Electronic device having a housing for suppression of electromagnetic noise

According to an embodiment, an electronic device includes a housing, metal patches, and a first metal member. The housing includes a bottom, a lid, and a side unit. The side unit is disposed to enclose a space between the bottom and the lid. A circuit substrate is disposed on a bottom surface of the bottom. The side unit is conductive and connected to a ground potential. The metal patches are disposed on a lid surface of the lid. The metal patches are arranged periodically in a first direction and a second direction. The second direction intersects the first direction. The metal patches are connected to the ground potential. The first metal member is disposed on the lid surface. The first metal member is connected to the ground potential. The first metal member includes a first portion. The first portion contacts a first surface of the side unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No.2014-170945, filed on Aug. 25, 2014; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electronic device.

BACKGROUND

A circuit substrate is placed in a housing to suppress noise caused by the circuit operation and corrosion due to external air. For an electronic device including such a housing including a circuit substrate, it is desirable for the noise generated in the interior of the housing to be low.

DETAILED DESCRIPTION

According to an embodiment, an electronic device includes a housing, a plurality of metal patches, and a first metal member. The housing includes a bottom, a lid, and a side unit. The side unit is disposed to enclose a space between the bottom and the lid. A circuit substrate is disposed on a bottom surface of the bottom. The bottom surface is a surface of the bottom on the interior side of the housing. The side unit is conductive and connected to a ground potential. The metal patches are disposed on a lid surface of the lid. The metal patches are arranged periodically in a first direction and a second direction. The lid surface is a surface of the lid on the interior side of the housing. The second direction intersects the first direction. The metal patches are connected to the ground potential. The first metal member is disposed on the lid surface. The first metal member is connected to the ground potential. The first metal member extends in the first direction. The first metal member includes a first portion. The first portion contacts a first surface of the side unit. The first surface is one surface of the side unit on the interior side of the housing.

Description Of Embodiments

The drawings are schematic or conceptual; and the relationships between the thicknesses and widths of portions, the proportions of sizes between portions, etc., are not necessarily the same as the actual values thereof. Further, the dimensions and/or the proportions may be illustrated differently between the drawings, even in the case where the same portion is illustrated.

In the drawings and the specification of the application, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate.

First, an electronic device according to a first embodiment of the invention will be described usingFIG. 1toFIG. 3B.

FIG. 1is a perspective view of the electronic device according to the first embodiment of the invention.

FIG. 2is a top view of the electronic device1shown inFIG. 1.

FIG. 3Ais an A-A′ cross-sectional view of the top view shown inFIG. 2.FIG. 3Bis a B-B′ cross-sectional view of the top view shown inFIG. 2.

A portion of a lid1103is not shown inFIG. 1to describe the interior of the electronic device1. Similarly inFIG. 2, a portion of the lid1103is not shown to describe the interior of the electronic device1.

In the embodiment, “electronic device” is a concept including devices that utilize electronic circuits.

The electronic device1includes a housing110. The housing110includes a bottom1101, a lid1103that opposes the bottom1101and seals the interior of the housing110, and a side unit1102that is disposed to enclose the space between the bottom1101and the lid1103. The bottom1101and the side unit1102are conductive and are formed from a metal. The bottom1101and the side unit1102are connected to a common ground line. For example, a printed wiring board may be used as the lid1103. The printed wiring board is, for example, an insulative substrate having a surface on which a pattern of a conductor is printed using printing technology.

A circuit substrate101is disposed on a surface1101aof the bottom1101on the interior side of the housing110. The circuit substrate101is, for example, a substrate having an electronic circuit component disposed on a surface or in the interior. Three power amplifiers103,105, and107are further disposed on the bottom surface1101ato form a three-stage amplifier. The circuit substrate101is electrically connected to the bottom1101by a screw111; and the circuit substrate101and the bottom1101are connected to a common ground line.

Multiple metal patches109are disposed on a surface1103aof the lid1103on the interior side of the housing110. The metal patches109are arranged periodically in a first direction and a second direction intersecting the first direction. The metal patches109are connected to the ground potential. The metal patches109that are arranged periodically form an EBG (Electromagnetic Band Gap). As an example, the first direction is an X-direction shown inFIG. 1; and the second direction is a Y-direction shown inFIG. 1.

The side unit1102of the housing110has a first surface P1(hereinbelow, called the surface P1), a second surface P2(hereinbelow, called the surface P2), a third surface P3(hereinbelow called the surface P3), and a fourth surface P4(hereinbelow called the surface P4). In the embodiment, the surfaces P1and P3oppose each other; and the surfaces P2and P4oppose each other.

Multiple first metal members113and multiple second metal members115are disposed on the lid surface1103a.

The first metal members113and the second metal members115are connected to the ground potential. To form an EBG for electromagnetic noise of a prescribed frequency, it is favorable for the first metal members113to be arranged periodically so that the widths of the first metal members113are equal to each other in the second direction, and the first metal members113adjacent to each other in the second direction have equal spacing. Some of the first metal members113extend in the first direction, are arranged periodically along the surface P1, and respectively include portions contacting the surface P1. Other first metal members113extend in the direction opposite to the first direction, are arranged periodically along the surface P3, and respectively include portions contacting the surface P3. In other words, some of the first metal members113extend in the direction from the surface P1toward the surface P3; and other first metal members113extend in the direction from the surface P3toward the surface P1. Also, to form the EBG for the electromagnetic noise of the prescribed frequency, it is favorable for the second metal members115to be arranged periodically along the surface P2so that the widths of the second metal members115are equal to each other in the first direction, and the second metal members115adjacent to each other in the first direction have equal spacing. The second metal members115extend in the second direction and respectively include second portions contacting the surface P2.

InFIG. 1, the metal members that contact both the surface P1and the surface P2are both first metal members113and second metal members115. Similarly, the metal members that contact both the surface P2and the surface P3are both first metal members113and second metal members115.

“The first metal members113being arranged periodically” also includes the case where the widths of the first metal members113in the second direction are different from each other. In other words, if the first metal members113adjacent to each other in the second direction have equal spacing, the first metal members113are considered to be arranged periodically in the second direction even in the case where the widths of the first metal members113in the second direction are different from each other.

Similarly, “the second metal members115being arranged periodically” also includes the case where the widths of the second metal members115in the first direction are different from each other. In other words, if the second metal members115adjacent to each other in the first direction have equal spacing, the second metal members115are considered to be arranged periodically in the first direction even in the case where the widths of the second metal members115in the first direction are different from each other.

Each of the first metal members113is arranged with a portion of the multiple metal patches109in the first direction. In other words, in the case where a prescribed imaginary line that extends in the first direction is considered, the first metal member113and a portion of the multiple metal patches109exist on the imaginary line. Also, each of the second metal members115is arranged with a portion of the metal patches109in the second direction. In other words, in the case where a prescribed imaginary line that extends in the second direction is considered, the second metal member115and a portion of the multiple metal patches109exist on the imaginary line.

The housing110includes a first protrusion117protruding in the first direction from the side unit1102, and a second protrusion119protruding in the direction opposite to the first direction from the side unit1102. Further, third metal members121that include third portions contacting the first protrusion117are disposed at the lid surface1103a;and fourth metal members123that include fourth portions contacting the second protrusion119is disposed at the lid surface1103a.The third metal members121are arranged in the first direction; and each of the third metal members121extends in the direction opposite to the second direction. The fourth metal members123are arranged in the first direction; and each of the fourth metal members123extends in the direction opposite to the second direction. The third metal members121and the fourth metal members123are connected to the ground potential. The spacing between the third metal members121in the first direction and the spacing between the fourth metal members123in the first direction are determined to form the EBG for the electromagnetic noise of the prescribed frequency.

InFIG. 1, the metal members that contact both the surface P1and the first protrusion117are both first metal members113and third metal members121. Similarly, the metal members that contact both the surface P3and the second protrusion119are both first metal members113and fourth metal members123.

The third metal members121and the fourth metal members123are arranged in the first direction. In other words, in the case where a prescribed imaginary line that extends in the first direction is considered, the third metal members121and the fourth metal members123exist on the imaginary line.

The first metal member113has two sides extending in the first direction and one side extending in the second direction. The other second to fourth metal members115to123similarly have sides extending in prescribed directions. The first to fourth metal members113to123are quadrilaterals as viewed in plan. In the embodiment, the first to fourth metal members113to123are rectangles as viewed in plan.

In the embodiment as shown inFIG. 2, the first metal members113, the second metal members115, the third metal members121, and the fourth metal members123are disposed inside a space S1enclosed with the surface P2, a portion of the surface P1, a portion of the surface P3, the first protrusion117, and the second protrusion119.

An input port131to which a high frequency signal is input is disposed on the surface P2side; and an output port133is disposed on the surface P4side.

A first metal film125is disposed between the side unit1102and the lid1103. The first metal members113and the second metal members115are portions of the first metal film125that protrude from the first metal film125. The first metal members113and the second metal members115are portions of the first metal film125that are not interposed between the side unit1102and the lid1103.

The first metal member113includes a first portion1131contacting the surface P1; and the second metal member115includes a second portion1151contacting the surface P2.

FIG. 4is a perspective view showing the state of the lid1103as viewed obliquely from belowFIG. 1. The metal patches109, the first metal members113, the second metal members115, the third metal members121, the fourth metal members123, and the first metal film125are disposed on the lid surface1103a.

As shown inFIG. 4, the first metal members113, the second metal members115, the third metal members121, and the fourth metal members123are portions of the first metal film125protruding toward the interior side of the housing110or toward the space S1side. Accordingly, a material included in the first to fourth metal members113to123is the same as a material included in the first metal film125. The first to fourth metal members113to123are portions of the first metal film125that are not interposed between the side unit1102and the lid1103.

A second metal film129is disposed at the upper surface of the lid1103(the surface on the side opposite to the lid surface1103a). The first metal film125and the metal patches109are electrically connected to the second metal film129by multiple vias127piercing the lid1103. The second metal film129is electrically connected to the bottom1101via the side unit1102of the housing110and is connected to the ground potential. In other words, the first metal film125and the metal patches109are electrically connected to each other and are connected to a common ground line.

For example, the first metal film125and the metal patches109are formed by forming a patterned metal film as shown inFIG. 4on the printed wiring board used as the lid1103by plating. Accordingly, in the embodiment, a material included in the first metal film125is the same as a material included in the metal patches109.

To suppress the noise more effectively, it is favorable for a distance A between the first metal members113that are adjacent to each other and between the second metal members115that are adjacent to each other to be not less than ¼ and not more than 1/2 the wavelength of the high frequency wave input to the input port131.

Also, it is favorable for a length B to be not less than 1/20 and not more than ⅙ the wavelength of the high frequency wave input to the input port131, where the length B is the length in the first direction of the first metal member113from the first portion1131contacting the surface P1or the length in the second direction of the second metal member115from the second portion1151contacting the surface P2. In other words, the length B is the length of the first metal member113from the surface P1to the end portion in the first direction or the length of the second metal member115from the surface P2in the second direction as viewed in plan.

In the electronic device1according to the embodiment, it is favorable for the metal patches109, the first metal members113, and the second metal members115to have the following relationship to effectively reduce the electromagnetic noise of the prescribed frequency.

In the first direction and the second direction, the metal patches109adjacent to each other have equal spacing. In the second direction, the first metal members113are arranged so that the distance between the first metal members113adjacent to each other is equal to the distance between the metal patches109adjacent to each other. In the first direction, the second metal members115are arranged so that the distance between the second metal members115adjacent to each other is equal to the distance between the metal patches109adjacent to each other. The distance from the end portion of the first metal member113to the most proximal metal patch109in the first direction and the distance from the end portion of the second metal member115to the most proximal metal patch109in the second direction are equal to the distance between the metal patches109adjacent to each other.

Here,FIG. 6shows simulation results comparing the noise intensity in the interior of the electronic device1that includes the first to fourth metal members113to123, the first protrusion117, and the second protrusion119and in the interior of an electronic device of a comparative example that does not include the first to fourth metal members113to123, the first protrusion117, and the second protrusion119.

InFIG. 6, the horizontal axis is the frequency of the high frequency wave that is input; and the vertical axis is the input-output characteristic from the input port131to the output port133of the housing110.

The broken line illustrates the result of the electronic device of the comparative example; and the solid line illustrates the result of the electronic device1according to the embodiment. For example, the comparative example has a gain of −20 dB for an input signal of 0 dBm at 14.6 GHz. Accordingly, for a signal having an output of 0 dBm or more and a gain greater than 20 dB, the power amplifier undesirably oscillates. Conversely, in the electronic device1according to the embodiment, the resonant frequency of the housing can be −60 dB or less in the frequency range of 14.00 GHz to 15.00 GHz.

FIGS. 7A to 7Dshow other simulation results of the electronic device1and the comparative example described above.

FIGS. 7A to 7Dare results of performing electromagnetic field analysis of the near field in a prescribed region of the housing interior for the electronic device1and the comparative example.FIG. 7Ashows the analysis result of the magnetic field of the comparative example; andFIG. 7Bshows the analysis result of the electric field of the comparative example.FIG. 7Cshows the analysis result of the magnetic field of the electronic device1; andFIG. 7Dshows the analysis result of the electric field of the electronic device1. InFIGS. 7A to 7D, the electric field or the magnetic field is displayed as being stronger as the color becomes lighter (whiter) and weaker as the color becomes darker (blacker).

As a result of diligent research performed by the inventors, it was found that the magnitude of the noise generated in the housing interior has a relationship particularly with the magnetic field strength in the housing interior. ComparingFIGS. 7A and 7C, it can be seen that compared to the comparative example, the magnetic field strength is weaker for the electronic device1. On the other hand, comparingFIGS. 7B and 7D, compared to the comparative example, the electric field strength is stronger for the electronic device1.

Accordingly, it can be seen that in the electronic device1of the embodiment, the magnetic field strength of the housing110interior is suppressed by increasing the electric field strength of the housing110interior; and as a result, the noise can be suppressed.

The noise can be largely divided into coupling of the inter-lead capacitance on the circuit substrate, and noise that propagates through space. The noise of the former can be suppressed by a filter circuit or by increasing the lead spacing because it is sufficient to break the capacitive coupling between the leads. On the other hand, it is difficult to use a filter to reduce the noise that propagates through space of the latter. To solve this problem, a method may be considered in which a material that absorbs electromagnetic waves or suppresses the reflections of electromagnetic waves is adhered to the side walls inside the housing. However, this method is problematic in that the circuit operation shifts from the initial design because the dielectric constant of the material that is adhered is added to the dielectric constant of the initial circuit design. Also, there is a secondary problem in that it takes time during development to determine by experiment the location to adhere the material.

Housings can be largely divided into resin housings and metal housings. In particular, in the case of a circuit for which it is indispensable to shield the noise from the outside, at least a portion of the housing is formed of a metal. In such a case, the metal portion of the housing is connected to the ground potential. However, in the case where such a metal housing is used, problems include reflections of the electromagnetic waves inside the housing by the side walls and/or the ceiling which causes housing resonance and/or oscillations of the electronic circuit disposed inside the housing. The noise that is caused by the reflections of the electromagnetic waves inside the housing increases more easily as the height of the housing is reduced. An electronic device having a low housing height is problematic in that it is not easy to sufficiently reduce the noise using only the metal patches109; and as a result, the metal housing height cannot be reduced.

Conversely, according to the structure of the embodiment in which the EBG is formed not only by the multiple metal patches109but also the first metal members113, the second metal members115, the third metal members121, and the fourth metal members123that are connected to the ground potential and formed of metals, the oscillation of the amplifiers and the resonance of the housing can be suppressed effectively as in the results shown inFIG. 6. Therefore, even in the case where the height of the housing110is low, it is possible to reduce the noise generated in the interior of the housing110.

According to the embodiment as in the results shown inFIGS. 7A to 7D, the resistance to the magnetic field can be increased at the vicinity of the side unit1102that is formed of a metal. Therefore, it is possible to favorably reduce the magnetic field strength of the electromagnetic waves reflected by the side unit1102and the electromagnetic waves traveling along the side unit1102. As a result, an electronic device can be provided in which it is possible to reduce the noise generated in the interior while suppressing the noise entering from the outside.

In the embodiment, because the printed wiring board is used as the lid1103, the weight of the housing110is light; and it is possible to make the housing110inexpensively.

In the electronic device1, the space S1is defined using the first protrusion117and the second protrusion119. Generally, there is a tendency for the noise generated in the housing interior to increase as the space of the housing interior increases in the in-plane direction of the bottom where the circuit substrate101is disposed. It is possible to reduce the noise by dividing the space in the in-plane direction of the bottom1101by the first protrusion117and the second protrusion119.

In the embodiment, the gain of the power amplifier107is the largest among the power amplifiers103,105, and107. It is possible to effectively reduce the noise by disposing the power amplifier107inside the space S1.

By providing the third metal members121that contact the first protrusion117and the fourth metal members123that contact the second protrusion119, it is possible to suppress the noise inside the housing110even further. By providing the first protrusion117and the second protrusion119, it is possible to increase the region where metal members for reducing the noise can be disposed.

Although the first metal members113and the second metal members115are disposed only in the region facing the space S1in the embodiment, the first metal members113and the second metal members115may be disposed in other regions.

Although multiple metal members are disposed in the embodiment, as long as at least one metal member is disposed, the effect of reducing the magnetic field strength in the interior of the housing110is obtained; and it is possible to reduce the noise generated in the interior of the housing110.

In the embodiment, the first metal members113, the second metal members115, the third metal members121, and the fourth metal members123are portions of the first metal film125; and a material of the first to fourth metal members113to123is the same as a material of the first metal film125. However, this is not limited thereto; and the first to fourth metal members113to123may be formed of materials different from that of the first metal film125.

In the embodiment, a material of the first metal film125is the same as a material of the metal patches109. However, this is not limited thereto; and the first metal film125and the metal patches109may be formed from mutually-different materials.

An electronic device according to a second embodiment of the invention will now be described usingFIG. 8. In the electronic device2, the configurations of the first metal member and the second metal member are different from those of the electronic device1according to the first embodiment.

In the embodiment, an end portion1412of a first metal member141in the first direction has an arc configuration. A hollow portion1413is made between the end portion1412and first portions1411contacting the surface P1. Similarly, a second metal member143includes an end portion1432in the second direction; and a hollow portion1433is made between the end portion1432and second portions1431contacting the surface P2.

In the embodiment as well, the noise in the interior of the housing110can be reduced further by disposing the first metal member141and the second metal member143than in the case where the first metal member141and the second metal member143are not disposed.

Although not-shown inFIG. 8, in addition to the first metal member141and the second metal member143, the electronic device2may include a third metal member and a fourth metal member that include end portions having arc configurations similar to those of the first metal member141and the second metal member143.

Hereinabove, embodiments of the invention are described with reference to specific examples. However, the invention is not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components such as the housing, the circuit substrate, the metal patch, the input port, the output port, the power amplifier, etc., from known art; and such practice is within the scope of the invention to the extent that similar effects can be obtained.

In the description of the embodiment, the expressions “bottom” and “lid” are used for the purpose of description.

These terms merely refer to the portions of the housing such that the portion where the circuit substrate is disposed is referred to as the bottom, and the wall opposing the bottom is referred to as the lid. In other words, the bottom is not necessarily positioned at the lower part of the housing; and the bottom and the lid may be inverted when the electronic device is mounted, etc.

Moreover, all electronic devices practicable by an appropriate design modification by one skilled in the art based on the electronic devices described above as embodiments of the invention also are within the scope of the invention to the extent that the spirit of the invention is included.