JP2000124565A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit board which can be easily manufactured at a low cost and where cross talk can be lessened between wirings. SOLUTION: A circuit board is equipped with two transmission lines 101-1 and 101-2 and a dummy line 102 which is located between the transmission lines 101-1 and 101-2 and transmits no signals, where both the ends of the dummy line 102 are each terminated with a resistor 103 whose impedance is equal to the characteristic impedance of the dummy line 102. That is, a dummy line that transmits no signals is arranged adjacent to one of signal transmitting wirings, and both the ends of the dummy line are each terminated with impedance equal to its characteristic impedance, so that a circuit board where cross talk between signal transmitting wirings can be easily obtained at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board for transmitting digital signals, and more particularly to a circuit board for transmitting a high-speed signal having a clock frequency of 100 MHz or more, which can reduce cross-talk between parallel wirings. It relates to a circuit board.

[0002]

2. Description of the Related Art In recent years, the flow of digital circuits at high speeds has been tremendous, and the clock frequency of CPUs has exceeded 400 MHz, and is increasing further. Accordingly, the data transmission speed between the CPU and the memory has been required to be improved.
Clock frequency. In such a high speed, crosstalk in a data transmission line has become a problem. This is because the CPU and the memory controller are physically separated from each other due to restrictions in consideration of the physical shape and heat radiation, and between them, the data transmission line must be connected. In addition, from the viewpoint of physical shape and expandability, the connection between the memory controller and various peripheral devices typified by the memory, the video card, and the communication device needs to be similarly connected by a data transmission line. Such a data transmission line is usually composed of at least 16, and in most cases 64 lines. When such a large number of lines are arranged, particularly when arranged as parallel lines, crosstalk between the lines becomes a problem.

To cope with such a problem, Japanese Patent Laid-Open No.
In -97229, it is devised to arrange adjacent wirings in different layers. Japanese Patent Application Laid-Open No. 9-1484
In the case of 89, although it is not strictly a wiring in this case, it is devised that any one of a ground, power supply and floating dummy electrode is provided between the signal electrodes.

[0004]

However, in the method disclosed in Japanese Patent Laid-Open No. 6-97229,
Absolute cost rises by making multilayer wiring,
When using different layers, especially the inner layer and the surface layer, the effective permittivity of the line is different, and as a result, the signal propagation speed between the lines is different, so that it is difficult to propagate the signal at the same timing. There is a problem that wiring is difficult because the via pitch must be wider than the line width / space width. Japanese Patent Application Laid-Open No. 9-
In the method of providing a dummy electrode between signal transmission lines as in 148489, a crosstalk signal induced by the dummy electrode is reflected at the end of the dummy electrode because the dummy electrode is ground, power supply, or floating, thereby suppressing crosstalk. There was a problem that the effect was reduced.

An object of the present invention is to provide a circuit board which can be easily manufactured at low cost and can reduce crosstalk between wirings in consideration of the conventional problem of crosstalk between wirings. It is assumed that.

[0006]

According to the present invention, there are provided a plurality of signal transmission lines arranged substantially in parallel, and a signal transmission line arranged at least next to at least one of the plurality of lines. The circuit board includes at least one dummy line, and both ends of the dummy line are terminated by the same impedance as the characteristic impedance of the dummy line.

[0007] With the above configuration, the crosstalk signal induced in the dummy line is absorbed by the terminal provided at the terminal part, so that the crosstalk suppressing effect is high. Therefore, in order to prevent a reduction in the effective wiring density (the amount occupied by the signal transmission line in the wiring), which has always been a problem when installing such a dummy line, it is sufficient to insert the signal transmission line every other line. Effects can be obtained.

In order to terminate the dummy line, it is necessary to mount a component or to make a component in a circuit board. Generally speaking, the space required for installing such a component is as follows. In many cases, it is wider than the space required for arranging the signal transmission lines. For this reason, by terminating a plurality of components, the installation space for components can be reduced.

Since the dummy line is not for transmitting a signal, the characteristic impedance may be set to any value. Considering the space utilization efficiency, the higher the value is, the better the utilization efficiency is. Can be reduced, resulting in lower costs.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing an embodiment. (First Embodiment) FIG. 1 is a schematic diagram showing a circuit board according to a first embodiment of the present invention. In FIG. 1, 10
1-1 and 101-2 are data transmission lines, 102 is a dummy line, and 103 is a terminating resistor having the same value as the characteristic impedance of the dummy line 102. Here, the characteristic impedance of each of the data transmission lines 101-1 and 101-2 and the dummy line 102 is designed to be 50 ohms. 10
Reference numeral 4 denotes a semiconductor element for transmitting data, and reference numeral 105 denotes a semiconductor element for receiving data. Generally, data is transmitted and received in parallel with semiconductor elements for data transmission and reception in both directions, but for simplicity, only one of them is described here. The same applies to the following embodiments. In such a configuration, the data transmission line 10
1-1, a signal was transmitted, and a crosstalk signal induced in the data transmission line 101-2 was measured.

A similar experiment was conducted on a circuit in which a dummy line was arranged on one side of a data transmission line as shown in FIG. In FIG. 2, 201-1 and 201-2 are data transmission lines, 202 is a dummy line, and 203 is a terminating resistor having the same value as the characteristic impedance of the dummy line 202. 204 is a semiconductor element for data transmission, 2
Reference numeral 05 denotes a semiconductor element for receiving data. A signal is applied to the data transmission line 201-1 and the data transmission line 201
The crosstalk signal induced at -2 was measured. Comparing the two cases, the crosstalk voltage was lower in the case of FIG.

Also, as shown in FIG. 3, the case where dummy lines are arranged on both sides of the data transmission line was examined. In FIG. 3, 301-1, 301-2, 301-3 are data transmission lines, and 302 is a dummy line. Reference numeral 303 denotes a termination resistor having the same value as the characteristic impedance of the dummy line 302. 304 is a semiconductor element for sending data, and 305
Is a semiconductor element for receiving data. Signals were applied to the data transmission lines 301-1 and 301-2, and the voltage induced on the data transmission line 301-3 was measured. Normally, crosstalk is expected to be observed from both sides because crosstalk occurs from both sides. However, a lower crosstalk voltage than the configuration in FIG. 1 was obtained. (Second Embodiment) FIG. 4 is a schematic diagram showing a circuit board according to a second embodiment of the present invention. In FIG.
1-1, 401-2, and 401-3 are data transmission lines;
02 is a dummy line. Numeral 403 denotes a terminating resistor having the same value as the characteristic impedance corresponding to the dummy lines 402. 404 is a semiconductor element for transmitting data, and 405 is a semiconductor element for receiving data. All line impedances are matched to 50 ohms. Here, the characteristic impedance of the dummy line 402 is 50 ohms, and the number N of the dummy lines to be combined is two, so that the impedance of the termination resistor 403 is R = Z
/ N = 50/2 = 25 ohms. Therefore, the two dummy lines 402 are collectively terminated at both ends with a resistor 403 of 25 ohms. In this configuration, the data transmission line 40
Signals were transmitted to 1-1 and 401-2, and the crosstalk voltage was measured as in the eleventh embodiment. As in the case of FIG. 3, it was possible to obtain a low crosstalk voltage, and at the same time, it was possible to use only two resistance elements which would normally require four. (Third Embodiment) FIG. 5 is a schematic diagram showing a circuit board according to a third embodiment of the present invention. In FIG. 5, 50
1-1 and 501-2 are data transmission lines, 502 is a dummy line, and 503 is a terminating resistor having the same value as the characteristic impedance of the dummy line 502. 504 is a semiconductor element for sending data, and 505 is a semiconductor element for receiving data. In the present embodiment, the data transmission line 50
1-1 and 501-2 are 50 ohms and the dummy line 502 is
Has matched the characteristic impedance to 100 ohms,
Therefore, both ends of the dummy line 502 are terminated with a resistance of 100 ohms. In this configuration, the signal is transmitted to the data transmission line 501-1,
The crosstalk voltage induced at -2 was measured. Also in this case, a low crosstalk voltage can be obtained as in the first embodiment. Further, by setting the characteristic impedance of the dummy line higher than the characteristic impedance of the data transmission line, the space occupied by the wiring can be reduced.

[0013]

As apparent from the above description, according to the present invention, at least one dummy line which does not transmit a signal is arranged next to at least one of a plurality of signal transmission lines, Since both ends of the dummy line are terminated by the same impedance as the characteristic impedance of the dummy line, there is an advantage that a circuit board that can reduce crosstalk between wirings for signal transmission can be easily manufactured at low cost. Have.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a circuit board according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing another example in the first embodiment.

FIG. 3 is a schematic diagram showing another example of the first embodiment.

FIG. 4 is a schematic view showing a circuit board according to a second embodiment of the present invention.

FIG. 5 is a schematic view showing a circuit board according to a third embodiment of the present invention.

[Explanation of symbols]

101-1, 101-2 Data transmission line 102 Dummy line 103 Resistance having the same value as the characteristic impedance of dummy line 104 Semiconductor element for transmitting data 105 Semiconductor element for receiving data

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Iwaki 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F-term (reference) 5E338 AA00 BB75 CC01 CC09 CD13 EE13 EE32

Claims (4)

[Claims] 1. A plurality of wirings for signal transmission arranged substantially in parallel, and at least one of the plurality of wirings
A circuit board, comprising: at least one dummy line that is arranged next to a book and does not transmit a signal; and both ends of the dummy line are terminated by the same impedance as the characteristic impedance of the dummy line. 2. The circuit board according to claim 1, wherein the dummy line is disposed at least on at least one of the plurality of wirings. 3. When there are a plurality of dummy lines, and when N dummy lines out of the plurality of dummy lines are collectively terminated, the characteristic impedance of the dummy lines is Z, and R = Z 3. The circuit board according to claim 1, wherein the circuit board is terminated by an impedance R represented by / N. 4. The circuit board according to claim 1, wherein a characteristic impedance of the dummy line is higher than a characteristic impedance of the signal transmission wiring.