Wireless communication system and control method

Abstract

To prevent a reduction in communication quality caused by the positional deviation between apparatuses that perform radio communication by electromagnetic field coupling.SOLUTION: A radio communication system has: a first coupler having a first pair of electrodes extending in a predetermined direction; a second coupler having a second pair of electrodes making electromagnetic field coupling with the first pair of electrodes; a first circuit transmitting or receiving a differential signal via the first coupler; and a second circuit transmitting or receiving a differential signal via the second coupler. The first pair of electrodes have a first electrode and a second electrode. The second pair of electrodes have a third electrode at least partially opposite to the first electrode and a fourth electrode at least partially opposite to the second electrode. On a flat surface perpendicular to the predetermined direction, the width of the third electrode is smaller than the width of the first electrode, the width of the fourth electrode is smaller than the width of the second electrode, and the clearance in the width direction between the third electrode and fourth electrode is different from the clearance in the width direction between the first electrode and the second electrode. The first coupler or the second coupler has a mechanism allowing the first coupler and the second coupler to move relatively in the predetermined direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wireless communication system and a control method. [Background technology]

[0002] In recent years, medical equipment and industrial robots are increasingly equipped with cameras and other devices, and systems are increasingly transmitting large amounts of data, such as image signals, at high speed between a fixed part and a moving part that moves parallel to and / or rotates relative to the fixed part. For example, in a CT scanner, a rotating part, a gantry, is used to capture multiple X-ray images at different rotation angles, and a computer installed in the fixed part processes the acquired X-ray images according to a predetermined algorithm to create images for diagnosis or examination. For this purpose, multiple X-ray images are transferred from the rotating part to the fixed part.

[0003] Patent Document 1 discloses a communication system for performing data communication between a rotating unit and a fixed unit in such a CT device. The communication system described in Patent Document 1 includes a differential transmission line positioned and attached substantially along an overall annular rotating frame, and a differential coupler attached to the fixed frame. The differential coupler is positioned and disposed in a passage sufficiently close to the differential transmission line so that it can receive a signal applied to the differential transmission line by wireless coupling with the differential transmission line. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 08-224233 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 has a structure in which the cross sections of the differential coupler and the signal conductors of the differential transmission line have the same cross section size along the rotation axis of the rotating part and are arranged symmetrically facing each other. However, with this structure, if there is misalignment between the rotating part and the fixed part in the direction of the rotation axis of the rotating part, the positional relationship between the differential coupler and the signal conductors of the differential transmission line will shift laterally, causing significant fluctuations in the differential signal received by the differential coupler. As a result, communication quality may deteriorate and errors may occur in data transmitted from the rotating part to the fixed part. Similar issues may arise not only in systems communicating between fixed and rotating parts, but also in systems that perform wireless communication using electromagnetic coupling, such as systems communicating between a fixed part and a moving part that moves in parallel.

[0006] In view of the above-mentioned problems, the present invention provides a technique capable of suppressing a decrease in communication quality due to a positional shift between devices that perform wireless communication by electromagnetic field coupling. [Means for solving the problem]

[0007] A wireless communication system according to an aspect of the present invention includes the following configuration: a first coupler having a first pair of electrodes extending in a predetermined direction; a second coupler having a second pair of electrodes electromagnetically coupled with the first pair of electrodes; a first circuit for transmitting or receiving a differential signal through the first coupler; a second circuit for transmitting or receiving a differential signal through the second coupler; the first pair of electrodes includes a first electrode and a second electrode; the second pair of electrodes includes a third electrode at least partially facing the first electrode and a fourth electrode at least partially facing the second electrode; In a plane perpendicular to the predetermined direction, a width of the third electrode is smaller than a width of the first electrode, a width of the fourth electrode is smaller than a width of the second electrode, and a separation distance between the third electrode and the fourth electrode in the width direction is different from a separation distance between the first electrode and the second electrode in the width direction; The first coupler or the second coupler has a mechanism that allows the first coupler and the second coupler to move relatively in a predetermined direction. [Effects of the Invention]

[0008] According to the present invention, a decrease in communication quality due to misalignment between devices that perform wireless communication by electromagnetic field coupling is suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a close-proximity communication system according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a differential transmission line and a differential coupler according to the first embodiment. [Figure 3A] 10A and 10B are diagrams illustrating fluctuations in a received differential signal in a conventional close-proximity communication system. [Figure 3B] 5A and 5B are diagrams illustrating the principle of suppressing fluctuations in a received differential signal according to the first embodiment. [Figure 4] FIG. 2 is a cross-sectional view of an evaluation sample according to the first embodiment. [Figure 5] FIG. 10 is a diagram showing a simulation result according to the second embodiment. [Figure 6] FIG. 10 is a cross-sectional view of a close-proximity communication system according to a third embodiment. [Figure 7] 10A and 10B are a perspective view and a cross-sectional view of a close-proximity communication system according to a fourth embodiment. [Figure 8] FIG. 13 is a perspective view of a proximity communication system according to a fifth embodiment. [Figure 9] 13A and 13B are diagrams illustrating the principle of suppressing fluctuations in a received differential signal according to a sixth embodiment. [Figure 10] 13A and 13B are diagrams illustrating the principle of suppressing fluctuations in a received differential signal according to the seventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0011] First Embodiment FIG. 1 is a perspective view of a proximity communication system as an example of a wireless communication system including a transmitter and a receiver according to a first embodiment. The transmitter includes a differential transmission line 1 as a transmission coupler and a transmission circuit 3. The receiver includes a differential coupler 2 as a reception coupler and a reception circuit 4. The differential transmission line 1 and the differential coupler 2 are arranged so as to face each other at least partially. A differential signal output from the transmission circuit 3 is received by the reception circuit 4 through the electromagnetically coupled transmission coupler and reception coupler. More specifically, when a differential signal is applied from the transmission circuit 3 to the differential transmission line 1, a differential signal is output from the differential coupler 2 due to electromagnetic coupling between the differential transmission line 1 and the differential coupler 2, and the output differential signal is received by the reception circuit 4. The reception circuit 4 shapes the received differential signal, which is a wireless signal, into a desired digital signal waveform and outputs it. That is, the reception circuit 4 is connected to a pair of differential signal lines 21 and 22 of the differential coupler 2 and detects the differential signal received by the pair of differential signal lines. The digital signal output from the receiving circuit 4 is used for various signal processing. That is, the pair of differential signal lines 21 and 22 is a pair of electrodes that function as an antenna for receiving a differential signal wirelessly.

[0012] The transmitter circuit 3 has the function of outputting a differential signal to the transmitter coupler. If necessary, the transmitter circuit 3 may include an amplifier, an attenuator, or various filter circuits. Furthermore, if the transmitter circuit 3 includes a divider or the like for distributing the differential signal, it can transmit power to multiple transmitter couplers simultaneously. The receiver circuit 4 has the function of converting the radio signal into a digital signal, and is specifically implemented by a comparator circuit or the like. Filter circuits such as damping resistors, low-pass filters, high-pass filters, band-pass filters, band-stop filters, and common-mode filters may be connected to the receiver circuit 4 for noise reduction or other purposes. The receiver circuit 4 may also include a multiplexer for combining multiple received signals. As described above, the transmitter coupler and receiver coupler are configured by a combination of a differential transmission line 1 and a differential coupler 2.

[0013] 1 shows a proximity communication system in which the transmitting coupler is configured with a differential transmission line 1 and the receiving coupler is configured with a differential coupler 2, with the differential transmission line 1 being larger than the differential coupler 2. However, the size relationship between the differential transmission line 1 and the differential coupler 2 is not limited to this, and the differential transmission line 1 may be smaller than the differential coupler 2. In other words, the system may be configured such that a differential signal is applied to differential signal lines 21 and 22 and is received by differential signal lines 11 and 12.

[0014] The differential transmission line 1 is formed of a flat cable, a flexible substrate, a printed circuit board, or the like. For example, in the differential transmission line 1, a pair of differential signal lines 11 and 12 having a microstrip structure or a conplanar structure are formed on an insulating material such as FR-4. A differential signal is applied to the pair of differential signal lines 11 and 12 from a transmission circuit 3. That is, the pair of differential signal lines 11 and 12 are a pair of electrodes that function as antennas for wirelessly transmitting differential signals. The differential signal lines 11 and 12 may be formed on an inner layer or a surface layer of a multilayer substrate. If the differential signal lines 11 and 12 are formed on a surface layer, it is preferable to cover the differential signal lines with a protective material such as a resist material. A GND layer 10 is formed on the surface of the differential transmission line 1 opposite to the surface on which the differential signal lines 11 and 12 are arranged.

[0015] In the differential transmission line 1, the widths of the differential signal lines 11 and 12 (differential signal line widths) and the distance between the differential signal lines 11 and 12 (signal line distance (electrode distance)) are determined so as to achieve a desired characteristic impedance. One end of the differential signal lines 11 and 12 is terminated by a termination circuit 5, and the other end is connected to a transmission circuit 3. For example, the differential signal line width and the signal line distance are determined so as to achieve a differential impedance of 100 Ω. However, the differential signal line width and the signal line distance are not particularly limited as long as they match the transmission circuit 3 and the termination circuit 5. Furthermore, if it is desired to form a long differential transmission line 1, this can be achieved by connecting multiple substrates as shown in FIG. 1. In this case, the differential signal lines of each connected substrate only need to have approximately the same differential characteristic impedance and be electrically connected, and there are no restrictions on the electrical material constants or layer configuration of the substrates.

[0016] Like the differential transmission line 1, the differential coupler 2 can be formed on a printed circuit board or the like. In the differential coupler 2, both ends of the differential signal lines 21 and 22 are arranged in an electrically open state. The differential signal lines 21 and 22 receive the differential signals applied to the differential signal lines 11 and 12 of the differential transmission line 1 by electromagnetic coupling and supply the signals to the receiving circuit 4. A GND layer 20 (see FIG. 2(a)) is formed on the surface of the differential coupler 2 opposite to the surface on which the differential signal lines 21 and 22 are arranged. While FIG. 1 shows a configuration in which the receiving circuit 4 is electrically connected to approximately the center of each of the differential signal lines 21 and 22 in the longitudinal direction, this is not limiting. For example, the differential signal lines 21 and 22 may be so-called directional couplers, in which one end of each is terminated in a termination circuit and the other end is connected to the receiving circuit 4. The length of the differential coupler 2 is shorter than the length of the differential transmission line 1 and is adjusted according to the transmission speed of the differential signals. Moreover, the differential transmission line 1 and the differential coupler 2 are arranged so as to be relatively movable in a predetermined direction (for example, a direction substantially perpendicular to the direction in which the differential signal lines 21 and 22 are arranged, i.e., the left-right direction in FIG. 1 ) while maintaining a positional relationship in which they are at least partially opposed to each other. For example, the differential transmission line 1 is arranged on the moving / rotating side, and the differential coupler 2 is arranged on the fixed side. Alternatively, the differential transmission line 1 is arranged on the fixed side, and the differential coupler 2 is arranged on the moving / rotating side. A suitable example is a configuration in which the differential transmission line 1 is arranged on the rotating part (gantry) side of a CT scanner, and the differential coupler 2 is arranged on the fixed part side, and X-ray information is transmitted from the rotating part to the fixed part. However, both the differential transmission line 1 and the differential transmission line 2 may be movable. The proximity communication system has a driving unit (movement control unit) such as a motor for moving at least one of the differential transmission lines 1 and 2 in a predetermined direction.

[0017] In this embodiment, electromagnetic field coupling includes both electric field coupling and magnetic field coupling. That is, wireless communication between couplers may be performed by electric field coupling, magnetic field coupling, or both electric field coupling and magnetic field coupling. Magnetic field coupling includes electromagnetic induction and magnetic field resonance. Note that this embodiment will mainly describe wireless communication using electric field coupling. In this embodiment, the direction connecting the centers of gravity of differential signal line 21 and differential signal line 22 is approximately the same as the direction connecting the centers of gravity of differential signal line 11 and differential signal line 22. Furthermore, the size and shape of differential signal line 11 and differential signal line 22 are approximately the same. However, the relationship between the sizes and shapes of the differential signal lines is not limited to this.

[0018] Next, the differences in the configuration between the proximity communication system according to the first embodiment and a conventional proximity communication system will be described with reference to Fig. 2. Fig. 2(a) is a cross-sectional view of a conventional differential transmission line 1 and differential coupler 2 as disclosed in Patent Document 1. As shown in Fig. 2(a), the sum of the differential signal line width (w) and the distance between the signal lines (g) in the differential transmission line 1 and the differential coupler 2 is equal, being w1. The signal line widths of the differential signal lines 11 and 12 and the differential signal lines 21 and 22 are all equal. Furthermore, the distance (gap) between the differential signal lines 11 and 12 and the differential signal lines 21 and 22 is G.

[0019] 2(b) is a cross-sectional view of the differential transmission line 1 and the differential coupler 2 according to the first embodiment. The sum w2 of the differential signal line width and the distance between the signal lines of the differential coupler 2 is smaller than the sum w1 of the differential signal line width and the distance between the signal lines of the differential transmission line 1. The line widths of the pair of differential signal lines 11 and 12 and the pair of differential signal lines 21 and 22 are equal, and in this example, the line width of the differential signal lines 21 and 22 is narrower than the line width of the differential signal lines 11 and 12. The differential coupler 2 is disposed relative to the differential transmission line 1 so that the center axes of the differential signal lines are as closely aligned as possible, with a gap G between the differential signal lines. The differential transmission line 1 is formed with a differential signal line 11 for transmitting a non-inverted signal and a differential signal line 12 for transmitting an inverted signal. A non-inverted signal and an inverted signal are induced in the differential signal lines 21 and 22 formed on the differential coupler 2 by the differential signal lines 11 and 12 of the differential transmission line 1, respectively.

[0020] The principle behind the close-proximity communication system of the first embodiment being resistant to lateral misalignment will be described with reference to Figures 3A and 3B. Figures 3A and 3B are diagrams illustrating the received voltage when lateral misalignment occurs between the differential transmission line 1 and the differential coupler 2 shown in Figure 2. Note that the lateral misalignment refers to a misalignment in a direction perpendicular to the transmission direction of the differential signal (the direction from the differential transmission line 1 toward the differential coupler 2) and perpendicular to the movement direction of the differential coupler 2 (the longitudinal direction of the differential signal lines 11 and 12).

[0021] First, we will explain the case of a conventional close-proximity communication system in which the sum of the differential signal line width and the distance between the signal lines in the differential transmission line 1 and the differential coupler 2 is equal, as shown in Figure 2(a). As shown on the left side of Figure 3A, when the centers of the sum of the differential signal line width and the distance between the signal lines in the differential transmission line 1 and the differential coupler 2 are aligned (no lateral misalignment occurs), a maximum coupling state is reached. In this case, the amplitudes of the inverted and non-inverted signals that the differential coupler 2 can receive are the same and at their maximum. Hereinafter, the differential voltage, which is the difference in amplitude between the inverted and non-inverted signals in this state, is defined as 1.

[0022] The right side of Figure 3A shows the state in which a lateral shift Y, which is a shift perpendicular to the direction of transmission of the differential signals, has occurred from the state shown on the left side of Figure 3A. In this case, both differential signal lines are moved away from the opposing differential signal lines. As a result, the amplitudes of the inverted and non-inverted signals that can be received by differential coupler 2 are both reduced (30% reduction in the illustrated example), and the differential voltage, which is the difference between these amplitudes, also becomes smaller. More precisely, as shown on the right side of Figure 3A, differential signal line 21, in which the non-inverted signal is induced, moves closer to differential signal line 12, in which the inverted signal is transmitted, so that the voltages induced in differential signal line 21 are partially canceled out, and the non-inverted signal induced in differential signal line 21 becomes smaller.

[0023] Next, we will explain the case of the proximity communication system according to this embodiment. Here, as shown in FIG. 2(b), we will explain the case where the sum w2 of the differential signal line width and the distance between the signal lines of the differential coupler 2 is narrower than the sum w1 of the differential signal line width and the distance between the signal lines of the differential transmission line 1. As shown on the left side of FIG. 3B, when the differential transmission line 1 and the differential coupler 2 are arranged facing each other so that their central axes coincide (the centers of w1 and w2 coincide), the inverted signals and the non-inverted signals are not in a maximum coupling state. Therefore, the differential voltage level that the differential coupler 2 can receive is smaller than that shown on the left side of FIG. 3A. However, because the degree of coupling between the differential signal lines is the same, the received voltages of the inverted signal and the non-inverted signal are the same, maintaining balance. In FIG. 3B, the amplitudes of the non-inverted signal and the inverted signal are both 0.35, and the differential voltage is 0.7.

[0024] The right side of Figure 3B shows the case where a lateral shift Y, a shift perpendicular to the signal transmission direction, occurs from the state on the left side of Figure 3B. Because the differential signal line 11 on the differential transmission line 1 and the differential signal line 21 on the differential coupler 2 move apart, the non-inverted signal induced in the differential signal line 21 becomes smaller. In the example of Figure 3B, the amplitude value decreases from 0.35 to 0.25. However, because the differential signal line 12 on the differential transmission line 1 and the differential signal line 22 on the differential coupler 2 move closer to each other (approaching the maximum coupling state), the inverted signal induced in the differential signal line 22 becomes larger. In the example of Figure 3B, the amplitude value increases from 0.35 to 0.4. Therefore, the change in the differential voltage that can be received by the differential coupler 2 (0.7 → 0.65) is smaller than the change in the differential voltage that can be received by the differential coupler 2 (1.0 → 0.7) when a lateral shift occurs in Figure 3A.

[0025] Based on the above principle, by making the sum w2 of the differential signal line width and the distance between the signal lines of the differential coupler 2 smaller than the sum w1 of the differential signal line width and the distance between the signal lines of the differential transmission line 1, it is possible to reduce the fluctuation in the differential voltage due to lateral shift.

[0026] The following are actual measurement results for verifying the effects of the first embodiment. The differential transmission line 1 and differential coupler 2 used a fluororesin substrate NPC-H220A manufactured by Nippon Pillar Packing Co., Ltd. with a nominal thickness of 1.6 mm as the base material. The copper foil thickness of the differential transmission line 1 and differential coupler 2 was 35 μm, and the GND width was 30 mm. The differential signal line width of the differential transmission line 1 was 5 mm, and the distance between the signal lines was 4.8 mm. Therefore, the sum of the differential signal line width and distance between the signal lines of the differential transmission line 1 and the sum of the differential signal line width and distance between the signal lines of the differential coupler 2 were each 14.8 mm. A CML-format differential signal was supplied from an FPGA to one end of the differential signal lines 11 and 12 of the differential transmission line 1 via an RF amplifier. The transmission signal pattern was PRBS7, and the transmission data rate was 2 Gbps. The other ends of the differential signal lines 11 and 12 were connected to GND via 51 Ω chip resistors.

[0027] Two types of proximity communication systems were prepared as evaluation samples using the differential transmission line 1 described above and the two types of differential couplers 2 described below. These will be referred to as evaluation sample 1 and evaluation sample 2 below.

[0028] Figure 4(a) shows a cross-sectional view of the differential transmission line 1 and differential coupler 2 of evaluation sample 1. The differential signal lines 21 and 22 of differential coupler 2 of evaluation sample 1 have a differential signal line width of 5 mm and a distance between the signal lines of 4.8 mm, the same dimensions as the differential signal lines 11 and 12 of differential transmission line 1. The length of differential coupler 2 is 30 mm, and the signal is extracted from the center to the opposite side of differential signal lines 21 and 22 through a via. The signal was then connected to a U.FL (Hirose Electric Co., Ltd.) connector, converted to an SMA connector, and the waveform was measured with an oscilloscope. The measurement results are shown in Table 1. Table 1 shows that when there was a 1.2 mm lateral shift from the state with no lateral shift, the amplitude attenuated to approximately just under 80%.

[0029] Figure 4(b) shows a cross-sectional view of the differential transmission line 1 and differential coupler 2 of evaluation sample 2. The differential signal lines 21 and 22 of differential coupler 2 of evaluation sample 2 have a differential signal line width of 4 mm and a distance between the signal lines of 1.6 mm, which are narrower than the differential signal lines 11 and 12 of differential transmission line 1. In other words, the sum of the differential signal line width and distance between the signal lines of differential coupler 2, w2 (= 9.6 mm), is smaller than the sum of the differential signal line width and distance between the signal lines, w1 (= 14.8 mm), of differential transmission line 1. As with evaluation sample 1, the fluctuations in the received differential voltage of evaluation sample 2 were measured with an oscilloscope, and the results are shown in Table 2. Table 2 shows that even when there is a 1.2 mm lateral shift from a state with no lateral shift, the reduction in the amplitude of the received signal is suppressed to about 2%.

[0030] [Table 1] [Table 2]

[0031] The above measurement results show that, compared to when the sum of the differential signal line widths and inter-signal line distances of the differential transmission line 1 and differential coupler 2 are equal, when the sum of the differential signal line widths and inter-signal line distances of the differential transmission line 1 and differential coupler 2 is smaller than the sum of the differential transmission line 1, fluctuations in the received signal due to lateral shift can be suppressed more effectively.

[0032] As described above, the near-field communication system of the first embodiment can suppress fluctuations in differential signal voltage due to lateral misalignment, thereby providing a system with improved communication quality in near-field wireless communication. Furthermore, narrowing the distance between the signal lines of the differential coupler 2 also reduces the effect of being less susceptible to external noise. Furthermore, by configuring the differential signal lines 21 and 22 so that they are electrically connected to the receiving circuit 4 at approximately the center of their line lengths, as shown in FIG. 1, the length of the differential coupler is halved, thereby increasing the transmission speed and enabling signal reception regardless of the power supply direction of the differential transmission lines.

[0033] Second Embodiment In the first embodiment, two evaluation samples were used to actually measure fluctuations in the received voltage level with an oscilloscope to verify the effectiveness. In the second embodiment, a 3D electromagnetic field simulation was used to calculate fluctuations in the received voltage using the differential signal line width and the distance between the signal lines of the differential coupler as parameters. Table 3 lists the parameters of the evaluation samples. In Table 3, in evaluation sample 1, the sum of the differential signal line width and the distance between the signal lines of differential transmission line 1 and differential coupler 2 is the same. In evaluation samples 2 to 4, the differential signal line width and the distance between the signal lines of differential coupler 2 are each smaller than those of differential transmission line 1. That is, in evaluation samples 2 to 4, the sum of the differential signal line width and the distance between the signal lines of differential coupler 2 is smaller than the sum of the differential signal line width and the distance between the signal lines of differential transmission line 1. Hereinafter, w1 and w2 are also referred to as the width of the differential signal line pair.

[0034] [Table 3]

[0035] Figure 5 shows the results of a simulation of the fluctuation in received voltage due to lateral misalignment for evaluation samples 1 to 4 listed in Table 3. The horizontal axis represents the amount of lateral misalignment, normalized by half the sum of the differential signal line width and the distance between the signal lines of differential transmission line 1, i.e., 7.4 mm. The vertical axis represents the received voltage, normalized by the received voltage when the signals are directly facing each other. The gap between the differential transmission line and the differential coupler is 1 mm. It can be seen that evaluation samples 2 and 3 are more resistant to lateral misalignment than evaluation sample 1, provided that the lateral misalignment occurring in the proximity communication system is up to approximately 20% of the width of the differential signal line pair in differential transmission line 1 (approximately 3 mm in this embodiment). Furthermore, the parameters of evaluation sample 3 indicate that the width of the differential signal line pair in differential coupler 2 up to approximately half the width of the differential signal line pair in differential transmission line 1 is effective against lateral misalignment. In other words, it is preferable that the width of the differential signal line pair in differential transmission line 1 be at least half the width of the differential signal line pair in differential coupler 2.

[0036] Third Embodiment FIG. 6 shows a cross-sectional view of a differential transmission line 1 and a differential coupler 2 of a proximity communication system according to a third embodiment. In the third embodiment, the connection positions of vias 31 and 32 for extracting signals from differential signal lines 21 and 22 of the differential coupler 2 are examined. The dimensions of the differential transmission line 1 and the differential signal lines of the differential coupler 2 are the same as those of the evaluation sample 2 of the second embodiment. In the third embodiment, the positions of the vias 31 and 32, which extract signals from the differential signal lines 21 and 22 of the differential coupler 2 to the back surface, on the differential signal lines 21 and 22 are used as parameters. FIG. 6( a) shows an example in which vias are arranged in the center of the differential signal lines 21 and 22, with a via-to-via distance of 5.6 mm. FIG. 6( b) shows an example in which vias are arranged inside the differential signal lines 21 and 22, with a via-to-via distance of 1.6 mm. FIG. 6( c) shows an example in which vias are arranged outside the differential signal lines 21 and 22, with a via-to-via distance of 9.6 mm. The lateral offset is 1.5 mm. The rest is the same as in the second embodiment.

[0037] Table 4 shows the results of a simulation of received voltage fluctuations. In Table 4, the simulation results are shown for evaluation sample 1 in Fig. 6(a), evaluation sample 2 in Fig. 6(b), and evaluation sample 3 in Fig. 6(c). Table 4 shows that it is preferable to position the via at a position closer to the other signal line than the center of the line width of a pair of differential signal lines, and that the inner end of the pair of differential signal lines (Fig. 6(b)) is more preferable. In other words, it is preferable to connect the via (receiving circuit) at a position closer to the other electrode than the center of gravity of each electrode of a pair.

[0038] [Table 4]

[0039] <Fourth embodiment> FIG. 7(a) is a perspective view of a proximity communication system according to a fourth embodiment, and FIG. 7(b) is a cross-sectional view of a differential transmission line 1 and a differential coupler 2 according to the fourth embodiment. In the fourth embodiment, the width w6 of the differential signal line pair of the differential coupler 2 is wider than the width w1 of the differential signal line pair of the differential transmission line 1. In principle, the same effect as a configuration in which the width of the differential signal line pair of the differential coupler 2 is narrower than the width of the differential signal line pair of the differential transmission line 1 (for example, the configuration of the first embodiment) can be achieved. Furthermore, in the configuration of the fourth embodiment, the distance between the signal lines in the differential transmission line 1 is shorter, which enables stronger coupling between the differential signal pairs and suppression of radiation noise.

[0040] As described above, according to the near-field communication system of the fourth embodiment, the distance between the signal lines of the differential transmission lines is narrowed, making it resistant to lateral misalignment and capable of suppressing noise radiation from the differential transmission lines. Note that the configuration described in the fourth embodiment (the configuration in which the width of the differential signal line pair of the differential transmission lines is smaller than the width of the differential signal line pair of the differential coupler) can be applied to the configurations described in the first to third embodiments. That is, regarding the relationship in size between the differential signal line pair of the differential transmission lines and the differential signal line pair of the differential coupler described in the first to third embodiments, the differential transmission lines may be replaced with the differential coupler, and the differential coupler may be replaced with the differential transmission lines, respectively.

[0041] Fifth Embodiment Fig. 8 shows a perspective view of a proximity communication system according to a fifth embodiment. As shown in Fig. 8, it is also possible to provide a plurality of differential couplers 2, 2' for a differential transmission line 1. This configuration is suitable for making bus wiring contactless. Furthermore, by giving each of the plurality of differential couplers 2 frequency characteristics and adding them together in a receiving circuit, it is possible to achieve a wide bandwidth.

[0042] As described above, according to the proximity communication system of the fifth embodiment, it is possible to receive signals from the differential transmission line 1 using a plurality of differential couplers 2. Furthermore, by configuring the differential couplers to have different frequency characteristics and combine signals, it is possible to achieve broadband communication.

[0043] Sixth Embodiment 9 is a cross-sectional view of a differential transmission line 1 and a differential coupler 2 according to the sixth embodiment. The sum w1 of the differential signal line width and the distance between the signal lines of the differential transmission line 1 is approximately equal. Differential signal line widths 11 and 12 of the differential transmission line 1 are wider than differential signal line widths 21 and 22 of the differential coupler 2. The differential signal line width w4 of the differential transmission line 1 is narrower than the differential signal line width w3 of the differential coupler 2.

[0044] The right side of Figure 9 shows the state where a lateral shift Y, which is a shift perpendicular to the direction of transmission of the differential signals, has occurred from the state on the left side of Figure 9. The lateral shift of differential coupler 2 by distance Y changes the degree of coupling between differential signal lines 11 and 12 of differential transmission line 1 and differential signal lines 21 and 22 of differential coupler 2. 9a and 9b represent the degree of coupling between differential signal lines 1 and differential coupler 2 in terms of voltage. The higher the voltage, the higher the degree of coupling. In the state without lateral shift shown on the left side of Figure 9, the degree of coupling 91 between differential signal lines 11 and 21 and the degree of coupling 92 between differential signal lines 12 and 22 are both 0.4 V, resulting in a differential voltage of 0.8 V. Negative values ​​of the differential voltage are not shown here.

[0045] In the state shown on the right side of Figure 9, differential coupler 2 is shifted laterally by Y, so that differential signal lines 11 and 21 face each other, and the degree of coupling 93 between them is increased. Conversely, the distance between differential signal lines 12 and 22 increases due to differential coupler 2 being shifted laterally by Y, and the degree of coupling 94 between them is weakened. In Figure 9b, the degree of coupling 93 between differential signal lines 11 and 21 is 0.5 V, and the degree of coupling 94 between differential signal lines 12 and 22 is 0.25 V. As a result, the differential voltage is 0.75 V, which is not a significant decrease in coupling compared to when there is no lateral shift (0.8 V in this example). Therefore, the differential signal line arrangement shown in Figure 9 can maintain communication even when differential coupler 1 is shifted laterally.

[0046] Seventh Embodiment 10 is a cross-sectional view of a differential transmission line 1 and a differential coupler 2 according to the seventh embodiment. The differential coupler 2 has an arrangement in which the sum w11 of the differential signal line width and the distance between the signal lines is wider than the sum w1 of the differential signal line width and the distance between the signal lines of the differential transmission line 1. However, as in FIG. 9, the differential signal line widths 11 and 12 of the differential transmission line 1 are wider than the differential signal line widths 21 and 22 of the differential coupler 2, and the distance w4 between the differential signal lines of the differential transmission line 1 is narrower than the distance w3 between the differential signal lines of the differential coupler 2.

[0047] The right side of Fig. 10 shows a state in which a lateral shift Y, which is a shift in the direction perpendicular to the transmission direction of the differential signal, has occurred from the state shown on the left side of Fig. 10. As a result of differential coupler 2 being shifted laterally by distance Y, the degree of coupling between differential signal lines 11 and 12 of differential transmission line 1 and differential signal lines 21 and 22 of differential coupler 2 changes.

[0048] Reference numerals 10a and 10b indicate the degree of coupling between the differential signal lines between each differential coupler, expressed as voltage. The higher the voltage, the stronger the degree of coupling. In reference numeral 10a, the degree of coupling 101 between differential signal lines 11 and 21 and the degree of coupling 102 between differential signal lines 12 and 22 are both 0.35V, resulting in a differential voltage of 0.7V. Negative values ​​of the differential voltage are not shown here.

[0049] Compared with the coupling degree in FIG. 9, in the configuration of FIG. 10, since the differential signal lines 21 and 22 are arranged outside the differential signal lines 11 and 12 of the differential transmission line 1, the coupling degree is weakened. 10a represents the coupling degree before the differential coupler 2 is displaced, and 10b represents the coupling degree when the differential coupler 2 is displaced horizontally by Y. The coupling degree 103 is increased because the differential signal line 11 and the differential signal line 21 face each other due to the horizontal displacement of the differential coupler 2 by Y. Conversely, the coupling degree 104 is weakened because the distance between the differential signal line 12 and the differential signal line 22 is increased due to the horizontal displacement of the differential coupler 2 by Y. In this example, the coupling degree 103 between the differential signal line 11 and the differential signal line 21 is 0.5V, and the coupling degree 104 between the differential signal line 12 and the differential signal line 22 is 0.2V. As a result, the differential voltage is 0.7V, which is equal to the coupling degree of 0.7V when there is no horizontal displacement. Therefore, it can be seen that the arrangement of the differential signal lines shown in FIG. 10 can maintain communication even when the differential coupler 1 is horizontally displaced.

[0050] In FIG. 3B, the case where the distance between the differential signal lines 21 and 22 is narrower than the distance between the differential signal lines 11 and 12 is described. In contrast, for the arrangement of the differential signal lines of the differential couplers in FIGS. 9 and 10, w4 < w3. In this case, since the distance between the differential signal lines 21 and 22 in FIGS. 9 and 10 is increased, the capacitive coupling between the lines is reduced, and the high-frequency characteristics are improved. Considering the mounting space of the differential coupler, the arrangement of the differential signal lines can be considered.

[0051] As described above, in the communication system of each of the above embodiments, the distance between the center of gravity of the differential signal line 21 and the center of gravity of the differential signal line 22 is different from the distance between the center of gravity of the differential signal line 11 and the center of gravity of the differential signal line 22. With such a configuration, even if a horizontal displacement occurs between the differential transmission line 1 and the differential coupler 2, the change in the differential voltage is small, and the deterioration of the communication quality due to the positional displacement between devices performing wireless communication by electromagnetic field coupling is suppressed.

Explanation of Reference Numerals

[0052] 1: Differential transmission line, 2: Differential coupler, 11, 12, 21, 22: Differential signal lines, 3: Transmission circuit, 4: Reception circuit, 5: Terminal circuit

Claims

1. a first coupler having a first pair of electrodes extending in a predetermined direction; a second coupler having a second pair of electrodes electromagnetically coupled with the first pair of electrodes; a first circuit for transmitting or receiving a differential signal through the first coupler; a second circuit for transmitting or receiving a differential signal through the second coupler; the first pair of electrodes includes a first electrode and a second electrode; the second pair of electrodes includes a third electrode at least partially facing the first electrode and a fourth electrode at least partially facing the second electrode; In a plane perpendicular to the predetermined direction, a width of the third electrode is smaller than a width of the first electrode, a width of the fourth electrode is smaller than a width of the second electrode, and a separation distance between the third electrode and the fourth electrode in the width direction is different from a separation distance between the first electrode and the second electrode in the width direction; A wireless communication system, wherein the first coupler or the second coupler has a mechanism that allows the first coupler and the second coupler to move relatively in a predetermined direction.

2. a first coupler having a first pair of electrodes extending in a predetermined direction; a second coupler having a second pair of electrodes electromagnetically coupled with the first pair of electrodes; a first circuit for transmitting or receiving a differential signal through the first coupler; a second circuit for transmitting or receiving a differential signal through the second coupler; the first pair of electrodes includes a first electrode and a second electrode; the second pair of electrodes includes a third electrode at least partially facing the first electrode and a fourth electrode at least partially facing the second electrode; In a plane perpendicular to the predetermined direction, a width of the third electrode is larger than a width of the first electrode, a width of the fourth electrode is larger than a width of the second electrode, and a separation distance between the third electrode and the fourth electrode in the width direction is different from a separation distance between the first electrode and the second electrode in the width direction; A wireless communication system, wherein the first coupler or the second coupler has a mechanism that allows the first coupler and the second coupler to move relatively in a predetermined direction.

3. 2. The wireless communication system according to claim 1, wherein the distance between the third electrode and the fourth electrode in the width direction in a plane perpendicular to the predetermined direction is smaller than the distance between the first electrode and the second electrode in the width direction.

4. The first pair of electrodes have the same size and shape, 4. The wireless communication system according to claim 1, wherein the second pair of electrodes have the same size and shape.

5. The wireless communication system according to any one of claims 1 to 4, characterized in that it has a movement control means for moving at least one of the first coupler and the second coupler in a predetermined direction while maintaining a positional relationship in which the first pair of electrodes and the second pair of electrodes are at least partially opposed to each other using the relatively movable configuration.

6. 6. The wireless communication system according to claim 5, wherein the movement control means has a rotation axis and is configured to move the device in a circumferential direction around the rotation axis.

7. 7. The wireless communication system according to claim 1, wherein the length of each of the first pair of electrodes in the predetermined direction is different from the length of each of the second pair of electrodes in the predetermined direction.

8. 8. The wireless communication system according to claim 1, wherein, in a plane perpendicular to the predetermined direction, a first sum of the width of each of the first pair of electrodes and the separation distance in the width direction is different from a second sum of the width of each of the second pair of electrodes and the separation distance in the width direction.

9. 9. The wireless communication system according to claim 8, wherein the smaller of the first sum and the second sum is equal to or greater than half of the other sum.

10. 10. The wireless communication system according to claim 1, wherein the second circuit is connected to each of the second pair of electrodes through vias.

11. 11. The wireless communication system according to claim 1, wherein the wireless communication system is attached to a CT device.

12. 12. The wireless communication system according to claim 1, wherein at least one of the first coupler and the second coupler is disposed on a gantry of a CT apparatus.

13. 13. The wireless communication system according to claim 11, wherein the wireless communication system wirelessly communicates X-ray information.

14. the first circuit is a transmission circuit that transmits a differential signal; When the second circuit is a receiving circuit that receives a differential signal, 14. The wireless communication system according to claim 1, wherein the receiving circuit includes a filter circuit.

15. A control method for a wireless communication system having a first coupler having a first pair of electrodes extending in a predetermined direction, and a second coupler having a second pair of electrodes electromagnetically coupled to the first pair of electrodes, the method comprising: a first step of transmitting or receiving a differential signal through the first coupler; a second step of transmitting or receiving a differential signal through the second coupler; the first pair of electrodes includes a first electrode and a second electrode; the second pair of electrodes includes a third electrode at least partially facing the first electrode and a fourth electrode at least partially facing the second electrode; In a plane perpendicular to the predetermined direction, a width of the third electrode is smaller than a width of the first electrode, a width of the fourth electrode is smaller than a width of the second electrode, and a separation distance between the third electrode and the fourth electrode in the width direction is different from a separation distance between the first electrode and the second electrode in the width direction; A control method for the first coupler or the second coupler, characterized in that the first coupler and the second coupler move relatively in the predetermined direction.

16. A control method for a wireless communication system having a first coupler having a first pair of electrodes extending in a predetermined direction, and a second coupler having a second pair of electrodes electromagnetically coupled to the first pair of electrodes, the method comprising: a first step of transmitting or receiving a differential signal through the first coupler; a second step of transmitting or receiving a differential signal through the second coupler; the first pair of electrodes includes a first electrode and a second electrode; the second pair of electrodes includes a third electrode at least partially facing the first electrode and a fourth electrode at least partially facing the second electrode; In a plane perpendicular to the predetermined direction, a width of the third electrode is larger than a width of the first electrode, a width of the fourth electrode is larger than a width of the second electrode, and a separation distance between the third electrode and the fourth electrode in the width direction is different from a separation distance between the first electrode and the second electrode in the width direction; A control method for the first coupler or the second coupler, characterized in that the first coupler and the second coupler move relatively in the predetermined direction.

17. 17. The control method according to claim 16, wherein a distance between outer ends of the first electrode and the second electrode in a plane perpendicular to the predetermined direction is smaller than a distance between outer ends of the third electrode and the fourth electrode.

18. 18. The control method according to claim 15, wherein the relative movement involves moving at least one of the first coupler and the second coupler in a predetermined direction while maintaining a positional relationship in which the first pair of electrodes and the second pair of electrodes are at least partially opposed to each other.

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