground conductor of differential signal lines on electrical boards 207 Metal that is conductive to components

Claims

1. A communication device that communicates by electromagnetic field coupling with other communication devices, A first conductor that transmits or receives a signal by electromagnetic field coupling, A metal member that functions as the ground for the first conductor, A second conductor connected to the first conductor, One end is connected to the second conductor, The other side has an electrode to which one of the transmitting circuit, receiving circuit, or terminating resistor is connected, A communication device characterized by having the following features.

2. The first conductor and the second conductor are planar conductors. The communication device according to claim 1, characterized in that the first conductor is connected to the second conductor on a surface different from the surface on which the signal is transmitted or received by electromagnetic field coupling.

3. The first conductor has a first differential signal line, The second conductor has a second differential signal line, The communication device according to claim 1 or 2, characterized in that the center spacing of the first differential signal line and the center spacing of the second differential signal line are substantially the same.

4. The first differential signal line and, The aforementioned metal member, The characteristic impedance of a first transmission line having, The second differential signal line and, A third conductor is positioned apart from the second differential signal line, The characteristic impedance of the second transmission line having is approximately the same as that of the second transmission line having The communication device according to feature 3.

5. The communication device according to claim 4, characterized in that the first conductor is configured on a first substrate. Place.

6. The communication device according to claim 5, characterized in that the first substrate is a flexible substrate.

7. The communication device according to claim 4, characterized in that the second conductor, the electrode, and the third conductor are configured on a second substrate.

8. The communication device according to claim 7, characterized in that the second conductor and the third conductor are configured in different layers of the second substrate.

9. The communication device according to claim 8, characterized in that the second substrate is made of a dielectric material.

10. The communication device according to claim 9, characterized in that the dielectric material is a fluororesin.

11. The communication device according to claim 10, characterized in that the third conductor of the second substrate is connected to the metal member via a screw or conductive adhesive.

12. The first conductor and, A metal member that functions as the ground for the first conductor, A second conductor connected to the first conductor, One end is connected to the second conductor, The other side has an electrode to which one of the transmitting circuit, receiving circuit, or terminating resistor is connected, A transmitting or receiving device having, A transmitting or receiving device having a fourth conductor positioned at a distance from the first conductor and electromagnetically coupled to the first conductor, A wireless communication system characterized by having the following features.

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