JP2000049554A - Lowpass filter and circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lowpass filter which secures attenuation that is two to four times as large waves as a passing frequency, is miniaturized and is made short in height and to provide a circuit board that can be incorporated together with a bandpass filter. SOLUTION: A stripline 32 and an electrode 31 are formed on a dielectric layer 10a, striplines 34 and 35 which are less than one turn and a capacitance formation electrode 33 are formed on a dielectric layer 10b, a 4th stripline 37 that is less than one turn and an electrode 36 are formed on a dielectric layer 10c, the striplines 32 and 34 and the striplines 35 and 37 are connected by viahole conductors 42 and 43 respectively, the electrode 33 and the electrodes 31 and 36 are made to face each other and the striplines 32 and 34 and the striplines 35 and 37 are partially or entirely overlapped seen from the direction of lamination.

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 laminated board incorporated in a circuit board for a high-frequency module and used for a filter or a duplexer incorporated in a high-frequency circuit radio section such as a portable telephone. Low-pass filter and circuit board.

[0002]

2. Description of the Related Art Conventional laminated low-pass filters include:
For example, one disclosed in JP-A-7-336176 is known. FIG. 7 shows a low-pass filter disclosed in this publication, and FIG. 8 is an equivalent circuit diagram of the low-pass filter.

In this low-pass filter, the dielectric layer 51a
To 51f are laminated, and an inductor 52 is formed on the dielectric layer 51b by a linear or bent conductor pattern (meaning line), and the dielectric layers 51c and 51c are formed.
Electrodes 53a and 53b for capacitors are formed on d.
Thereby, a capacitor connected in parallel with the inductor 52 is formed.

[0004] A dielectric layer 5 is formed on the dielectric layer 51e.
Capacitor electrodes 54a and 54b are formed facing the ground electrode 55 formed on 1f, and a capacitor is formed between the ground electrode 55 and the capacitor electrodes 54a and 54b.

This low-pass filter has poles in its frequency characteristics and can secure attenuation at a frequency near the pass band, and uses a dielectric layer having a relative dielectric constant of about 5 to occupy a vertical area of 3 in a 2-GHz band. .2mm x 1.6mm
Has been realized.

[0006]

However, in the low-pass filter disclosed in Japanese Patent Application Laid-Open No. 7-336176, a plurality of attenuation poles cannot be formed. There has been a problem that the attenuation cannot be secured and a wideband low-pass filter cannot be formed.

In order to secure the attenuation of twice, three times and four times the passing frequency, means for connecting two low-pass filters as shown in FIG. 9 to secure the attenuation. Can be considered.

However, it is necessary to reduce the electromagnetic coupling between the first circuit and the second circuit. In addition, since the current flowing in the opposing portions of the meander lines constituting the respective inductors is in the opposite direction, the inductance generated by the opposing portions tends to decrease the inductance. In order to obtain the required inductance, the line length must be increased, which causes a problem that the filter size increases.

Conventionally, when a low-pass filter is formed, a dielectric having a relative dielectric constant of about 5 to 8 is used. Therefore, a circuit is required together with a filter such as a band-pass filter which requires the use of a dielectric layer having a high relative dielectric constant. It is difficult to incorporate the band-pass filter into a circuit board, and even if both are incorporated, it is necessary to obtain a large capacity. Therefore, there is a problem that the size of the band-pass filter increases and the circuit board increases in size.

On the other hand, when a low-pass filter is incorporated together with a filter such as a band-pass filter, that is, when a low-pass filter is formed using a dielectric layer having a high relative dielectric constant, the inductance component of the strip line becomes small. Compared to the example, the distance between the opposing meander lines must be wider and the line length must be longer,
There was a problem that the filter size was increased. Further, there is a problem that unnecessary parasitic capacitance is generated between the strip line and the ground electrode, thereby deteriorating the insertion loss of the low-pass filter.

In recent years, with the miniaturization of mobile phones, there has been a strong demand for miniaturization of electronic components, and modularization of electronic components has been promoted. Filters such as low-pass filters and band-pass filters, impedance matching circuits, etc. It is required to incorporate the passive circuit into the circuit board, and it is difficult to cope with the conventional low-pass filter of the separately attached type.

Further, in recent years, with the dualization of portable telephones (for example, both the 900 MHz band and the 1800 MHz band can be transmitted and received), the reception filter is simply provided with two filters.
And two transmission filters are required, and the number of filters will increase as triples and multiple systems advance in the future. However, increasing the size of mobile phones is not allowed,
Further miniaturization is required.

Therefore, there is a need for a low-pass filter that can be built in a circuit board using a dielectric having a high relative permittivity so that it can be built together with a band-pass filter. Also,
For example, if the height of the chip component to be mounted is 0.7 mm at maximum, so that it can be built into a circuit board used for electronic components requiring a height reduction of 2 mm or less, the thickness of the filter must be limited to 1.2 mm or less at maximum. Must.

Therefore, in order to incorporate a bandpass filter as described above, it is desirable that the relative permittivity of the substrate material be high. However, by increasing the relative permittivity, the line length for forming an inductance component necessary for a low-pass filter is increased, the filter size is increased, and unnecessary parasitic capacitance is increased and the characteristics are deteriorated. Is a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to make it possible to secure the attenuation of twice, three times, and four times the passing frequency, and to reduce the size and height. An object of the present invention is to provide a circuit board capable of providing a low-pass filter and having good characteristics, and at the same time, having a small size and a low profile even when incorporated together with a plurality of filters including a band-pass filter. Aim.

[0016]

A low-pass filter according to the present invention comprises at least a first, a second, and a third dielectric layer sequentially laminated, and a first strip having less than one turn on the first dielectric layer. Forming a line and a first electrode, forming second and third strip lines and a capacitance forming electrode of less than one turn on the second dielectric layer, and forming a second and third strip line of less than one turn on the third dielectric layer. Forming four strip lines and a second electrode, connecting the first strip line and the second strip line, and connecting the third strip line and the fourth strip line by via-hole conductors to form an inductor;
A capacitor is formed with the capacitance forming electrode, the first electrode, and the second electrode facing each other, and further, the first strip line and the second strip line, and the third strip line and the fourth strip line are insulated from each other. Some or all of them overlap when viewed from the stacking direction of the body layers.

Here, it is desirable that the winding directions of the inductor formed by the first strip line and the second strip line and the inductor formed by the third strip line and the fourth strip line are opposite. Further, it is desirable that the capacitance forming electrode is formed between the second strip line and the third strip line. Further, it is desirable that ground electrodes are provided below the first strip line and above the fourth strip line via a dielectric layer. Furthermore, it is desirable that the thickness of the second and third dielectric layers is smaller than the thickness of the dielectric layer between the ground electrode and the first strip line and between the ground electrode and the fourth strip line.

A circuit board according to the present invention includes the above-described low-pass filter and another filter.

[0019]

In the low-pass filter of the present invention, strip lines of less than one turn formed on different dielectric layers are connected by via-hole conductors, and the strip lines formed on different dielectric layers are connected to the dielectric layers. By forming them so as to overlap each other when viewed from the lamination direction, a structure in which the strip lines are wound is formed, and the current flowing through the strip lines formed on different dielectric layers flows in the same direction, and the dielectric layers are formed. Due to the interaction of the strip lines facing each other, the inductance component can be increased as compared with the above-mentioned conventional meander type line,
The occupied area of the strip line can be reduced. In particular, the effect is more significant when incorporated together with the bandpass filter in the circuit board.

Further, since the strip lines formed on the different dielectric layers are formed so as to overlap each other when viewed from the lamination direction of the dielectric layers, the distribution constants are formed between the strip lines formed on the different dielectric layers. A capacitance forming electrode for forming a capacitor and a first electrode;
The area of the second electrode can be reduced. Also in this case, the effect is particularly greater when the device is incorporated together with the bandpass filter in the circuit board.

In addition, the winding direction of the inductor formed by the first strip line and the second strip line and the winding direction of the inductor formed by the third strip line and the fourth strip line are reversed, so that the inductor is formed. Can be reduced, a plurality of attenuation poles can be formed, and attenuation of twice, three times and four times higher than the passing frequency can be secured.

Further, by forming the capacitance forming electrode between the second strip line and the third strip line, the interval between the second strip line and the third strip line is maximized, and the coupling between the inductors is further improved. The number of attenuation poles can be reduced, and a plurality of attenuation poles can be formed, and the attenuation of twice, three times, and four times the passing frequency can be secured.

As described above, even if a dielectric material having a high relative dielectric constant is used, the inductor has a wound structure, so that the strip line forming the inductor can be shortened as compared with a conventional meander line. Since the relative dielectric constant is high, the area of the capacitance forming electrode and the first and second electrodes can be reduced, and good characteristics can be maintained as a low-pass filter, and the size and height can be reduced. Accordingly, it is possible to reduce the size and height of the circuit board including the band-pass filter and the low-pass filter.

[0024]

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

In FIG. 1, reference numeral 1 denotes an insulating base,
It is also a dielectric. A surface electrode 13 is formed on the surface of the insulating base 1. Various chip components such as a capacitor, an inductor, and a diode are mounted on the surface electrode 13.
The surface electrode 13 also functions 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 14 and an end surface input / output electrode 15. The end face ground electrode 14 is built in the insulating base 1 or connected to a ground electrode formed on the back surface.

Further, the end face input / output electrode 15 is connected to an input / output electrode built in the insulating substrate 1 or formed on the back surface thereof.
Acts as an input / output for antenna, transmission, reception or power supply. A wavy line portion F in the insulating base 1 represents a filter, and a pattern configuration thereof will be described below.

In FIG. 2, the insulating substrate 1 is formed by sequentially laminating five dielectric layers 10a to 10e.

The ground electrode 2 is provided on the lower surface of the dielectric layer 10a.
0, and a surface electrode 13 serving as an input / output electrode is formed,
On its upper surface, an open stub electrode (first electrode) 31
And a first strip line 32 of less than one turn are formed, and the first strip line 32 is connected to the open stub electrode 31.

On the upper surface of the dielectric layer 10b, a capacitance forming electrode 33, a second strip line 34 and a third strip line 35 of less than one turn are formed, and the capacitance forming electrode 33 is composed of strip lines 34 and 35. Between the strip lines 34 and 35.

On the upper surface of the dielectric layer 10c, an open stub electrode (second electrode) 36 and a fourth strip line 37 of less than one turn are formed, and the fourth strip line 37 is connected to the open stub electrode 36. ing.

A ground electrode 38 is provided on the main surface of the dielectric layer 10d.
However, a surface electrode 13 serving as an input / output electrode is formed on the main surface of the dielectric layer 10e.

The first strip line 32 and the second strip line 34, the third strip line 35 and the fourth strip line 37 are connected by via-hole conductors 42 and 43, and the open stub electrode 31 and the surface electrode 13, and the open stub electrode 36 and the surface electrode 13 are connected by via-hole conductors 44 and 45, respectively.

The capacitor forming electrode 33 and the open stub electrodes 31 and 36 are formed to face each other as shown in FIG. 3, thereby forming a capacitor. FIG.
FIG. 4 is a perspective view of a pattern below the cross section of the dielectric layer 10d, in which the ground electrode 20 and the surface electrode 13 on the lower surface of the dielectric layer 10a are omitted.

The ground electrodes 20, 38 are common to the ground electrodes on the circuit board.

In the case of the low-pass filter of the present invention, as described above, since the dielectric layers 10a to 10e have a high relative dielectric constant because they are incorporated in the circuit board together with the band-pass filter, the dielectric substrates 10a to 10c Strip lines 32, 37, electrodes 31, 33, 3 formed on the main surface
6, and unnecessary parasitic capacitance generated between the ground electrodes 20 and 38 is increased, and the inductance component of the strip line formed on the main surface of the dielectric layers 10a to 10c is smaller than when the relative dielectric constant is low. .

Therefore, the thickness of each of the dielectric layers 10b and 10c is made smaller than those of the other dielectric layers 10a and 10d.
Strip lines 32 formed on the main surfaces 0a to 10c,
Each of the strip lines 34, 35, and 37 is a strip line of less than one turn, and as shown in FIG. In this way, the inductor L1 in the equivalent circuit diagram of FIG. 4 is formed, and as shown in FIG.
4 and 37 are arranged so as to overlap each other when viewed from the lamination direction, and are connected and wound by the via-hole conductor 43, whereby the structure shown in FIG.
Constitute the inductor L2 in the equivalent circuit diagram of FIG.

Further, the overlapping strip lines 32, 3
4, a parasitic capacitance C4a shown in the equivalent circuit of FIG. 4 is generated, and a parasitic capacitance C5a is generated between the overlapped strip lines 35 and 37.

The parasitic capacitances C4a and C5a are formed by the capacitor C4 formed between the open stub electrode 31 formed on the upper surface of the dielectric layer 10a and the capacitance forming electrode 33 formed on the upper surface of the dielectric layer 10b, and the dielectric layer Capacitors C4 and C5 have the same function as capacitor C5 formed between capacitance forming electrode 33 formed on the upper surface of 10b and open stub electrode 36 formed on the upper surface of dielectric layer 10c.
Capacity can be reduced. Therefore, the open stub electrode 31 formed on the upper surface of the dielectric layer 10a, the capacitance forming electrode 33 formed on the upper surface of the dielectric layer 10b, and the open stub electrode 3 formed on the upper surface of the dielectric layer 10c.
6 has a smaller area than an area required when the parasitic capacitances C4a and C5a do not occur.

Further, since the dielectric layers 10a to 10e have a high relative dielectric constant, a parasitic element formed between the strip line 32 formed on the upper surface of the dielectric layer 10a and the open stub electrode 31 and the ground electrode 20 is formed. The capacitance, that is, the capacitor C1 shown in FIG. 4 is constituted, the strip lines 34 and 35 formed on the upper surface of the dielectric layer 10b, and the capacitance forming electrode 3
3, a parasitic capacitance formed between the ground electrodes 20 and 38, that is, a capacitor C2 shown in FIG. 4, and a strip line 37 formed on the main surface of the dielectric layer 10c, an open stub electrode 36 and a ground electrode And a capacitor C3 shown in FIG.

The low-pass filter having the above-described structure is formed, for example, by forming strip lines 32, 34, 35, 37, open stub electrodes 31, 36, a capacitance forming electrode 33, a ground electrode 20, 38
It is manufactured by applying a conductive paste so as to obtain a green sheet on which the conductive paste is applied, and by firing and integrating.

The dielectric material constituting the insulating base 1 has a relative dielectric constant of 1 since a band-pass filter is incorporated.
It is preferable that the Q value is high at 5 to 25 and τf is close to 0.
For example, aMgO.bCaO.cTiO ₂ (25 ≦ a ≦
35, 0.3 ≦ b ≦ 7, 60 ≦ c ≦ 70, a + b + c =
100, a, b, c is 3-20 parts by weight boron terms _of B ₂ O ₃ to 100 parts by weight of the main component consisting of weight ratio), and lithium those containing 1 to 10 parts by weight Li ₂ O ₃ in terms of There is.

It is desirable that each electrode of the filter is formed to have a low-resistance conductor such as copper, silver, or gold. The insulating base is preferably fired simultaneously with the conductive paste using a low-temperature firing material of about 900 to 1000 ° C., and can be efficiently manufactured by simultaneous firing at a low temperature.

In the low-pass filter configured as described above, the strip lines 32 and 36 and the ground electrodes 20 and
Unnecessary parasitic capacitance generated between the 38 can be reduced. Moreover, the strip lines 32 and 34 and the strip line 3
5, 37 are wound, and different dielectric layers 10
a, 10b, strip line 3 formed on 10c
2 and 34 and the currents flowing through the strip lines 35 and 37 flow in the same direction, and the strip lines 32 and 34 and the dielectric layer 10c facing each other via the dielectric layer 10b.
The interaction of the strip lines 35 and 37 confronting each other makes it possible to increase the inductance component as compared with the above-mentioned conventional meander type line, and to reduce the occupied area for forming the necessary strip lines. The required inductance can be ensured in a small area.

The different dielectric layers 10a, 10b, 1
By forming the strip lines 32, 34 and the strip lines 35, 37 formed on 0c so as to overlap each other when viewed from the lamination direction of the dielectric layers 10a to 10e,
Since the capacitance can be formed between the strip lines 32 and 34 and between the strip lines 35 and 37 in a distributed manner, the area of the capacitance forming electrode 33 and the open stub electrodes 31 and 36 forming the capacitor can be reduced. it can.

Further, the first strip line 32 and the second
An inductor formed by the strip line 34;
By reversing the winding direction of the inductor formed by the strip line 35 and the fourth strip line 37,
The coupling between these inductors can be reduced,
A plurality of attenuation poles can be formed, and two
The attenuation of the double, triple, and fourth harmonics can be secured.

FIG. 5 shows a simulation result of the transmission characteristics of the low-pass filter when the coupling between the inductors changes. Thus, when the coupling between the inductors is large, a plurality of attenuation poles cannot be formed, but when the coupling is small, a plurality of attenuation stations can be secured. Therefore, with the above structure, a plurality of attenuation poles generated on the equivalent circuit can be formed, and the attenuation of twice, three times and four times the passing frequency can be secured.

Further, by forming the capacitance forming electrode 33 between the second strip line 34 and the third strip line 35, the distance between the second strip line 34 and the third strip line 35 is maximized, and the inductor is formed. The coupling between them can be further reduced, a plurality of attenuation poles can be formed, and the attenuation of twice, three times and four times the passing frequency can be secured.

Therefore, even if a dielectric material having a high relative dielectric constant is used, since the inductor has a wound structure, the strip lines 32, 34, 35, and 37 forming the inductor can be formed as compared with a conventional meander line. Since the length can be shortened and the relative dielectric constant is high, the area of the capacitance forming electrode 33 and the open stub electrodes 31 and 36 can be reduced, and good characteristics can be maintained as a low-pass filter, and the size and height can be reduced. Thus, it is possible to reduce the size and height of the circuit board including the band-pass filter and the low-pass filter.

[0050]

EXAMPLE A circuit board incorporating a low-pass filter according to the present invention shown in FIGS. 1 to 4 was manufactured using a dielectric material having a relative permittivity of 20. The size of the circuit board is 10mm x 10mm
× 1.0 mm, and the exclusive area of the electrode pattern of the filter portion F shown in FIG. 3 was 3.0 mm × 3.0 mm.
The thickness between the ground electrodes was set to 0.9 mm. Further, the value of the inductor shown in the equivalent circuit diagram of FIG.
And by setting the value of the capacitor to C4５C5,
Multiple attenuation poles were formed.

FIG. 6 shows the frequency characteristic results of the low-pass filter formed on the circuit board. From this result, 900
0.5 dB insertion loss, 2nd harmonic attenuation 36 in MHz band
dB, third harmonic attenuation 41 dB, fourth harmonic attenuation 46 d
B was obtained.

[0052]

According to the low-pass filter of the present invention, the inductance component can be made larger than that of the conventional meander line due to the interaction of the strip lines facing each other via the dielectric layer, and the occupied area of the strip line can be increased. Since the capacitance can be reduced and the capacitance can be formed in a distributed manner between the strip lines formed on different dielectric layers, the capacitance forming electrode forming the capacitor and the first electrode and the second electrode can be formed. The area can be reduced.

[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 directly above.

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

5 is a graph showing a characteristic difference due to coupling between inductors in the equivalent circuit diagram of FIG. 4;

FIG. 6 is a graph showing frequency characteristics of the low-pass filter of the present invention.

FIG. 7 is an exploded perspective view showing a conventional low-pass filter.

FIG. 8 is an equivalent circuit diagram of a conventional low-pass filter.

FIG. 9 is an equivalent circuit diagram when two conventional low-pass filters are connected.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating base 10a-10e ... Dielectric layer 20, 38 ... Earth electrode 31, 36 ... Open stub electrode 32, 34, 35, 37 ... Strip line 33 ... Capacitance formation Electrodes 42-45: Via-hole conductor

Claims (6)

[Claims] A first strip line and a first electrode having less than one turn are formed on said first dielectric layer, said first strip line and said first electrode being formed on said first dielectric layer; Second
Forming second and third strip lines having less than one turn and a capacitance forming electrode on the dielectric layer; forming fourth strip lines and second electrodes having less than one turn on the third dielectric layer; A first strip line and a second strip line, and a third strip line and a fourth strip line are respectively connected by via-hole conductors to form an inductor, and the capacitance forming electrode faces the first electrode and the second electrode, respectively. To form a capacitor,
A low-pass filter, wherein a first strip line and a second strip line and a third strip line and a fourth strip line partially or entirely overlap with each other as viewed from the direction of lamination of the dielectric layers. 2. The winding direction of the inductor formed by the first strip line and the second strip line and the winding direction of the inductor formed by the third strip line and the fourth strip line are opposite to each other. 2. The low-pass filter according to 1. 3. The low-pass filter according to claim 1, wherein the capacitance forming electrode is formed between the second strip line and the third strip line. 4. The method according to claim 1, wherein ground electrodes are provided below the first strip line and above the fourth strip line via a dielectric layer. Low pass filter as described. 5. The semiconductor device according to claim 1, wherein the thickness of the second and third dielectric layers is smaller than the thickness of the dielectric layer between the ground electrode and the first strip line and between the ground electrode and the fourth strip line. The low-pass filter according to claim 4, wherein: 6. A circuit board comprising the low-pass filter according to claim 1 and another filter.