JPH10303521A - Transmission line board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the differential impedance matching and avoid the deterioration of a signal quality by a method wherein a plurality of wiring layers are formed on a board and one electric signal line of a pair of data transmission circuits and the other electric signal line are laid so as to be in parallel with the different wiring layers respectively. SOLUTION: A wiring layer 3 and a wiring layer 4 are formed on both the surfaces of an insulating layer 2 which is the base film of a flexible printed board cable and covered with coating layers 5 respectively. A plurality of signal lines 6 and signal lines 7 whose widths are approximately 200 μm are laid in the wiring layer 3 and the wiring layer 4 respectively. The signal lines 6 and the signal lines 7 are so laid as uneven parallel lines and the (-) line of a differential signal is wired as the signal line 6 and the (+) line of the differential signal is wired as the signal line 7. The horizontal direction separation distance and the thicknesswise separation distance between the signal line 6 and the signal line 7 are approximately 250 μm and approximately 25 μm respectively. With this constitution, the differential impedance of the signal lines is near 100 Ω and matched with an insulation resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a transmission line substrate.

[0002]

2. Description of the Related Art In recent years, in a portable personal computer (hereinafter, referred to as a PC), a liquid crystal display (hereinafter, referred to as an LCD) has a larger screen, and the resolution has been increased. Also,
In desktop personal computers, liquid crystal displays have come to be used instead of CRT displays in order to save space and power. As the LCD screen size and resolution increase,
The data transfer speed to the LCD has increased, and it has become difficult to transfer data using the conventional signal transfer method. Therefore, a low-amplitude differential transmission system has been proposed as a system for transmitting a signal at high speed. The differential transmission method means that a signal (+
This is a method of generating two-phase signals, ie, a line and an inverted signal (−line), and transmitting the signal using two signal lines. In this method, +
Because the line and the-line are electromagnetically coupled, the antenna loop area formed by the signal line and the return current path can be made close to zero, and the differential mode noise can be reduced compared to the conventional single-ended transmission system. The transmission can be reduced and the transmission can be performed at high speed. In addition, in order to strengthen the electromagnetic coupling, this transmission is generally performed by using +
2. Description of the Related Art A cable called a twisted pair in which two electric wires of a wire are twisted into a pair is used.

[0003]

However, in a notebook PC, it is difficult to wire a twisted pair cable due to the limitation of the housing shape. For example, when a cable for LCD signals (5 sets of 10 cables) is made with a twisted pair, the diameter becomes about 5 mm. Usually, the gap between the LCD and the housing is 2-3 mm on the side,
Since it is about 0.5 mm on the back surface, it is impossible to pass this cable through. For this reason, notebook PCs use LCD
Cable to a flexible printed board (F
It is necessary to use a flat cable such as a PC) cable.

FIG. 3 shows a layer structure of a generally used FPC. It has a wiring layer 111 and a coating layer 113 covering both surfaces of the wiring layer, and a signal line is inserted into the wiring layer 111.

Here, the negative line 1 of the differential signal is
17 and a + line 118, and a layer thickness 116, a line width 115,
The line distance 114 is a general FPC value shown in FIG.
The signal line is made of copper (conductivity 5.8 × 10 ⁷ ), the wiring layer 111
When the differential impedance (impedance between pairs) is calculated from the electromagnetic field analysis using the coating layer 113 (excluding the signal line) and the coating layer 113 as polyimide (dielectric constant 3.5), the value is 166Ω. However, the terminating resistance is determined for the impedance of the differential transmission line.
(Low voltage differential siganaling) or the like, the impedance is 100Ω. Therefore, in this configuration, reflection or waveform distortion occurs due to impedance mismatch, radiation noise increases, and signal quality deteriorates. In order to lower the impedance, a method of narrowing the line distance 114 or increasing the line width 115 can be considered. However, the former has a risk of short-circuit, and the latter has a possibility of increasing the cable area. When the signal layer 112 is provided with the insulating layer 110 interposed therebetween as shown in FIG. 4 and the-line 117 and the + line 118 are arranged opposite to the wiring layer 111 and the wiring layer 112, the differential impedance is 20 Ω. It will be smaller.

As described above, in the conventional method, the differential impedance is significantly higher or lower than the impedance required by the differential transmission circuit. For this reason, there has been a problem that radiation noise may increase due to impedance mismatching and signal quality may deteriorate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a circuit board for transmitting a differential transmission circuit, in which differential impedances are matched to prevent signal quality from deteriorating.

[0008]

According to another aspect of the present invention, there is provided a data transmission circuit in which a line for transmitting two electric signals is a pair of data transmission lines, wherein one of the transmission lines has an electric signal. A substrate for transmitting a differential transmission circuit in which the sum of the voltage of the line and the voltage of the other transmission line is always constant, the substrate having a plurality of wiring layers, and one of the pair of data transmission circuits. The electric signal path and the other electric signal path are arranged in parallel on different wiring layers on the substrate.

Further, the flexible substrate is characterized in that the transmission path has a horizontal distance between two electric signal paths of 100 to 350 μm and an insulating layer having a thickness of 20 to 50 μm.

The substrate for transmitting the differential transmission circuit has a fold, and one electric signal path and the other electric signal path of the pair of data transmission circuits are disposed on the left and right of the fold of the substrate. That is.

Further, a transmission line substrate having one electric signal path of the differential transmission circuit and a transmission line substrate having the other electric signal path are arranged so as to overlap with each other.

Further, it is desirable that the impedance between the two electric signal paths in the transmission path is equal to the terminating resistance. In addition, the transmission line substrate is an FPC.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. This embodiment is a case where the present invention is applied to LVDS which is one of the differential transmission systems. FIG. 16 shows a model of the LVDS circuit. 160 is an LVDS driver model, 161 is a terminating resistor, and 162 is a differential transmission line. The terminating resistance 161 is 100Ω. Therefore, the differential impedance of the transmission line 162 is set to 100Ω.
By doing so, the impedance of the terminating resistor can be matched with that of the impedance.

FIG. 1 is a plan view of an FPC cable, and FIG. 2 is a cross-sectional view taken along a line AB shown in FIG. The FPC cable 1 includes an insulating layer 2 serving as a base, wiring layers 3 and 4 formed on both surfaces of the insulating layer 2, and a coating layer 5 covering these wiring layers. A plurality of signal lines 6 and 7 having a width of 200 μm are inserted into the wiring layers 3 and 4 respectively. In this embodiment, the insulating layer 2, the wiring layer (excluding the signal lines), and the coating layer 5 are each formed of polyimide.

Further, in this embodiment, a connector 8 is provided on the FPC cable 1 for connection with another circuit or device. The signal pin 9 of the connector 8 is connected to the wiring layer 3,
The connection between the signal line and the connector 8 is made in the wiring layer 3. Therefore, the signal line 7 in the wiring layer 4 is connected to the connector 8 via the through hole 10.

As shown in FIG. 2, the signal lines 6 and 7 are arranged as parallel lines having different levels. In this embodiment, the distance between the signal line 6 and the signal line 7 is 2 in the horizontal direction.
The thickness was 50 μm and 25 μm in the thickness direction. Then, the minus line of the differential signal is wired to the signal line 6 and the plus line of the differential signal is wired to the signal line 7. By doing so, the differential impedance of the signal line can be set to around 100Ω.

In the present embodiment, the minus line of the differential signal is wired to the signal line 6 and the plus line of the differential signal is wired to the signal line 7, but the reverse is also possible. Further, the layer for wiring the + line and the-line may be changed for each signal.

Next, the distance between the + line and the-line will be described in detail. FIG. 5 is an enlarged view of a portion 11 surrounded by a dotted line in FIG. The horizontal distance (line interval p) 20 between the signal line 6 and the signal line 7 differs depending on the width w21 of the signal line and the thickness d22 of the insulating layer. For example, in the case of a signal line width w = 200 μm and an insulating layer thickness d = 25 μm, which is a general FPC, the impedance between the − line and the + line is set by setting the line interval p to 250 μm by electromagnetic field simulation. It can be around 100Ω (± 5%).

Line widths w = 50, 100, 150, 200,
FIG. 6 shows the relationship between the insulation layer thickness d22 and the line interval p20 at 250, 300, 350, and 400 μm, where the impedance between the − and + lines is 100Ω. Line spacing p that satisfies this
By arranging the-and + wires apart from each other, the impedance between the pairs can be kept near 100Ω, and the LVDS
And a high-quality signal can be sent. The insulation layer thickness d = 25 μm, line width w = 200 μ
In the case of m, it corresponds to the point 61 in FIG. 6, the line interval p is 250 μm, and the impedance between the − line and the + line is 100.
It is around Ω.

FIG. 7 shows a second embodiment in which the present invention is applied to a notebook personal computer. This personal computer includes a main body housing 30 and a display housing 31. A circuit board 32,
It is composed of a keyboard 33 and the like. The circuit board 32 has a CP
U34, a display LSI 35, a connector 36 for connecting the FPC 1 of the present invention, and the like. A signal from the display LSI 35 passes through a connector, passes through the FPC 1 of the present invention,
Is transmitted to By applying the FPC of the present invention, the impedance of the terminating resistor can be matched with the impedance, so that reflection and radiation noise can be reduced. In a conventional notebook personal computer, a noise filter was inserted into a plating shield of a housing or a signal on a circuit board in order to prevent unnecessary radiation noise, but by using the FPC of the present invention, It is possible to reduce the number of these noise countermeasure components, and it is possible to reduce the cost and mount the components at a high density.

Next, a third embodiment in which an FPC insertion type connector is mounted on a circuit board to be connected will be described with reference to FIGS. The layer configuration of the FPC is the same as in the first embodiment. In this case, there is no need to provide a connector on the surface of the FPC, and the coating layer 5 covering the signal layer at the FPC end 140 is eliminated, and the signal layer can be exposed to the surface to connect to a plug-in type connector. FIG. 15 is a sectional view of the dotted frame portion 141 of FIG. 14 as viewed from the side. The end portion of the FPC is not provided with the coating layer 5, and the signal layers 3 and 4 are exposed on the surface. By doing so, when this part is inserted into the plug-in connector on the circuit board, the signal line can be connected to the circuit on the circuit board. Also in this case, the differential impedance can be matched with the terminating resistor as in the first embodiment, and a high-quality signal can be transmitted.

Next, FIG. 8 is a sectional view of a fourth embodiment in which the wiring layers of the FPC cable are formed in a plurality of layers. In this embodiment,
Although three wiring layers are used, three or more wiring layers may be used. The FPC cable 81 is composed of wiring layers 3, 4 and 4, sandwiching the insulating layer 2, and a coating layer 5 covering the surface of the FPC cable 81. In the wiring layer 3, the wiring layer 4, and the wiring layer 82, a plurality of signal lines 84, 85, and 83 are inserted, respectively. Then, one (+ line or − line) of the pair of differential signals is wired to the signal line 84, and the other (− line or + line) is wired to the signal line 83. The signal line 85 is a power supply line other than the differential signal, a control signal, and the like.
The impedance between the pair of the signal line 84 and the signal line 83 is
It is arranged as a parallel line with a step difference at a distance equal to the terminal resistance. As a result, impedance matching is achieved,
High quality signals can be sent.

Next, a fifth embodiment will be described. FIG. 9 is a sectional view of a fifth embodiment in which the spacing between the negative and positive lines of the differential signal is changed for each pair line. FPC cable 91
Is the same as the layer configuration of the first embodiment (FIG. 2). The differential signal 92 is composed of a signal line 94 in the wiring layer and a signal line 95 in the wiring layer. The signal line 95 is located at a distance from the signal line 94 to the right in the drawing, at a distance where the impedance between the pair is equal to the terminating resistance. Separate and arrange as parallel lines with different levels. On the other hand, the differential signal 93 is composed of the signal line 96 of the wiring layer and the signal line 97 of the wiring layer, and the impedance between the pair is equal to the terminating resistance in the left direction of the drawing with respect to the signal line 96. It is arranged as a parallel line with a step at a distance. As described above, the direction in which the negative and positive lines of the differential signal are separated may be changed for each pair of the negative and positive lines. Further, the layer for wiring the-line and the + line may be changed for each pair.

Next, a sixth embodiment will be described. FIG. 10 is a sectional view of the sixth embodiment in which a ground line 101 serving as a guard pattern is inserted between differential signal lines. In the fifth embodiment, since the electromagnetic coupling between the signal line 95 and the signal line 97 which are not a pair of differential signals is strengthened and the quality of the signal line may be degraded, the ground line 101 is provided between different pairs. By doing so, the electromagnetic coupling between the signal line 94 and the signal line 97 and the signal line 98, and between the signal line 95 and the signal line 96 and the signal line 97 is reduced, so that a higher quality signal can be transmitted.

Next, a seventh embodiment is shown in FIG. This is a case where the present invention is applied to an FPC having a single signal layer. This F
The PC 102 has a fold 103 near the center of the width of the FPC.
And a plurality of signal lines on the left and right. In the present embodiment, five lines (a total of ten lines) are arranged on the left and right, and the left signal line is connected to the L1 signal lines 108, L2
The signal line 107, the L3 signal line 106, the L4 signal line 105,
The L5 signal line 104 and the right signal line are located near the fold 103 from the R1 signal line 109, the R2 signal line 120, and the R
3 signal line 121, R4 signal line 122, R5 signal line 123
And The pair of differential signals is connected to the L1 signal line 108.
, R1 signal line 109, L2 signal line 107 and R2 signal line 1
20, L3 signal line 106 and R3 signal line 121, L4 signal line 105 and R4 signal line 122, L5 signal line 104 and R5
It is made with the signal line 123.

Further, the difference in distance from the fold of the two signal lines forming a pair is determined when the signal line is folded at the fold 103 (FIG. 12).
Then, the distance is set such that the impedance between the pair is equal to the terminating resistance. For example, when the signal line 108 and the signal line 109 are folded at the fold 103 (FIG. 12), the signal line 108 and the signal line 109 are separated by a distance 124 at which the impedance between the pair becomes equal to the terminating resistance.
Distance 125 between L1 signal line 108 and fold 103 and R1
The difference between the distance 126 between the signal line 109 and the fold is made equal to the distance 124 at which the impedance becomes equal to the terminal resistance.
By doing so, impedance matching can be achieved with a single-layer FPC, and a high-quality signal can be transmitted.

Next, an eighth embodiment is shown in FIG. This embodiment is composed of two FPCs. A plurality of signal lines 134 are connected to the FPC 131 and a plurality of signal lines 135 are connected to the FPC 132. The differential signal is one of the signals (+ line or-
Is connected to the signal line 134, and the other (− or + line) is connected to the signal line 135. Then, the FPC 131 and the FPC 13
No. 2 is mounted by being shifted laterally and overlapping at a distance 133 where the impedance between the pair of the signal line 134 and the signal line 135 is equal to the terminating resistance. By doing so, impedance matching can be achieved, and a high-quality signal can be transmitted.

Next, a ninth embodiment is shown in FIG. This embodiment is an example in which the present invention is applied to a printed circuit board.
Is a diagram showing a part of the cross section. This embodiment comprises a signal layer 171, a signal layer 173, a signal layer 176, a signal layer 177, a power supply layer 174, and a ground layer 175 with a coating layer 170 covering the surface and an insulating layer 172 sandwiched therebetween. In this embodiment, a six-layer substrate having four signal layers is used, but any number of layers may be used. Then, the signal layer 171, the signal layer 173, and the signal layer 17
6, a plurality of signal lines are wired in the signal layer 177.
Here, one (+ line or − line) of the pair of differential signals 179 is wired to the signal line 178, and the other (− line or + line) is wired to the signal line 180. Also, the signal line 18
1, a signal line 182 is a signal other than the differential signal. The signal line 178 and the signal line 180 are arranged as parallel lines having different levels so that the impedance between the pair is equal to the terminating resistance. As a result, the impedance is matched, and a high-quality signal can be transmitted.

[0029]

When differential transmission is performed, by arranging the + line and the-line in different layers in parallel at different levels, matching of the terminating resistance and impedance can be easily achieved, and high-quality signals can be transmitted.
Radiated noise can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a sectional view of an FPC according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view of an FPC.

FIG. 4 is a cross-sectional view of an FPC.

FIG. 5 is an explanatory diagram of an embodiment of the present invention.

FIG. 6 is a characteristic diagram showing a relationship among a line width, a line interval, and an insulating layer thickness.

FIG. 7 is a perspective view illustrating an example in which the present invention is applied to an information processing apparatus.

FIG. 8 is a sectional view of an FPC according to a fourth embodiment of the present invention.

FIG. 9 is a sectional view of an FPC according to a fifth embodiment of the present invention.

FIG. 10 is a sectional view of an FPC according to a sixth embodiment of the present invention.

FIG. 11 is an explanatory diagram of an FPC according to a seventh embodiment of the present invention.

FIG. 12 is an explanatory view of a seventh embodiment of the present invention.

FIG. 13 is an explanatory view of an eighth embodiment of the present invention.

FIG. 14 is an explanatory view of a third embodiment of the present invention.

FIG. 15 is a sectional view of a connector insertion type FPC.

FIG. 16 is a model circuit diagram of an LVDS.

FIG. 17 is an explanatory view of a ninth embodiment of the present invention.

[Explanation of symbols]

1 FPC cable, 6 signal line, 7 signal line, 8 connector, 9 connector signal pin, 10 through hole.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiichiro Yokokura 810 Shimoimaizumi, Ebina-shi, Kanagawa Prefecture Hitachi Systems Office Systems Division

Claims (8)

[Claims] 1. A data transmission circuit comprising two electric signal transmission lines as a pair of data transmission lines, wherein the sum of the voltage of one electric signal line and the voltage of the other transmission line is one of the transmission lines. In a substrate that transmits a differential transmission circuit that is always constant, the substrate has a plurality of wiring layers, and one electric signal path and the other electric signal path of the pair of data transmission circuits are formed by the substrate. A transmission line substrate characterized by being arranged in parallel on different wiring layers. 2. The flexible substrate according to claim 1, wherein the horizontal distance between the two electric signal paths is 100 to 350 μm, and the thickness of the insulating layer is 20 to 50 μm. 3. A data transmission circuit in which two electric signal transmission lines are used as a pair of data transmission lines, wherein the sum of the voltage of one electric signal line and the voltage of the other transmission line is one of the transmission lines. In a substrate that transmits a differential transmission circuit that is always constant, the substrate has a fold, and among the pair of data transmission circuits, one electric signal path and the other electric signal path are provided on the left and right sides of the fold of the substrate. A transmission line substrate characterized by being arranged. 4. The transmission line board according to claim 4, wherein the impedance between the two electric signal paths is equal to the terminating resistance when the electric signal path is folded at the fold. 5. A data transmission circuit comprising two electric signal transmission lines as a pair of data transmission lines, wherein the sum of the voltage of one electric signal line and the voltage of the other transmission line is one of the transmission lines. A transmission line substrate comprising: a transmission line substrate having one electric signal path of a differential transmission circuit, which is always constant; and a transmission line substrate having the other electric signal path, which are superposed. 6. The transmission line substrate according to claim 1, wherein the impedance between the two electric signal paths is equal to the terminating resistance. 7. The transmission line substrate according to claim 1, wherein said transmission line substrate comprises a flexible printed cable. 8. An information processing apparatus using the transmission line substrate according to claim 1, 2, 3, 4, 5, 6, or 7 for a display signal line.