Communications equipment

Abstract

A communication device includes a communication connector (12), a communication control circuit (11), and a common mode filter (13). The communication control circuit (11) controls communication established through the communication connector (12). The common mode filter (13) is connected to each of the communication control circuit (11) and the communication connector (12) to relay communication. The wavelength corresponding to the clock frequency of an electrical signal emitted from the communication control circuit (11) is represented as λ, and the electrical length of a signal path that resonates by a reflected wave generated by reflecting the electrical signal by the common mode filter (13) is closer to an even multiple of λ / 2 than an odd multiple.

Description

Technical Field

[0001] The present invention relates to a communication device having a built-in printed circuit board to which a communication connector and a control circuit thereof are mounted. Background Art

[0002] In recent years, wired connection communication standards such as High-Definition Multimedia Interface (HDMI) (registered trademark) 2.1 for performing data communication with an external communication device at an extremely high-speed clock frequency have emerged. Summary of the invention

[0003] Technical issues

[0004] In communication devices that communicate at high-speed clock frequencies as described above, the occurrence of noise (unwanted electromagnetic radiation) associated with communication becomes a problem. As part of the anti-noise countermeasure, there is a case where a common mode filter is arranged between an integrated circuit (communication control circuit) that sends and receives communication signals and a communication connector. However, how to arrange the common mode filter has yet to be fully studied.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a communication device capable of effectively suppressing the occurrence of noise in the case of performing communication with an external communication device by using a wired connection via a communication connector.

[0006] Solution to the problem

[0007] The communication device according to the present invention includes a communication connector, a communication control circuit and a common mode filter. The communication control circuit controls the communication established through the communication connector. The common mode filter is connected to each of the communication control circuit and the communication connector to relay the communication. The wavelength corresponding to the clock frequency of the electrical signal sent from the communication control circuit is represented as λ, and the electrical length of the signal path that generates resonance by the reflected wave generated by the common mode filter reflecting the electrical signal is closer to an even multiple of λ / 2 rather than an odd multiple. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a partial plan view of a built-in printed circuit board of a communication device according to an embodiment of the present invention.

[0009] Figure 2 is a partial cross-sectional view of a built-in printed circuit board of a communication device according to an embodiment of the present invention.

[0010] Figure 3 is a graph illustrating the effect of the position of the common mode filter on noise.

[0011] Figure 4 is a schematic diagram describing the relationship between the position of the common mode filter and the electrical length. DETAILED DESCRIPTION

[0012] Embodiments of the present invention will be described in detail below based on the accompanying drawings.

[0013] Figure 1 1 is a schematic partial plan view of a built-in printed circuit board 10 of a communication device 1 according to an embodiment of the present invention. Figure 2 1 is a schematic partial cross-sectional view of a printed circuit board 10. The communication device 1 is an electronic device such as a home game console, and includes a printed circuit board (PCB) 10, a communication control circuit 11 mounted to the printed circuit board 10, a communication connector 12, and a common mode filter (CMF) 13, as shown in FIG. Figure 1 In addition, Figure 2 As illustrated in FIG. 1 , the shield member 20 is arranged on the front surface of the printed circuit board 10 in such a manner as to cover the communication control circuit 11. It should be noted that Figure 1 The shield member 20 is not illustrated.

[0014] Various circuit elements required for the operation of the communication device according to the present embodiment are mounted to the printed circuit board 10. In the present embodiment, it is assumed that the printed circuit board 10 is a multilayer circuit board having a signal layer (inner layer) not only on its front surface but also on its inner side. A ground pattern G is formed on the front surface of the printed circuit board 10, and the ground pattern is used as a reference potential for the electronic circuit provided on the printed circuit board 10. Figure 1 , the ground pattern G is illustrated as shaded.

[0015] The communication control circuit 11 is an integrated circuit that controls the data communication performed with the external communication device through the communication connector 12. Specifically, the communication control circuit 11 generates and outputs an electrical signal to be sent to the external communication device through the communication connector 12. The communication control circuit 11 sends the electrical signal at a predetermined clock frequency according to a predetermined communication standard. Here, as a specific example, it is assumed that the communication control circuit 11 sends the electrical signal obtained by encoding video data, audio data, etc. according to the HDMI 2.0 standard and the HDMI 2.1 standard to the external communication device. It is also assumed that the communication control circuit 11 sends the electrical signal at a clock frequency of up to 8GHz. It should be noted that although the communication control circuit 11 mainly transmits data in the present embodiment, in addition to this, data transmitted from the external communication device can also be received. However, it should be noted that it is assumed that the average amount of data transmitted from the communication control circuit 11 to the external communication device is greater than the average amount of data received from the external device.

[0016] The communication connector 12 is arranged on the outer edge of the printed circuit board 10 and is connected with a communication cable supporting the communication standard of the communication connector. The communication device 1 is connected with an external communication device in a wired manner through the communication cable for data communication.

[0017] The common mode filter 13 is arranged between the communication control circuit 11 and the communication connector 12 to relay the communication between the communication control circuit 11 and the communication connector 12. In other words, the communication control circuit 11 and the communication connector 12 are not directly connected through a printed circuit, and each is connected to the common mode filter 13 through a signal line. The common mode filter 13 reduces the common mode noise of a specific frequency included in the relayed electrical signal. However, it should be noted that the common mode filter 13 does not need to reduce the common mode noise of signals of all clock frequencies emitted from the communication control circuit 11, and can only reduce the common mode noise of signals of some clock frequencies. In the present embodiment, it is assumed that the common mode filter 13 is intended for communication under the HDMI 2.0 standard, and does not remove noise from the electrical signal of the high-speed clock frequency under the HDMI2.1 standard.

[0018] The communication control circuit 11 and the common mode filter 13 are connected through a signal line 14 formed on the front surface of the printed circuit board 10. In addition, the communication connector 12 and the common mode filter 13 are connected through a signal line 15. It should be noted that in the present embodiment, it is assumed that data communication is performed with an external communication device through four signal lines, and both the signal line 14 and the signal line 15 include four parallel signal lines.

[0019] The signal line 15 includes a signal line 15a, a signal line 15b, and a signal line 15c. The signal line 15a is formed on the front surface of the printed circuit board 10 and is coupled to the common mode filter 13. The signal line 15b is formed in an inner layer of the printed circuit board 10. The signal line 15c is formed on the front surface of the printed circuit board 10 and is coupled to the communication connector 12. The signal line 15a and the signal line 15b are electrically connected through a through hole 16a formed in the printed circuit board 10. In addition, the signal line 15b and the signal line 15c are electrically connected through a through hole 16b formed in the printed circuit board 10.

[0020] When the communication control circuit 11 communicates at a high-speed clock frequency through the communication connector 12, noise is emitted into the surrounding environment. The inventors of the present invention have found through research conducted through simulation and measurement that the reflected wave generated by the electric signal (traveling wave) emitted from the communication control circuit 11 being reflected by the common mode filter 13 has a significant influence on the overall noise. Therefore, by arranging the common mode filter 13 as described above in a manner to reduce the influence of the reflected wave caused by the common mode filter 13, the occurrence of noise can be suppressed.

[0021] Specifically, the occurrence of noise can be suppressed by keeping the communication control circuit 11 and the common mode filter 13 at a distance determined to be commensurate with the value of the clock frequency generating noise. In contrast, the distance from the common mode filter 13 to the communication connector 12 has a relatively small effect on the occurrence of noise, and is therefore relatively freely determined in terms of circuit design convenience, etc.

[0022] In particular, by setting the electrical length Le at which the wave reflected by the common mode filter 13 resonates to an integral multiple of the wavelength λ corresponding to the clock frequency for which anti-noise measures are required (i.e., an even multiple of λ / 2), such resonance that the traveling wave and the reflected wave cancel each other can be generated, thereby suppressing external noise emission. Here, the electrical length Le is given by √ ε·D represents, where D is a physical distance contributing to the signal path of the resonance of the reflected wave, and ε is a dielectric constant of a dielectric included in the printed circuit board 10. Therefore, the emitted noise can be suppressed in the case where the distance D is close to:

[0023] D=(1 / √ ε)n·λ.

[0024] Here, n is an integer equal to or greater than 1.

[0025] Figure 3 The simulation results of the case where the length L1 of the signal line 15 from the communication control circuit 11 to the common mode filter 13 changes are illustrated. The curve graph in the figure illustrates the simulation results of the case where the clock frequency is 6 GHz and the case where the clock frequency is 8 GHz, the horizontal axis represents the length L1 of the signal line 15 between the communication control circuit 11 and the common mode filter 13, and the vertical axis represents the value of the far-field electric field strength. The greater the electric field strength, the greater the noise caused by the communication of the communication control circuit 11. As illustrated in the figure, the size of the noise changes periodically in proportion to the change in the length L1, and its period corresponds to the wavelength λ of the corresponding clock frequency. More specifically, the noise peak appears at a position where the electrical length corresponds to an odd multiple of λ / 2.

[0026] Example Figure 3 The graph of the simulation results in indicates that the far-field electric field intensity takes a minimum value at a position where the length L1 is close to 0. However, the inventors have confirmed that, unlike the simulation results, the size of the noise is reduced not at the position where the length L1 becomes 0 but at a farther position in the actual device. The reason for this is that it is assumed that not only the signal line 14 outside the communication control circuit 11 up to the common mode filter 13 but also the internal packaging structure of the communication control circuit 11 not considered in the above simulation contributes to the resonance between the communication control circuit 11 and the common mode filter 13.

[0027] The die inside the communication control circuit 11 is connected to the connection terminal outside the communication control circuit 11 through a line (conductor) such as wire bonding. The die and the wire may contribute to the resonance between the traveling wave and the reflected wave. However, it is difficult to identify the die size and line length inside the communication control circuit 11. Therefore, the position of the common mode filter 13 is determined in consideration of the line length inside the communication control circuit 11 assumed based on the physical size of the communication control circuit 11.

[0028] Specifically, the distance D at which the wave reflected from the common mode filter 13 resonates is the sum of the length L1 of the signal line 15 and the length L2 of the signal path inside the communication control circuit 11, and the electrical length Le is the sum of the distance D. √ ε times.

[0029] Le= √ ε(L1+L2)

[0030] When the electrical length Le is closer to an even multiple of λ / 2 than to an odd multiple of λ / 2, the occurrence of noise can be reduced. In other words, when n is an integer equal to or greater than 1 and the following relationship is satisfied, the emitted noise is reduced more than in other cases.

[0031] n·λ-λ / 4< √ ε(L1+L2) <n·λ+λ / 4

[0032] This relationship indicates that the difference between the electrical length Le and the length of an even multiple of λ / 2 is smaller than λ / 4.

[0033] More preferably, the emitted noise is reduced by satisfying the following relationship.

[0034] n·λ-λ / 8< √ ε(L1+L2) <n·λ+λ / 8

[0035] This relational expression indicates that the difference between the electrical length Le and the length of an even multiple of λ / 2 is smaller than λ / 8.

[0036] In these formulas, λ is a wavelength corresponding to the clock frequency for which anti-noise countermeasures are required for all clock frequencies of the electrical signal emitted from the communication control circuit 11. In particular, this λ may be a wavelength corresponding to the maximum clock frequency (8 GHz in the present embodiment) of the electrical signal emitted from the communication control circuit 11. In addition, in the case where anti-noise countermeasures are required for a clock frequency lower than this frequency (e.g., 6 GHz), noise during communication at two clock frequencies may also be suppressed by determining the position of the common mode filter 13 in such a manner that the above relationship is also satisfied for the second wavelength corresponding to the clock frequency.

[0037] Here, although L2 is the length of the signal path inside the communication control circuit 11, in the case where the internal structure of the communication control circuit 11 is unknown, the length as described below can be approximately regarded as L2. Specifically, the electrical length Le is calculated by regarding the sum of the distance L2a from the center position of the communication control circuit 11 to the side to which the signal line 15 is connected and the distance L2b from the center position to the farthest connection terminal on the opposite side of the signal line 15 as the length L2. Figure 4 is a schematic diagram describing the length L2 and the distance D that produce resonance in this case.

[0038] The shielding member 20 includes a plate-shaped conductive member such as a metal plate and is arranged to be opposite to the printed circuit board 10 and to cover the circuit elements arranged on the front surface of the printed circuit board 10. The outer edge of the shielding member 20 is electrically connected to the ground pattern G formed on the front surface of the printed circuit board 10. This allows the shielding member 20 to prevent the noise generated inside the shielding member 20 from propagating outwardly.

[0039] As described so far, the communication control circuit 11 and the common mode filter 13 are connected by the signal line 14, and the signal line 14 is arranged on the front surface of the printed circuit board 10. Therefore, there is no signal path between the communication control circuit 11 and the common mode filter 13 that moves between the layers of the printed circuit board 10.

[0040] At the same time, the signal line 15 between the common mode filter 13 and the communication connector 12 includes a signal line 15b formed inside the printed circuit board 10 in the middle. Therefore, the signal line 15 is connected to the printed circuit board 10 through a through-hole connection layer formed at both ends of the signal line 15b. The inventors have found that in the case of such a signal path where there is a connection layer, noise is likely to leak from these parts. Therefore, an interlayer connection point is not set in the communication path between the common mode filter 13 and the communication control circuit 11, which is the main noise emission source, but such an interlayer connection point is set in the communication path between the common mode filter 13 and the communication connector 12.

[0041] In a plan view, the outer edge of the shielding member 20 intersects the signal line 15b passing through the inner layer. This makes it possible to bring the outer edge of the shielding member 20 into contact with the ground pattern G on the front surface of the printed circuit board 10 without causing the signal path between the communication control circuit 11 and the communication connector 12 to interrupt the ground pattern G. This makes it possible for the shielding member 20 to accommodate the communication control circuit 11, the common mode filter 13, and the signal line 14 connecting them, and prevent the noise emitted from these components from propagating to the outside.

[0042] As described above, according to the communication device 1 of this embodiment, it is possible to effectively suppress the noise caused by the reflected wave of the electrical signal emitted from the communication control circuit 11 to the common mode filter 13, and prevent the communication control circuit 11 from emitting large noise when communicating by using a high-speed clock.

[0043] It should be noted that the embodiments of the present invention are not limited to the above. For example, although it has been stated in the above description that the communication control circuit 11 communicates according to the HDMI standard, the present invention is not limited thereto, and the communication control circuit 11 may be a circuit that communicates according to various communication standards. In addition, although it has been stated in the above description that the maximum clock frequency of the signal sent and received between the communication control circuit 11 and the communication connector 12 is 8 GHz, the present invention is not limited thereto, and the communication control circuit 11 may communicate at various clock frequencies. In this case, it is only necessary to determine the position of the common mode filter 13 so as to provide an electrical length close to an integer multiple of the wavelength λ corresponding to the clock frequency for which anti-noise countermeasures are required (in particular, the maximum clock frequency used by the communication control circuit 11 to send and receive signals).

[0044] In addition, although it has been stated in the above description that the communication device 1 is a home game console, the communication device 1 according to an embodiment of the present invention is not limited to this and may be various devices having a communication control circuit 11 and a communication connector 12 for performing wired communication, such as a personal computer, a portable game console, and a smart phone.

[0045] Reference numerals list

[0046] 1: Communication equipment

[0047] 10: Printed Circuit Board

[0048] 11: Communication control circuit

[0049] 12: Communication connector

[0050] 13: Common mode filter

[0051] 14, 15: Signal line

[0052] 16:Through hole

[0053] 20: Shielding component

Claims

1. A communication device, comprising: Communication connectors; a communication control circuit adapted to control communications established through the communication connector; a common mode filter connected to each of the communication control circuit and the communication connector to relay the communication; as well as One or more first signal lines, the one or more first signal lines connecting the communication control circuit and the common mode filter, wherein: The wavelength corresponding to the clock frequency of the electrical signal sent from the communication control circuit is denoted as λ, The electrical length of the one or more first signal lines that resonate due to a reflected wave generated by reflecting the electrical signal by the common mode filter is closer to an even multiple of λ / 2 than to an odd multiple.

2. The communication device according to claim 1, wherein A difference between the electrical length of the one or more first signal lines and a length that is an even-numbered multiple of λ / 2 is smaller than λ / 8.

3. The communication device according to claim 1 or 2, wherein The one or more first signal lines connecting the communication control circuit and the common mode filter are arranged on the front surface of the printed circuit board, and One or more second signal lines connecting the common mode filter and the communication connector include paths extending between layers of the printed circuit board.

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