Communication apparatus and communication system

Abstract

To provide a communication apparatus that can make high-speed data transmission, and is adopted to a rotational movable part.SOLUTION: A communication apparatus includes: a differential transmission path that is formed by a first electrode and a second electrode for performing radio communication with another communication apparatus through electromagnetic field coupling; and communication means of transmitting a signal to the differential transmission path or receiving a signal from the differential transmission path. A first end of the differential transmission path is connected to the communication means, and a second end is terminated by a termination member. The first electrode and the second electrode are formed in an appropriate arc chape into an outer side and an inner side as a center of a predetermined shaft. A filter part for correcting a transportation delay difference by a wiring length difference of the first and second electrodes is inserted into the differential transmission path.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to wireless communication technology. [Background technology]

[0002] In recent years, there have been communication systems that apply communication devices to rotating movable parts such as the joints of robot hands and robot arms and the camera platform used in network cameras, and communicate using the communication devices. By making the communication using the communication devices in such rotating movable parts wireless, there are advantages such as enabling infinite rotation and improving maintainability by eliminating the risk of wiring breakage. Patent Document 1 discloses a communication system that enables contactless data transmission by using electromagnetic coupling between a differential transmission line arranged in a ring shape on a dielectric substrate of a communication device (transmitting side) in a rotating movable part, and a coupler in the opposing communication device (receiving side). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6304906 Summary of the Invention [Problem to be solved by the invention]

[0004] Taking network cameras as an example, the amount of data transmitted via communication devices applied to rotating movable parts is increasing year by year as camera performance improves, and faster data transmission is also required in wireless communication. Furthermore, devices are becoming thinner and thinner to improve ease of installation, and the communication devices themselves need to be made thinner. According to the communication device disclosed in Patent Document 1, a low profile is achieved by providing a ring-shaped differential transmission line on a dielectric substrate. However, there is a problem in that the increase in speed is limited by the influence of the propagation delay difference caused by the difference in wiring length between the two conductors that make up the differential transmission line.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a communication device that is applied to a rotating movable part and that enables high-speed data transmission. [Means for solving the problem]

[0006] As one means for achieving the above object, a communication device of the present invention has the following configuration: That is, the communication device has a differential transmission path formed by a first electrode and a second electrode for performing wireless communication with another communication device by electromagnetic coupling, and a communication means for transmitting a signal to the differential transmission path or receiving a signal from the differential transmission path, a first end of the differential transmission path is connected to the communication means and a second end is terminated by a termination member, the first electrode and the second electrode are formed in a substantially arc shape on the outside and inside with a predetermined axis as a center, and a filter section for correcting a propagation delay difference caused by a wiring length difference between the first electrode and the second electrode is inserted on the differential transmission path. Effect of the Invention

[0007] According to the present invention, there is provided a communication device that is applied to a rotating movable part and that enables high-speed data transmission. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1A shows an example of the configuration of a wireless communication system according to the first embodiment, FIG. 1B shows an example of the configuration in which a common mode filter is disposed on the rear surface of a dielectric substrate, and FIG. 1C shows the phase shift characteristics with and without a common mode filter. [Diagram 2] 1A to 1J are diagrams for explaining problems with the conventional technology. [Diagram 3] FIG. 1A is a perspective view of a simulation model without a common mode filter, and FIG. 1B is a perspective view of a simulation model with a common mode filter. [Figure 4]FIG. 1A is a diagram showing an example of the configuration of a wireless communication system according to a modified example of the first embodiment, and FIG. 1B shows phase shift characteristics with and without a common mode filter. [Diagram 5] 13 illustrates an example of the configuration of a wireless communication system according to a second embodiment. [Figure 6] 13 illustrates an example of the configuration of a wireless communication system according to a third embodiment. [Figure 7] 13 illustrates an example of the configuration of a wireless communication system according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Note that the embodiment described below is one example of a means for realizing the present invention, and should be appropriately modified or changed depending on the configuration of the device to which the present invention is applied and various conditions, and the present invention is not limited to the embodiment described below.

[0010] <First embodiment> [Wireless communication system configuration] 1(a) is a diagram showing an example of the configuration of a wireless communication system 1 according to this embodiment. The wireless communication system 1 includes a communication device 10 on the transmitting side and a communication device 20 on the receiving side. The communication device 10 includes differential transmission paths 101, 101', amplifier circuits 105-1 to 105-4, and a transmission circuit 106. In this embodiment, the differential transmission paths 101, 101' are provided on a dielectric substrate (not shown) for the purpose of reducing the height. The communication device 20 includes a coupler 200, a shaping circuit 201, and a receiving circuit 202. The wireless communication system 1 also includes a rotation control means (not shown) that controls at least one of the coupler 200 and the differential transmission paths 101, 101' to rotate while maintaining the coupler 200 and the differential transmission paths 101, 101' facing each other. As a result, the coupler 200 and the differential transmission paths 101, 101' rotate relatively around the rotation axis 30. The configurations of the communication device 10 and the communication device 20 will be specifically described below with reference to FIG.

[0011] [Configuration of communication device 10 (transmitting side)] First, a description will be given of the configuration of the transmitting communication device 10. The communication device 10 includes differential transmission paths 101, 101′, amplifier circuits 105-1 to 105-4, and a transmission circuit . The transmission circuit 106 converts the received signal into a differential signal and outputs it to the amplifier circuits 105-1 to 105-4. For example, the transmission circuit 106 receives a serial digital interface (SDI) signal with a characteristic impedance of 75Ω that is transmitted in a single end, converts the SDI signal into a differential signal, and outputs it to the amplifier circuits 105-1 to 105-4. In the example shown in Fig. 1(a), the transmission circuit 106 outputs a differential signal plus, which is a differential digital signal, to the amplifier circuits 105-1 and 105-4, and outputs a differential signal minus, which is a differential digital signal, to the amplifier circuits 105-2 and 105-3.

[0012] The transmission circuit 106 according to the present embodiment is assumed to be a fan-out circuit (a circuit having the maximum number of outputs that can be connected to a circuit at a subsequent stage), and is connected to the amplifier circuits 105-1 to 105-4. Alternatively, the output signal from the transmission circuit 106 may be distributed by a means such as a distributor and input to the amplifier circuits 105-1 to 105-4. Since the amplifier circuits 105-1 to 105-4 have the same configuration, they may be collectively referred to as the amplifier circuit 105 in the following description. In FIG. 1(a), the transmission circuit 106 and the amplifier circuit 105 are connected by a single line in a schematic manner, but a resistor divider or a Wilkinson splitter (distributor) that divides a high-frequency signal may be inserted, and an element such as a resistor may be inserted.

[0013] The amplifier circuit 105 amplifies the signal received from the transmission circuit 106 and outputs the amplified signal to the differential transmission paths 101 and 101'. Specifically, the amplifier circuits 105-1 and 105-2 output the amplified signal to the differential transmission path 101 via the lines 121 and 122, respectively. Furthermore, the amplifier circuits 105-3 and 105-4 output the amplified signal to the differential transmission path 101' via the lines 122' and 121', respectively. In this embodiment, the lines 121, 122, 122', and 121' have approximately equal electrical lengths. Note that, if the level of the output signal from the transmission circuit 106 is sufficiently high, the amplifier 105 may be omitted.

[0014] The differential transmission path 101 is composed of conductors (also called electrodes) 111, 112 formed in an arc shape around the rotating shaft 30. In the example shown in FIG. 1(a), the conductors 111, 112 are formed in an arc shape (annular shape) around the rotating shaft 30, but they may be formed in an approximately arc shape (for example, within a predetermined distance from the rotating shaft 30) around the rotating shaft 30. The conductors 111, 112 have a power supply unit 102 at one end, and the power supply unit 102 is connected to the amplifier circuits 105-1, 105-2 via the lines 121, 122. As a result, a differential signal plus or a differential signal minus amplified by the amplifier circuit 105 is input to the conductors 111, 112. The conductors 111, 112 have a termination unit 104 at the other end, and are terminated with a termination resistor (termination member) that is approximately equal to the characteristic impedance of the differential transmission path 101. In addition, since the conductor 111 and the conductor 112 are each formed in a ring shape, there is a difference in wiring length between the conductor 111 and the conductor 112. With reference to Fig. 1(a), the conductor 111 and the conductor 112 are formed on the outer side and the inner side, respectively, when viewed from the reference direction parallel to the rotation axis 30, so the wiring length of the conductor 111 is longer than the wiring length of the conductor 112. The differential transmission path 101' is configured in the same manner as the differential transmission path 101. In the differential transmission path 101', components with a prime symbol "'" attached to their reference numerals are the same as corresponding components without a prime symbol, and therefore descriptions thereof will be omitted.

[0015] The differential transmission lines 101, 101' need to be able to ensure coupling with the coupler 200 (described later) that rotates relatively around the rotation axis 30 so as to be able to communicate with it at all rotation angles. For this reason, the power supply units 102, 102' and the termination units 104, 104' are disposed adjacent to each other (i.e., within a predetermined distance) as shown in the figure. When the coupler 200 moves from the termination unit 104 to 104' (or vice versa), a positive differential signal and a negative differential signal are output to the conductors 111, 112, 111', 112' so that the phase of the signal transmitted to the coupler 200 is continuous.

[0016] As described above, the conductor 112 is formed inside the conductor 111 when viewed from the reference direction parallel to the rotation axis 30. Therefore, a propagation delay difference occurs due to the difference in wiring length between the conductors 111 and 112. That is, a phase shift (phase difference) occurs between the positive differential signal in the conductor 111 and the positive differential signal in the conductor 112. In order to suppress the influence of such a phase shift on communication, in this embodiment, a common mode filter that attenuates a common mode noise current is inserted on the differential transmission line. Specifically, the common mode filter A is connected (implemented) in series on the differential transmission line 101, and the common mode filter A' is connected (implemented) in series on the differential transmission line 101'. It is generally known that the phase shift between the differential signals can be offset by inserting a common mode filter in the differential transmission line.

[0017] The common mode filter A may be inserted at any position on the differential transmission line 101, but in the example of FIG. 1(a), it is inserted on a center line 103 of the differential transmission line 101. That is, the common mode filter A is inserted at a substantially central position between the two ends of the differential transmission lines 101 and 101'. Here, "substantially central" means that, for example, the angle between the power supply unit 102 and the position of the common mode filter A, and the angle between the termination unit 104 and the position of the common mode filter A, are within a predetermined range, with the rotation axis 30 as the center. Similarly, the common mode filter A' is inserted on a center line 103' of the differential transmission line 101'. Note that the common mode filter A and the common mode filter A' may be filter units having a function of correcting (including offsetting and absorbing) the phase shift between the differential signals (propagation delay difference between conductors), and are not particularly limited in form.

[0018] The common mode filter A may be inserted on the surface of the dielectric substrate opposite to the surface on which the differential transmission path 101 is arranged. For the sake of explanation, the surface of the dielectric substrate on which the differential transmission path 101 is arranged is referred to as the front surface, and the surface opposite to the front surface is referred to as the back surface. FIG. 1(b) shows a part of a configuration example of the wireless communication system 1 when the common mode filter A is inserted on the back surface of the dielectric substrate. When the common mode filter A is inserted on the front surface (i.e., the same surface as the surface on which the differential transmission path 101 is arranged), it is necessary to make the gap between the communication device 10 and the communication device 20 wider by the height of the common mode filter A. On the other hand, as shown in FIG. 1(b), when the common mode filter A is inserted on the back surface (i.e., the surface opposite to the surface on which the differential transmission path 101 is arranged), it is not necessary to consider the height of the component, and the distance between the communication device 10 and the communication device 20 can be reduced. This makes it possible to make the reception signal level (for example, voltage level) in the communication device 20 larger than when the common mode filter A is inserted on the front surface of the dielectric substrate. The above description can be similarly applied to the arrangement of the common mode filter A' on the differential transmission line 101'.

[0019] [Configuration of communication device 20 (receiving side)] Next, a description will be given of the configuration of the receiving communication device 20. The communication device 20 includes a coupler 200, a shaping circuit 201, and a receiving circuit 202. The coupler 200 has conductors 211 and 212, which are arranged so as to be electromagnetically coupled to the differential transmission paths 101 and 101' in the communication device 10, respectively. Specifically, the conductor 211 is arranged so as to face at least a portion of the conductor 111 or 111', and the conductor 212 is arranged so as to face at least a portion of the conductor 112 or 112', and the electromagnetically coupled state is maintained. The coupler 200 is also configured to rotate relatively to the differential transmission path 101 around the rotation axis 30. With this configuration, in the wireless communication system 1, wireless communication is realized from the communication device 10 to the communication device 20 while rotating relatively around the rotation axis 30.

[0020] The shaping circuit 201 has a function of converting the radio signal excited by the electromagnetic coupling in the coupler 200 into an analog signal that can be handled as an electric signal. In this embodiment, the input impedance of the shaping circuit 201 is set to a high impedance of several tens of kΩ. As a result, the input impedance becomes large even in the low frequency range due to the capacitive component caused by the electromagnetic coupling between the differential transmission lines 101, 101' and the coupler 200, and the signal of the low frequency band component is also transmitted to the shaping circuit 201. Therefore, the received waveform generated at the input end of the shaping circuit 201 can be transmitted while maintaining its rectangular shape. Furthermore, the shaping circuit 201 has a function of amplifying the waveform of the received signal to a voltage level at which the receiving circuit 202 in the subsequent stage can distinguish between 0 and 1 of the digital signal.

[0021] The receiving circuit 202 converts the voltage level of the signal received from the shaping circuit 201 to match the desired interface specifications for the downstream components (not shown) and outputs the converted signal. For example, the receiving circuit 202 converts the voltage level of the signal received from the shaping circuit 201 and outputs it as an SDI signal. The receiving circuit 202 may also have a reclocking function that regenerates a clock using clock data recovery (CDR).

[0022] [Effect of inserting a common mode filter] Next, the effect of inserting a common mode filter (common mode filters A and A' in FIG. 1(a)) will be described. Here, the differential transmission line 101 having the conductors 111 and 112 will be described as an example, but the same explanation can be applied to the differential transmission line 101' having the conductors 111' and 112'.

[0023] (1) Issues when a common mode filter is not added First, the problem in the case where a common mode filter is not added (conventional technology) will be described. In the power supply unit 102 in the communication device 10 shown in FIG. 1(a), the phases of the positive and negative differential signals output by the transmission circuit 106 match. However, if the propagation delay difference caused by the difference in wiring length between the conductor 111 and the conductor 112 is ΔT, a phase shift of ΔT occurs in the termination unit 104. FIGS. 2(a) to 2(j) are diagrams for explaining the problem in the conventional technology, and show examples of waveforms in which the propagation delay difference (phase shift amount) ΔT shifts from 0 to 1 unit interval (hereinafter abbreviated as UI) by 0.25 UI. UI is 1 bit period (signal period). In FIGS. 2(a) to 2(j), the horizontal axis indicates time, which is normalized by 1 UI. The vertical axis indicates the voltage level normalized by the voltage of the positive and negative differential signals.

[0024] 2(a), (c), (e), (g), and (i) (i.e., the diagrams on the left side of FIG. 2) show the waveform of the positive voltage level of the differential signal fed to the conductor 111 in the differential transmission line 101 and the waveform of the negative voltage level of the differential signal fed to the conductor 112. Here, the solid line represents the voltage level of the positive differential signal fed to the conductor 111, and the dotted line represents the voltage level of the negative differential signal fed to the conductor 112. Note that in FIG. 2(i), the solid line and the dotted line overlap. 2(b), (d), (f), (h), and (j) (i.e., the diagrams on the right side of Fig. 2) show the voltage levels of the differential signals that are the output signals of the shaping circuit 201, that is, the waveforms of the difference voltages between the voltage levels of the positive and negative differential signals shown in the diagrams on the left side of Fig. 2. For the sake of explanation, the output signals (differential signals) of the shaping circuit 201 are also referred to as received signals.

[0025] As shown in Fig. 2(b), when ΔT=0UI, that is, when there is no phase difference between conductor 111 and conductor 112, the maximum voltage level (maximum amplitude) of the received signal is twice (=4) the voltage level (=2) of the positive and negative differential signals shown in Fig. 2(a). In addition, if the rise and fall times of the positive and negative differential signals in Fig. 2(a) are 0.5, then the rise and fall times of the received signal are also 0.5, as shown in Fig. 2(b).

[0026] On the other hand, as shown in Fig. 2(f), when ΔT=0.5UI, that is, when the phase between conductor 111 and conductor 112 is shifted by 0.5UI, the slope of the rising and falling edges of the received signal is smaller than that of the case of ΔT=0UI shown in Fig. 2(b). Specifically, when ΔT=0.5UI, the maximum amplitude of the received signal is the same (=4) as that of the case of ΔT=0UI shown in Fig. 2(b). However, the rising and falling times of the received signal are 1, which is twice as long as 0.5 for the case of ΔT=0UI shown in Fig. 2(b), and therefore the slope of the rising and falling edges of the received signal is half that of the case of ΔT=0UI. Furthermore, in Fig. 2(b), the time position of the zero crossing point of the voltage level of the received signal is 0.75+N (N is an integer), which is the same as the time position of the zero crossing point of the received level of the positive and negative differential signals shown in Fig. 2(a).In contrast, in Fig. 2(f), the time position of the zero crossing point of the voltage level of the received signal is 1+N (N is an integer), which is shifted by 0.25 UI. From these, it can be seen that when ΔT=0.5UI, the voltage level waveform of the received signal is deteriorated in the time domain compared to when ΔT=0UI.

[0027] When the propagation delay difference ΔT increases further from 0.5 UI shown in Fig. 2(f) to ΔT=0.75UI and ΔT=1UI, the voltage level of the received signal drops further, as shown in Fig. 2(h) and Fig. 2(j), respectively. When ΔT=1UI, that is, when the propagation delay difference between conductor 111 and conductor 112 shifts by one bit of the digital signal, the voltage level of the received signal becomes 0, as shown in Fig. 2(j), and it is clear that it becomes difficult to detect the received signal.

[0028] In this way, in the differential transmission line 101, the propagation delay amount ΔT of the conductors 111 and 112 increases toward the termination 104, and the waveform of the voltage level of the received signal is distorted as shown in Figures 2(b), (d), (f), (h), and (j). It is easy to predict that such a problem becomes more prominent as the speed of the communication signal increases, and that this will hinder the realization of high-speed communication. In other words, if the speed of the signal transmitted from the communication device 10 increases, the communication device 20 that receives the signal will not be able to receive the signal accurately if there is no common mode filter, and as a result, high-speed communication (data transmission) will not be realized.

[0029] (2) Effect of adding a common mode filter Next, a description will be given of the effect of adding the common mode filter A in this embodiment. Note that the same explanation as for the common mode filter A can be applied to the common mode filter A'.

[0030] As shown in FIG. 1(a), in this embodiment, the common mode filter A is inserted at approximately half the position of the differential transmission line 101. That is, the common mode filter A is disposed so that the lengths of the conductors 111 and 112 from the power supply unit 102 to the common mode filter A are approximately equal to the lengths of the conductors 111 and 112 from the common mode filter A to the termination unit 104. As can be seen from FIGS. 2(h) and 2(j), if a phase shift of more than 0.5 UI occurs, the maximum amplitude of the voltage level of the received signal is degraded. Therefore, as one embodiment, it is desirable to insert the common mode filter A at a position where the phase shift (propagation delay difference) is 0.5 UI or less (0.5 unit interval or less).

[0031] From the viewpoint of a reference direction parallel to the rotation axis 30, the angle between a predetermined position between the power supply unit 102 and the power supply unit 102' and the approximate center of the coupler 200 in the communication device 20 is defined as Φ, with the rotation axis 30 as the center. The angle Φ can be defined as the relative position of the communication device 20 with respect to the communication device 10. FIG. 1(c) shows the characteristics of the phase shift amount (propagation delay difference between the conductor 111 and the conductor 112) between the differential signal plus and the differential signal plus with respect to the angle Φ (relative position of the communication device 20 with respect to the communication device 10) with and without the common mode filter A. The horizontal axis of FIG. 1(c) shows the angle Φ, and the vertical axis shows the phase shift amount. Also, S on the vertical axis represents the maximum phase shift amount without the common mode filter A. Also, in FIG. 1(c), the thin solid line represents the characteristics without the common mode filter A, and the thick solid line represents the characteristics with the common mode filter A.

[0032] It can be seen that without common mode filter A, the phase shift increases as angle Φ increases, that is, as coupler 200 (receiving device 20) approaches termination unit 104. On the other hand, with common mode filter A, the phase shift is offset (canceled) by the common mode filter when angle Φ passes π / 2 (=90°). As angle Φ increases further, the characteristics change such that a phase shift occurs again.

[0033] From FIG. 1(c), it can be seen that by inserting the common mode filter A, the maximum phase shift becomes S / 2, which is half of the maximum phase shift S when the common mode filter A is not inserted. By inserting the common mode filter A, it is possible to reduce the maximum phase shift to about half compared to when the common mode filter A is not inserted. This enables faster communication. Referring to FIG. 2, as described above, when there is no common mode filter, the larger the propagation delay difference ΔT (i.e., the larger the phase shift of the differential signal in the differential transmission line 101), the more the voltage level waveform of the received signal in the communication device 20 deteriorates. On the other hand, by inserting the common mode filter, the increase in deterioration of the voltage level waveform of the received signal can be avoided, and faster communication can be achieved.

[0034] [Effects verified through simulation] The effect of inserting a common mode filter will be described below with reference to the results of electromagnetic field simulation. The simulation was performed using a simulation model of a wireless communication system 1 having a configuration as shown in Figs. 3(a) and (b). Fig. 3(a) is a perspective view of the simulation model without a common mode filter A, and Fig. 3(b) is a perspective view of the simulation model with a common mode filter A. In Figs. 3(a) and (b), the same components as those in the wireless communication system 1 shown in Fig. 1(a) are given the same reference numerals. In this electromagnetic field simulation, the S parameters of a common mode noise filter DLM0QSB350HY2D manufactured by Murata Manufacturing Co., Ltd. were used. As shown in Figs. 3(a) and (b), this simulation was performed using a model with a semi-arc configuration to reduce calculation costs, but the same explanation can be applied to the case of using a model with the configuration shown in Fig. 1(a) (i.e., annular configuration).

[0035] The differential transmission path 101 is formed as a copper pattern on a dielectric substrate 400, and the coupler 200 is disposed at a position spaced a predetermined transmission distance dZ from the differential transmission path 101 in the direction of the rotation axis. The differential transmission path 101 is a microstrip line, and the conductor 401 is a GND conductor that forms a reference potential. The dielectric substrate 400 has a hollow structure so that a mechanical rotation axis or an axial slip ring used for power transmission / low-speed communication can be inserted. Port1 is a transmission port, and Port2 is a termination port. The receiving communication device 20 including the coupler 200 is disposed at a position rotated 150° from Port1 (i.e., the angle Φ indicating the relative position of the communication device 20 with respect to the communication device 10=150°). The parameters set in this simulation are as shown in Table 1.

[0036] [Table 1]

[0037] The results of the eye diagram measurement of the received signal by this simulation are shown in Fig. 3(c) and (d). Fig. 3(c) shows the eye diagram without common mode filter A, and Fig. 3(d) shows the eye diagram with common mode filter A. The transmission rate is set to 3Gbps, assuming a 3G-SDI signal. The results of the measurement of the eye diagrams shown in Fig. 3(c) and (d) are summarized in Fig. 3(e). As shown in Fig. 3(e), it can be seen that the rise time (Eye Rise Time) and fall time (Eye Fall Time) are improved by inserting common mode filter A. It can also be seen that the amount of jitter (Eye JitterP2P) is improved by about 44% (129.6-72.6 ≒ 129.6 × 0.44). These results show that the eye diagram of the received signal can be improved by inserting common mode filter A.

[0038] In addition, in this simulation, the phase shift due to the difference in wiring length between conductors 111 and 112 at angle Φ = 150° is about 0.3 UI, and the phase shift at 90° is about 0.18 UI. This simulation shows that the phase shift of about 0.18 UI can be sufficiently canceled by adding common mode filter A. As mentioned above, it is desirable to insert common mode filter A at a position where the phase shift is 0.5 UI or less.

[0039] <Modification of the first embodiment> FIG. 4(a) shows a configuration example of a wireless communication system 4 according to a modified example of this embodiment. In the wireless communication system 4, two common mode filters (common mode filter A and common mode filter B) are inserted in a differential transmission path 101 of a communication device 10. In the configuration shown in FIG. 4(a), the common mode filter A and the common mode filter B are equally arranged and inserted in the differential transmission path 101. That is, the common mode filter A and the common mode filter B are inserted so that the distance from the power supply unit 102 of the differential transmission path 101 to the common mode filter A, the distance from the common mode filter A to the common mode filter B, and the distance from the common mode filter B to the termination unit 104 of the differential transmission path 101 are approximately equal. In the differential transmission path 101′, the common mode filter A′ and the common mode filter B′ are inserted in the same manner as the insertion form of the common mode filter A and the common mode filter B in the differential transmission path 101. In this modification, an example in which two common mode filters are inserted into the differential transmission lines 101 and 101' will be described as an example, but three or more common mode filters may be inserted. In either case, the multiple common mode filters may be inserted between the two ends of the differential transmission lines 101 and 101' at approximately equal intervals. Here, approximately equal intervals means that, for example, the angle between one end of the differential transmission lines 101 and 101' and the position of a common mode filter disposed near that end, and the angle between the position of an adjacent common mode filter, are within a predetermined range, with the rotation axis 30 as the center.

[0040] Fig. 4(b) shows the characteristics of the phase shift amount (difference in propagation delay between conductors 111 and 112) between the positive differential signal and the positive differential signal versus angle Φ (the relative position of communication device 20 with respect to communication device 10) with and without common mode filters A and B. As in Fig. 1(c), the horizontal axis indicates angle Φ, and the vertical axis indicates the phase shift amount. Also, S on the vertical axis represents the maximum phase shift amount without common mode filters A and B. Also in Fig. 4(b), the thin solid line represents the characteristics without common mode filters A and B, and the thick solid line represents the characteristics with common mode filters A and B.

[0041] The characteristics without the common mode filters A and B are similar to those in Fig. 1(c) In other words, as the angle Φ increases, that is, as the coupler 200 (receiving device 20) approaches the termination 104, the phase shift increases. On the other hand, when the common mode filters A and B are present, the phase shift is cancelled at the points where the angle Φ is π / 3 (=60°) and 2π / 3 (=120°). Therefore, it is theoretically possible to reduce the maximum phase shift amount S when the common mode filters A and B are inserted to one third. That is, by adding two common mode filters at equal intervals, it is theoretically possible to reduce the phase shift amount to one (2+1) times. In general, it is theoretically possible to reduce the phase shift amount to one (N+1) times by adding N common mode filters at equal intervals. As a result, even if a signal with a higher speed is transmitted from the communication device 10 compared to the above embodiment, the signal can be received by the receiving device 20, and a higher communication speed is realized. Therefore, it can be said that it is effective to increase the number of common mode filters in order to handle high-speed communication.

[0042] In this manner, in the present embodiment and the modified example, one or more common mode filters are inserted in each of the differential transmission paths 101, 101' of the communication device 10 in order to cancel the phase shift of the signal caused by the wiring difference between the two conductors (electrodes) constituting the differential transmission path. This enables high-speed wireless data transmission between the communication device 10 and the communication device 20 when the communication device 10 and / or the communication device 20 are applied to a rotating movable part. In addition, by providing the differential transmission paths 101, 101' on the dielectric substrate of the communication device 10, the communication device 10 can be made low-profile. The common mode filter may be mounted on the front side (the same side as the differential transmission paths 101, 101') or the back side (see FIG. 1(c)) of the dielectric substrate. By mounting the common mode filter on the back side of the dielectric substrate, the distance between the communication device 10 and the communication device 20 can be reduced, thereby enabling more efficient data transmission.

[0043] In this embodiment, the input impedance of the shaping circuit 201 of the communication device 20 on the receiving side is set to a high impedance of several tens of kΩ, but the present invention is not limited to this. For example, the input impedance of the shaping circuit 201 may be set to a low impedance such as a differential impedance of 100Ω. In this case, the transfer characteristic from the differential transmission lines 101 and 101' to the coupler 200 is similar to that of an HPF (high pass filter) in which the degree of coupling is weak in a low frequency band and is high in a high frequency band. Therefore, only high frequency components are transferred from the differential transmission lines 101 and 101' to the coupler 200. Specifically, an incomplete differential waveform (an edge signal generated at the rising edge and falling edge of a digital signal input to the differential transmission lines 101 and 101') of the signal input to the differential transmission lines 101 and 101' is generated in the coupler 200. For this reason, the shaping circuit 201 is not a simple amplifier circuit, but rather needs to use a circuit for restoring the differential waveform to a binary digital signal of "1" and "0", such as a hysteresis comparator.

[0044] <Second embodiment> Next, a second embodiment will be described. Fig. 5 shows an example of the configuration of a wireless communication system 5 according to this embodiment. The wireless communication system 5 differs from the wireless communication system 1 in Fig. 1(a) described in the first embodiment in that a communication device 40 is used instead of the transmitting communication device 10. Note that the same components as those in the wireless communication system 1 in the first embodiment are given the same reference numerals and descriptions are omitted. Also, components with "A" or "B" attached to the reference numerals are the same as the corresponding components in the communication device 10 shown in Fig. 1 that are not attached with "A" or "B".

[0045] As described in the first embodiment, taking the differential transmission path 101 of the communication device 10 in FIG. 1(a) as an example, a phase shift occurs due to the difference in wiring length between the two conductors 111 and 112 that configure the differential transmission path 101. Therefore, the phase shift increases as the wiring length increases. Therefore, the communication device 40 according to this embodiment has shorter differential transmission paths 101A, 101B, 101A', and 101B' instead of the differential transmission paths 101 and 101' of the communication device 10.

[0046] Specifically, in the first embodiment, the differential transmission lines 101 and 101' are each configured to have a length of approximately 180° from the viewpoint of a reference direction parallel to the rotation axis 30, but in this embodiment, the differential transmission lines 101A, 101B, 101A', and 101B' are configured to have a length of approximately 90° from the viewpoint. The communication device 10 shown in FIG. 1(a) has two differential transmission lines 101 and 101', but the communication device 40 according to this embodiment has four differential transmission lines 101A, 101B, 101A', and 101B'. Therefore, the communication device 40 has another identically configured transmission circuit 106B, an amplifier circuit 105B, and differential transmission lines 101B and 101B' arranged symmetrically with respect to the center line 103. The transmission circuit 106A and the transmission circuit 106B are configured to transmit the same signal.

[0047] In this manner, in this embodiment, the difference in wiring length between the two conductors (electrodes) constituting each of the differential transmission paths 101A, 101B, 101A', and 101B' in the communication device 10 is reduced. This makes it possible to reduce the phase shift caused by the difference in wiring length. Also, as in the first embodiment, common mode filters are inserted in the differential transmission paths 101A, 101B, 101A', and 101B'. This provides the same effects as those described in the first embodiment.

[0048] It is also possible to configure the transmission circuits 106A and 106B to transmit different signals (data) instead of the same signal. In this case, by increasing the number of communication devices on the receiving side, it becomes possible to achieve multi-channel and faster data transmission.

[0049] <Third embodiment> Next, a third embodiment will be described. Fig. 6 shows an example of the configuration of a wireless communication system 6 according to this embodiment. The wireless communication system 6 includes a receiving communication device 61 and a transmitting communication device 62. Note that the same components as those in the wireless communication system 1 in Fig. 1(a) described in the first embodiment are given the same reference numerals and description thereof will be omitted. The wireless communication system 6 is configured such that a signal is transmitted from a coupler 200 to differential transmission paths 101, 101', inverse to the transmitting / receiving relationship in the wireless communication system 1 according to the first embodiment.

[0050] The communication device 61 has differential transmission paths 101, 101', multiplexers 611, 611', a shaping circuit 612, and a receiving circuit (not shown). The communication device 62 has a coupler 200, amplifier circuits 621-1, 621-2, and a transmitting circuit 622. In this embodiment, the differential transmission paths 101, 101' are provided on a dielectric substrate for the purpose of reducing the height, similar to the communication device 10 according to the first embodiment. Furthermore, similar to the wireless communication system 1 according to the first embodiment, the wireless communication system 6 has a rotation control means (not shown) that controls the coupler 200 and the differential transmission paths 101, 101' to rotate relatively around the rotation axis 30 while maintaining an opposing state. The configurations of the communication device 62 and the communication device 61 will be specifically described below with reference to FIG.

[0051] [Configuration of communication device 62 (transmitting side)] First, a description will be given of the configuration of the communication device 62. The communication device 62 includes a coupler 200, amplifier circuits 621-1 and 621-2, and a transmission circuit 622. The transmission circuit 622 receives, for example, an SDI signal, converts the signal into a differential signal, and outputs the signal to the amplifier circuits 621-1 and 621-2. Specifically, the transmission circuit 622 outputs a positive differential signal, which is a differential digital signal, to the amplifier circuit 621-1, and outputs a negative differential signal, which is a differential digital signal, to the amplifier circuit 621-2. The amplifier circuits 621-1 and 621-2 amplify the signal received from the transmission circuit 622 at a desired amplification degree and output the signal to the coupler 200. The coupler 200 has conductors 211 and 212, and a positive differential signal is input to the conductor 211, and a negative differential signal is input to the conductor 212. The conductor 211 is arranged so that at least a portion of the conductor 111 or conductor 111' in the communication device 61 and the conductor 212 is arranged so that at least a portion of the conductor 112 or conductor 112' in the communication device 61 faces each other, and a state in which they are coupled by electromagnetic coupling is maintained. Although the transmission circuit 622, the amplifier circuits 621-1 and 621-2, and the coupler 200 are typically connected by a single line, a resistor divider that divides a high-frequency signal or the like may be inserted.

[0052] [Configuration of communication device 61 (receiving side)] Next, a description will be given of the configuration of the communication device 61. The communication device 61 has differential transmission paths 101, 101', multiplexers 611, 611', a shaping circuit 612, and a receiving circuit (not shown). An electric signal is excited in the differential transmission lines 101 and 101' by the electromagnetic field generated by the coupler 200. Specifically, a positive differential signal is induced in the conductors 111 and 111', and a negative differential signal is induced in the conductors 112 and 112' by the conductors 211 and 212 of the coupler 200. The conductor 111 of the differential transmission line 101 and the conductor 111' of the differential transmission line 101' are input to the multiplexer 611 via paths 121 and 121', respectively. Moreover, the conductor 112 of the differential transmission line 101 and the conductor 112' of the differential transmission line 101' are input to the multiplexer 611' via paths 122 and 122', respectively. Whether a positive or negative differential signal is induced in either or both of the differential transmission lines 101 and 101' depends on the degree of electromagnetic coupling, i.e., the angle Φ, between the differential transmission line 101 and the coupler 200 and between the differential transmission line 101' and the coupler 200. Therefore, two multiplexers, multiplexers 611 and 611', are used so that a signal can be received from the coupler 200 even if the coupler 200 is coupled to either the differential transmission line 101 or the differential transmission line 101'.

[0053] The multiplexer 611 outputs a negative differential signal, and the multiplexer 611' outputs a positive differential signal, which are input to the shaping circuit 612 as differential signals. In this embodiment, the input impedance of the shaping circuit 612 is set to be approximately equal to the characteristic impedance of the differential transmission lines 101 and 101'. Therefore, the transfer characteristic from the coupler 200 to the differential transmission lines 101 and 101' is similar to that of an HPF (high pass filter) in which the degree of coupling is weak in the low frequency range and the degree of coupling is high in the high frequency range. Therefore, only high frequency components are transferred from the coupler 200 to the differential transmission lines 101 and 101'. Specifically, an incomplete differential waveform of the signal input to the coupler 200 is generated in the differential transmission lines 101 and 101'. Therefore, the shaping circuit 612 in this embodiment is realized by a circuit for restoring the differential waveform to a binary digital signal of "1" and "0", for example, a hysteresis comparator. A receiving circuit (not shown) connected to the rear stage of the shaping circuit 612 may convert the voltage level of the signal received from the shaping circuit 612 to conform to the specifications of a desired interface and output the converted signal. The receiving circuit may also have a reclocking function that regenerates a clock using a CDR.

[0054] In this embodiment, as in the above embodiment, common mode filters (common mode filters A, A' in FIG. 6) are inserted into the differential transmission paths 101, 101'. By inserting the common mode filters, it is possible to suppress the influence on communication caused by the propagation delay difference (phase shift) caused by the difference in wiring length between the conductor 111 and the conductor 112 (or the conductor 111' and the conductor 112'). Note that the explanation in the above embodiment can be applied to the insertion position of the common mode filters.

[0055] In this manner, in this embodiment, wireless communication is realized from the communication device 62 to the communication device 61 while rotating relatively around the rotation axis 30. Also, as in the first embodiment, a common mode filter is inserted in the differential transmission paths 101, 101' in the communication device 61. This provides the same effects as those described in the first embodiment. Note that, as described in the second embodiment, it is also possible to configure a wireless communication system so that the differential transmission paths 101, 101' are shorter than the differential transmission paths 101A, 101B, 101A', 101B'.

[0056] <Fourth embodiment> Next, a fourth embodiment will be described. FIG. 7 shows an example of the configuration of a wireless communication system 7 according to this embodiment. The wireless communication system 7 includes a transmitting communication device 71 and a receiving communication device 72. The communication device 71 has a differential transmission path 101, amplifier circuits 105-1 and 105-2, and a transmitting circuit 106. The communication device 72 has a coupler 200, a shaping circuit 201, and a receiving circuit 202. Compared with the wireless communication system 1 in FIG. 1(a) described in the first embodiment, the wireless communication system 7 has a configuration in which components on the differential transmission path 101' side are excluded. Also, the differential transmission path 101 is configured so that the angle θ between the power supply unit 102 and the termination unit 104 is π / 2 (=90°). Note that the same components as those in the wireless communication system 1 in the first embodiment are given the same reference numerals and will not be described.

[0057] The wireless communication system 7 has a rotation control means (not shown) that controls the coupler 200 and at least one of the differential transmission paths 101, 101' to rotate back and forth while maintaining the coupler 200 and the differential transmission path 101 facing each other. The rotation angle in the back and forth rotation is smaller than 360°, and is 90° in the example of FIG. 7. In addition, the common mode filter A is inserted at a position of θ / 2 (=45°). The communication device 71 in this embodiment is suitable for application to a rotary movable part that is premised on back and forth rotation (wherein infinite rotation is not required), such as a tilt part of a pan-tilt camera.

[0058] In this manner, in this embodiment, even if the rotation angle of the coupler 200 with respect to the differential transmission line 101 around the central axis 30 is smaller than 360°, wireless communication is realized from the communication device 71 to the communication device 72 while rotating relatively around the rotation axis 30. Note that, although the rotation angle is set to be smaller than 360° in this embodiment, it is not limited thereto, and the rotation angle can be freely set by adjusting the transmission line length of the differential transmission line 101. Also, as in the first embodiment, a common mode filter is inserted in the differential transmission lines 101 and 101' in the communication device 61. This provides the same effects as those described in the first embodiment. Note that, as described in the third embodiment, it is also possible to configure a wireless communication system so that the functions of the transmitting side and the receiving side are interchanged.

[0059] The disclosure of this embodiment includes the following configurations and methods. (Configuration 1) A communication device comprising: a differential transmission path formed by a first electrode and a second electrode for performing wireless communication with another communication device by electromagnetic coupling; and communication means for transmitting a signal to the differential transmission path or receiving a signal from the differential transmission path, wherein a first end of the differential transmission path is connected to the communication means and a second end is terminated by a termination member, the first electrode and the second electrode are formed in an approximately arc shape on the outside and inside with a predetermined axis as a center, and a filter section for compensating for a propagation delay difference due to a wiring length difference between the first electrode and the second electrode is inserted on the differential transmission path.

[0060] (Configuration 2) The communication device according to configuration 1, wherein the filter section is a common mode filter.

[0061] (Configuration 3) The communication device according to configuration 1, wherein the differential transmission path is provided on a dielectric substrate.

[0062] (Configuration 4) The communication device according to configuration 3, wherein the filter section is provided on the same surface of the dielectric substrate as the differential transmission path is provided on.

[0063] (Configuration 5) The communication device according to configuration 3, wherein the filter section is provided on a surface of the dielectric substrate opposite to a surface on which the differential transmission path is provided.

[0064] (Configuration 6) The communication device according to configuration 1, wherein the filter section is inserted at a position on the differential transmission line where a propagation delay difference from the first end is 0.5 unit interval or less.

[0065] (Configuration 7) The communication device according to configuration 1, wherein a plurality of the filter sections are inserted on the differential transmission path.

[0066] (Configuration 8) The communication device according to configuration 7, wherein the plurality of filter sections are inserted at approximately equal intervals on the differential transmission path between the first end and the second end.

[0067] (Configuration 9) A communication device comprising: a first differential transmission path formed by a first electrode and a second electrode for performing wireless communication with another communication device by electromagnetic field coupling; a second differential transmission path formed by a third electrode and a fourth electrode for performing the wireless communication with the other communication device; a first communication means for transmitting a signal to the first differential transmission path or receiving a signal from the first differential transmission path; and a second communication means for transmitting a signal to the second differential transmission path or receiving a signal from the second differential transmission path, wherein the first differential transmission path and the second differential transmission path are disposed adjacent to each other, and each of the first differential transmission path and the second differential transmission path is a first end of the first differential transmission path is connected to the first communication means and the second communication means, and a second end of the first differential transmission path is terminated by a termination member, the first electrode and the second electrode are formed in a substantially arc shape on the outside and the inside with a predetermined axis as a center, the third electrode and the fourth electrode are formed in a substantially arc shape on the outside and the inside with the axis as a center, a first filter unit for compensating for a propagation delay difference due to a wiring length difference between the first electrode and the second electrode is inserted on the first differential transmission path, and a second filter unit for compensating for a propagation delay difference due to a wiring length difference between the third electrode and the fourth electrode is inserted on the second differential transmission path.

[0068] (Configuration 10) A communication system having a first communication device and a second communication device, wherein the first communication device has a differential transmission path formed by a first electrode and a second electrode for performing wireless communication with the second communication device by electromagnetic field coupling, and a communication means for transmitting a signal to the differential transmission path or receiving a signal from the differential transmission path, a first end of the differential transmission path is connected to the communication means, and a second end is terminated by a termination member, the first electrode and the second electrode are formed in an approximately arc shape on the outside and inside with a predetermined axis as a center, and a filter section for compensating for a propagation delay difference due to a wiring length difference between the first electrode and the second electrode is inserted on the differential transmission path.

[0069] (Configuration 11) The communication system according to configuration 10, further comprising a rotation control means for rotating at least one of the first communication device and the second communication device about the predetermined axis. [Explanation of symbols]

[0070] 1;4;5;6;7: wireless communication system, A;A';B;B': common mode filter, 10;20;40;61;62;71;72: communication device, 101;101';101A;101A';101B;101B': differential transmission line, 102;102';102A;102A';102B;102B': power supply section, 103;103': center line, 104;104';104A;104A';104B;104B': termination section, 105-1; 105-2; 105-3; 105-4; 105A-1; 105A-2; 105A-3; 105A-4; 105B-1; 105B-2; 105B-3; 105B-4; 621-1; 621-2: Amplification circuit, 106: 106A; 106B; 622: Transmission circuit, 111; 111'; 112; 112': Conductor (electrode), 200: Coupler, 201; 612: Shaping circuit, 202: Receiving circuit, 211; 212: Conductor, 611; 611': Multiplexer

Claims

1. A communication device, comprising: a differential transmission path formed by a first electrode and a second electrode for performing wireless communication with another communication device by electromagnetic coupling; a communication means for transmitting a signal to the differential transmission line or receiving a signal from the differential transmission line, a first end of the differential transmission line is connected to the communication means, and a second end of the differential transmission line is terminated by a termination member; The first electrode and the second electrode are formed in a generally arc shape on the outside and inside with a predetermined axis as a center, a filter unit for correcting a propagation delay difference caused by a wiring length difference between the first electrode and the second electrode is inserted on the differential transmission line; A communication device comprising:

2. 2. The communication device according to claim 1, wherein the filter section is a common mode filter.

3. The communication device according to claim 1 , wherein the differential transmission path is provided on a dielectric substrate.

4. 4. The communication device according to claim 3, wherein the filter section is provided on the same surface of the dielectric substrate as the differential transmission path.

5. 4. The communication device according to claim 3, wherein the filter section is provided on a surface of the dielectric substrate opposite to a surface on which the differential transmission path is provided.

6. 2. The communication device according to claim 1, wherein the filter section is inserted at a position on the differential transmission line where a propagation delay difference from the first end is 0.5 unit interval or less.

7. 2. The communication device according to claim 1, wherein a plurality of said filter sections are inserted on said differential transmission path.

8. 8. The communication device according to claim 7, wherein the filter sections are inserted at substantially equal intervals between the first end and the second end on the differential transmission line.

9. A communication device, comprising: a first differential transmission path formed by a first electrode and a second electrode for performing wireless communication with another communication device by electromagnetic coupling; a second differential transmission path formed by a third electrode and a fourth electrode for performing the wireless communication with the other communication device; a first communication means for transmitting a signal to the first differential transmission path or receiving a signal from the first differential transmission path; a second communication means for transmitting a signal to the second differential transmission path or receiving a signal from the second differential transmission path; the first differential transmission path and the second differential transmission path are disposed adjacent to each other, a first end of each of the first differential transmission path and the second differential transmission path is connected to the first communication means and the second communication means, respectively, and a second end of each of the first differential transmission path and the second differential transmission path is terminated by a termination member; The first electrode and the second electrode are formed in a generally arc shape on the outside and inside with a predetermined axis as a center, and the third electrode and the fourth electrode are formed in a generally arc shape on the outside and inside with the axis as a center, a first filter section for compensating for a propagation delay difference caused by a wiring length difference between the first electrode and the second electrode is inserted on the first differential transmission path, and a second filter section for compensating for a propagation delay difference caused by a wiring length difference between the third electrode and the fourth electrode is inserted on the second differential transmission path. A communication device comprising:

10. A communication system having a first communication device and a second communication device, The first communication device is a differential transmission path formed by a first electrode and a second electrode for performing wireless communication with the second communication device by electromagnetic coupling; a communication means for transmitting a signal to the differential transmission line or receiving a signal from the differential transmission line, a first end of the differential transmission line is connected to the communication means, and a second end of the differential transmission line is terminated by a termination member; The first electrode and the second electrode are formed in a substantially arc shape on the outside and inside with a predetermined axis as a center, a filter unit for correcting a propagation delay difference caused by a wiring length difference between the first electrode and the second electrode is inserted on the differential transmission line; A communication system comprising:

11. 11. The communication system according to claim 10, further comprising a rotation control means for rotating at least one of the first communication device and the second communication device about the predetermined axis.

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