JP5879679B2 - Circuit board and arrangement method of noise countermeasure component - Google Patents

Description

  The present invention relates to a circuit board and a noise countermeasure component placement method, and more particularly, to a circuit board on which a noise countermeasure component is mounted and a noise countermeasure component placement method.

  In recent years, with the downsizing, thinning, and high-speed driving of portable electronic devices, noise generated from digital circuits in portable electronic devices is mixed into the receiving circuit via the antenna, so-called a phenomenon that degrades the reception sensitivity. Self-contamination is a problem. Here, Non-Patent Document 1 discloses a technique for evaluating the optimum arrangement location of a noise source from the degree of overlap (correlation) of the magnetic field distribution of the noise source and the antenna in the self-contamination problem. .

  According to the technique described in Non-Patent Document 1, it is shown that the optimal arrangement location of the noise source can be set based on the correlation coefficient calculated from the magnetic field distribution of the antenna and the magnetic field distribution of the noise source. That is, according to this technique, for example, noise countermeasures can be taken by laying out such that the overlap between the magnetic field distribution of a noise source such as an IC or wiring and the magnetic field distribution of an antenna becomes small.

Tomoya Maekawa, Hideki Iwaki, Toru Yamada, Junichi Ogawa, “Proposal of Optimal Noise Source Placement Method Using Near Magnetic Field Distribution”, IEICE Technical Report, The Institute of Electronics, Information and Communication Engineers, EMCJ 2008-14 (2008-6), p41-46

  As described above, according to the technique described in Non-Patent Document 1, noise countermeasures can be taken by changing the layout of the circuit board. However, changing the layout of the circuit board may require a large amount of labor and man-hours. Further, if noise countermeasures cannot be performed without changing the layout, there is a problem that the degree of freedom in circuit board design is hindered.

  The present invention has been made to solve the above problems, and provides a circuit board capable of reducing the noise level without changing the layout of the circuit board, and a method for arranging noise countermeasure components. For the purpose.

  A circuit board according to the present invention is a circuit board on which a plurality of electronic components are mounted. The circuit board is included in the plurality of electronic components and is in the vicinity of the electronic component that is a noise source and the electronic component that is the noise source. And a closed annular loop conductor arranged at a position where a magnetic field generated around a noise source passes by a current flowing in the circuit.

  According to the circuit board of the present invention, the closed loop-shaped conductor is disposed in the vicinity of the electronic component that becomes the noise source and at a position where the magnetic field generated around the noise source by the current flowing through the noise source passes. The By the way, when a magnetic field generated from a noise source passes through a loop of a closed annular loop conductor, an induced current is induced in the loop conductor in accordance with a change in magnetic flux density. This induced current flows in a direction that prevents a change in magnetic flux density due to a noise source. Therefore, the current leaked from the noise source to the circuit board can be reduced by preventing the magnetic flux density from being changed by the noise source by the induced current. As a result, the noise level can be reduced without changing the layout of the circuit board.

  In the circuit board according to the present invention, it is preferable that the loop conductor is arranged at a position where the central axis of the loop is substantially parallel to the direction of the magnetic field generated by the current flowing through the noise source.

  In this case, the magnetic flux passing through the region surrounded by the loop conductor increases, and the amount of change in the magnetic flux density increases accordingly. Therefore, the induced current induced in the loop conductor increases so as to prevent the magnetic flux density from being changed by the noise source. Therefore, it becomes possible to reduce noise more effectively.

  The circuit board according to the present invention is preferably provided with an antenna for receiving and / or transmitting radio waves.

  As described above, the current leaked from the noise source to the circuit board is reduced by preventing the magnetic flux density from being changed by the noise source due to the induced current induced in the loop conductor. Therefore, the coupling between the noise source and the antenna can be reduced. As a result, the S / N ratio of the reception power of the antenna is improved, and the reception sensitivity can be improved.

  In the circuit board according to the present invention, the loop-shaped conductor is formed so that the conductor is wound a plurality of times and the start end and the end of the conductor are connected through the inside of the wound loop. It is preferable.

  In this case, since the conductor is wound a plurality of times to form the loop conductor, the induced current induced in the loop conductor can be increased. Therefore, the noise reduction effect can be further enhanced. Further, since the start end and the end of the loop-shaped conductor are connected to each other through the inside of the loop, the area surrounded by the loop can be increased. Therefore, even when the size is limited, noise can be reduced more efficiently.

  Further, the loop-shaped conductor may be formed so that the conductor is wound a plurality of times, and the start end and the end of the conductor are connected through the outside of the wound loop.

  In this case, since the conductor is wound a plurality of times to form the loop conductor, the induced current induced in the loop conductor can be increased. Therefore, the noise reduction effect can be further enhanced. In addition, since the start end and the end end of the loop-shaped conductor are connected to each other through the outside of the loop, manufacturing is easy and production efficiency can be improved.

  In the circuit board according to the present invention, it is preferable that a lumped component is inserted in the middle of the loop of the loop-shaped conductor.

  In this way, it is possible to control the impedance of the entire loop without changing the shape of the loop conductor itself. For example, by inserting a coil (inductance) or a capacitor (capacitance) as a lumped component, the resonance frequency of the loop conductor can be controlled. For example, the resonance frequency is adjusted to the noise frequency. Can do. In that case, since the impedance becomes maximum with respect to noise corresponding to a narrow band centered on the resonance frequency, the noise can be more effectively reduced. Further, for example, by inserting a resistor as a lumped constant component, when an induced current is induced so as to prevent a change in magnetic flux density due to a noise source, the induced current can be changed to heat.

  In the circuit board according to the present invention, it is preferable that the loop-shaped conductor includes a wiring pattern formed on the circuit board, and the loop is formed through the wiring pattern.

  In this way, since there is no gap between the loop conductor and the circuit board, the gap between the loop conductor and the circuit board is smaller than when the loop conductor is arranged away from the circuit board. There is no passing magnetic field. Therefore, the noise reduction effect can be improved. Further, since the loop-shaped conductor is directly attached to the circuit board, the reliability of the attachment and the accuracy of the attachment position can be improved.

  In the circuit board according to the present invention, it is preferable that a lumped component is inserted in the middle of the wiring pattern.

  Also in this case, as described above, the impedance of the entire loop can be controlled without changing the shape of the loop conductor itself. For example, since the resonance frequency can be controlled by inserting a coil (inductance) or a capacitor (capacitance) as a lumped constant component, for example, the resonance frequency can be matched to the noise frequency. Further, for example, by inserting a resistor as a lumped constant component, when an induced current is induced so as to prevent a change in magnetic flux density due to a noise source, the induced current can be changed to heat. Further, in this case, by using a chip type electronic component such as a chip capacitor or a chip resistor as the lumped constant component, the mounter of the chip type electronic component can be used for mounting, thereby improving productivity. Can do.

  The noise countermeasure component placement method according to the present invention includes a noise source specifying step for specifying a noise source included in a circuit board on which a plurality of electronic components are mounted, and a current flowing through the noise source specified in the noise source specifying step. The magnetic field direction specifying step for specifying the direction of the magnetic field generated around the noise source, the magnetic field direction of the noise source specified in the vicinity of the noise source and in the magnetic field direction specifying step, and the center axis of the loop are approximately. A disposing step of disposing a closed annular loop conductor at a parallel position.

  According to the arrangement method of the noise countermeasure component according to the present invention, the closed loop-shaped conductor is disposed in the vicinity of the noise source and at a position where the magnetic field generated around the noise source by the current flowing through the noise source passes. The Therefore, the current leaked from the noise source to the circuit board can be reduced by preventing the magnetic flux density from being changed by the noise source due to the induced current induced in the loop conductor. As a result, the noise level can be reduced without changing the layout of the circuit board.

  According to the present invention, since the closed loop-shaped conductor is disposed in the vicinity of the noise source and at a position where the magnetic field generated by the current flowing through the noise source passes, the layout of the circuit board is not changed. It becomes possible to reduce the noise level.

It is the perspective view and principal part enlarged view which show the structure of the circuit board which concerns on 1st Embodiment. It is a top view which shows the direction (magnetic line of force) of the magnetic field in the circuit board which concerns on 1st Embodiment. It is a top view which shows the direction (magnetic line of force) of a magnetic field when there is no loop-shaped conductor. It is a graph which shows the simulation result of insertion loss. It is a figure which shows the loop-shaped conductor used for the circuit board which concerns on 2nd Embodiment. It is a figure which shows the loop-shaped conductor used for the circuit board which concerns on 3rd Embodiment. It is a figure which shows the loop-shaped conductor used for the circuit board which concerns on 4th Embodiment. It is a figure which shows the loop-shaped conductor attached to the circuit board which concerns on 5th Embodiment. It is a figure which shows the loop-shaped conductor attached to the circuit board which concerns on 6th Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted.

[First Embodiment]
First, the configuration of the circuit board 10 according to the embodiment will be described with reference to FIG. FIG. 1 is a perspective view and a main part enlarged view showing the configuration of the circuit board 10.

  The circuit board 10 is a rectangular double-sided board. The circuit board 10 includes a rectangular substrate (insulating layer) 11 made of a dielectric such as FR-4. Wiring layers 12 and 13 including a circuit pattern made of a conductor such as copper foil, a power supply pattern, and a ground pattern are formed on both surfaces of the substrate 11 by a method such as etching. Here, in the present embodiment, the wiring layer 12 is a solid ground layer (hereinafter, the wiring layer 12 may be referred to as a ground layer 12). In FIG. 1, the details of the pattern are not shown. Further, the shape of the circuit board 10 is not limited to a rectangle. Furthermore, the circuit board 10 is not limited to a double-sided board, and may be a single-sided board or a multilayer board.

  An antenna 20 is connected to the upper end of the circuit board 10. In the present embodiment, a monopole antenna formed using a copper wire (φ = 1 mm) is used as the antenna 20. In addition, an IC 30 serving as a noise source and a plurality of electronic components (not shown) are mounted on the circuit board 10 by soldering or the like.

  As IC30 used as a noise source, the power supply IC used for a switching regulator etc. are mentioned, for example. In the power supply IC, for example, noise occurs due to current flowing between the ground in the power supply IC and the ground on the circuit board 10 side to which the ground terminal of the power supply IC is connected. If the noise generated in this way enters the antenna 20, there is a possibility that the reception sensitivity is deteriorated.

  On the circuit board 10, a closed annular loop conductor 40 is attached to the vicinity of the IC 30 serving as a noise source (left adjacent in FIG. 1) by an adhesive material, an adhesive, or soldering. The loop-shaped conductor 40 is formed in a “mouth” shape by a wire made of a metal (conductor) such as copper having a rectangular cross section. In addition, the cross-sectional shape of the used wire is not limited to a rectangle, and may be, for example, a circle, an ellipse, or a polygon. Further, the shape of the loop is not limited to the “mouth” shape, and may be, for example, a ring shape or a polygonal shape. The size of the loop conductor 40 can be set arbitrarily. However, for example, 0603 size (0.6 × 0.3 × 0.3 mm) or 1005 size (1.0 × 0.5 × 0.5 mm) used in SMD (Surface Mount Device). It is preferable that the standard size is unified.

  When the loop-shaped conductor 40 is attached to the circuit board 10, a position where a magnetic field generated around the IC 30 due to a current flowing in the ground of the IC 30 serving as a noise source passes, more preferably, the central axis of the loop-shaped conductor 40 is a noise. It is disposed at a position that is substantially parallel to the direction of the magnetic field generated by the source (that is, a position where the opening surface of the loop and the magnetic field are substantially orthogonal). The loop-shaped conductor 40 only needs to be arranged at a position where the central axis thereof is substantially parallel to the direction of the magnetic field generated around the IC 30. The arrangement is as shown in FIG. For example, the IC 30 may be any one of the top, bottom, front, back, left and right of the IC 30.

  Here, a method for arranging the loop-shaped conductor 40 will be described. First, an IC 30 (hereinafter also simply referred to as “noise source 30”) serving as a noise source is specified from electronic components mounted on the circuit board 10 (noise source specifying step). More specifically, the noise source 30 can be specified by measuring a magnetic field generated when a current flows. Note that the noise source 30 may be specified by measuring the electric field instead of the magnetic field.

  Subsequently, the direction of the magnetic field generated around the noise source 30 by the current flowing through the specified noise source 30 is specified (magnetic field direction specifying step). More specifically, when a magnetic field probe is applied to the noise source 30, the direction of the magnetic field can be specified from the directionality of the magnetic field probe.

  Then, a closed loop-shaped conductor 40 is disposed in the vicinity of the noise source 30 and at a position substantially parallel to the central axis of the loop with respect to the magnetic field direction of the specified noise source 30 (arrangement). Step).

  As described above, according to the circuit board 10, the loop conductor 40 has a magnetic field generated around the IC 30 by the current flowing in the ground of the IC 30 and the central axis of the loop in the vicinity of the IC 30 that is a noise source. It arrange | positions in the position used as substantially parallel (preferably parallel).

  Here, FIG. 2 shows the direction of magnetic field (lines of magnetic force) around the noise generation source 31 (the portion where noise generation is specified) 31 and the loop conductor 40 in the IC (noise source) 30 50 mm above the circuit board 10. Further, FIG. 3 shows the direction of magnetic field (lines of magnetic force) around the noise source 31 when there is no loop-like conductor 40. 2 and 3, the noise generation source 31 simulates the wiring connecting the ground in the IC 30 and the ground of the circuit board 10, and the tip of the noise generation source 31 is made of sheet metal or wire. A shorted loop (1 mm × 1 mm) was formed.

  As indicated by an arrow in FIG. 3, when there is no loop conductor 40, the magnetic field (lines of magnetic force) of the noise generation source 31 exits from one end of the noise generation source 31 in the Y-axis direction, and is not disturbed. (Or an ellipse) is drawn toward the other end of the noise source 31. On the other hand, the loop-shaped conductor 40 is disposed in the vicinity of the noise source 31 and at a position where the center axis of the loop is parallel to the Y axis (that is, the direction of the magnetic field) (above the noise source 31 in FIG. 2). In this case, since an induced current is induced in the loop conductor 40 so as to prevent the magnetic flux density from being changed by the noise source 31, as shown in FIG. 2, the magnetic field (magnetic field lines) of the noise source 31 emitted in the Y-axis direction is used. ) Is distorted and disturbed by the loop conductor 40. As described above, the magnetic field excited by the current of the noise generation source 31 is disturbed by the induced current induced in the loop conductor 40, so that the current leaked from the noise generation source 31 to the circuit board 10 is reduced. Therefore, the coupling between the noise generation source 31 and the antenna 20 is reduced. As a result, the S / N ratio of the reception power of the antenna 20 is improved, and the reception sensitivity is improved.

  In order to confirm the noise countermeasure effect of the circuit board 10 according to the present embodiment, the insertion loss, which is an amount quantitatively indicating the isolation between the antenna 20 and the noise generation source 31, was analyzed by electromagnetic field simulation. Next, referring to FIG. 4, the noise countermeasure effects of the circuit board 10 according to the present embodiment and the circuit board (comparative example) not provided with the loop-shaped conductor 40 will be described by showing simulation results. Here, in the simulation, the size of the circuit board 10 is the length L: 80 mm, the width W is 40 mm, the thickness t is 1 mm, the size of the antenna 20 is the diameter φ: 1 mm, the length L is 80 mm, and the noise generation source. The size of 31 was set as length L: 1 mm, width W: 0.5 mm, and thickness t: 1 mm. Further, the size of the loop-shaped conductor 40 was set to a length L: 1 mm, a width W: 1 mm, and a thickness t: 1 mm.

  Using the circuit board 10 according to the present embodiment shown in FIG. 2 and the circuit board (comparative example) in which the loop conductor 40 shown in FIG. 3 is not provided, the S parameter S21 is obtained and the result is obtained. The noise countermeasure effect of each of the circuit board 10 and the comparative example was evaluated. Note that S21 is a ratio transmitted to port 2 (antenna 20) when a signal is input to port 1 (noise generation source 31), that is, a forward transmission coefficient. Therefore, it can be evaluated that the smaller the value of S21, the larger the insertion loss, that is, the greater the noise countermeasure effect.

  FIG. 4 shows the simulation results of the circuit board 10 according to the present embodiment shown in FIG. 2 and the circuit board (comparative example) in which the loop conductor 40 shown in FIG. 3 is not provided. The horizontal axis of the graph shown in FIG. 4 is frequency (GHz), and the vertical axis is S21 (dB). In the graph of FIG. 4, the simulation result (S21) of the circuit board 10 is indicated by a solid line, and the simulation result (S21) of the comparative example is indicated by a broken line.

  As shown in FIG. 4, in the circuit board 10 according to the present embodiment, compared with a circuit board (comparative example) in which the loop-shaped conductor 40 is not provided, in a frequency region of 0.7 to 1.1 GHz, It was confirmed that S21 decreased (that is, insertion loss increased) by about 3 to 6 dB, and isolation (coupling) between the antenna 20 and the noise source 31 was improved.

  According to the present embodiment, the closed loop-shaped conductor 40 is disposed in the vicinity of the noise generation source 31 (noise source 30) and at a position where a magnetic field generated by the current flowing through the noise generation source 31 passes. Therefore, an induced current is induced in the loop conductor 40 so as to prevent the magnetic flux density from being changed by the noise generation source 31, and the magnetic field (lines of magnetic force) generated by the noise generation source 31 is distorted and disturbed by the loop conductor 40. As described above, the magnetic field excited by the current of the noise generation source 31 is disturbed by the induced current induced in the loop conductor 40, so that the current leaked from the noise generation source 31 to the circuit board 10 is reduced. As a result, the noise level mixed in the receiving circuit via the antenna 20 can be reduced without changing the layout of the circuit board 10.

  Further, according to the present embodiment, the loop conductor is located at a position where the central axis of the loop is substantially parallel to the direction of the magnetic field generated around the noise source 31 due to the current flowing through the noise source 31 (noise source 30). 40 is arranged. Therefore, the magnetic flux passing through the region (inside the loop) surrounded by the loop conductor 40 increases, and the amount of change in the magnetic flux density increases accordingly. For this reason, the induced current induced in the loop-shaped conductor 40 increases so as to prevent the magnetic flux density from being changed by the noise source 31. Therefore, it becomes possible to reduce noise more effectively.

  Further, according to the present embodiment, as described above, the induced current induced in the loop conductor 40 prevents the magnetic flux density from being changed by the noise generation source 31 (noise source 30). Current leaks from the circuit board 10 to the circuit board 10. Therefore, the coupling between the noise generation source 31 and the antenna 20 can be reduced. As a result, the S / N ratio of the reception power of the antenna 20 is improved, and the reception sensitivity can be improved.

[Second Embodiment]
In the circuit board 10 described above, the loop conductor 40 having one turn (single) is used, but the number of turns of the loop conductor is not limited to one, and may be wound a plurality of times. Next, the configuration of the loop conductor used in the circuit board according to the second embodiment will be described with reference to FIG. FIG. 5 is a diagram showing a configuration of the loop conductor 41 used in the circuit board according to the present embodiment. Other circuit board configurations are the same as those of the first embodiment described above, and are not shown.

  The loop-shaped conductor 41 is different from the loop-shaped conductor 40 described above in that a linear conductor having a rectangular cross section is formed by winding three times. Moreover, in the loop-shaped conductor 41, the starting end and termination | terminus of a linear conductor are connected through the outer side of the wound loop. In addition, the frequency | count of winding is not restricted to 3 times, 2 times or 4 times or more may be sufficient. Other configurations are the same as or similar to the loop-shaped conductor 40 described above, and thus detailed description thereof is omitted here. The loop-shaped conductor 41 is also arranged in the vicinity of the IC 30 serving as a noise source, and at a position where the magnetic field generated around the IC 30 due to the current flowing in the ground of the IC 30 and the central axis of the loop are substantially parallel (more preferably parallel). Is done.

  According to this embodiment, since the linear conductor is wound three times to form the loop conductor 41, the induced current induced in the loop conductor 41 can be increased. Therefore, the noise reduction effect can be further enhanced. Moreover, since it is comprised so that the start end and termination | terminus of the loop-shaped conductor 41 may pass through the outer side of a loop, manufacture is easy and can improve production efficiency.

[Third Embodiment]
In the loop-shaped conductor 41 described above, the starting end and the terminal end of the linear conductor are connected through the outside of the wound loop, but may be configured to be connected through the inside of the loop. . Next, the configuration of the loop-shaped conductor used in the circuit board according to the third embodiment will be described with reference to FIG. FIG. 6 is a diagram showing a configuration of the loop conductor 42 used in the circuit board according to the present embodiment. Other circuit board configurations are the same as those of the first embodiment described above, and are not shown.

  The loop-shaped conductor 42 is the same as the loop-shaped conductor 41 described above in that a linear conductor having a rectangular cross section is wound three times, but the start and end of the linear conductor are wound. It differs from the loop conductor 41 described above in that it is connected through the inside of the loop. Since other configurations are the same as or similar to the loop-shaped conductor 41 described above, detailed description thereof is omitted here. The loop conductor 42 is also arranged in the vicinity of the IC 30 that is a noise source, and at a position where the magnetic field generated around the IC 30 due to the current flowing in the ground of the IC 30 and the central axis of the loop are substantially parallel (more preferably parallel). Is done.

  According to the present embodiment, since the linear conductor is wound three times to form the loop conductor 42, the induced current induced in the loop conductor 42 can be increased. Therefore, the noise reduction effect can be further enhanced. Moreover, since the start end and the end of the loop-shaped conductor 42 are configured to be connected through the inside of the loop, the area surrounded by the loop can be further increased. Therefore, even when the size is limited, noise can be reduced more efficiently.

[Fourth Embodiment]
Next, the configuration of the loop conductor used in the circuit board according to the fourth embodiment will be described with reference to FIG. FIG. 7 is a diagram illustrating a configuration of the loop conductor 43 used in the circuit board according to the present embodiment. Other circuit board configurations are the same as those of the first embodiment described above, and are not shown.

  The loop conductor 43 is different from the loop conductor 42 described above in that a lumped constant component 50 is inserted in the middle of the loop and a loop is formed via the lumped constant component 50. Since the other configuration is the same as or similar to the loop-shaped conductor 42 described above, detailed description thereof is omitted here. Here, examples of the lumped constant component 50 include a coil (inductance), a capacitor (capacitance), and a resistance. In the present embodiment, the lumped constant component 50 is inserted into the loop-shaped conductor 42 described above. However, the lumped constant component 50 is inserted into the loop-shaped conductor 40 or the loop-shaped conductor 41 described above instead of the loop-shaped conductor 42. It is good also as a structure.

  The loop-shaped conductor 43 is also arranged in the vicinity of the IC 30 that is a noise source, and at a position where the magnetic field generated around the IC 30 due to the current flowing through the ground of the IC 30 and the central axis of the loop are substantially parallel (more preferably parallel). Is done.

  According to this embodiment, it is possible to control the impedance of the entire loop without changing the shape of the loop conductor 43 itself. For example, the resonance frequency of the loop conductor 43 can be controlled by inserting a coil (inductance) or a capacitor (capacitance) as the lumped constant component 50. Can be matched. In that case, since the impedance becomes maximum with respect to noise corresponding to a narrow band centered on the resonance frequency, the noise can be more effectively reduced. In addition, for example, when an induced current is induced so as to prevent a change in magnetic flux density by the noise source 30 (noise generation source 31) by inserting a resistor as the lumped constant component 50, the induced current is converted into heat. Can be changed.

[Fifth Embodiment]
Next, the configuration of the circuit board according to the fifth embodiment will be described with reference to FIG. FIG. 8 is a diagram illustrating a configuration of the loop conductor 44 attached to the circuit board 10D according to the present embodiment. In FIG. 8, the same or equivalent components as those in the first embodiment described above are denoted by the same reference numerals.

  The loop conductor 44 includes an open loop conductor 44O and a wiring pattern (the ground layer 12 in the present embodiment) formed on the circuit board 10D that connects both ends of the open loop conductor 44O. This is different from the loop-shaped conductor 40 described above in that a loop is formed via the (ground layer 12). Other configurations are the same as or similar to the loop-shaped conductor 40 described above, and thus detailed description thereof is omitted here.

  The open loop conductor 44O is a conductive member formed in a “U” shape with an opening directed toward the circuit board 10D. As described above, in the loop conductor 44, a loop is formed by the open loop conductor 44 O and the ground layer (wiring pattern) 12. Both ends of the open loop conductor 44O are connected to the ground layer 12 of the circuit board 10D by soldering. In the present embodiment, the ground layer 12 is used as a wiring pattern for connecting both ends of the open loop conductor 44O. However, a dedicated wiring pattern may be formed on the circuit board. Further, the shape of the open loop conductor 44O is not limited to the “U” shape, and may be, for example, a “U” shape.

  The size of the open loop conductor 44O can be set arbitrarily. However, for example, it is preferable that the standard sizes such as 0603 size and 1005 size adopted in SMD are unified. The open-loop conductor 44O is mounted by a chip mounter after solder printing on the circuit board 10 by a cream solder printer, for example, as in a general SMD. However, it is fixed to the circuit board 10 by being melted. The loop conductor 44 is also arranged in the vicinity of the noise generation source 31 and at a position where the magnetic field generated by the current flowing through the noise generation source 31 and the central axis of the loop are substantially parallel (more preferably parallel). .

  According to the present embodiment, since there is no gap between the loop conductor 44 and the circuit board 10D, the loop conductor 44 and the circuit board are compared with the case where the loop conductor is disposed away from the circuit board. There is no magnetic field passing between 10D. Therefore, the noise reduction effect can be improved. Moreover, since the loop-shaped conductor 44 is directly attached to the circuit board 10D by soldering, the attachment reliability and the accuracy of the attachment position can be improved.

[Sixth Embodiment]
Next, the configuration of the circuit board according to the sixth embodiment will be described with reference to FIG. FIG. 9 is a diagram showing a configuration of the loop-shaped conductor 45 attached to the circuit board 10E according to the present embodiment. In FIG. 9, the same or equivalent components as those in the fifth embodiment described above are denoted by the same reference numerals.

  The loop conductor 45 is formed on the circuit board 10E, and the wiring pattern 14 that connects one end of the open loop conductor 44O and one end of the lumped component 50, the other end of the lumped component 50, and the ground layer 12 Is different from the loop-shaped conductor 44 described above in that it includes a wiring pattern 15 for connecting. Further, in the loop-shaped conductor 45, the above-described loop-shaped conductor 44 and the above-described loop-shaped conductor 44 are different in that the lumped constant component 50 is inserted in the middle of the wiring patterns 14 and 15 (and the ground layer 12) connecting both ends of the open-loop conductor 44O. Is different. That is, in the loop-shaped conductor 45, a loop is formed by the open-loop-shaped conductor 44 O, the wiring patterns 14 and 15, the lumped constant component 50, and the ground layer (wiring pattern) 12. Other configurations are the same as or similar to those of the loop-shaped conductor 44 described above, and thus detailed description thereof is omitted here. As described above, the lumped constant component 50 includes a coil (inductance), a capacitor (capacitance), and a resistance.

  The loop conductor 45 is also disposed in the vicinity of the noise generation source 31 and at a position where the magnetic field generated by the current flowing through the noise generation source 31 and the central axis of the loop are substantially parallel (more preferably parallel).

  According to the present embodiment, as described above, the impedance of the entire loop can be controlled without changing the shape of the loop conductor 45 itself. For example, the resonance frequency of the loop conductor 45 can be controlled by inserting a coil (inductance) or a capacitor (capacitance) as the lumped constant component 50. Can be matched. Further, for example, by inserting a resistor as the lumped constant component 50, when an induced current is induced so as to prevent a change in magnetic flux density due to a noise source, the induced current can be changed to heat. Furthermore, according to the present embodiment, since a chip type electronic component such as a chip capacitor or a chip resistor is used as the lumped constant component 50, the mounter of the chip type electronic component can be used for mounting. Can be improved.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, one loop conductor 40 to 45 is arranged on the circuit boards 10, 10 </ b> D, and 10 </ b> E, but a plurality of loop conductors 40 to 45 may be arranged.

10, 10D, 10E Circuit board 11 Board (insulating layer)
12 Wiring layer (ground layer)
13 Wiring layer 14, 15 Wiring pattern 20 Antenna 30 IC
31 Noise source 40, 41, 42, 43, 44, 45 Loop conductor 44O Open loop conductor 50 Lumped constant components

Claims (6)

In a circuit board on which a plurality of electronic components are mounted and an antenna for receiving and / or transmitting radio waves is attached,
Electronic components included in the plurality of electronic components mounted on the circuit board and identified as noise sources,
The magnetic field is generated in the vicinity of the electronic component specified as the noise source and in accordance with the direction of the magnetic field specified to be generated around the electronic component by the current flowing through the electronic component specified as the noise source. A three-dimensionally formed closed annular loop-shaped conductor that is disposed and attached at a passing position ;
The circuit board, wherein the loop conductor includes a ground layer formed on the circuit board, and a loop through which an induced current flows is formed through the ground layer .   2. The loop-shaped conductor is disposed at a position where a central axis of the loop is substantially parallel to a direction of a magnetic field generated by a current flowing through an electronic component specified as the noise source. Circuit board. The circuit board according to claim 1 or 2, characterized in that lumped components are inserted in the middle of the loop of the loop-shaped conductor.   The circuit board according to claim 1, wherein the loop-shaped conductor includes a wiring pattern formed on the circuit board, and a loop through which an induced current flows is formed via the wiring pattern. The circuit board according to claim 4 , wherein a lumped constant component is inserted in the middle of the wiring pattern. A noise source specifying step for specifying a noise source included in a circuit board on which a plurality of electronic components are mounted and an antenna for receiving and / or transmitting radio waves is attached;
A magnetic field direction specifying step for specifying a direction of a magnetic field generated around the noise source by a current flowing through the noise source specified in the noise source specifying step;
An annular loop-shaped conductor closed is disposed in the vicinity of the noise source and at a position where the magnetic field direction of the noise source specified in the magnetic field direction specifying step is substantially parallel to the central axis of the loop. A placement step for attaching ,
In the arranging step, the loop conductor is arranged and attached so as to form a loop including a ground layer formed on the circuit board and through which an induced current flows. How to arrange countermeasure parts.

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