Flexible flat cable, flexible flat cable with connector, and electronic apparatus

Abstract

A flexible flat cable according to an embodiment comprises: a plurality of conductor lines arranged parallel to each other; and an insulating layer provided around the plurality of conductor lines. The plurality of conductor lines include: a plurality of transmission lines arranged in a row in a cross section orthogonal to a longitudinal direction of the plurality of conductor lines; and at least one open line having both ends electrically open. The plurality of transmission lines include: a plurality of ground lines; and a pair of first signal lines and a pair of second signal lines located between the plurality of ground lines in the cross section. The open line is located, in the cross section, on a first direction side of the pair of first signal lines, the first direction being orthogonal to an arrangement direction of the plurality of transmission lines.

Description

Flexible Flat Cable, Flexible Flat Cable with Connector, and Electronic Device

[0001] The present disclosure relates to a flexible flat cable, a flexible flat cable with a connector, and an electronic device. The present application claims priority based on Japanese Patent Application No. 2025-031555 filed on February 28, 2025, and incorporates all the content described in the said Japanese application by reference.

[0002] Patent Document 1 discloses a shielded flexible flat cable. This flexible flat cable has a plurality of conductors arranged parallel to each other. The plurality of conductors include two pairs of signal lines for differential transmission, a ground line arranged between the two pairs of signal lines, an insulating layer, and a shield layer. The insulating layer is provided around the two pairs of signal lines and the ground line. The shield layer covers the outer peripheral surface of the insulating layer. The shield layer and the ground line are electrically connected to each other. Accordingly, the shield layer and the ground line surround the periphery of each of the two pairs of signal lines. This suppresses crosstalk between the two pairs of signal lines.

[0003] International Publication No. WO 2019 / 208247

[0004] A flexible flat cable according to an embodiment includes a plurality of conductor lines arranged parallel to each other, and an insulating layer provided around the plurality of conductor lines. The plurality of conductor lines include a plurality of transmission lines aligned in a single row in a cross section orthogonal to the longitudinal direction of the plurality of conductor lines, and at least one open line with both ends electrically open. The plurality of transmission lines include a plurality of ground lines, and a pair of first signal lines and a pair of second signal lines located between the plurality of ground lines in the cross section. The open line is located, in the cross section, on a first direction side of the pair of first signal lines, the first direction being orthogonal to the arrangement direction of the plurality of transmission lines.

[0005] Figure 1 is a diagram showing an example of an electronic device according to the embodiment. Figure 2 is a perspective view showing an example of a flexible flat cable according to the embodiment. Figure 3 is a cross-sectional view taken along the line III-III in Figure 2. Figure 4 is a plan view showing the end of the flexible flat cable according to the embodiment. Figure 5 is a cross-sectional view of a flexible flat cable according to the first modified example. Figure 6 is a cross-sectional view of a flexible flat cable according to the second modified example. Figure 7 is a cross-sectional view of a flexible flat cable according to the third modified example. Figure 8 is a graph showing the frequency characteristics of insertion loss for the embodiment and comparative example. Figure 9 is a graph showing the frequency characteristics of reflection loss for the embodiment and comparative example. Figure 10 is a graph showing the frequency characteristics of near-end crosstalk for the embodiment and comparative example. Figure 11 is a graph showing the frequency characteristics of far-end crosstalk for the embodiment and comparative example.

[0006] [Problems this disclosure aims to solve] In the conventional flexible flat cable described above, the shield layer and the ground wire are bonded to each other with a conductive adhesive and electrically connected. In recent years, with the increasing demand for cost reduction, the conventional example described above has a relatively complex configuration in which the shield layer and the ground wire are bonded with a conductive adhesive. From the viewpoint of cost reduction, there is a need for a technology that can effectively reduce crosstalk with a simpler configuration.

[0007] This disclosure aims to provide a technology that can effectively reduce crosstalk.

[0008] [Effects of this disclosure] According to this disclosure, crosstalk can be effectively reduced.

[0009] [Description of Embodiments in this Disclosure] First, the contents of the embodiments will be listed and described. [Summary of Embodiments]

[0010] (1) The flexible flat cable according to the embodiment comprises a plurality of conductor lines arranged parallel to each other, and an insulating layer provided around the plurality of conductor lines. The plurality of conductor lines include a plurality of transmission lines arranged in a row in a cross section perpendicular to the longitudinal direction of the plurality of conductor lines, and at least one open line with both ends electrically open. The plurality of transmission lines include a plurality of ground lines, and a pair of first signal lines and a pair of second signal lines located between the plurality of ground lines in the cross section. The open line is located in the cross section on the side of the pair of first signal lines in a first direction perpendicular to the arrangement direction of the plurality of transmission lines. According to the above configuration, the open line reflects and absorbs the crosstalk components radiated from the pair of first signal lines and the pair of second signal lines. As a result, the transmission of crosstalk components between the pair of first signal lines and the pair of second signal lines can be suppressed. As a result, crosstalk between the pair of first signal lines and the pair of second signal lines is effectively reduced.

[0011] (2) The flexible flat cable described in (1) above may further include a shielding layer provided on the outer surface of the insulating layer. In this case, noise from the pair of first signal lines and the pair of second signal lines can be shielded, and the pair of first signal lines and the pair of second signal lines can be shielded from external noise.

[0012] (3) In the flexible flat cable described in (1) or (2) above, the position of at least one of the pair of first signal lines in the direction of arrangement and the position of the open line in the direction of arrangement may overlap with each other. In this case, the open line can be positioned in a location that can become a path for crosstalk components. This makes it possible to effectively suppress the mutual transmission of crosstalk components between the pair of first signal lines and the pair of second signal lines.

[0013] (4) In any one of the flexible flat cables described in (1) to (3) above, if there are multiple open lines, the multiple open lines may include a pair of first open lines located on the first direction side of the pair of first signal lines in the cross section. In this case, an open line is provided for each of the pair of first signal lines. This makes it possible to more effectively suppress the transmission of crosstalk components between the pair of first signal lines and the pair of second signal lines.

[0014] (5) In addition, in the flexible flat cable described in (4) above, the plurality of open lines may further include a pair of second open lines located in the cross section on the second direction side, which is the opposite direction to the first direction of the pair of first signal lines. In this case, the pair of first open lines can reflect and absorb the crosstalk component on the first direction side of the pair of first signal lines, and the pair of second open lines can reflect and absorb the crosstalk component on the second direction side of the pair of first signal lines.

[0015] (6) In the flexible flat cable described in (5) above, the plurality of open lines may further include a pair of third open lines located on the first direction side of the pair of second signal lines in the cross section, and a pair of fourth open lines located on the second direction side of the pair of second signal lines in the cross section. In this case, open lines are provided on the first direction side and the second direction side of each of the signal lines included in the pair of first signal lines and the pair of second signal lines. This makes it possible to further effectively suppress the transmission of crosstalk components between the pair of first signal lines and the pair of second signal lines.

[0016] (7) In the flexible flat cable described in (6) above, the pair of first open lines and the pair of third open lines may be arranged in a row along the arrangement direction in the cross-section, and the pair of second open lines and the pair of fourth open lines may be arranged in a row along the arrangement direction in the cross-section. In this case, if the insulating layer is made up in multiple layers along the arrangement lines of the multiple transmission lines and the arrangement lines of the multiple open lines in the cross-section, it becomes easy to provide multiple conductor lines arranged along each arrangement line.

[0017] (8) In any one of the flexible flat cables described in (1) to (7) above, each of the multiple transmission lines may have extensions at both ends that extend beyond the ends of the open line. In this case, if connectors are provided at both ends of the multiple transmission lines, the terminals of the connectors are connected to the extensions, and the open line is not connected to the terminals of the connectors. Thus, the open line can be made electrically isolated.

[0018] (9) In any one of the flexible flat cables described in (1) to (8) above, the pair of first signal lines may have first connection ends connected to a first differential transmission line, and the pair of second signal lines may have second connection ends connected to a second differential transmission line. In this case, differential signals are transmitted through the pair of first signal lines, and other differential signals are transmitted through the pair of second signal lines.

[0019] (10) A flexible flat cable with a connector, which is an embodiment from another viewpoint, comprises a flexible flat cable and connectors provided at both ends of the flexible flat cable. The flexible flat cable comprises a plurality of conductor lines arranged parallel to each other and an insulating layer provided around the plurality of conductor lines. The plurality of conductor lines include a plurality of transmission lines arranged in a row in a cross section perpendicular to the longitudinal direction of the plurality of conductor lines and at least one open line which is an unconnected portion whose ends are not connected to the terminals of the connector. The plurality of transmission lines include a plurality of ground lines and a pair of first signal lines and a pair of second signal lines whose ends are connected to the terminals of the connector and which are located between the plurality of ground lines in the cross section. The open line is located in the cross section on the first direction side of the pair of first signal lines which is perpendicular to the arrangement direction of the plurality of transmission lines.

[0020] (11) Another embodiment of the electronic device from another viewpoint comprises a first electronic device, a second electronic device that exchanges a first differential signal and a second differential signal with the first electronic device, and a flexible flat cable connecting the first electronic device and the second electronic device. The flexible flat cable comprises a plurality of conductor lines arranged parallel to each other, and an insulating layer provided around the plurality of conductor lines. The plurality of conductor lines include a plurality of transmission lines arranged in a row in a cross section perpendicular to the longitudinal direction of the plurality of conductor lines, and at least one open line with both ends electrically open. The plurality of transmission lines include a plurality of ground lines, and a pair of first signal lines and a pair of second signal lines located between the plurality of ground lines in the cross section. The pair of first signal lines are lines for the first differential signal. The pair of second signal lines are lines for the second differential signal. The open line is located in the cross-section on the side of the pair of first signal lines that is perpendicular to the arrangement direction of the plurality of transmission lines.

[0021] [Details of Embodiments] Preferred embodiments will be described below with reference to the drawings. At least some of the embodiments described below may be combined in any way.

[0022] [Configuration of the electronic device] Figure 1 is a diagram showing an example of an electronic device according to the embodiment. In Figure 1, the electronic device 100 comprises a first electronic device 101, a second electronic device 102, and a flexible flat cable 103 with a connector. The flexible flat cable 103 with a connector connects the first electronic device 101 and the second electronic device 102. The first electronic device 101 and the second electronic device 102 exchange a first differential signal and a second differential signal with each other.

[0023] The first electronic device 101 has a first differential transmission line 101a and a second differential transmission line 101b. The second electronic device 102 has a third differential transmission line 102a and a fourth differential transmission line 102b. The first differential transmission line 101a and the third differential transmission line 102a are connected via a flexible flat cable 103 with a connector. A first differential signal is exchanged between the first differential transmission line 101a and the third differential transmission line 102a. The second differential transmission line 101b and the fourth differential transmission line 102b are connected via a flexible flat cable 103 with a connector. A second differential signal is exchanged between the second differential transmission line 101b and the fourth differential transmission line 102b.

[0024] The flexible flat cable 103 with connectors comprises a flexible flat cable 1, a first connector 111, and a second connector 112. The first connector 111 and the second connector 112 are provided at the ends of the flexible flat cable 1.

[0025] The first connector 111 has a plurality of first terminals 111a. The plurality of first terminals 111a are electrically connected to the transmission lines included in the flexible flat cable 1. When the first connector 111 is plugged into the first electronic device 101, the plurality of first terminals 111a electrically connect the transmission lines of the flexible flat cable 1 to the differential transmission lines 101a and 101b of the first electronic device 101.

[0026] The second connector 112 has a plurality of second terminals 112a. The plurality of second terminals 112a are electrically connected to the transmission lines included in the flexible flat cable 1. When the second connector 112 is plugged into the second electronic device 102, the plurality of second terminals 112a electrically connect the transmission lines of the flexible flat cable 1 to the differential transmission lines 102a and 102b of the second electronic device 102. As a result, the first differential transmission line 101a and the third differential transmission line 102a are connected, and the second differential transmission line 101b and the fourth differential transmission line 102b are connected.

[0027] [About the configuration of the flexible flat cable] Figure 2 is a perspective view showing an example of a flexible flat cable according to the embodiment. Figure 3 is a cross-sectional view taken along the line III-III in Figure 2. The flexible flat cable 1 according to the embodiment is a cable that electrically connects a first electronic device 101 and a second electronic device 102 inside an electronic device 100.

[0028] In the following explanation, the three mutually orthogonal directions in each figure will be referred to as the X direction, Y direction, and Z direction. Also, as shown in Figure 2, one direction of the X direction will be referred to as the X1 direction, and the opposite direction of the X1 direction will be referred to as the X2 direction. One direction of the Y direction will be referred to as the Y1 direction, and the opposite direction of the Y1 direction will be referred to as the Y2 direction. One direction of the Z direction will be referred to as the Z1 direction, and the opposite direction of the Z1 direction will be referred to as the Z2 direction. Figure 3 shows a cross-section of the flexible flat cable 1 along the X-Z plane as viewed from the Y2 direction side.

[0029] In Figure 2, the longitudinal direction of the flexible flat cable 1 (hereinafter also referred to as FFC1) is along the Y direction. The width direction of FFC1 is along the X direction. In the following explanation, it will be assumed that FFC1 is arranged in a state extended in the Y direction, as shown in Figure 2.

[0030] FFC1 includes multiple conductor lines 2, an insulating layer 4, and a shielding layer 6. In other words, FFC1 is a shielded flexible flat cable. The multiple conductor lines 2 are flat rectangular conductors made of copper or the like. The width dimensions of the multiple conductor lines 2 along the X direction are the same for all of them. The multiple conductor lines 2 extend along the Y direction and are arranged parallel to each other. The multiple conductor lines 2 extend over almost the entire length (Y direction) of FFC1.

[0031] The multiple conductor lines 2 include multiple transmission lines 8 and multiple open lines 14. As shown in Figure 3, the multiple transmission lines 8 are arranged in a line along the X direction in a cross section perpendicular to the longitudinal direction of the multiple conductor lines 2. The multiple transmission lines 8 are arranged along a first arrangement line P1. The first arrangement line P1 is a straight line along the arrangement of the multiple transmission lines 8 in a cross section perpendicular to the longitudinal direction. The first arrangement line P1 is a line along the X direction located approximately in the center of the Z direction of the FFC 1. The multiple transmission lines 8 include multiple ground lines 10, a pair of first signal lines 11, and a pair of second signal lines 12.

[0032] The multiple ground lines 10 are arranged in a line along the first alignment line P1 in a cross section perpendicular to the longitudinal direction. The multiple ground lines 10 include a first ground line 10a, a second ground line 10b, a third ground line 10c, and a fourth ground line 10d. The first ground line 10a, the second ground line 10b, the third ground line 10c, and the fourth ground line 10d are arranged in order along the X1 direction. The Y2 direction end of each of the multiple ground lines 10 is electrically connected to the first terminal 111a (Figure 1) of the first connector 111. The Y1 direction end of each of the multiple ground lines 10 is electrically connected to the second terminal 112a (Figure 1) of the second connector 112. The terminals connected to the multiple ground lines 10 are connected to the grounding lines of the first electronic device 101 and the second electronic device 102.

[0033] As shown in Figure 3, the pair of first signal lines 11 and the pair of second signal lines 12 are located between the multiple ground lines 10 in a cross section perpendicular to the longitudinal direction of the multiple conductor lines 2. The pair of first signal lines 11 are used as transmission lines for the first differential signal. The Y2 direction end of each of the pair of first signal lines 11 is electrically connected to the first terminal 111a (Figure 1) of the first connector 111. The Y1 direction end of each of the pair of first signal lines 11 is electrically connected to the second terminal 112a (Figure 1) of the second connector 112. The pair of second signal lines 12 are used as transmission lines for the second differential signal. The Y2 direction end of each of the pair of second signal lines 12 is electrically connected to the first terminal 111a (Figure 1) of the first connector 111. The Y1 direction end of each of the pair of second signal lines 12 is electrically connected to the second terminal 112a (Figure 1) of the second connector 112.

[0034] As shown in Figure 3, the pair of first signal lines 11 are located between the first ground line 10a and the second ground line 10b. The pair of first signal lines 11 are aligned along the first array line P1. As shown in Figure 3, the pair of second signal lines 12 are located between the third ground line 10c and the fourth ground line 10d. The pair of second signal lines 12 are aligned along the first array line P1. Two ground lines 10 (second ground line 10b and third ground line 10c) are interposed between the pair of first signal lines 11 and the pair of second signal lines 12.

[0035] Thus, the multiple ground lines 10, the pair of first signal lines 11, and the pair of second signal lines 12 are arranged in a line along the first arrangement line P1. Furthermore, the multiple ground lines 10, the pair of first signal lines 11, and the pair of second signal lines 12 are arranged at equal intervals in the X direction.

[0036] Each of the multiple open lines 14 has an electrically open end. Furthermore, each of the multiple open lines 14 is not grounded. In other words, when the pair of first signal lines 11 and the pair of second signal lines 12 are used as transmission lines, both ends of the multiple open lines 14 are electrically open without being connected to connectors or the like. As a result, the multiple open lines 14 are not connected to equipment or the like, nor are they grounded. Therefore, the multiple open lines 14 are electrically floating. Note that the thickness of the multiple open lines 14 in this embodiment is thinner than the thickness of the multiple transmission lines 8. However, the thickness of the multiple open lines 14 may be the same as the thickness of the multiple transmission lines 8, or it may be thicker than the thickness of the multiple transmission lines 8.

[0037] The multiple open lines 14 include a pair of first open lines 14a, a pair of second open lines 14b, a pair of third open lines 14c, and a pair of fourth open lines 14d. As shown in Figure 3, the pair of first open lines 14a are located on the first direction side (Z1 direction side) of the pair of first signal lines 11 in a cross section perpendicular to the longitudinal direction. The first direction is the direction perpendicular to the arrangement direction (X direction) of the multiple transmission lines 8. The position of the pair of first open lines 14a in the X direction coincides with the position of the pair of first signal lines 11 in the X direction. The pair of second open lines 14b are located on the second direction side (Z2 direction side) of the pair of first signal lines 11 in a cross section perpendicular to the longitudinal direction. The second direction is the opposite direction to the first direction. The position of the pair of second open lines 14b in the X direction coincides with the position of the pair of first signal lines 11 in the X direction.

[0038] The pair of third open lines 14c are located on the first direction side (Z1 direction side) of the pair of second signal lines 12 in a cross section perpendicular to the longitudinal direction. The positions of the pair of third open lines 14c in the X direction coincide with the positions of the pair of second signal lines 12 in the X direction. The pair of fourth open lines 14d are located on the second direction side (Z2 direction side) of the pair of second signal lines 12 in a cross section perpendicular to the longitudinal direction. The positions of the pair of fourth open lines 14d in the X direction coincide with the positions of the pair of second signal lines 12 in the X direction.

[0039] As shown in Figure 3, the pair of first open lines 14a and the pair of third open lines 14c are arranged in a line along the arrangement direction (X direction) of the multiple transmission lines 8. The pair of first open lines 14a and the pair of third open lines 14c are arranged along the second arrangement line P2. The second arrangement line P2 is a straight line along the arrangement of the pair of first open lines 14a and the pair of third open lines 14c in a cross section perpendicular to the longitudinal direction. The second arrangement line P2 is parallel to the first arrangement line P1 and is located on the Z1 direction side of the first arrangement line P1. The pair of second open lines 14b and the pair of fourth open lines 14d are arranged in a line along the arrangement direction (X direction) of the multiple transmission lines 8, as shown in Figure 3. The pair of second open lines 14b and the pair of fourth open lines 14d are arranged along the third arrangement line P3. The third alignment line P3 is a straight line in a cross-section perpendicular to the longitudinal direction that aligns with the arrangement of the pair of second open lines 14b and the pair of fourth open lines 14d. The third alignment line P3 is parallel to the first alignment line P1 and is located on the Z2 side of the first alignment line P1. The distance in the Z direction between the first alignment line P1 and the second alignment line P2 is the same as the distance in the Z direction between the first alignment line P1 and the third alignment line P3.

[0040] The insulating layer 4 is provided around the multiple conductor lines 2. The insulating layer 4 covers the sides of the multiple conductor lines 2 and is interposed between the multiple conductor lines 2. In this way, the insulating layer 4 insulates the multiple conductor lines 2 from each other. The insulating layer 4 also maintains the arrangement of the multiple conductor lines 2. The insulating layer 4 is formed by laminating multiple sub-layers. For example, the insulating layer 4 is formed by laminating at least four sub-layers separated along the first arrangement line P1, the second arrangement line P2, and the third arrangement line P3. As the multiple sub-layers to be laminated, for example, a flexible resin film is used. As the material of the film, polyester resin, polyphenylene sulfide resin, and polyimide resin are used. Examples of polyester resins include polyethylene terephthalate resin, polyethylene naphthalate resin, and polybutylene naphthalate resin. In addition, an adhesive layer made of an insulating material may be interposed between the multiple sub-layers.

[0041] In the present embodiment, the plurality of conductor lines 2 are arranged along the first arrangement line P1, the second arrangement line P2, and the third arrangement line P3. Therefore, when laminating a plurality of sublayers, the plurality of conductor lines 2 can be arranged, and it becomes easy to provide the plurality of conductor lines arranged along each plane.

[0042] The shield layer 6 is laminated on the outer surface of the insulating layer 4. The shield layer 6 includes a pair of shield films 16. The pair of shield films 16 cover the insulating layer 4 from the Z1 direction side and the Z2 direction side. Ends of the pair of shield films 16 in the X direction are bonded to each other at an end face of the insulating layer 4 in the X direction. Thereby, the shield layer 6 is configured. For the shield layer 6 (the pair of shield films 16), for example, a resin film on which a conductor such as aluminum is vapor-deposited is used. The shield layer 6 shields noise generated when a signal is applied to the pair of first signal lines 11 and the pair of second signal lines 12, and can also shield the pair of first signal lines 11 and the pair of second signal lines 12 against external noise.

[0043] According to the FFC 1 having the above configuration, when the pair of first signal lines 11 and the pair of second signal lines 12 are used as transmission lines, the plurality of open lines 14 reflect and absorb crosstalk components radiated from the pair of first signal lines 11 and the pair of second signal lines 12. Thereby, transmission of crosstalk components between the pair of first signal lines 11 and the pair of second signal lines 12 can be suppressed. As a result, crosstalk between the pair of first signal lines 11 and the pair of second signal lines 12 is effectively reduced.

[0044] That is, according to the FFC 1 of the present embodiment, unlike the above-mentioned conventional flexible flat cable, it does not have a configuration in which the shield layer and the ground line are bonded with a conductive adhesive, so crosstalk can be reduced with a simpler configuration.

[0045] The crosstalk reduction effect may vary depending on the spacing d1 (Figure 3) between the multiple open lines 14 and the pair of first signal lines 11 (pair of second signal lines 12). A smaller spacing d1 increases the crosstalk reduction effect, but increases the insertion loss in the pair of first signal lines 11. A larger spacing d1 decreases the insertion loss in the pair of first signal lines 11, but reduces the crosstalk reduction effect. Therefore, the spacing d1 is determined by considering the balance between the crosstalk reduction effect and the insertion loss.

[0046] Figure 4 is a plan view showing the end of the FFC1 according to the embodiment. In Figure 4, parts of the insulating layer 4 and the shielding layer 6 of the FFC1 are omitted. As shown in Figure 4, the pair of first open lines 14a overlap with the pair of first signal lines 11 in a plan view. Also, the pair of third open lines 14c overlap with the pair of second signal lines 12 in a plan view. In other words, the positions of the pair of first signal lines 11 in the direction of arrangement (X direction) and the positions of the pair of first open lines 14a in the direction of arrangement (X direction) overlap with each other. Also, the positions of the pair of second signal lines 12 in the direction of arrangement (X direction) and the positions of the pair of third open lines 14c in the direction of arrangement (X direction) overlap with each other. Similarly, the positions of the pair of first signal lines 11 in the X direction and the positions of the pair of second open lines 14b in the X direction also overlap with each other, and the positions of the pair of second signal lines 12 in the X direction and the positions of the pair of fourth open lines 14d in the X direction also overlap with each other.

[0047] In this way, the positions of the signal lines 11 and 12 in the X direction and the position of the open line 14 in the X direction overlap, so that the open line 14 is positioned in a location where it can become a path for crosstalk components. As a result, the multiple open lines 14 can effectively suppress the mutual transmission of crosstalk components between the pair of first signal lines 11 and the pair of second signal lines 12.

[0048] Further, as shown in FIG. 4 and FIG. 2, the lengths of the plurality of open lines 14 in the Y direction are shorter than the length of the transmission line 8. The lengths of the plurality of open lines 14 in the Y direction are the same as each other. The positions of both end portions in the Y direction of each of the plurality of transmission lines 8 coincide with the position of the end surface 1a in the Y direction of the FFC 1. Both end portions in the Y direction of each of the plurality of open lines 14 are located at positions spaced apart from the end surface 1a in the Y direction.

[0049] As shown in FIG. 4, a pair of end edges 14a1 of the pair of first open lines 14a are located on the Y1 direction side relative to the end surface 1a. Similarly, a pair of end edges 14c1 of the pair of third open lines 14c are also located on the Y1 direction side relative to the end surface 1a. Note that the pair of end edges 14a1 are end edges on the Y2 direction side of the pair of first open lines 14a. The pair of end edges 14c1 are end edges on the Y2 direction side of the pair of third open lines 14c. Further, a pair of end edges of the pair of second open lines 14b and a pair of end edges of the pair of fourth open lines 14d are also located on the Y1 direction side relative to the end surface 1a. In other words, the plurality of transmission lines 8 have a plurality of extended portions 8a that extend beyond the end edges of the plurality of open lines 14.

[0050] Therefore, the Y-direction region E between the end face 1a and the edges of the multiple open lines 14 does not contain any open lines 14. Figure 4 shows the Y2-direction end of the FFC1, but the Y1-direction end of the FFC1 has the same configuration as the Y2-direction end of the FFC1. Therefore, the multiple transmission lines 8 also have multiple extensions 8a at the Y1-direction end, and region E also exists at the Y1-direction end of the FFC1 (Figure 2). Thus, the FFC1 has regions E at both ends where no multiple open lines 14 exist. The first connector 111 is provided within the region E at the Y2-direction end of the FFC1. Therefore, the first terminal 111a of the first connector 111 is connected to the multiple extensions 8a and is not electrically connected to the multiple open lines 14. The second connector 112 is provided within the region E at the Y1-direction end of the FFC1. Therefore, the second terminal 112a of the second connector 112 is connected to the multiple extensions 8a and is not electrically connected to the multiple open lines 14. In this way, both ends of each of the multiple open lines 14 are not electrically connected to the connectors 111 and 112, and the multiple open lines 14 are electrically open. In other words, both ends of the open lines 14 are unconnected portions that are not connected to the terminals 111a and 112a of the connectors 111 and 112.

[0051] As described above, the pair of first signal lines 11 are used as transmission lines for the first differential signal, and the pair of second signal lines 12 are used as transmission lines for the second differential signal. Therefore, in Figure 4, the extensions 8a of the pair of first signal lines 11 are connected to the first differential transmission line 101a of the first electronic device 101 via the first connector 111. The extensions 8a of the pair of first signal lines 11 on the Y1 direction side are connected to the third differential transmission line 102a of the second electronic device 102 via the second connector 112. In other words, the extensions 8a of the pair of first signal lines 11 constitute the first connection ends connected to the first differential transmission line 101a. As a result, the first differential signal is transmitted through the pair of first signal lines 11.

[0052] Furthermore, in Figure 4, the extensions 8a of the pair of second signal lines 12 are connected to the second differential transmission line 101b of the first electronic device 101 via the first connector 111. The extensions 8a of the pair of second signal lines 12 on the Y1 direction side are connected to the fourth differential transmission line 102b of the second electronic device 102 via the second connector 112. In other words, the extensions 8a of the pair of second signal lines 12 constitute a second connection end that is connected to the second differential transmission line 101b. As a result, the second differential signal is transmitted through the pair of second signal lines 12.

[0053] [Regarding the modified example] Figure 5 is a cross-sectional view of the FFC1 according to the first modified example. This modified example differs from the above embodiment in that a ground line 10e is interposed between the pair of first signal lines 11 and the pair of second signal lines 12. The configuration is the same in other respects.

[0054] As in this modified example, even when there is only one ground line 10 between the pair of first signal lines 11 and the pair of second signal lines 12, there are multiple open lines 14, so that crosstalk between the pair of first signal lines 11 and the pair of second signal lines 12 is effectively reduced.

[0055] Figure 6 is a cross-sectional view of the FFC1 according to the second modified example. This modified example differs from the above embodiment in that the width dimension in the X direction of the plurality of open lines 14 is larger than the width dimension in the X direction of the plurality of transmission lines 8. In this case as well, crosstalk between the pair of first signal lines 11 and the pair of second signal lines 12 is effectively reduced.

[0056] In this modified example, the case where the width dimension in the X direction of the multiple open lines 14 is larger than the width dimension in the X direction of the multiple transmission lines 8 is illustrated, but the width dimension in the X direction of the multiple open lines 14 may be smaller than the width dimension in the X direction of the multiple transmission lines 8.

[0057] Figure 7 is a cross-sectional view of the FFC1 according to the third modified example. This modified example differs from the above embodiment in that the positions of the multiple open lines 14 in the X direction are offset from the positions of the pair of first signal lines 11 and the pair of second signal lines 12.

[0058] In this modified example, the pair of first open lines 14a and the pair of second open lines 14b are offset in the X1 direction relative to the pair of first signal lines 11. The positions of the pair of first signal lines 11 and the pair of first open lines 14a in the X direction overlap with each other, and similarly, the positions of the pair of first signal lines 11 and the pair of second open lines 14b in the X direction also overlap with each other. The pair of third open lines 14c and the pair of fourth open lines 14d are offset in the X2 direction relative to the pair of second signal lines 12. The positions of the pair of second signal lines 12 and the pair of third open lines 14c in the X direction overlap with each other, and similarly, the positions of the pair of second signal lines 12 and the pair of fourth open lines 14d in the X direction also overlap with each other. Therefore, the pair of first signal lines 11 and the pair of open lines 14a and 14b overlap with each other in a plan view. Furthermore, the pair of second signal lines 12 and the pair of open lines 14c and 14d also overlap each other in a plan view. In this case as well, crosstalk between the pair of first signal lines 11 and the pair of second signal lines 12 is effectively reduced.

[0059] [Other] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. For example, the above embodiments and modifications illustrate a case where four open lines 14 are provided for a pair of first signal lines 11 and a pair of second signal lines 12. However, it is sufficient to have at least one open line 14. In this case, the open line 14 is located on at least one side of either the pair of first signal lines 11 or the pair of second signal lines 12 in the Z1 or Z2 direction. In this case, it is sufficient that the position of the open line 14 in the X direction and the position of the pair of signal lines in the X direction overlap.

[0060] Furthermore, a pair of open lines 14 may be provided for only one of the pair of first signal lines 11 and the pair of second signal lines 12, or two pairs of open lines 14 may be provided. When a pair of open lines 14 is provided for a pair of signal lines, the pair of open lines 14 is provided in only one of the Z1 and Z2 directions. When two pairs of open lines 14 are provided for a pair of signal lines, a pair of open lines 14 is provided in both the Z1 and Z2 directions.

[0061] Furthermore, the above embodiments and modifications illustrate a case where the FFC1 comprises a pair of first signal lines 11 and a pair of second signal lines 12. However, the FFC1 may also comprise one or more pairs of third signal lines. In this case, the pair of third signal lines are arranged between a plurality of ground lines 10, similar to the pair of first signal lines 11 and the pair of second signal lines 12.

[0062] Furthermore, in the above embodiments and modifications, the example given is that each of the multiple open lines 14 is composed of a single line extending over almost the entire longitudinal area of ​​the FFC 1. However, the open lines 14 may be provided in only a part of the entire longitudinal area of ​​the FFC 1, as long as they have a length corresponding to the frequency (wavelength) of the signal transmitted through the multiple transmission lines 8. Alternatively, the open lines 14 may be composed of multiple divided lines arranged in a single line over the entire longitudinal area of ​​the FFC 1. In other words, the open lines 14 may be divided in the longitudinal direction. In this case, the length of each of the multiple divided lines is determined according to the frequency (wavelength) of the signal transmitted through the multiple transmission lines 8.

[0063] The scope of the present invention is indicated by the claims, not in the sense described above, and is intended to include the meaning of equivalents to the claims and all modifications within the scope.

[0064] [Regarding Verification Tests] Next, we will explain the verification tests conducted on the above-mentioned flexible flat cable. In the verification tests, models were constructed for the examples and comparative examples shown below, and the characteristics of each example and comparative example were determined by computer simulation using these models.

[0065] - The FFC1 used in the connector-equipped flexible flat cable 103 shown in the embodiment was constructed as a model for the embodiment. The dimensions of each part in the embodiment were set as follows: Length L1 (Figure 2: Y-direction length of FFC1, ground line 10, and signal lines 11, 12): 50 mm Length L2 (Figure 2: Y-direction length of multiple open lines 14): 45 mm Width W1 (Figure 3: Z-direction width of insulating layer 4): 0.7 mm Spacing d1 (Figure 3: Spacing between open lines 14 and signal lines 11, 12): 0.21 mm Width W2 (Figure 3: X-direction width of open lines 14 and signal lines 11, 12): 0.28 mm Spacing d2 (Figure 3: Pitch of adjacent conductor lines 2): 0.52 mm Thickness of ground line 10 and signal lines 11, 12: 0.05 mm Thickness of open line 14: 0.03 mm

[0066] Furthermore, the impedances of the pair of first signal lines 11 and the pair of second signal lines 12 in FFC1 were set to 102Ω. Polyethylene was assumed as the material for the insulating layer 4, with a relative permittivity εr = 2.25 and a dielectric loss tangent tanδ = 0.001.

[0067] - A comparative example was constructed by removing several open lines 14 from the comparative example example.

[0068] - Comparison of Examples and Comparative Examples The S-parameter S21 was determined as the insertion loss when the Y1 direction end of the pair of first signal lines 11 was designated as port 1, the Y2 direction end of the pair of first signal lines 11 was designated as port 2, the Y1 direction end of the pair of second signal lines 12 was designated as port 3, and the Y2 direction end of the pair of second signal lines 12 was designated as port 4. Similarly, S11 was determined as the return loss, S31 as the near-end crosstalk (NEXT), and S41 as the far-end crosstalk (FEXT).

[0069] Figure 8 is a graph showing the frequency characteristics of the insertion loss for the embodiment and comparative example. In Figure 8, the horizontal axis represents the frequency of the transmission signal, and the vertical axis represents the insertion loss (S21). Also, in Figure 8, the solid line represents the graph for the embodiment, and the dashed line represents the graph for the comparative example. As shown in Figure 8, there is no significant difference between the insertion loss of the embodiment and the insertion loss of the comparative example. Therefore, from this result, it can be confirmed that the open line 14 does not affect the passage characteristics of the signal lines 11 and 12.

[0070] Figure 9 is a graph showing the frequency characteristics of the reflection loss for the example and comparative example. In Figure 9, the horizontal axis represents the frequency of the transmission signal, and the vertical axis represents the reflection loss (S11). Also, in Figure 9, the solid line represents the graph for the example, and the dashed line represents the graph for the comparative example. As shown in Figure 9, there is no significant difference between the reflection loss of the example and the reflection loss of the comparative example. Therefore, from this result, it can be confirmed that the open line 14 does not affect the reflection characteristics of the signal lines 11 and 12.

[0071] Figure 10 is a graph showing the frequency characteristics of near-end crosstalk for the example and comparative example. In Figure 10, the horizontal axis represents the frequency of the transmitted signal, and the vertical axis represents the near-end crosstalk (S31). Also, in Figure 10, the solid line represents the graph for the example, and the dashed line represents the graph for the comparative example. As shown in Figure 10, it can be seen that the near-end crosstalk of the example is reduced across the entire frequency band of 0-20 GHz, which is the measurement range, compared to the near-end crosstalk of the comparative example.

[0072] Figure 11 is a graph showing the frequency characteristics of far-end crosstalk for the example and comparative example. In Figure 11, the horizontal axis represents the frequency of the transmitted signal, and the vertical axis represents the far-end crosstalk (S41). Also, in Figure 11, the solid line represents the graph for the example, and the dashed line represents the graph for the comparative example. As shown in Figure 11, it can be seen that the far-end crosstalk of the example is reduced across the entire frequency band of 0-20 GHz, which is the measurement range, compared to the far-end crosstalk of the comparative example.

[0073] As described above, the verification test results confirm that the flexible flat cable according to the embodiment can effectively reduce crosstalk. However, the effects of the embodiments of this disclosure are not limited to the above-described embodiments.

[0074] 1 Flexible flat cable 1a End face 2 Conductor line 4 Insulation layer 6 Shield layer 8 Transmission line 8a Extension 10 Ground line 10a First ground line 10b Second ground line 10c Third ground line 10d Fourth ground line 10e Ground line 11 First signal line 12 Second signal line 14 Open line 14a First open line 14a1 Edge 14b Second open line 14c Third open line 14c1 Edge 14d Fourth open line 16 Shield film 100 Electronic equipment 101 First electronic device 101a First differential transmission line 101b Second differential transmission line 102 Second electronic device 102a Third differential transmission line 102b Fourth differential transmission line 103 Flexible flat cable with connector 111 First connector 111a First terminal 112 Second connector 112a Second terminal E Area P1 First plane P2 Second plane P3 Third plane W1 Width W2 Width d1 Spacing d2 Spacing

Claims

1. A flexible flat cable comprising: a plurality of conductor lines arranged parallel to each other; and an insulating layer provided around the plurality of conductor lines, wherein the plurality of conductor lines include: a plurality of transmission lines arranged in a row in a cross section perpendicular to the longitudinal direction of the plurality of conductor lines; and at least one open line with both ends electrically open, wherein the plurality of transmission lines include: a plurality of ground lines; and a pair of first signal lines and a pair of second signal lines located between the plurality of ground lines in the cross section, wherein the open line is located in the cross section on the first direction side of the pair of first signal lines perpendicular to the arrangement direction of the plurality of transmission lines.

2. The flexible flat cable according to claim 1, further comprising a shielding layer provided on the outer surface of the insulating layer.

3. The flexible flat cable according to claim 1 or 2, wherein the position of at least one of the pair of first signal lines in the direction of arrangement and the position of the open line in the direction of arrangement overlap with each other.

4. The flexible flat cable according to any one of claims 1 to 3, wherein the open lines are plurality, and the plurality of open lines include a pair of first open lines located on the first direction side of the pair of first signal lines in the cross-section.

5. The flexible flat cable according to claim 4, wherein the plurality of open lines further include a pair of second open lines located in the cross-section on the second direction side, which is opposite to the first direction of the pair of first signal lines.

6. The flexible flat cable according to claim 5, further comprising: a pair of third open lines located on the first direction side of the pair of second signal lines in the cross-section; and a pair of fourth open lines located on the second direction side of the pair of second signal lines in the cross-section.

7. The flexible flat cable according to claim 6, wherein the pair of first open lines and the pair of third open lines are arranged in a row along the arrangement direction in the cross-section, and the pair of second open lines and the pair of fourth open lines are arranged in a row along the arrangement direction in the cross-section.

8. The flexible flat cable according to any one of claims 1 to 7, wherein each of the plurality of transmission lines has an extension at both ends that extends beyond both ends of the open line.

9. The flexible flat cable according to any one of claims 1 to 8, wherein the pair of first signal lines have first connection ends connected to a first differential transmission line, and the pair of second signal lines have second connection ends connected to a second differential transmission line.

10. A flexible flat cable with a connector, comprising: a flexible flat cable; and connectors provided at both ends of the flexible flat cable, wherein the flexible flat cable comprises: a plurality of conductor lines arranged parallel to each other; and an insulating layer provided around the plurality of conductor lines, wherein the plurality of conductor lines include: a plurality of transmission lines arranged in a row in a cross section perpendicular to the longitudinal direction of the plurality of conductor lines; and at least one open line which is an unconnected portion whose ends are not connected to the terminals of the connector, wherein the plurality of transmission lines include: a plurality of ground lines; and a pair of first signal lines and a pair of second signal lines whose ends are connected to the terminals of the connector and which are located between the plurality of ground lines in the cross section, wherein the open line is located in the cross section on the first direction side of the pair of first signal lines which is perpendicular to the arrangement direction of the plurality of transmission lines.

11. The device comprises a first electronic device, a second electronic device that exchanges a first differential signal and a second differential signal with the first electronic device, and a flexible flat cable connecting the first electronic device and the second electronic device, wherein the flexible flat cable comprises a plurality of conductor lines arranged parallel to each other, and an insulating layer provided around the plurality of conductor lines, wherein the plurality of conductor lines include a plurality of transmission lines arranged in a row in a cross section perpendicular to the longitudinal direction of the plurality of conductor lines, and at least one open line with both ends electrically open, wherein the plurality of transmission lines include a plurality of ground lines, and a pair of first signal lines and a pair of second signal lines located between the plurality of ground lines in the cross section, wherein the pair of first signal lines are lines for the first differential signal, and the pair of second signal lines are lines for the second differential signal. The open line is an electronic device located in the cross-section on the side of the pair of first signal lines in a first direction perpendicular to the arrangement direction of the plurality of transmission lines.

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