JP4992394B2 - Printed wiring board - Google Patents

Description

  The present invention relates to a printed wiring board in which a ground layer, an insulating layer, and a power supply layer are laminated, and more particularly to a printed wiring board on which an analog circuit and a digital circuit are mixedly mounted.

  When a digital circuit and an analog circuit are mounted on a printed wiring board, it is necessary to consider interference between the digital circuit and the analog circuit. Such interference problems between digital circuits and analog circuits often reduce the degree of design freedom of circuit designers, and in order to prevent this interference, the arrangement of each circuit is devised and the electromagnetic separation between each other is improved. It is necessary to devise such as securing the above (see, for example, Patent Document 1).

On the other hand, as a configuration for suppressing noise emission to the space of the power supply noise, the dielectric constant of the insulating layer is increased (refer to Patent Document 2) or decreased at the center portion and the peripheral portion of the printed wiring board (Patent Document 3). Technology) is disclosed. However, in these techniques, in order to obtain the effect, the surroundings must be surrounded and different insulating layers must be disposed, and the mounting positions of components are limited.
Japanese Patent Laid-Open No. 3-214486 JP 2005-129618 A JP-A-9-0077331

  However, for example, in the method according to Patent Document 1, it is necessary to newly provide a dedicated metal case, which greatly restricts mounting design.

  Further, in order to prevent interference between the digital circuit and the analog circuit, it is not a structure covering the periphery like a metal case, but a shield member made of a conductive material such as metal for the purpose of providing an electromagnetic shield on a part, for example, Therefore, a configuration such as adding a cover or the like, and separately providing each ground of the digital circuit and the analog circuit is a widely used technique, not to mention literature.

  Needless to say, the addition of the shielding member as described above places many restrictions on the mounting design of the printed wiring board, and the separation of the ground complicates the ground wiring system inside the electronic device. It was something that narrowed the degree.

  Patent Document 2 and Patent Document 3 are technologies devised for other purposes, and in order to solve the problems posed by the present invention, there are restrictions on the mounting position of different insulators and the like, which can be used effectively. It wasn't.

  When a circuit that is desired to avoid mutual electromagnetic interference, for example, an analog circuit and a digital circuit are mounted on the same printed wiring board, techniques such as placement of electromagnetic shields and ground separation have been used. However, these limit the mounting design of the printed wiring board and make the design difficult.

  Therefore, the present invention provides a printed wiring board that has a simple structure, reduces electromagnetic noise transmitted from the power supply of an arbitrary power supply layer to the power supply of another power supply layer, and can improve the degree of freedom of design of the printed wiring board. The purpose is to provide.

In order to achieve the above-described object, a printed wiring board according to the present invention includes a plurality of power supply layers independent from each other in direct current, a ground layer disposed to face these power supply layers, and between the power supply layer and the ground layer. And a plurality of insulating layers provided corresponding to the respective power supply layers. Of the plurality of insulating layers , the dielectric constant of the insulating layer corresponding to an arbitrary power source layer for which electromagnetic interference from the other power source layer is desired to be kept lower than that of the insulating layer corresponding to the other power source layer .

According to the printed wiring board configured as described above, among the plurality of power supply layers, the dielectric constant of the insulating layer corresponding to any power supply layer for which electromagnetic interference from other power supply layers is desired to be kept low can be reduced. By making it larger than the dielectric constant of the insulating layer corresponding to the layer, it is possible to suppress the electromagnetic noise generated in any power supply layer from being transmitted to the power supply of another power supply layer.

  The plurality of insulating layers included in the printed wiring board according to the present invention may have the dielectric constant of the insulating layer corresponding to any of the power supply layers being maximized, and the dielectric constant may be decreased in order from the insulating layer.

  Moreover, as for the several insulating layer with which the printed wiring board which concerns on this invention is equipped, only the insulating layer corresponding to arbitrary power supply layers may make a dielectric constant larger than the said other insulating layer.

  Further, the plurality of power supply layers provided in the printed wiring board according to the present invention can obtain a good effect in a configuration including a power supply layer for digital circuits and a power supply layer for analog circuits.

According to the present invention, in a configuration including a plurality of DC independent power supply layers, the dielectric constant of an insulating layer corresponding to an arbitrary power supply layer is larger than the dielectric constant of an insulating layer corresponding to another power supply layer. By doing so, it is possible to prevent electromagnetic noise generated in an arbitrary power supply layer from being transmitted to the power supply of another power supply layer. That is, according to the present invention, it is possible to reduce electromagnetic noise transmitted from a power source of an arbitrary power source layer to a power source of another power source layer with a simple structure, and to secure a degree of freedom in designing a printed wiring board. Can do.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

  1A and 1B are schematic views for explaining the layer configuration of the printed wiring board of the present embodiment. In FIG. 2, the top view of the printed wiring board of this embodiment is shown. In FIG. 2, the structure of the insulating layer and the power supply layer, which are the main parts of the present invention, is shown, and the ground layer is not shown.

  As shown in FIGS. 1 (a) and 1 (b), the printed wiring board of the first embodiment is provided with a power supply layer 6 having a power supply (not shown) and a power supply layer 6 facing the power supply layer 6. A ground layer (ground layer) 7 for grounding and an insulating layer 8 disposed between the power supply layer 6 and the ground layer 7 are configured as a so-called multilayer printed board.

  In addition, a digital circuit 11 and an analog circuit 12 are mounted on the printed wiring board, and the power supply layer 6 includes a power supply layer 6a for a digital circuit having power supplies independent of each other in terms of DC, and a power supply for an analog circuit. Divided into layers 6b.

  The power supply layer 6a for the digital circuit and the power supply layer 6b for the analog circuit are each formed in a rectangular shape, and power supply decoupling capacitors (to be described later) are arranged at the corners of the four corners of the main surface. On each power supply layer 6a, 6b, although not shown, a signal wiring layer electrically connected to each power supply is provided.

  As shown in FIG. 2, the insulating layer 8 is divided into a digital circuit insulating layer 8a and an analog circuit insulating layer 8b at positions corresponding to the power supply layers 6a and 6b. .

  In the printed wiring board of this embodiment, the dielectric constant of the insulating layer 8a for digital circuits is smaller than the dielectric constant of the insulating layer 8b for analog circuits. Specifically, the insulating layer composed of the insulating layers 8a and 8b has a configuration in which a plurality of types of single insulators having different dielectric constants are combined on a printed wiring board.

  With respect to the printed wiring board according to the embodiment configured as described above, an operation of suppressing the influence of noise caused by the digital circuit 11 on the analog circuit 12 will be described.

(Function)
In a condition where the propagation distance r is larger with respect to the wavelength λ of the electromagnetic wave, that is, in the far field, the electric field strength E is expressed by

Here, H is the magnetic field strength, μ is the magnetic permeability, ε is the dielectric constant, μ _S is the relative magnetic permeability, and ε _S is the relative dielectric constant.

Here, when the relative permittivity of the insulator between the power supply layer and the ground layer of the digital circuit is ε _D and the relative permittivity of the insulator between the power supply layer and the ground layer of the analog circuit is ε _A When the relative permeability of both insulators is 1, the electric field strength between the power supply layer and the ground layer in the digital circuit is E _D , the magnetic field strength is H _A , and the power supply layer and the ground layer in the analog circuit are the electric field intensity E _a between, the magnetic field strength and H _a, the electric field strength between the respective power supply layer and a ground layer than (equation 1), is expressed by the following equation.

From (Equation 1) and (Equation 2), it can be seen that the ratio of the electric field strength to the magnetic field strength, that is, the spatial impedance is changed by changing the relative permittivity ε _D and ε _A. Further, by defining the relationship between the relative dielectric constants ε _D and ε _A , which is a feature of the present invention, as ε _D <ε _A , the spatial impedance between the power supply layer and the ground layer in the digital circuit is the same as that in the analog circuit. It can be seen that it is higher than the spatial impedance.

Moreover, since the influence by changing the dielectric constant appears greatly in the electric field strength, the relationship between the electric field strengths E _D and E _A can be expressed as E _D > E _A when the above equations are compared.

  Here, the relationship between the electric field intensity E and the voltage V is shown by the following equation (Equation 4). If there is no change in the distance d between the power supply layer and the ground layer, the relationship between the power supply layer and the ground layer is shown. It is derived that the power supply voltage of the analog circuit is lower than the power supply voltage of the digital circuit described above.

  On the other hand, when the propagation distance r is a sufficiently small distance with respect to the wavelength λ of the electromagnetic wave, that is, in the case of direct current that can be considered as this extreme state for low frequencies, (Equation 1) does not hold, Even if the dielectric constant ε is changed, the voltage across the both ends is not affected.

  This can be easily understood from the fact that when a voltage is applied across the capacitor, the voltage does not decrease at DC and the voltage decreases at high frequency.

  Therefore, two different power supply layers are sandwiched between the power supply layer and the ground layer by arranging the two power supply layers so as to face the ground layer via insulating layers made of materials having different dielectric constants. There is a difference in the spatial impedance in the insulator.

  As a result, the difference in electric field strength causes a difference in the high-frequency voltage between the power supply layer and the ground layer, but it does not affect the DC voltage, but as a function, it supplies the desired DC power supply. However, the propagation of high frequency noise can be controlled.

  As described above, according to the printed wiring board of the present embodiment, the dielectric constant of the insulating layer 8 a in the digital circuit 11 is made smaller than the dielectric constant of the insulating layer 8 b in the analog circuit 12. Electromagnetic noise generated in the power supply can be prevented from being transmitted to the power supply of the analog circuit 12. That is, according to the present embodiment, electromagnetic noise transmitted from the power supply of the digital circuit 11 to the power supply of the analog circuit 12 can be reduced.

  Therefore, according to the present embodiment, the digital circuit 11 can be designed without special consideration to suppress interference with the analog circuit 12, and the degree of freedom in designing the printed wiring board can be ensured. Can do.

(Other embodiments)
In other embodiments, the same members as those in the above-described embodiments are denoted by the same reference numerals and description thereof is omitted. FIG. 3 shows another embodiment from the same direction as FIG.

  As shown in FIG. 3, the printed wiring board of the present embodiment is different from the above-described embodiment in that the analog circuit 12 is arranged so as to be biased to the corners on the main surface of the printed wiring board.

  Also in the printed wiring board of the present embodiment, the dielectric constant of the insulating layer 8a for digital circuits is made smaller than the dielectric constant of the insulating layer 8b for analog circuits, as in the above-described embodiment. Specifically, the insulating layer is formed by combining a plurality of types of single insulators having different dielectric constants on a printed wiring board.

  As in the present embodiment, the power supply layer for the analog circuit and the power supply layer for the digital circuit are separated from each other regardless of the form shown in FIGS. This arrangement may be adopted as long as each insulating layer corresponding to each power supply layer is divided for each region where electromagnetic noise is desired to be separated.

  Further, the analog circuit power supply layer 6b shown in FIGS. 1, 2 and 3 is used for a digital circuit having a supply voltage different from the supply voltage of the digital circuit power supply layer 6a instead of the analog circuit. It may be a power supply layer, especially when one digital circuit has a relatively high voltage and the other digital circuit has a relatively low voltage (the other circuit is more susceptible to electromagnetic noise than one circuit). When it is easy to receive), the dielectric constant of the insulating layer 8a is made smaller than the dielectric constant of the insulating layer 8b, and the power supply layer 6a in the figure is used as a high voltage power supply layer and the power supply layer 6b is used as a low voltage power supply layer. However, the effect of reducing the interference of electromagnetic noise can be obtained.

  Note that the printed wiring board of the above-described embodiment is applied to a configuration including two power supply layers, but may be applied to a configuration including another power supply layer independent of DC. In such a configuration, the dielectric constant of the insulating layer corresponding to any power supply layer where the electromagnetic interference from other power supply circuits is to be kept low is set to be the highest, and the dielectric constant of the insulating layer corresponding to the remaining power supply layers is set. Is set smaller. At this time, the remaining plurality of power supply layers may also be set differently so that the dielectric constant of the insulating layer sequentially decreases.

  Similarly, when the printed wiring board of the embodiment has a configuration in which signal wiring is provided in the vicinity of the power supply layer, the dielectric constant of the insulating layer corresponding to an arbitrary power supply layer for which electromagnetic interference from the signal wiring is to be reduced is the highest. The dielectric constant of the insulating layer corresponding to the remaining power supply layer is set small. At this time, the remaining plurality of power supply layers may also be set differently so that the dielectric constant of the insulating layer sequentially decreases.

  In the above-described embodiment, the power supply layer is divided into the digital circuit and the analog circuit. However, the power supply layer is divided for each power supply layer provided corresponding to each of the plurality of analog circuits having different fundamental frequencies. Alternatively, a configuration that is divided for each power supply layer provided corresponding to each of digital circuits having different operating voltages may be used.

  Subsequently, as a more specific embodiment, the effect of reducing noise in the first embodiment will be described with reference to the calculation result of the electric field strength level.

  FIG. 4 is a diagram for explaining how the noise generated in the digital circuit affects the analog circuit in comparison with the embodiment and the conventional example. FIG. 4A shows the result of the planar distribution of the electric field strength level in the conventional example, and FIG. 4B shows the result of the planar distribution of the electric field strength level in the example. 4 (a) and 4 (b), the planar distribution of the electric field intensity level is shown by contour lines, and the density is shown in lighter color (white) as the electric field level is higher, and the density is higher as the electric field level is lower. The color (black) is shown. FIG. 4C and FIG. 4D show calculation models of the printed wiring board of the example. The planar distribution of the electric field intensity levels shown in FIGS. 4 (a) and 4 (b) is a case where power is supplied at a frequency of 900 MHz as a representative example under the arrangement conditions shown in FIGS. 4 (c) and 4 (d). It is the result calculated by electromagnetic field simulation.

  As shown in FIGS. 4C and 4D, the printed wiring board includes an insulating layer 6a between the power layer 6a for the digital circuit and the power layer 6b for the analog circuit and the ground layer 7. 6b are respectively arranged.

  Further, in the printed wiring board, generally used power supply decoupling capacitors 15 are arranged at four corners between the power supply layers 6a and 6a and the ground layer 7, respectively. In addition, the noise source 16 is disposed between the power supply layer 6 a and the ground layer 7 in the digital circuit 11, and the state in which this noise propagates between the power supply layer 6 b and the ground layer 7 in the analog circuit 12 is represented by the power supply layer. Calculation by electromagnetic field simulation was performed as the electric field strength at the intermediate point between 6a and 6b and the ground layer 7.

In the configuration of the conventional example, as shown in FIG. 4A, the dielectric constant ε _D of the insulating layer in the digital circuit is set to “4”, and the dielectric constant ε _A of the insulating layer in the analog circuit is also “4”. Is set. That is, as a conventional example, a result in a configuration in which the same material is used for each insulating layer of a digital circuit and an analog circuit is shown.

On the other hand, as shown in FIG. 4B, the electric field intensity distribution according to this example is set such that the relative dielectric constant ε _D of the insulating layer 8a in the digital circuit is set to “4” and the relative dielectric constant in the insulating layer 8b of the analog circuit. The rate ε _A is set to “10”. That is, in this embodiment, the relationship of ε _D <ε _A that is a feature of the present invention is satisfied.

  As is clear from the comparison of the results shown in FIGS. 4A and 4B, the power supply layer 6b and the ground layer 7 in the analog circuit 12 shown in the white line encircled portion on the right side in FIGS. 4A and 4B. As described with reference to (Equation 4), the voltage of the power supply noise can be reduced as a result.

  Next, as a second embodiment, an effect of reducing noise will be described for a configuration in which a noise source is connected to a wiring arranged close to a printed wiring board.

  FIG. 5 is the same as FIG. 4 except that the current flowing in the wiring arranged close to the power supply layer is regarded as noise, and the degree of the influence is compared between the example and the conventional example. FIG. FIG. 5A shows the result of the planar distribution of the electric field intensity level in the conventional example, and FIG. 5B shows the result of the planar distribution of the electric field intensity level in the example. FIG. 5C and FIG. 5D show calculation models of the printed wiring board of the example. The planar distribution of the electric field intensity levels shown in FIGS. 5 (a) and 5 (b) is a case where power is supplied at a frequency of 900 MHz as a representative example under the arrangement conditions shown in FIGS. 5 (c) and 5 (d). It is the result calculated by electromagnetic field simulation.

  As shown in FIGS. 5C and 5D, the wiring 17 to which the noise source 16 is connected is disposed close to the power supply layer of the printed wiring board.

  In the conventional example, as shown in FIG. 5A, there is a difference between the electric field intensity generated between the power supply layer and the ground layer in the digital circuit and the electric field intensity generated between the power supply layer and the ground layer in the analog circuit. Absent.

  On the other hand, in this embodiment, as shown in FIG. 5 (b), the electric field strength between the power supply layer 6b and the ground layer 7 in the analog circuit 12 is clearly reduced, as shown in FIG. 5 (a). It is clearly improved compared to the conventional example. In addition, the level of the electric field strength between the power supply layer 6a and the ground layer 7 in the digital circuit 11 is slightly reduced. Thus, according to the present embodiment, it was possible to suppress the coupling of power supply noise to the analog circuit 12 handling a weak signal.

  As described above, when it is considered that noise is coupled from the wiring 17 arranged close to the printed wiring board, the configuration of the present embodiment is adopted, so that the coupling of the power supply noise by the wiring 17 is suppressed, and the wiring 17 As a result, the influence on the analog circuit 12 is reduced and an improvement is achieved as compared with the conventional example.

  In particular, in an analog circuit that handles a weak signal, the purpose is to suppress the intrusion of noise from the outside such as the wiring 17 and to maintain a stable operation of the analog circuit, that is, a high S / N ratio (signal to noise ratio). Is effective.

  Although the multilayer printed wiring board according to the above-described embodiment has been described as having the power supply layers 6a and 6b, the ground layer 7, and the insulating layers 8a and 8b, it is actually configured to further include a signal wiring layer. A four-layer printed wiring board is assumed, and the same effect can be obtained even with such a configuration.

  However, the description so far regarding the relationship between the power supply layer and the ground layer can also be applied to a multilayer printed wiring board having other layers, and two layers in which the power supply layer and the signal wiring layer are mixed in one layer. Of course, the present invention can also be applied to a substrate (double-sided substrate).

  The printed wiring board according to the present invention is applied to, for example, a configuration in which an analog circuit that handles a weak signal and a general digital circuit are mixedly mounted. It is also suitable for use with printed wiring boards in which low-voltage circuits are mounted. Moreover, the printed wiring board according to the present invention is suitable for use in electronic devices such as wireless and wired communication devices, where improvement in signal-to-noise ratio (S / N ratio) affects performance.

It is a schematic diagram shown in order to demonstrate the layer structure of the printed wiring board of this embodiment. It is a schematic diagram which shows a response | compatibility of each power supply layer and each insulating layer in the printed wiring board of this embodiment. It is a schematic diagram which shows the structure of each power supply layer and each insulating layer in the printed wiring board of other embodiment. It is a figure for demonstrating the effect which reduces the noise produced when a digital circuit interferes with an analog circuit. It is a figure for demonstrating the effect which reduces the influence by the wiring arrange | positioned in the position close | similar to a power supply layer.

Explanation of symbols

6a Power supply layer for digital circuit 6b Power supply layer for analog circuit 7 Ground layer 8a Insulation layer for digital circuit 8b Insulation layer for analog circuit 11 Digital circuit 12 Analog circuit 15 Power supply decoupling capacitor 16 Noise source 17 Wiring

Claims (4)

A plurality of power supply layers independent in direct current, a ground layer disposed to face the power supply layer, and a plurality of power supply layers provided corresponding to the power supply layers between the power supply layer and the ground layer, respectively. With an insulating layer,
Among the plurality of insulating layers, the dielectric constant of an insulating layer corresponding to an arbitrary power source layer for which electromagnetic interference from other power source layers is desired to be low is larger than that of the insulating layer corresponding to the other power source layer. Printed wiring board. A plurality of said insulating layer, a printed wiring board as set forth in the insulating layer corresponding to the arbitrary power layer to claim 1 having a dielectric constant in the order is small. The plurality of the insulating layer, wherein only the insulating layer, the printed wiring board according to claim 1, the dielectric constant is larger than the other of the insulating layer corresponding to the arbitrary power layer.   The printed wiring board according to any one of claims 1 to 3, wherein the plurality of power supply layers include a power supply layer for a digital circuit and a power supply layer for an analog circuit.

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