JP3580707B2 - Low-pass filter and circuit board - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a low-pass filter and a circuit board, and more particularly to a laminated high-frequency low-pass filter and a circuit board which are incorporated in a circuit board for an RF module and are used in a filter or a duplexer incorporated in a high-frequency circuit radio section of a portable telephone or the like. About.
[0002]
[Prior art]
As a conventional laminated high-frequency low-pass filter, for example, there is a filter disclosed in Japanese Patent Application Laid-Open No. 9-214273. FIG. 5 shows a low-pass filter disclosed in this publication, and reference numerals 61 to 68 indicate dielectric layers. FIG. 6 is an equivalent circuit diagram.
[0003]
Ground electrodes 69a to 69c are provided on the upper surfaces of the dielectric layers 61, 65 and 67, respectively, and a pair of strip lines 70a and 70b are provided on the upper surfaces of the dielectric layers 62, 63 and 64, respectively. Are formed with capacitance forming electrodes 71a to 71c.
[0004]
The strip lines 70a and the strip lines 70b on the upper surfaces of the dielectric layers 62, 63, 64 are connected by via-hole conductors 72a, 72b to form an inductor. This is represented as lines 81a and 81b.
[0005]
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 equivalent to the equivalent circuit shown in FIG. In the figure, they are represented as capacitors 82a, 82b, 82c.
[0006]
[Problems to be solved by the invention]
However, in the low-pass filter disclosed in the above publication, as shown in FIG. 6, since there are two stages of Π-type LC circuits, two strip lines 81a and 81b having a length corresponding to the pass frequency are required. However, there has been a problem that miniaturization is hindered.
[0007]
If the number of Π-type LC circuits is reduced to one in order to promote miniaturization, there is a problem that the attenuation characteristics of the low-pass filter deteriorate.
[0008]
In addition, with the miniaturization of mobile phones, there is a strong demand for miniaturization of electronic components, and modularization of electronic components has progressed. Filters such as low-pass filters, high-pass filters, band-pass filters, and matching circuits for impedance matching have been developed. It is required that the passive circuit be built in the circuit board, and it is difficult to cope with the conventional low-pass filter of the separate type.
[0009]
Furthermore, with the dualization of mobile phones (for example, both the 900 MHz band and the 1800 MHz band can be transmitted and received), two reception filters and two transmission filters are simply required. As systemization progresses, the number of filters increases. However, an increase in the size of the mobile phone is not allowed, and further downsizing is required.
[0010]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a low-pass filter and a circuit board that can be reduced in size, secure an attenuation amount, and can be built into a circuit board.
[0011]
[Means for Solving the Problems]
Low pass filter of the present invention, in the laminate comprising a dielectric layer stacked, an inductor and one ends of the two strip lines are respectively formed on different dielectric layers formed by connecting the via-hole conductors, the different dielectric A capacitor comprising a pair of first capacitance forming electrodes formed between the body layers and connected to the other end of the strip line , wherein the inductor and the capacitor are formed between a pair of ground electrodes, and A second capacitance forming electrode is formed opposite to the ground electrode, and the second capacitance forming electrode is connected to the via hole conductor connecting the two strip lines by a via hole conductor . Here, it is desirable to form first capacitance forming electrodes at both ends of the inductor.
[0012]
A circuit board according to the present invention includes the above-described low-pass filter.
[0013]
[Action]
In the low-pass filter of the present invention, one end of each of the strip lines formed between different dielectric layers is connected by a via-hole conductor, and the second end of the strip line formed between the dielectric layers different from the strip line is connected to one end of the strip line. Since the capacitance forming electrodes are connected by via-hole conductors, a new attenuation pole can be formed on the high-frequency side of the low-pass filter, and the stop band can be increased. Therefore, even if the size is reduced by reducing the number of stages, the amount of attenuation can be secured.
[0014]
That is, referring to FIG. 4, a first attenuation pole A is formed by an inductor having one end of a strip line connected by a via-hole conductor and a capacitor including a pair of first capacitance forming electrodes. The second attenuation pole B existing on the very high frequency side of A is moved to the vicinity of the first attenuation pole A by forming a capacitor including the second capacitance forming electrode and the ground electrode substantially at the center of the inductor. And the rejection bandwidth can be increased.
[0015]
For example, if the capacitance is increased by increasing the area of the second capacitance forming electrode or shortening the distance from the ground electrode, the second attenuation pole B becomes closer to the first attenuation pole. By adjusting the area and the distance to the ground electrode, the second attenuation pole B can be moved so as to obtain a desired stop bandwidth.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is an external perspective view of a circuit board incorporating a low-pass filter of the present invention, FIG. 2 is a transparent perspective view showing a pattern configuration, and FIG. 3 is an equivalent circuit diagram.
[0017]
In FIG. 1, reference numeral 1 denotes an insulating base and also a dielectric. The surface electrode 3 is formed on the surface of the insulating base 1. Various chip products such as a capacitor, an inductor, and a diode are mounted on the surface electrode 3. The surface electrode 3 also functions as an input / output electrode of an element such as a filter built in the insulating base 1.
[0018]
An end face electrode is formed on the side surface of the insulating base 1, and there are two types of end face earth electrode 4 and end face input / output electrode 5. The end face earth electrode 4 is connected to an earth electrode built in the insulating base 1 or formed on the back surface.
[0019]
The end face input / output electrode 5 is connected to an input / output electrode built in the dielectric layer or formed on the back surface, and plays a role as an input / output of an antenna, transmission, reception, power supply, or the like. A broken line portion F in the insulating base 1 represents a filter, and its pattern configuration will be described below.
[0020]
In FIG. 2, reference numerals 11 and 12 are ground electrodes, which are common to the ground electrode on the circuit board. Reference numerals 21 and 22 denote first capacitance forming electrodes, which form an input / output capacitance between the first capacitance forming electrodes 21 and 22.
[0021]
The insulating substrate 1 is composed of five dielectric layers 10a to 10e, and the first capacitance forming electrodes 21, 22 and the ground electrode 12 are formed on the upper surfaces of the dielectric layers 10b, 10c, 10d, respectively. The ground electrode 11 is formed on the lower surface of the dielectric layer 10a.
[0022]
Reference numerals 23 and 24 denote strip lines. One ends of the strip lines 23 and 24 are connected to each other by a via-hole conductor 32, and these constitute an inductor.
[0023]
Reference numeral 27 denotes a second capacitance forming electrode, which forms a capacitance with the ground electrode 11. By adjusting the capacitance formed between the second capacitance forming electrode and the ground electrode 11, the second attenuation pole on the higher frequency side than the first attenuation pole can be moved to the vicinity of the first attenuation pole. The characteristics can be improved.
[0024]
In addition, as shown in FIG. 2, the connection between the electrodes is performed by via-hole conductors 31 to 34. That is, the input / output electrode 16 is connected to the input / output land 28 of the filter through the via-hole conductor 31. The lands 25 and 26 are connected by the via-hole conductor 32, and the two-layer strip lines 23 and 24 are connected. The first capacitance forming electrode 22 of the filter and the surface electrode 3 are connected by the via-hole conductor 33, and input and output of the filter can be performed by the surface electrode 3 and the input / output electrode 16. Further, the second capacitance forming electrode 27 is connected to the land 25 which is a connection point between the strip line 23 and the via-hole conductor 32 by the via-hole conductor 34, thereby forming a capacitance with the ground electrode 11.
[0025]
The layer configuration of the low-pass filter of the present invention will be described in detail. The ground electrode 11 and the input / output electrode 16 are formed on the lower surface of the dielectric layer 10a, and the second capacitance forming electrode 27 is formed on the upper surface.
[0026]
A first capacitance forming electrode 21 and a strip line 23 are formed on the upper surface of the dielectric layer 10b. A land 25 is formed at one end of the strip line 23, and an input / output land 28 and the first capacitance forming electrode 21 are formed at the other end. I have.
[0027]
A first capacitance forming electrode 22 and a strip line 24 are formed on the upper surface of the dielectric layer 10c. A land 26 is formed at one end of the strip line 24, and the first capacitance forming electrode 22 is formed at the other end.
[0028]
The ground electrode 12 is formed on the upper surface of the dielectric layer 10d, and the surface electrode 3 is formed on the upper surface of the dielectric 10e. The position of the via-hole conductor 33 of the ground electrode 12 is in a state where the ground electrode 12 is pulled out, that is, is opened so that the ground electrode 12 and the via-hole conductor 33 are not connected.
[0029]
Such a low-pass filter includes, for example, forming a through hole for a via hole at a position to be a via hole in a plurality of unfired green sheets, filling the through hole with a conductive paste, and filling the conductive paste with such a conductive paste. The strip lines 23 and 24, the first capacitance forming electrodes 21 and 22, the ground electrodes 11 and 12, the second capacitance forming electrodes 27, the lands 25 and 26, the input / output electrodes 16, the surface electrodes 3, It is manufactured by applying a conductive paste so as to form the lands 28, laminating green sheets coated with the conductive paste, and sintering and integrating them.
[0030]
Each of the five dielectric layers 10a to 10e may be formed from a single green sheet or a stack of 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 base 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.
[0031]
As a dielectric material constituting the insulating base 1, a built-in strip line can realize an impedance of about 50Ω and a small and high-performance bandpass filter can be built in. It is preferable that the Q value is high and τf is close to 0. For example, with respect to 100 parts by weight of a main component composed of aMgO.bCaO.cTiO ₂ (25 ≦ a ≦ 35, 0.3 ≦ b ≦ 7, 60 ≦ c ≦ 70, a + b + c = 100, unit: wt%), boron 3-20 parts by weight containing compound in terms _{of B} 2 _{O 3,} and the like of the lithium-containing compound _Li 2 _{O 3} that is added to 10 parts by weight basis.
[0032]
Each electrode of the filter is preferably formed using a low-resistance conductor such as copper, silver, or gold so as not to deteriorate the loss of the built-in filter and line. The insulating substrate is preferably co-fired with the above conductor using a low-temperature firing material of about 900 to 1000 ° C., and can be efficiently manufactured by low-temperature simultaneous firing.
[0033]
FIG. 3 shows an equivalent circuit of the low-pass filter of the present invention, which will be described.
[0034]
Reference numeral 51 represents a capacitance between input and output, and means a capacitance between the first capacitance forming electrodes 21 and 22. Reference numeral 52 denotes a strip line (mainly functioning as an inductor), which includes the strip lines 23 and 24 and the via-hole conductor 32. The pass frequency band and the attenuation pole position can be controlled by the input / output capacitance 51 and the strip line 52. Reference numerals 53 and 54 denote stray capacitances between the first capacitance forming electrodes 21 and 22 and the ground electrodes 11 and 12. If the stray capacitances are large, impedance matching of the line cannot be achieved, and the insertion loss of the filter deteriorates. In the present filter, the stray capacitance is suppressed by making the dielectric layers 10a and 10d between the first capacitance forming electrodes 21 and 22 and the ground electrodes 11 and 12 as thick as possible.
[0035]
Reference numeral 55 denotes a capacitance between the second capacitance forming electrode 27 and the ground electrode 11.
[0036]
In this filter, the voltage distribution of the low-pass filter at the pass frequency (900 MHz band) shows the maximum value at the input / output and the minimum value at the lands 25 and 26 which are the connection points of the strip lines. In addition, at the first attenuation pole position (1800 MHz band), the input shows the maximum value and the output shows the minimum value. Therefore, in these frequency bands, the capacitance 55 between the second capacitance forming electrode 27 and the ground electrode 11 has almost no effect.
[0037]
However, on the high frequency side, there is a frequency at which the voltage at the input / output is minimum and the voltage at the connection point is maximum. At this time, the insertion loss becomes minimal and shows a maximum value at the connection point, so that the capacitance value between the second capacitance forming electrode 27 and the ground electrode 11 affects the frequency.
[0038]
As a result, the second attenuation pole, which should originally be located on the higher frequency side, appears near the first attenuation pole, and the attenuation characteristic of the low-pass filter is improved.
[0039]
【Example】
A circuit board incorporating the low-pass filter of the present invention shown in FIGS. 1 to 3 was manufactured.
[0040]
The size of the circuit board was 10 mm × 10 mm × 1.0 mm, and the area occupied by the electrode patterns of the filter portion (capacitance forming electrode, strip line, land, etc.) was 3.0 mm × 1.2 mm. The occupied area of the electrode pattern refers to the area when the filter portion of the dielectric layer 10c in FIG. 2 is viewed from above.
[0041]
The thickness of the dielectric layer between the ground electrodes 11 and 12 was 0.9 mm. Using a dielectric material having a relative dielectric constant of 20, the total length and line width of the strip lines 23 and 24 are 8.4 mm and 0.1 mm, respectively, and the size of the first capacitance forming electrodes 21 and 22 is 0.7 × 1. .1 mm, the size of the second capacitance forming electrode 27 is 0.5 × 0.5 mm, and the distance from the ground electrode 11, that is, the measurement result of the frequency characteristic when the thickness of the dielectric layer 10a is 0.2 mm. Is shown in FIG.
[0042]
From the results of FIG. 4, the attenuation in the 900 MHz band was 0.30 dB and the attenuation in 2f (1800 MHz band) was 30 dB. The attenuation at 3f (2700 MHz band) was 35 dB.
[0043]
【The invention's effect】
In the low-pass filter of the present invention, one end of a strip line formed between different dielectric layers is connected by a via-hole conductor, and a second line formed between one dielectric layer different from the strip line is connected to one end of the strip line. Since the capacitor forming electrodes are connected by via-hole conductors, a new attenuation pole can be formed on the high-frequency side of the low-pass filter, and the rejection bandwidth can be increased. Therefore, even if the size is reduced by reducing the number of stages, the amount of attenuation can be secured, and the low-pass filter can be built in the substrate.
[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 an equivalent circuit diagram of the low-pass filter of the present invention.
FIG. 4 is a graph showing frequency characteristics of the low-pass filter of the present invention.
FIG. 5 is an exploded perspective view showing a conventional low-pass filter.
FIG. 6 is an equivalent circuit diagram of a conventional low-pass filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Insulating base 3 ... Surface electrode 4 ... End face earth electrode 5 ... End face input / output electrode 16 ... Input / output electrodes 10a-10e ... Dielectric layers 11, 12 ... Earth Electrodes 21 and 22 First capacitance forming electrodes 23 and 24 Strip lines 25 and 26 Land 27 Second capacitance forming electrodes 31 to 34 Via hole conductor F Filter

Claims (3)

The dielectric layer in the laminate formed by laminating a plurality inductor comprising the one ends of the two strip lines are respectively formed on different dielectric layers and connected by via hole conductors, wherein the strip line on the different dielectric layers A capacitor formed of a pair of first capacitance forming electrodes connected to the other end, respectively , the inductor and the capacitor being formed between a pair of ground electrodes, and facing the ground electrode. A low-pass filter, wherein a second capacitance forming electrode is formed by connecting the second capacitance forming electrode to the via hole conductor connecting the two strip lines with a via hole conductor . 2. The low-pass filter according to claim 1, wherein first capacitance forming electrodes are formed at both ends of the inductor. A circuit board comprising the low-pass filter according to claim 1.

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