JP2001068958A - Low-pass filter and circuit board - Google Patents

Abstract

(57) Abstract: A low-pass filter that can realize a small size and a low profile and has a stable filter characteristic without a floating amount between strip lines increasing or decreasing even when lamination accuracy of a dielectric layer is poor. And a circuit board. A rectangular spiral first and second strip lines formed between different dielectric layers are provided in a laminate formed by laminating a plurality of dielectric layers.
4 includes an inductor having one end connected to each other by a via-hole conductor 32, and a capacitor comprising a pair of capacitance forming electrodes 21 and 22 formed between different dielectric layers 10, respectively. A pair of long sides 23a, 23b, 24a of the second strip lines 23, 24;
24b crossed each other as viewed from the lamination direction of the dielectric layer 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pass filter and a circuit board, and more particularly to a high-frequency filter incorporated in a circuit board for an RF module and used in a filter or a duplexer incorporated in a high-frequency circuit radio section of a portable telephone or the like. The present invention relates to a laminated low-pass filter and a circuit board suitable for use.

[0002]

2. Description of the Related Art As a conventional laminated high-frequency low-pass filter, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 9-214273. FIG. 6 shows a low-pass filter disclosed in this publication, and FIG. 7 is an equivalent circuit diagram.

In the figure, reference numerals 61 to 68 denote dielectric layers, and ground electrodes 69a to 69c are provided on the upper surfaces of the dielectric layers 61, 65 and 67, respectively.
A pair of strip lines 70a and 70b are formed on the upper surfaces of 3 and 64, respectively, and capacitance forming electrodes 71a to 71c are formed on an upper surface of the dielectric layer 66, respectively.

The strip lines 70a and the strip lines 70b on the upper surfaces of the dielectric layers 62, 63 and 64 are connected by via-hole conductors 72a and 72b to form an inductor. This inductor is equivalent to the equivalent circuit shown in FIG. , Are represented as strip lines 81a and 81b.

A capacitor is formed between the capacitance forming electrodes 71a to 71c on the upper surface of the dielectric layer 66 and the ground electrodes 69b and 69c on the upper surfaces of the dielectric layers 65 and 67.
This capacitor is represented as capacitors 82a, 82b, 82c in the equivalent circuit diagram of FIG.

[0006] With the downsizing and low profile of mobile phones, there is a strong demand for downsizing and low profile of electronic components, and modularization of electronic components is progressing, and filters such as low-pass filters, high-pass filters, band-pass filters, etc. , Passive circuits such as a matching circuit for impedance matching,
It is required to be built in a circuit board, and it is difficult to cope with the conventional low-pass filter of a separate type.

[0007] Further, with the dualization of mobile phones, simply two reception filters and two transmission filters are required, and the number of filters will increase in the future as triples and multiple systems are developed. Tend to do so. But,
The increase in the size of a mobile phone is not allowed, and a further reduction in size and height is required.

[0008]

However, as in the case of the low-pass filter disclosed in the above-mentioned publication, strip lines are formed in multiple layers so as to reduce the size. Alternatively, a problem arises in stabilizing the filter characteristics.

That is, when the height is reduced in order to achieve miniaturization, the strip lines 70 formed on the upper surfaces of the dielectric layers 62, 63, 64 partially overlap when viewed from the lamination direction of the dielectric layers 61 to 68. Therefore, there is a problem that the stripline 70 sandwiching the dielectric layers 63 and 64 increases the capacitive interference (stray capacitance) between the lines unnecessary for the low-pass filter, so that the target filter characteristic cannot be realized. In particular, when incorporating with a bandpass filter that requires the use of a dielectric layer with a high relative permittivity,
There was a problem that this tendency was large.

Further, for example, when the unsintered dielectric layers are stacked with a slight shift when stacked, the position of the strip line changes, the stray capacitance between these strip lines increases or decreases, and the filter characteristics are greatly affected. Had the problem of having a significant effect. For this reason, there has been a problem that a lamination technique having higher stability is required. In particular, when a dielectric layer having a high relative dielectric constant, which is advantageous for incorporating a band-pass filter or the like, is used, the above-described problem becomes significant.

On the other hand, when strip lines are formed without overlapping in multiple layers, and the dielectric layer is made thinner to cope with a reduction in height, the size of the device must be increased, that is, the occupied area must be increased. There was a problem that can not be.

The present invention has been devised in view of the above circumstances, and has as its object to realize a small-sized and low-profile, and to reduce the stray capacitance between strip lines even when the lamination accuracy of the dielectric layers is poor. An object of the present invention is to provide a low-pass filter and a circuit board having stable filter characteristics without increasing or decreasing.

[0013]

A low-pass filter according to the present invention comprises first and second rectangular spiral first and second strip lines respectively formed between different dielectric layers in a laminate formed by laminating a plurality of dielectric layers. And a capacitor formed of a pair of capacitance forming electrodes respectively formed between the different dielectric layers, and a pair of the first and second strip lines. The sides cross each other when viewed from the laminating direction of the dielectric layers.

By adopting such a configuration, since the pair of long sides of the first and second strip lines intersect, the stray capacitance between the strip lines can be reduced, and the unfired dielectric layer is formed. At the stage of laminating,
Even if the relative positions of the first strip line and the second strip line are slightly shifted, the stray capacitance between the strip lines hardly increases or decreases, and for example, a high relative dielectric constant advantageous for incorporating a band pass filter or the like. Even when the dielectric layer is used, the filter characteristics are hardly affected.

That is, when the unfired dielectric layers are stacked while being shifted from the original stacking position, and one long side of the first strip line and one short side of the second strip line approach each other, , The other long side of the first strip line is separated from the other short side of the second strip line,
When one long side of the second strip line and one short side of the first strip line are close to each other, the other long side of the second strip line is separated from the other short side of the first strip line. The stray capacitance between the first strip line and the second strip line hardly changes.

Further, since the occupied areas of the first strip line and the second strip line almost overlap with each other,
The occupied area of the strip line forming the inductor can be reduced.

Further, when viewed from the laminating direction of the dielectric layers, the first
And a pair of long sides of the second strip line are orthogonal to each other, and a long side of the first strip line and a short side of the second strip line, and a short side of the first strip line and the second side. It is desirable that the long side of the strip line is adjacent. By employing such a configuration, as described above, the increase and decrease of the stray capacitance between the first and second strip lines can be almost eliminated, and the area occupied by the strip lines for forming the inductor can be further reduced. Then, it can be minimized.

Further, the circuit board of the present invention has the above-mentioned low-pass filter built therein. As described above, since there is almost no change in stray capacitance due to lamination accuracy between lines, it is relatively easy to use a dielectric layer having a high relative dielectric constant. By using the layer, the line can be shortened and downsizing can be achieved, whereby it is possible to obtain a small-sized circuit board in which a band-pass filter can be easily incorporated.

[0019]

1 is a perspective view showing the appearance of a circuit board incorporating a low-pass filter of the present invention, FIG. 2 is a perspective view showing the pattern configuration of the low-pass filter of the present invention, and FIG. 3 is the strip line of FIG. FIG. 4 is an equivalent circuit diagram of the low-pass filter according to the present invention.

In FIG. 1, reference numeral 1 denotes an insulating base,
It is also a dielectric. A surface electrode 2 is formed on the surface of the insulating base 1. Various chip products (not shown) such as a capacitor, an inductor, and a diode are mounted on the surface electrode 2. The surface electrode 2 also serves as an input / output electrode of an element such as a filter built in the insulating base 1.

An end surface electrode is formed on the side surface of the insulating base 1, and there are two types, an end surface ground electrode 3 and an end surface input / output electrode 4. The end face ground electrode 3 is connected to a ground electrode built in the insulating substrate 1 or formed on the back surface. Further, the end face input / output electrode 4 is connected to an input / output electrode formed on the dielectric layer or on the back surface of the insulating base 1, and the antenna, transmission,
It plays a role of receiving or inputting and outputting power. A broken line portion F in the insulating base 1 represents a built-in low-pass filter, and a pattern configuration thereof will be described with reference to FIG.

In FIG. 2, reference numerals 11 and 12 denote ground electrodes which are common to the ground electrode of the circuit board. Reference numerals 21 and 22 denote capacitance forming electrodes.
The capacitance between input and output of the low-pass filter is formed between 1 and 22.

The insulating base 1 is made up of five dielectric layers 10
a to 10e, and the capacitance forming electrode 2
1, 22 and the ground electrode 12 are
b, 10c, 10d formed on the upper surface
Is formed on the lower surface of the dielectric layer 10a.

Numerals 23 and 24 denote first and second rectangular spiral strip lines, one ends of which are connected by via-hole conductors 32 to obtain necessary inductors.

Reference numeral 27 denotes a GND capacitance forming electrode, which forms a GND capacitance with the ground electrode 11.

As shown in FIG. 2, the connection between the electrodes is made by via-hole conductors 31-34. The surface electrode 2 is connected to an input / output land 28 of the filter through a via-hole conductor 31. The lands 25 and 26 are connected by the via hole conductor 32, and the first and second strip lines 23 and 24 of two layers are connected. Capacitor forming electrode 22 of filter and surface electrode 2 by via-hole conductor 33
Is connected. The via hole conductor 34 connects the land 25, which is the connection point between the first strip line 23 and the via hole conductor 34, to the GND capacitance forming electrode 27, and forms a GND capacitance between the ground electrode 11 and the ground electrode 11.

In the low-pass filter of the present invention,
As shown in FIG. 3, the strip lines 23 and 24 are formed so as to intersect at a plurality of locations. That is, the pair of long sides 24a and 24b of the second strip line 24 intersect with the pair of long sides 23a of the first strip line 23 when viewed from the lamination direction of the dielectric layer 10, and the long side of the second strip line 24 24b and a pair of long sides 23a and 23b of the first strip line 23 intersect as viewed from the laminating direction of the dielectric layer 10, and a pair of long sides 24a and 24b of the second strip line 24 and the first strip The pair of long sides 23 a and 23 b of the line 23 are orthogonal to each other at three points when viewed from the laminating direction of the dielectric layer 10. FIG. 3B is a diagram schematically showing this state.

Also, the long side 2 of the first strip line 23
3a, 23b and the short side 24 of the second strip line 24
c, 24d, and short side 2 of the first strip line 23
3c, 23d and the long side 24 of the second strip line 24
a and 24b are formed at predetermined intervals when viewed from the laminating direction of the dielectric layer 10.

In FIG. 3, reference numeral 41 denotes a portion where an input / output capacitance is formed (overlapping portion of the capacitance forming electrodes 21, 22), and reference numeral 42 denotes a land 25 for connecting the strip lines 23, 24 to the via-hole conductor 32. , 26 overlap each other. Then, a pair of long sides 23a, 23b, 24 of the first and second strip lines 23, 24
a, 24b cross each other at a plurality of positions when viewed from the laminating direction of the dielectric layer 10, thereby forming the strip lines 23, 2
4 and the strip lines 23 and 24
The inter-capacitance (floating capacitance) is reduced.

The layer structure of the low-pass filter of the present invention will be described in detail. A ground electrode 11 is provided on the lower surface of the dielectric layer 10a.
Is formed, and on the upper surface, a GND capacitance forming electrode 27 is formed.

The capacitance forming electrode 2 is provided on the upper surface of the dielectric layer 10b.
1. A first strip line 23 is formed. A land 25 is formed at one end of the first strip line 23, and an input / output land 28 and a capacitance forming electrode 21 are formed at the other end.

The capacitance forming electrode 2 is formed on the upper surface of the dielectric layer 10c.
2. A second strip line 24 is formed. A land 26 is formed at one end of the second strip line 24, and a capacitance forming electrode 22 is formed at the other end.

The ground electrode 12 is provided on the upper surface of the dielectric layer 10d.
Is formed, and a surface electrode 2 is formed on the upper surface of the dielectric 10e. The ground electrode 12 and the via-hole conductor 33
In order to prevent connection, the insertion position of the via-hole conductor 33 of the ground electrode 12 is in a state where the electrode is pulled out.

Such a low-pass filter includes, for example,
A plurality of unfired green sheets are provided with through holes for via holes at positions to be via hole conductors, and the through holes are filled with a conductive paste. The green sheets filled with the conductive paste are strip lines 23, 24 It is manufactured by applying a conductive paste to be used as the electrodes and the capacitance forming electrodes 21 and 22 and the ground electrodes 11 and 12, laminating green sheets to which the conductive paste is applied, and sintering and integrating them.

Each of the five dielectric layers 10a to 10e may be formed from one green sheet or by laminating a plurality of green sheets. In particular, a band-pass filter, a low-pass filter, a high-pass filter, a line that is a part of a matching circuit or a switch circuit, etc. built in the insulating substrate 1 (in FIG. If the layer configuration (omitted) is different from the low-pass filter of the present invention, a necessary layer configuration must be obtained by using a plurality of green sheets for each dielectric layer.

As the dielectric material constituting the insulating base 1, the impedance of the built-in strip line is 5
Since it is possible to realize a value close to 0Ω and incorporate a small-sized and high-performance bandpass filter, it is preferable to use a filter having a relative dielectric constant of 20 ± 5, a high Q value and a τf close to 0. For example,
aMgO.bCaO.cTiO ₂ (25 ≦ a ≦ 35,
0.3 ≦ b ≦ 7, 60 ≦ c ≦ 70, a + b + c = 10
0, a, b, c in the weight ratio), a boron-containing compound B _2
3 to 20 parts by weight in terms of O ₃ , the lithium-containing compound is Li
Examples include 1-10 parts by weight in terms of ₂ O ₃ .

Each electrode of the filter is made of copper, silver, or copper so as not to deteriorate the loss of the built-in filter and line.
It is desirable to use a low-resistance conductor such as gold.
The insulating base is preferably fired simultaneously with the circuit board using a low-temperature firing material of about 900 to 1000 ° C., and can be efficiently manufactured by firing at a low temperature.

FIG. 4 shows an equivalent circuit of the low-pass filter of the present invention, which will be described below. Reference numeral 51 denotes a capacitance between input and output, and means a capacitance between the capacitance forming electrodes 21 and 22.

Reference numeral 52 denotes a strip line (mainly functioning as an inductor), which is constituted by strip lines 23 and 24. Input / output capacitance 51 and strip line 5
2, it is possible to control the pass frequency band and the attenuation pole position. Reference numerals 53 and 54 denote capacitance forming electrodes 21 and 2
If the stray capacitance is large, the impedance of the strip line cannot be matched, and the insertion loss of the filter deteriorates. In this filter, the stray capacitance is suppressed by reducing the thickness of the dielectric layer between the capacitance forming electrodes and increasing the thickness of the dielectric layer between the capacitance forming electrode and the ground electrode as much as possible.

Reference numeral 55 denotes a capacitance between the GND capacitance forming electrode 27 and the ground electrode 11.

The attenuation characteristic in the high frequency range is controlled by the GND capacitor forming electrode 27.

By changing the size of the capacitance forming electrodes 21 and 22, it is possible to suppress a change in the input / output capacitance 51 and to stabilize the filter characteristics.

In the low-pass filter of the present invention, for example,
When the unsintered dielectric layers are stacked, they are stacked so as to deviate from the original stacking positions, and one long side 23 of the first strip line 23 is stacked.
a and one short side 24 c of the second strip line 24 approaches, the other long side 23 b of the first strip line 23 and the other short side 24
d are separated and the second strip line 2
4, when one long side 24b of the first strip line approaches one short side 23d of the first strip line, the other long side 24a of the second strip line 24 is separated from the other short side 23c of the first strip line 23. That is, the stray capacitance between the first strip line 23 and the second strip line 24 hardly changes, and the filter characteristics hardly change. For this reason, for example, even when a dielectric layer having a high relative dielectric constant, which is advantageous for incorporating a band pass filter or the like, is used, the filter characteristics are hardly affected.

As shown in FIG. 5, the long sides 23a and 23b of the first strip line 23, the short sides 24c and 24d of the second strip line 24, and the short sides 23c and 23d of the first strip line 23 , The long sides 24a, 24b of the second strip line 24 are formed adjacent to each other when viewed from the laminating direction of the dielectric layer 10, so that the occupied area of the strip lines 23, 24 can be further reduced. Miniaturization can be achieved.

[0045]

EXAMPLE A circuit board incorporating the low-pass filter of the present invention shown in FIGS. 1 to 4 was manufactured. The size of the circuit board is 7 mm × 5 mm × 0.8 mm, a dielectric material having a relative dielectric constant of 20 is used, and the total length and line width of the strip lines 23 and 24 are 7.2 mm and 0.1 mm, respectively. When the size of 21, 21 is 0.9 × 0.9 mm, the insertion loss is 0.35 dB, 1 in the 900 MHz band.
The attenuation in the 800 MHz band was 25 dB.

When only the pattern on the dielectric layer 10c is moved by 0.1 mm, the change in the attenuation pole position is 50M.
Hz and an attenuation of 20 dB or more.

As a comparative example, a low-pass filter was formed in the same manner as described above except that the upper and lower strip lines were formed so as to overlap each other when viewed from the laminating direction, and the filter characteristics were measured. When only the upper pattern was moved by 0.1 mm, the change in the attenuation pole position was 90
MHz, and the attenuation was about 15 dB.

[0048]

According to the low-pass filter of the present invention, even if the relative positions of the first strip line and the second strip line are slightly shifted in the step of laminating the unfired dielectric layers, the stray capacitance between the strip lines can be reduced. There is almost no increase or decrease, and even if, for example, a dielectric layer having a high relative dielectric constant, which is advantageous for incorporating a band-pass filter or the like, is used, the characteristics of the filter characteristics are hardly affected. Also,
Since the occupied areas of the first strip line and the second strip line almost overlap, the occupied area of the filter can be reduced.

Further, since there is almost no variation in stray capacitance due to lamination accuracy between lines, it is relatively easy to use a dielectric layer having a high relative dielectric constant. By using layers, the line can be shortened, and miniaturization can be achieved. This makes it possible to obtain a small circuit board in which a band-pass filter can be easily built.

[Brief description of the drawings]

FIG. 1 is an external perspective view of a circuit board incorporating a low-pass filter of the present invention.

FIG. 2 is a perspective view showing an electrode pattern of the low-pass filter of the present invention.

FIG. 3 is a perspective view of the electrode pattern of the low-pass filter of the present invention as viewed from the direction in which the dielectric layers are stacked.

FIG. 4 is an equivalent circuit diagram of the low-pass filter of the present invention.

FIG. 5 is a perspective view of an electrode pattern of another low-pass filter of the present invention, as viewed from a direction in which dielectric layers are stacked.

FIG. 6 is an exploded perspective view showing a conventional low-pass filter.

FIG. 7 is an equivalent circuit diagram of a conventional low-pass filter.

[Explanation of symbols]

 10a to 10e: Dielectric layers 21, 22: Capacitance forming electrode 23: First strip line 24: Second strip line 31 to 34: Via hole conductors 23a, 23b: First Long side of strip line 24a, 24b ... Long side of second strip line F ... Filter

Claims (3)

[Claims] 1. A laminated body formed by laminating a plurality of dielectric layers,
An inductor formed by connecting one ends of first and second rectangular spiral strip lines formed between the different dielectric layers with a via-hole conductor; and forming a pair of capacitances formed between the different dielectric layers, respectively. A low-pass filter comprising: a capacitor formed of an electrode; and a pair of long sides of the first and second strip lines intersecting each other as viewed from a lamination direction of the dielectric layers. 2. A pair of long sides of the first and second strip lines are orthogonal to each other when viewed from the direction of lamination of the dielectric layers, and a long side of the first strip line and the second side of the second strip line are perpendicular to each other.
The low-pass filter according to claim 1, wherein a short side of the strip line and a short side of the first strip line and a long side of the second strip line are adjacent to each other. 3. A circuit board incorporating the low-pass filter according to claim 1.