This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2009-1086, filed on Jan. 6, 2009, the entire contents of which are incorporated herein by reference.
The embodiments discussed herein are related to an electronic apparatus.
In recent years, countermeasures against electromagnetic interference (EMI) have been taken in electronic apparatuses such as desktop personal computers, notebook personal computers, and printers, which are information technology equipment. Each country has individualized regulations regarding electromagnetic compatibility (EMC). Manufacturers of information technology equipment cannot sell or ship products to any country unless the products comply with standards regarding the EMC regulation in that country. Examples of standards regarding the EMC regulation include the codes and rules of the Voluntary Control Council for Interference (VCCI) in Japan, the rules of the Federal Communications Commission (FCC) in the United States, and the international CISPR standards established by the Comité International Spécial des Perturbations Radioélectriques (International Special Committee on Radio Interference) (CISPR). Many countries adopt standards which are basically compatible with the CISPR standards. If the CISPR standards can be satisfied, the EMC regulations in individual countries can basically be satisfied.
Therefore, countermeasures against EMI (or countermeasures against electromagnetic noise) are implemented in many electronic apparatuses. Some of these electronic apparatuses include a printed board on which a slot member for receiving a memory is mounted. In general, a wiring pattern for a memory transmits high-speed signals. Such a signal generates high-level electromagnetic noise, and therefore it is difficult to take a countermeasure against the EMI caused by the memory.
Please refer to Japanese Laid-open Patent Publication No. 2009-141057.
According to an embodiment, an electronic apparatus includes a printed board having a mounting surface and a ground layer, a peripheral circuit of a memory, which is mounted in the electronic apparatus, being mounted on the mounting surface, a metal plate disposed above the mounting surface, and a plurality of conductive portions configured to electrically connect the ground layer and the metal plate to each other, wherein the peripheral circuit is mounted between the conductive portions.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
An example of a printed board includes two ground layers, a signal layer disposed between the two ground layers, and a power layer disposed between the two ground layers. A wiring pattern for a memory is provided on the signal layer disposed between the two ground layers. Since the wiring pattern for the memory is interposed between the two ground layers, the electromagnetic noise caused by the memory can be reduced.
However, recently, printed boards having only one ground layer have been used for the purpose of reducing costs. Unlike the printed board having two ground layers, in a printed board having only one ground layer, it is not possible to interpose the wiring pattern between two ground layers. Therefore, in the printed board having only one ground layer, there is a possibility that the noise caused by the memory will increase.
An electronic apparatus disclosed in this specification includes a metal plate, a printed board, and a plurality of conductive portions. The printed board includes a mounting surface on which a component of a peripheral circuit of a memory, which is mounted in the electronic apparatus, is mounted and a ground layer disposed such that the mounting surface is interposed between the metal plate and the ground layer. The conductive portions electrically connect the ground layer and the metal plate to each other. An imaginary line which interconnects connecting sections between the metal plate and the conductive portions crosses at least a part of a mounting area in which the component is mounted on the mounting surface.
The ground layer included in the printed board and the metal plate are electrically connected to each other; and the peripheral circuit is interposed between the ground layer included in the printed board and the metal plate. Therefore, the electromagnetic noise emitted from the peripheral circuit can be reduced. In addition, since the imaginary line which interconnects the connecting sections between the metal plate and the conductive portions crosses at least a part of the mounting area, the electromagnetic noise emitted from the peripheral circuit can be further reduced. Thus, the noise caused by the memory can be reduced.
An electronic apparatus disclosed in this specification includes a metal plate, a printed board, and a plurality of conductive portions. The printed board includes a slot member for a memory, a first surface which faces the metal plate and on which a component of a peripheral circuit of the memory is mounted, a second surface on which the slot member is mounted, and a ground layer. The conductive portions electrically connect the ground layer and the metal plate to each other. A plurality of imaginary lines which interconnect connecting sections between the metal plate and the conductive portions surround at least a part of a mounting area in which the component of the peripheral circuit is mounted.
As shown in
As shown in
The printed board 20 is provided with signal grounds 28 which are electrically connected to a ground layer G included in the printed board 20. The signal grounds 28 are electrically connected to the support plate 54 by conductive members 40. The conductive members 40 shown in
Main portions of the wiring pattern for the slot members 30 and the memories 30M are provided in the inner signal layers S interposed between the power layer V and the ground layer G. Substantially no wiring pattern for the slot members 30 is provided on the signal layers S on the surfaces of the printed board 20 at the outermost positions thereof. The wiring pattern for the slot members 30 and the memories 30M transmit high-speed signals. Therefore, the electromagnetic noise emitted from the printed board 20 can be reduced by the above-described structure.
As shown in
In addition, since the connecting sections P are positioned such that the connecting sections P surround the mounting area E as shown in
According to the present embodiment, the noise can be reduced even if there is only one ground layer. In the case where the number of the ground layer is one, the manufacturing cost of the printed board can be reduced.
In the present embodiment, the ground layer G included in the printed board 20 and the support plate 54 are electrically connected to each other by the conductive members 40. Therefore, the manufacturing cost and the noise can be reduced.
The distance between the connecting sections P which are closest to each other is preferably about one-fourth of a wavelength of an electromagnetic wave with a predetermined frequency. For example, first, the wavelength of the electromagnetic noise emitted from an area around the mounting area E in the case where the conductive members 40 are not provided can be measured. As a result of the measurement, the frequency of the electromagnetic noise to be reduced can be determined as, for example, 1,000 MHz. In this case, the wavelength of the electromagnetic wave with a frequency of 1,000 MHz is about 30 cm; and the distance corresponding to one-fourth of the wavelength is about 7.5 cm. Therefore, the distance between the connecting sections P which are closest to each other can be set to about 7.5 cm or less. Thus, the emission of the electromagnetic noise with a frequency of 1,000 MHz can be reduced.
A first modification will now be described.
Variations in the effect of reducing the noise caused by the memories in accordance with the number and positions of the connecting sections will now be described. Comparative experiments for observing the variations in the effect of reducing the noise in accordance with the number and positions of the connecting sections have been carried out.
Openings 14a and 14b are formed in the top surface 11 to prevent interference with the conductive members 40a and 40b, respectively. A piece of aluminum tape 42c is attached to the top surface 11, and the conductive member 40c is placed on the aluminum tape 42c. The aluminum tape 42c is electrically connected to a finger (not shown) provided on the printed board 20. The finger is electrically connected to a signal ground provided in the printed board 20. Thus, the aluminum tape 42c is electrically connected to the ground layer in the printed board 20; and therefore, the conductive member 40c is electrically connected to the ground layer in the printed board 20. The conductive member 40d and a piece of aluminum tape 42d also have a similar structure.
Openings 18 and 19 are formed in the recessed portion 15. The recessed portion 15 is made of a material which is not conductive, so that the electronic components mounted on the top surface 22 of the printed board 20 and the support plate 54 of the keyboard 50 can be prevented from coming into contact with each other. The openings 18 and 19 are formed in the recessed portion 15 to ensure sufficient spaces for connecting the keyboard 50 and the pointing device 80 to the printed board 20 with flexible printed boards.
First, an experiment was performed while the connection was provided at two positions by the conductive members 40a and 40b. The imaginary line ab does not pass through the mounting area E or the electronic component 32. The field intensity of the interfering wave of the electromagnetic wave with a frequency in the range of about 30 MHz to about 1,000 MHz was measured while the connection is provided at two positions by the conductive members 40a and 40b. The field intensity of the interfering wave was measured for both a horizontally polarized wave and a vertically polarized wave. The comparative experiments were performed to compare the case in which the connection was provided at two positions by the conductive members 40a and 40b with the cases in which the connection was provided under other conditions described below. The above-described condition is hereinafter called a first condition.
Next, an experiment was performed while the connection was provided at two positions by the conductive members 40a and 40c. This condition is hereinafter called a second condition. The imaginary line ac passes through the mounting area E. It is noted that not only the electronic component 32 but also vias (not shown), resistors (not shown), etc., which are electrically connected to the slot members 30, are disposed in the mounting area E. The distance between the conductive members 40a and 40c is larger than 7.5 cm. The noise-reducing effect obtained under the second condition was larger than that obtained under the first condition by about 3 dB to 7 dB.
Next, an experiment was performed while the connection was provided at three positions by the conductive members 40a, 40b, and 40d. This condition is hereinafter called a third condition. A part of the electronic component 32 is surrounded by the imaginary lines ab, bd, and ad. However, the electronic component 32 is not entirely surrounded. Among the imaginary lines ab, bd, and ad, the imaginary line bd has the largest length and the imaginary line ad has the smallest length. The distance between the conductive members 40a and 40d is smaller than 7.5 cm. However, the distance between the conductive members 40b and 40d is larger than 7.5 cm. The noise-reducing effect obtained under the third condition was larger than that obtained under the first condition by about 1 dB to 7 dB.
Next, an experiment was performed while the connection was provided at three positions by the conductive members 40a, 40b, and 40c. This condition is hereinafter called a fourth condition. The electronic component 32 is entirely surrounded by the imaginary lines ab, bc, and ac. The noise-reducing effect obtained under the fourth condition was larger than that obtained under the first condition by 4 dB to 12 dB. In addition, the noise-reducing effect under the fourth condition was obtained over a wider frequency range compared to the noise-reducing effect under the third condition.
Next, an experiment was performed while the connection was provided at four positions by the conductive members 40a to 40d. This condition is hereinafter called a fifth condition. In this case, both the mounting area E and the electronic component 32 are surrounded by the imaginary lines ab, bc, cd, and ad. The noise-reducing effect obtained under the fifth condition was larger than that obtained under the first condition by 4 dB to 13 dB.
Next, an experiment was performed while the connection was provided at two positions by the conductive members 40b and 40d. This condition is hereinafter called a sixth condition. The imaginary line bd passes through both the electronic component 32 and the mounting area E. The noise-reducing effect obtained under the sixth condition was larger than that obtained under the first condition by 3 dB to 7 dB. In addition, the noise-reducing effect obtained under the sixth condition was larger than that obtained under the third condition in which the connection was provided at three positions by the conductive members 40a, 40b, and 40d. According to the third condition, a part of the electronic component 32 is not surrounded by the imaginary lines ab, bd, and ad. Therefore, in the case where the number of connecting sections is three or more, the conductive members are preferably positioned such that the electronic component 32 can be entirely surrounded by the imaginary lines.
In the above-described embodiment, the mounting area E is interposed between the printed board 20 and the support plate 54 included in the keyboard 50. However, the mounting area E may also be interposed between a metal plate other than the keyboard 50 and the printed board 20. In addition, although a notebook personal computer is described as an example of an electronic apparatus, the electronic apparatus may also be other information technology equipment, such as a desktop personal computer and a printer.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present invention(s) has(have) been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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2009-1086 | Jan 2009 | JP | national |