JP2006210528A - Circuit for noise reduction, digital amplifier and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit for noise reduction which can reduce higher frequency components and can be reduced in size, and also to provide a digital amplifier and an electronic apparatus. <P>SOLUTION: The circuit for noise reduction includes an electric circuit board 2 which is formed with an installation hole 2a extended through the board 2 in the thickness direction. A divided core 6 formed of a magnetic substance is installed which is so formed as to cover the electric circuit board 2 from the edge of the electric circuit board 2 to the installation hole 2a. A wiring pattern 5 is also installed which is wound one or several times around the installation hole 2a in such a manner that it may pass through the inside of the divided core 6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a noise reduction circuit for reducing unnecessary noise from an output of the digital amplifier in an electronic device equipped with a digital amplifier for amplifying a digital signal, and a digital amplifier and an electronic device having the circuit. .

  In recent years, electronic devices having audio functions (sound output functions) such as DVDs, SACDs (Super Audio CDs), and CD / MDs have become widespread. Is required. In order to meet such a demand, a class D amplifier which is a digital amplifier is often used as an amplifier for an audio function.

  The digital amplifier converts an audio analog signal and an audio digital signal corresponding to the audio analog signal into a modulation pulse signal (PWM (Pulse Width Modulation) signal or PDM (Pulse Density Modulation) signal) corresponding to them, and power The power transistor of the output stage to which the voltage (Vcc) is applied is turned on / off based on the modulated pulse signal, and the modulated pulse signal is amplified in power. By removing unnecessary high-frequency components through an LPF (Low Pass Filter), an amplified audio analog signal can be obtained.

  In such a digital amplifier, a pulse-like modulated pulse signal is applied to the base of the transistor (or the gate of the FET), and in response to a change between the high level and the low level of the modulated pulse signal, Since the transistor operates as an ON / OFF switch, the output current of the transistor increases or decreases between 0 A (ampere) and the maximum value (Vcc / RL). When ON, the maximum current passes through the transistor. At this time, the resistance between the collector and emitter is extremely small, so the loss is close to zero in principle, but no current flows when OFF, so the loss is zero. Become.

  As described above, in the digital amplifier, the transistor performs a switching operation so that high-rate power conversion is possible, and since power loss can be reduced, heat generation is small. Heat generation can be reduced to about / 5.

  As a result, when the above digital amplifier is used, not only can the radiator for the output stage transistor be downsized, but also the capacity of the power supply circuit can be reduced, so that overall reduction in size, weight and power saving is possible. It becomes.

  By the way, even if the power-amplified dense / sparse wave output is directly input to the speaker, sound is normally reproduced. This is because the speaker itself has a mechanical low-pass characteristic, but since the high frequency carrier for modulation included in the power-amplified dense wave output is converted into heat together with the sound reproduction, the heat causes There is a risk of damaging the speaker. In addition, the speaker cord to which the power-amplified dense / sparse wave output is input or the speaker itself serves as an antenna, and has a disadvantage that high-frequency noise is radiated around.

  For this reason, in general, as shown in FIG. 3, a digital amplifier is provided with a noise filter, that is, an LPF as means for reducing a high-frequency carrier component that becomes unnecessary noise from the output. The LPF includes a wiring wire 25 connected between an output terminal 23a of a class D amplifier 23 provided on the electric circuit board 21 of the digital amplifier and an output terminal 21a of the electric circuit board 21, and a cylindrical ferrite. It is formed by winding the core 26 once or a plurality of times.

  In such an LPF, as shown in FIG. 4, it is understood that the effect of reducing the high-frequency signal (unnecessary noise) is larger when the first and second volumes are used. However, if the number of turns is increased, the reduction effect is increased. However, when the number of turns exceeds a certain value, the reduction effect is constant depending on the material of the ferrite core 26.

Patent Document 1 discloses a filter coil constituting a low-pass filter for removing carrier frequency provided in an output stage of a BTL (Bridged Tied Load) output method class D amplifier, and the winding directions are the same. A plurality of pairs of coils having inductance values are disposed adjacent to each other along the axial direction, and a magnetic shield wall is provided between different pairs of coils and is housed in one package.
JP2003-124029 (release date: April 25, 2003)

  However, in the conventional digital signal amplifier, when the noise is reduced, the electronic device due to the noise reduction due to the increase in the length of the wiring wire due to the increase in the shape of the core and the increase in the number of windings around the core. The problem of increase in size and cost increases arises.

  In addition, when reducing the noise of the output from the output stage transistor, which is a large current circuit section, the current flowing through the wiring wire increases, so it is necessary to make the wiring wire thicker, and further increase the size and cost of the electronic device. The problem of being up occurs.

  Also, in Patent Document 1, since a plurality of pairs of coils are housed in one package, that is, on a substrate in one package, there is a problem that their outer dimensions are large and there is a limit to downsizing. Arise.

  In order to solve the above problems, the noise reduction circuit of the present invention includes an electric circuit board having a hole portion penetrating in the thickness direction, and the substrate in a core shape from the outer edge of the electric circuit board to the hole portion. A core member made of a magnetic material formed so as to cover the wiring member, and a wiring pattern provided by winding the periphery of the hole one or more times so as to pass through the inside of the core member. It is characterized by that.

  According to the above configuration, the wiring pattern is provided by winding around the hole one or more times so as to pass through the inside of the core member, so that the inductance of the wiring pattern is larger than that of the core member in series. Can be formed. Therefore, in the above configuration, since the LPF can be configured by the serial inductance due to the wiring pattern, unnecessary high-frequency components included in the amplified output from the amplification means such as a digital amplifier can be removed by the LPF. It becomes possible.

  In addition, in the above configuration, it is possible to provide the core member so as to be embedded in the electric circuit board using the hole portion, and the external dimensions of the noise reduction circuit including the core member as compared with the conventional configuration. Can be reduced, and the size can be reduced.

  In the noise reduction circuit, the electric circuit board may include a multilayer board, and the wiring pattern may be formed on at least one of a surface of the multilayer board and each layer.

  According to the above configuration, the wiring pattern is formed on at least one of the surface and each layer in the multilayer substrate, thereby ensuring that the wiring pattern is wound around the core member once or a plurality of times. it can.

  In the noise reduction circuit, the electric circuit board may have a ground pattern corresponding to the wiring pattern. In the noise reduction circuit, the electric circuit board may be made of a thin plate material. In the noise reduction circuit, the electric circuit board preferably has a relative dielectric constant of 3 to 5.

  According to the above configuration, the series inductance due to the wiring pattern can be more reliably formed when the ground pattern, the thin plate material, and the relative dielectric constant are 3 to 5.

  In the noise reduction circuit, the magnetic body may be at least one selected from the group consisting of ferrite, sendust, permalloy dust, and iron carbonyl dust.

  In the noise reduction circuit, the core material is preferably formed in a columnar shape having a central axis along the surface direction of the electric circuit board.

  In the noise reduction circuit, it is preferable that the core material has a divided core shape in which a gap is formed by the electric circuit board.

  In order to solve the above-described problems, a digital amplifier according to the present invention includes any of the above-described noise reduction circuits and amplification means for amplifying a digital signal, and the amplification means is connected to the wiring pattern. It is characterized in that it is provided alongside the electric circuit board.

  In the digital amplifier, the amplification means is preferably a class D amplifier that amplifies a signal by a switching operation.

  In order to solve the above-described problems, an electronic apparatus according to the present invention includes any one of the above-described noise reduction circuits or any one of the above-described digital amplifiers.

  As described above, the noise reduction circuit according to the present invention covers an electric circuit board having a hole penetrating in the thickness direction and a core shape from the outer edge of the electric circuit board to the hole. The core member is formed of a magnetic body, and the wiring pattern is provided by winding the periphery of the hole one or more times so as to pass through the inside of the core member. .

  Therefore, in the above configuration, the core member is attached to the hole portion of the electric circuit board, and the wiring pattern is formed so as to wind the core portion, thereby forming a large current circuit portion. High-frequency components that are included in the output and become unnecessary noise can also be reduced by the above-described wiring pattern without using a conventional wiring wire.

  As a result, the above configuration has the effect of reducing the noise countermeasure cost by omitting the wiring wires as in the prior art and reducing the size of the electronic device by the hole and the wiring pattern.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to FIGS. 1 and 2. In an electronic device such as a CD / MD provided with a digital amplifier provided with a noise reduction circuit of the present invention, as shown in FIGS. The circuit board 2 is provided as a multilayer board (in this embodiment, the number of copper foil layers of the strip-like wiring pattern 5: two layers). In addition to the wiring pattern 5, a ground pattern (not shown) for grounding parallel to the wiring pattern 5 is also formed on the multilayer electric circuit board 2 with a copper foil.

The base material of the electric circuit board 2 is excellent in electric insulation (1 × 10 ¹³ Ω or more, more preferably 5 × 10 ¹³ Ω or more), and the relative dielectric constant at 1 MHz is 2 to 5, more preferably 1 MHz. It is sufficient that the relative dielectric constant is 2 to 4.8, more desirably, the relative dielectric constant at 1 MHz is 2 to 4, such as a fluororesin substrate, a polyimide substrate, and a low dielectric constant epoxy substrate (ratio at 1 MHz). The dielectric constant is 3.5 or 3.8). In the present embodiment, a low dielectric constant epoxy substrate (relative dielectric constant at 1 MHz is 3.5) is used. Although it does not specifically limit as thickness of the electric circuit board | substrate 2, 0.6 mm-2 mm (1 mm in this Embodiment) which are thin plate-like are mentioned.

  On the electric circuit board 2, a digital amplifier 3 is mounted, and an external connection terminal 4 for taking out the output of the digital amplifier 3 to the outside is provided at the end of the electric circuit board 2. The digital amplifier 3 only needs to be capable of amplifying a pulse signal (digital signal) by switching operation of a transistor in the output stage, and examples thereof include an audio class D amplifier, a fluorescent lamp, and a motor inverter.

In the electric circuit board 2, the wiring patterns 5 ₁ and 5 ₂ for electrically connecting the digital amplifier 3 and the external connection terminals 4 to each other are formed in a multilayer structure, for example, by copper foil by photolithography. Is formed. Wiring patterns 5 _1, while a first-layer wiring pattern of the electric circuit board 2, the wiring pattern 5 ₂ is a two-layer wiring pattern of the electric circuit board 2.

In addition to copper, aluminum, silver, gold, and alloys thereof can be used as the material for the wiring patterns 5 ₁ and 5 ₂ . Further, the thickness of each wiring pattern 5 ₁ , 5 ₂ can be set as needed, but for example, a thickness of 10 to 30 μm (thickness 18 μm in the present embodiment) is mentioned, and each wiring pattern 5 ₁ , 5 _{Although the} width | variety of 2 can also be set as needed, the width of 0.1-0.5 mm (in this Embodiment, width 0.2mm) is mentioned, for example.

Moreover, in the electric circuit board 2, through hole 5b for the terminating of the wiring pattern 5 ₁ and the starting end of the wiring pattern 5 ₂ are electrically connected to each other, through an electric circuit board 2 in the thickness direction The inside is filled with a conductive material such as copper. Further, through hole 5c for the wiring pattern 5 _second termination and the external connection terminal 4 is electrically connected to each other, through an electric circuit board 2 in the thickness direction, a conductive material such as copper therein Are filled and formed.

The electric circuit board 2 has divided cores (core members) 6 that form LPFs, which are noise filters for reducing high frequency components from the output of the digital amplifier 3, and wiring patterns 5 ₁ , 5 ₂ therein. Are provided so as to penetrate each of them. The split core 6 has a cylindrical outer shape and is made of a magnetic material such as ferrite. About the said external dimension, what is necessary is just to set according to the frequency of the high frequency component to reduce. In addition to ferrite, Sendust, Permalloy dust, iron carbonyl dust, and mixtures thereof can be used as the magnetic material. A part of each wiring pattern 5 ₁ , 5 ₂ penetrates inside the split core 6 along the axial direction of the split core 6. The other portions of the wiring patterns 5 ₁ , 5 ₂ are formed along the axial direction of the divided core 6 while facing the outer peripheral surface of the divided core 6.

  And in the electric circuit board 2, the attachment hole (hole part) 2a for attaching the division | segmentation core 6 to the division | segmentation core 6 is in the position close | similar to the edge part provided with the external connection terminal 4 of the electric circuit board | substrate 2. The electric circuit board 2 is provided through the thickness direction. The attachment hole 2 a is formed so that the opening end thereof is substantially rectangular from the thickness direction of the electric circuit board 2. Moreover, it is preferable that the long side part of the said opening edge part is substantially parallel to the edge part provided with the external connection terminal 4 of the electric circuit board 2.

  In addition, the split core 6 is configured so that the electric circuit board 2 is formed in a core shape from the end side portion having the external connection terminal 4 to the outer side edge of the electric circuit board 2 to the long side portion near the end side portion in the mounting hole 2a. It is formed so as to cover from above and below in the thickness direction. Thereby, the divided core 6 is divided by the electric circuit board 2 with a portion sandwiching the electric circuit board 2 as a gap, and the divided core 6 is divided by the gap interval and the relative dielectric constant of the electric circuit board 2. The permeability can be controlled.

Therefore, each wiring pattern 5 ₁ , 5 ₂ is wound twice along the axial direction of the divided core 6 along the axial direction of the divided core 6 in the present embodiment, and connected to the digital amplifier 3 and externally. Since the terminals 4 are provided so as to be electrically connected to each other, the inductance can be increased by the split core 6 in series.

Also, each wiring pattern 5 ₁ , 5 ₂ has a capacitance between the wiring pattern 5 ₁ , 5 ₂ and the ground pattern of the electric circuit board 2 at a position corresponding to each wiring pattern 5 ₁ , 5 ₂ that faces or is close to them. Can be formed in parallel.

Therefore, in the digital amplifier equipped with the noise reduction circuit of the present invention, each wiring pattern 5 ₁ , 5 ₂ can constitute an LPF by the series inductance (L) and the parallel capacitance (C). Therefore, unnecessary high-frequency components (which cause problems and inconveniences) included in the amplified output from the digital amplifier 3 can be removed by the LPF.

  Moreover, in the digital amplifier provided with the noise reduction circuit of the present invention, the split core 6 is provided so as to be embedded in the electric circuit board 2 by using the mounting hole 2a. The external dimensions of the noise reduction circuit including the core 6 can be reduced and the size is reduced.

  In the present embodiment, the wiring pattern 5 of the electric circuit board 2 has an example of two layers. However, the wiring pattern 5 may be three or more layers. In this case, if the number of layers is increased, the wiring pattern 5 becomes an electric circuit. Since it is also formed between the layers of the substrate 2, the number of turns of the wiring pattern 5 penetrating the divided core 6 can be increased, and the noise reduction effect can be further improved.

  In addition, in order to reduce noise in the output circuit portion and the power supply portion circuit portion of the digital amplifier 3, which are large current circuit portions, in the present invention, the copper foil thickness of the wiring pattern 5 on the electric circuit board 2 is increased. Just do it.

  When the noise reduction circuit of the present invention is used in a digital amplifier that amplifies a pulse signal by a switching operation, the digital amplifier can reduce the high-frequency component from the amplified output from the digital amplifier and can downsize the digital amplifier. High-frequency components can be reduced from the output from electronic devices such as DVD, CD / MD audio function units, electronic devices such as communication devices that amplify digital signals, and electronic devices such as motors and inverters of fluorescent lamps. Since the electronic device can be downsized, it can be suitably used in the audio field, communication field, power field, and lighting field.

It is a perspective view which shows the one surface of the digital amplifier provided with the circuit for noise reduction of embodiment based on this invention. It is a perspective view which shows the two-layer surface side of the said digital amplifier. It is a top view which shows the conventional digital amplifier. It is the graph which each represented the noise level change radiated | emitted from the digital amplifier with respect to the number of turns of the wiring wire of a core in the said conventional.

Explanation of symbols

2 Electric circuit board 2a Mounting hole (hole)
3 Digital amplifier (amplification means)
5 Wiring pattern 6 Divided core (core member)

Claims (11)

An electric circuit board provided with a hole penetrating in the thickness direction;
A core member made of a magnetic material formed so as to cover the substrate in a core shape from the outer edge of the electric circuit board to the hole;
A circuit for noise reduction, comprising: a wiring pattern that is wound around the hole portion once or a plurality of times so as to pass through the inside of the core member. The electrical circuit board includes a multilayer board,
The noise reduction circuit according to claim 1, wherein the wiring pattern is formed on at least one of a surface of the multilayer substrate and each layer.   The noise reduction circuit according to claim 2, wherein the electric circuit board has a ground pattern corresponding to the wiring pattern.   4. The noise reduction circuit according to claim 1, wherein the electric circuit board is made of a thin plate material.   5. The noise reduction circuit according to claim 1, wherein the electric circuit board has a relative dielectric constant of 3 to 5. 5.   6. The noise reduction according to claim 1, wherein the magnetic body is at least one selected from the group consisting of ferrite, sendust, permalloy dust, and iron carbonyl dust. Circuit.   The noise reduction circuit according to claim 1, wherein the core material is formed in a columnar shape having a central axis along the surface direction of the electric circuit board.   The noise reduction circuit according to claim 1, wherein the core material has a divided core shape in which a gap is formed by the electric circuit board. A noise reduction circuit according to any one of claims 1 to 8,
Amplifying means for amplifying the digital signal;
The digital amplifier, wherein the amplifying means is connected to the wiring pattern and provided alongside the electric circuit board.   10. The digital amplifier according to claim 9, wherein the amplifying means is a class D amplifier that amplifies a signal by a switching operation. An electronic apparatus comprising the noise reduction circuit according to any one of claims 1 to 8, or the digital amplifier according to claim 9 or 10.

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