JP2004235738A - Electronic apparatus and channel selector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a channel selector shielded with a shield case to reduce unwanted radiations. <P>SOLUTION: The electronic apparatus comprises a circuit board, a shield case for shielding the circuit board, and electromagnetic wave absorbing means attached to the shield case for absorbing surrounding electromagnetic waves. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic device and a tuning device, and more particularly, to an electronic device and a tuning device shielded by a shield case.
[0002]
[Prior art]
There are broadcast wave receiving devices for receiving terrestrial television broadcasts, satellite broadcasts, and digital radio broadcasts. Since such a receiving apparatus handles a high-frequency signal, unnecessary radiation is large.
[0003]
However, in electronic devices, the amount of unnecessary radiation in the surroundings is specified by standards. For this reason, in a broadcast wave receiving apparatus in which generation of unnecessary radiation is large, it is necessary to enhance the shielding property. Conventionally, in order to enhance the shielding performance, for example, the chassis is made of metal, and the chassis is shielded together. However, on the other hand, the chassis of the receiving device tends to be made of resin in order to reduce the weight and improve the design (see Patent Document 1).
[0004]
[Patent Document 1]
JP 2000-156586 A
[Problems to be solved by the invention]
However, when the chassis is made of resin in the conventional broadcast wave receiving device, the shielding property of the broadcast wave receiving device is reduced, and leakage of unnecessary radiation to the surroundings is increased. For this reason, it was necessary to reduce unnecessary radiation from each internal component. At this time, the tuner module, which is a channel selection device, handles high-frequency signals, so that unnecessary radiation is greatly reduced. Therefore, it is required to reduce unnecessary radiation from the tuner module.
[0006]
The present invention has been made in view of the above points, and has as its object to provide an electronic device and a tuning device that can reduce unnecessary radiation.
[0007]
[Means for Solving the Problems]
The present invention is characterized in that electromagnetic wave absorbing means (43, 44, 45) for absorbing surrounding electromagnetic waves is attached to a shield case (42) for shielding a circuit board (41).
[0008]
According to the present invention, unnecessary radiation generated from the circuit board (41) and the tuning device (31) are controlled by the electromagnetic wave absorbing means (43, 44, 45) attached to the shield case (42) of the tuning device (31). Unnecessary radiation around can be absorbed. As a result, unnecessary radiation from the device (23) on which the tuning device (31) is mounted can be significantly reduced.
[0009]
Note that reference numerals are for reference only, and do not limit the scope of the claims.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
First, a system to which the channel selection device of the present embodiment is applied will be described in detail.
[0011]
FIG. 1 is a system configuration diagram of a digital audio broadcasting system.
[0012]
In the digital audio broadcasting system 1, a digital audio signal is provided as a terrestrial wave from a broadcasting station 11 and is provided as a satellite wave via a satellite 12. The terrestrial wave and the satellite wave are received by the receiving system 13.
[0013]
The receiving system 13 includes a terrestrial wave receiving antenna 21, a satellite wave receiving antenna 22, a receiving device 23, an audio amplifier 24, and speakers 25L and 25R.
[0014]
The terrestrial wave receiving antenna 21 receives the terrestrial wave output from the broadcasting station 11 and supplies the received signal to the receiving device 23. The satellite wave receiving antenna 22 receives a satellite wave provided from the broadcasting station 11 via the satellite 12 and supplies the received signal to the receiving device 23.
[0015]
The receiving device 23 includes a tuner module 31, a demodulation circuit 32, a control circuit 33, and an operation unit 34. The received signal from the terrestrial wave receiving antenna 21 and the received signal from the satellite wave receiving antenna 22 are respectively supplied to the tuner module 31.
[0016]
2 is an assembly view of the tuner module 31, FIG. 3 is an exploded perspective view of the tuner module 31, and FIG. 4 (A) is a front view, FIG. 4 (B) is a rear view, FIG. 4 (C) is a top view, FIG. 4 (D) is a left side view, FIG. 4 (E) is a right side view, and FIG. Shows a bottom view.
[0017]
The tuner module 31 includes a circuit board 41, a shield case 42, and electromagnetic wave absorbing sheets 43, 44, and 45.
[0018]
FIG. 5 shows a configuration diagram of the circuit board 41. FIG. 5A is a top view, and FIG. 5B is a bottom view.
[0019]
The circuit board 41 is composed of a multilayer laminated circuit board. On the circuit board 41, a satellite wave signal receiving circuit 51 and a terrestrial wave signal receiving circuit 52 are formed on the upper surface side as shown in FIG. Further, a control circuit 53 for controlling the satellite wave signal receiving circuit 51 and the terrestrial wave signal receiving circuit 52 is formed on the lower surface side of the circuit board 41 as shown in FIG. 5B. In addition, the upper surface side and the lower surface side of the circuit board 41 are shielded by a ground plane arranged in the middle of the circuit board 41.
[0020]
The satellite wave signal receiving circuit 51 is formed in a substantially right half area on the upper surface side of the circuit board 41. The satellite wave signal receiving circuit 51 is provided with an antenna terminal Tant1. The antenna terminal Tant1 is provided at the upper right corner of the upper surface of the circuit board 41, and is connected to the satellite wave receiving antenna 21. The terrestrial signal receiving circuit 51 converts the satellite wave signal input to the antenna terminal Tant1 into an intermediate frequency signal.
[0021]
The terrestrial signal receiving circuit 52 is formed in a substantially left half area on the upper surface side of the circuit board 41. The terrestrial signal receiving circuit 52 is provided with an antenna terminal Tant1. The antenna terminal Tant2 is provided at the upper left corner of the upper surface of the circuit board 41, and is connected to the terrestrial wave receiving antenna 22. The terrestrial signal receiving circuit 52 converts the terrestrial signal input to the antenna terminal Tant2 into an intermediate frequency signal.
[0022]
The control circuit 53 includes an oscillation circuit for generating a local oscillation signal and the like supplied to the satellite wave signal reception circuit 51 and the terrestrial wave signal reception circuit 52. Further, on the circuit board 41, connection pins P11 to P1m and P21 to P2n are implanted downward from the lower surface. An external control signal is supplied to the connection pins P11 to P1m. The control circuit 53 controls the satellite wave signal receiving circuit 51 and the terrestrial wave signal receiving circuit 52 according to control signals from the connection pins P11 to P1m. From the connection pins P21 to P2n, an intermediate frequency signal converted by the satellite wave signal receiving circuit 51 and the terrestrial signal receiving circuit 52 is output.
[0023]
The connection pins P11 to P1m and the connection pins P21 to P2n are soldered to a circuit board of the receiving device 23 main body. The demodulation circuit 32 and the control circuit 34 are mounted on the circuit board of the main body of the receiving device 23. The connection pins P21 to P2n are connected to the demodulation circuit 32, and the connection pins P11 to P1m are connected to the control circuit 34. The demodulation circuit 32 demodulates an audio signal from the intermediate frequency signal from the tuner module 31.
[0024]
The audio signal demodulated by the demodulation circuit 32 is supplied to the audio amplifier 24 as an output of the receiving device 23. The audio amplifier 24 amplifies the audio signal from the receiving device 23 and drives the speakers 25L and 25R.
[0025]
The operation unit 33 of the receiving device 23 is composed of a key switch and the like, and is used for selecting a program and the like. The operation by the operation unit 33 is supplied to the control circuit 34.
[0026]
The control circuit 34 detects an operation by the operation unit 33 and supplies a control signal corresponding to the detection result to the connection pins P11 to P1m. The tuner module 31 controls a local oscillation frequency and the like according to a control signal from the control circuit 34, and is controlled so that a program according to the operation of the operation unit 33 is selected. Thus, the tuner module 31 outputs the intermediate frequency signal of the program according to the operation of the operation unit 33.
[0027]
The circuit board 41 is accommodated in a shield case 42 to handle a high-frequency signal of 2332.5 to 2345.0 MHz. The shield case 42 includes a case body 61, an upper cover 62, and a lower cover 63.
[0028]
The case body 61 is formed by pressing and bending a metal plate. The case main body 61 has a configuration in which the side plate portions 71 to 74 are connected by a connecting portion 75. At both ends of the side plate portions 72, 74, convex portions 81 for connecting the side plate portions 72, 74 to the side end portions of the side end portions 71, 73 are formed substantially at the center thereof. Holes 82 with which the convex portions 81 are engaged are formed at both side ends of the side plate portions 72 and 73. The case body 61 bends the side plates 71 to 74 so that the projections 81 of the side plates 72, 74 and the holes 82 of the side plates 71, 73 engage with each other at the connecting portion 75, and the projection 81 is formed into a hole. It is assembled by inserting it into the portion 82 and caulking.
[0029]
Further, the side plates 71 to 74 are formed on the outer surfaces thereof with protrusions 91 for locking the upper cover 62 and protrusions 92 for locking the lower cover 63. Further, on the side plate portions 71 to 74, a first claw portion 101 bent inward is formed between the convex portion 91 and the convex portion 92. The circuit board 41 is inserted into the case main body 61 from below the case main body 61, and the upper surface of the circuit board 41 contacts the first claw portion 101 and is positioned inside the case main body 61.
[0030]
A second claw 111 is formed below the side plate portions 71 to 74 so as to be bent inside the case body 61. The second claw 111 is bent toward the inside of the case body 61 in a state where the circuit board 41 is in contact with the first claw 101, and holds the circuit board 41 inside the case body 61. The circuit board 41 is held inside the case main body 61 by the first claw 101 and the second claw 111, and its ground pattern is soldered to the inner surface of the case main body 61. Fixed.
[0031]
Further, leg portions 121 for fixing to an external circuit board are formed at lower portions on both sides of the side plate portions 71 and 73. The leg 121 is inserted into a through hole formed in the ground pattern of the external circuit board and soldered. As a result, the case body 61 is set to the ground potential.
[0032]
Next, the upper cover 62 will be described.
[0033]
FIG. 6 shows a configuration diagram of the upper cover 62.
[0034]
The upper cover 62 includes a shield surface 131 and an engagement portion 132 that is bent downward around the shield surface 131. A cutout 141 for exposing the antenna terminal Tant1 and a cutout 142 for extending the antenna terminal Tant2 are formed in the shield surface 131. The notch 141 is formed in a portion of the shield surface 131 facing the antenna terminal Tant1. The notch 141 is formed in a portion of the shield surface 131 facing the antenna terminal Tant2.
[0035]
The engagement portions 132 are formed on four sides of the shield surface 131. The engaging portion 132 is bent toward the lower surface side of the shield surface 131, and a substantially central portion thereof is bent in a convex shape toward the shield surface 131. The engaging portion 132 has the convex portion engaged with the convex portion 91 from the outer peripheral side of the case main body 61, and the upper cover 62 is fixed to the case main body 61.
[0036]
In the left half area of the shield surface 131, a hole 151 for heat radiation is formed. The hole 151 releases the heat of the circuit board 41 to the outside.
[0037]
An electromagnetic wave absorbing sheet 43 is attached to the lower right half area of the shield surface 131 with a double-sided adhesive tape or the like. The electromagnetic wave absorbing sheet 43 is obtained by mixing sendust powder in ethylene propylene rubber. The size of the electromagnetic wave absorbing sheet 43 is 28.0 mm × 28.0 mm in width × length, and the thickness T is 1.0 mm. The electromagnetic wave absorbing sheet 43 is made of, for example, a material having an applied frequency of 0.1 to 3.0 GHz, and has an electrical characteristic of a magnetic loss of 2.0 or more at 0.6 GHz and a magnetic loss of 4.0 or more at 2.0 GHz. 0 or more, the volume resistivity is 1.0 × 10 ＾ 5 Ω · m or more, and the surface resistivity is 1.0 × 10 ＾ 5 Ω · m or more.
[0038]
Next, the lower cover 63 will be described.
[0039]
FIG. 7 shows a configuration diagram of the lower cover 63. FIG. 7A is a plan view of an outer surface, and FIG. 7B is a plan view of an inner surface.
[0040]
The lower cover 63 includes a shield surface 161 and an engaging portion 162 that is bent downward around the shield surface 161. The shield surface 161 has a hole 171 through which the connection pins P11 to P1m penetrate, and a hole 172 through which the connection pins P21 to P2n penetrate. The connection pins P11 to P1m extend to the outside of the shield case 42 through the holes 171 and are connected to an external circuit board. The connection pins P21 to P2n extend to the outside of the shield case 42 through the holes 172 and are connected to an external circuit board.
The engagement portions 162 are formed on four sides of the shield surface 161. The engaging portion 162 is bent toward the inner surface side of the shield surface 161, and a substantially central portion thereof is bent in a convex shape toward the shield surface 161. The engaging portion 162 is engaged with the protruding portion of the engaging portion 162 from the outer peripheral side of the case main body 61 so as to ride over the convex portion 92, and the lower cover 63 is fixed to the case main body 61.
[0041]
An electromagnetic wave absorbing sheet 44 is attached to the inner surface side of the shield surface 161 over substantially the entire surface thereof using a double-sided adhesive tape or the like. The electromagnetic wave absorbing sheet 44 is made of the same material as the electromagnetic wave absorbing sheet 43, has the same electrical characteristics, and is different in size from the electromagnetic wave absorbing sheet 43. The size of the electromagnetic wave absorbing sheet 44 is 53.0 mm × 32.0 mm in width × length, and the thickness T is 1.0 mm.
[0042]
An electromagnetic wave absorbing sheet 45 is attached to the outer surface of the shield surface 161 over substantially the entire surface thereof using a double-sided adhesive tape or the like. The electromagnetic wave absorbing sheet 45 is made of the same material as the electromagnetic wave absorbing sheet 43, has the same electrical characteristics, and is different in size from the electromagnetic wave absorbing sheet 43. The size of the electromagnetic wave absorbing sheet 45 is 53.0 mm × 32.0 mm in width × length, and the thickness T is 0.5 mm.
[0043]
By attaching the electromagnetic wave absorbing sheets 43, 44, 45 to the shield case 42, radio waves generated by the circuit board 41 are absorbed by the electromagnetic wave absorbing sheets 43, 44, 45, so that unnecessary radiation from the tuner module 31 can be suppressed. For example, in the case of the above configuration, an improvement of 6 dB was observed as compared with the case where the electromagnetic wave absorbing sheets 43, 44, and 45 were not attached.
[0044]
FIG. 8 is a diagram showing the relationship between the state of attachment of the electromagnetic wave absorbing sheet and the degree of improvement.
[0045]
State 1 is a state in which the electromagnetic wave absorbing sheet is not stuck at all, State 2 is a state in which the electromagnetic wave absorbing sheet 44 is stuck on the inner surface of the lower cover 63, and State 3 is a state in which the electromagnetic wave absorbing sheet 44 is stuck on the inner surface of the lower cover 63. A state where the electromagnetic wave absorbing sheet 45 is stuck on the outer surface, a state 4 is a state where the electromagnetic wave absorbing sheet 45 is stuck on the outer surface of the lower cover 63, and a state 5 is a state where the electromagnetic wave absorbing sheet 43 is stuck on the inner surface of the upper cover 62. State 6 is a state where the electromagnetic wave absorbing sheet 43 is stuck on the inner surface of the upper cover 62, and state 6 is a state where the electromagnetic wave absorbing sheet 45 is stuck on the outer surface of the lower cover 63. State 7 is a state where the electromagnetic wave absorbing sheet 45 is stuck on the inner surface of the upper cover 62. The electromagnetic wave absorbing sheet 43 is attached to the inner surface of the lower cover 63, and the electromagnetic wave absorbing sheet 43 is attached to the inner surface of the upper cover 62. A state in which the electromagnetic wave absorbing sheet 44 is attached to the inner surface of the lower cover 63, and the thickness T of the electromagnetic wave absorbing sheet 45 is twice the thickness T of the electromagnetic wave absorbing sheet 45, that is, 1 mm. State 9 is a state in which the electromagnetic wave absorbing sheet 43 is stuck on the inner surface of the upper cover 62, the electromagnetic wave absorbing sheet 44 is stuck on the inner surface of the lower cover 63, and the electromagnetic wave absorbing sheet 45 is stuck on the outer surface of the lower cover 63. Show.
[0046]
As shown in FIG. 8, an improvement of 2 dB was observed in the states 1, 4, and 5. Further, in the states 3, 6, and 7, an improvement of 4 dB was observed. Further, an improvement of 6 dB was observed in states 8 and 9.
[0047]
At this time, since the states 8 and 9 have the same degree of improvement, the weight and cost can be reduced by employing the state 9 using the electromagnetic wave absorbing sheet 45 having half the thickness of the electromagnetic wave absorbing sheet of the state 8. .
[0048]
Further, since the electromagnetic wave absorbing sheets 43, 44, and 45 are as thin as 1 mm and 0.5 mm, they can be attached without changing the shape of the tuner module 31 or the like. Therefore, unnecessary radiation can be cut by 6 dB without changing the design of the circuit and the shield case. Further, since the electromagnetic wave absorbing sheets 43, 44, and 45 need only be attached to the planar shield surfaces of the upper cover 62 and the lower cover 63, the construction is easy.
[0049]
As described above, by attaching the electromagnetic wave absorbing sheets 43, 44, and 45 to the tuner module 31, unnecessary radiation from the tuner module 31 can be cut by 6 dB. Thereby, unnecessary radiation of the entire receiving device 23 can be suppressed. As described above, since unnecessary radiation of the entire receiving device 23 can be suppressed, the chassis of the receiving device 23 can be made of resin.
[0050]
Further, since the electromagnetic wave absorbing sheets 43, 44, and 45 can also absorb unnecessary radiation in the surroundings, further reduction of unnecessary radiation can be expected.
[0051]
【The invention's effect】
As described above, according to the present invention, unnecessary radiation generated from the circuit board and unnecessary radiation around the tuning device can be absorbed by the electromagnetic wave absorbing means attached to the shield case of the tuning device. It has features such as the ability to significantly reduce unnecessary radiation from the installed equipment.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a digital audio broadcasting system.
FIG. 2 is an assembly diagram of a tuning device 31.
FIG. 3 is an exploded perspective view of the tuning device 31.
FIG. 4 is a configuration diagram of a circuit board 41.
FIG. 5 is a diagram for explaining effects.
FIG. 6 is a configuration diagram of an upper cover 62;
FIG. 7 is a configuration diagram of a lower cover 63.
FIG. 8 is a diagram showing the relationship between the state of attachment of the electromagnetic wave absorbing sheet and the degree of improvement.
[Explanation of symbols]
1 Digital Audio Broadcasting System 11 Broadcasting Station, 12 Satellite, 13 Receiving System 21 Antenna for Receiving Satellite Wave Broadcasting, 22 Antenna for Receiving Terrestrial Broadcasting Broadcasting 23 Receiving Device, 24 Audio Amplifier, 25L, 25R Speaker 31 Tuner Module, 32 Demodulation Circuit , 33 operation unit, 34 control circuit 41 circuit board, 42 shield case 43, 44, 45 electromagnetic wave absorption sheet 51 satellite wave signal receiving circuit, 52 terrestrial signal receiving circuit, 53 control circuit

Claims (14)

A circuit board,
A shield case for shielding the circuit board,
An electronic device comprising: an electromagnetic wave absorbing unit attached to the shield case for absorbing surrounding electromagnetic waves. 2. The electronic device according to claim 1, wherein the electromagnetic wave absorbing unit has a sheet shape and is adhered to the shield case. The shield case, a side plate holding a side surface of the circuit board,
A first cover attached to one opening surface of the side plate;
A second cover attached to the other opening surface of the side plate,
The electronic device according to claim 1, wherein the electromagnetic wave absorbing unit is attached to the first and / or second cover. A first electromagnetic wave absorbing sheet formed in a sheet shape and attached to an inner surface of the first cover;
A second electromagnetic wave absorbing sheet which is formed in a sheet shape and is attached to an outer surface of the second cover;
4. The electronic device according to claim 2, further comprising a third electromagnetic wave absorbing sheet formed in a sheet shape and attached to an inner surface of the second cover. 5. The electronic device according to claim 4, wherein the second electromagnetic wave absorbing sheet and the third electromagnetic wave absorbing sheet are attached to substantially the entire cover surface of the second cover. The electronic device according to claim 4, wherein the second electromagnetic wave absorbing sheet has a thickness that is approximately half the thickness of the third electromagnetic wave absorbing sheet. The first cover has a heat radiation hole for radiating heat of the circuit board formed over substantially half of the cover surface,
The electronic device according to claim 4, wherein the first electromagnetic wave absorbing sheet is attached to a region other than the heat radiation hole on the cover surface. A circuit board on which a tuning circuit for receiving broadcast waves and selecting a channel is mounted;
A shield case for shielding the circuit board,
An electromagnetic wave absorbing means attached to the shield case and absorbing surrounding electromagnetic waves. 9. The tuning device according to claim 8, wherein the electromagnetic wave absorbing means has a sheet shape and is adhered to the shield case. The shield case, a side plate holding a side surface of the circuit board,
A first cover attached to one opening surface of the side plate;
A second cover attached to the other opening surface of the side plate,
The tuning device according to claim 8, wherein the electromagnetic wave absorbing unit is attached to the first and / or second cover. A first electromagnetic wave absorbing sheet formed in a sheet shape and attached to an inner surface of the first cover;
A second electromagnetic wave absorbing sheet which is formed in a sheet shape and is attached to an outer surface of the second cover;
The channel selecting device according to claim 9, further comprising a third electromagnetic wave absorbing sheet formed in a sheet shape and attached to an inner surface of the second cover. The channel selecting device according to claim 11, wherein the second electromagnetic wave absorbing sheet and the third electromagnetic wave absorbing sheet are attached to substantially the entire cover surface of the second cover. The channel selecting device according to claim 10, wherein the second electromagnetic wave absorbing sheet has a thickness that is approximately half the thickness of the third electromagnetic wave absorbing sheet. The first cover has a heat radiation hole for radiating heat of the circuit board formed over substantially half of the cover surface,
The tuning device according to any one of claims 11 to 13, wherein the first electromagnetic wave absorbing sheet is attached to a region other than the heat radiation hole on the cover surface.

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