JP2000091807A - Dielectric band pass filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve attenuating characteristics at the low pass side of a pass band. SOLUTION: A band pass filter is constituted of the laminated body of substrates D1-D6 of a dielectric. Inside ground electrodes G1 and G2 to be connected with outside ground electrodes G4 and G5 are formed on substrates D1 and D5, and first and second pattern electrodes P1 and P2 constituting first and second resonators with the inside ground electrodes G1 and G2 are formed on a substrate D3, and a third pattern electrode P3 constituting a third resonator with the inside ground electrodes G1 and G2 is formed on a substrate D4. The fetch electrodes of the pattern electrodes P1 and P2 are connected with input and output electrodes S1 and S2, and the short-circuit edges are connected with the outside ground electrode G4, and the short-circuit edge of the pattern electrode P3 is connected with the ground electrode G4. Thus, the first, third, and second three element resonators can be constituted between the input and output electrodes, and the attenuating amounts at the low pass side can be increased with wide frequencies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a dielectric filter,
In particular, the present invention relates to a laminated dielectric bandpass filter incorporated in a portable wireless communication device such as a mobile phone.

[0002]

2. Description of the Related Art In recent years, with the spread of wireless communication systems such as PHS and mobile phones, there is a growing demand for smaller and more reliable mobile communication devices used in such systems. Based on such a demand, a chip-type LC bandpass filter as shown in an exploded perspective view of FIG. 6 has been proposed as a bandpass filter incorporated in an RF stage in a mobile communication device. The conventional dielectric bandpass filter shown in FIG. 6 is configured as a laminate of a rectangular protective layer 30, a dielectric substrate 12, an adhesive layer 22, a dielectric substrate 24, and a protective layer 32. . The ground electrode 14 is formed on substantially the entire surface of one of the dielectric substrates 12, and the two pattern electrodes 16a and 16b and the guard electrode 20 are formed on the other surface. A shield electrode 28 is formed on the entire surface. Pattern electrodes 16a, 16
b has extraction electrodes 18a and 18b.

FIG. 6 shows a conventional dielectric band-pass filter.
The filter has six terminal electrodes 3 on opposite sides of the laminate.
4a to 34f are formed, and terminal electrodes 36a and 36b are formed on other opposing side surfaces. These terminal electrodes and the electrodes inside the laminate are connected as follows. The terminal electrode 34a is connected to the pattern electrode 16a, the ground electrode 14, and the shield electrode 28. The terminal electrode 34b includes the guard electrode 20, the ground electrode 14,
And the shield electrode 28. Terminal electrode 34
c is connected to the pattern electrode 16b, the ground electrode 14, and the shield electrode 28. Terminal electrodes 34d-3
4f is connected to the ground electrode 14 and the shield electrode 28. The terminal electrode 36a is connected to the extraction electrode 18a. The terminal electrode 36b is connected to the extraction electrode 18b.

In a conventional dielectric bandpass filter having such a structure, an equivalent circuit thereof is represented as shown in FIG. Note that CX and M indicate electromagnetic capacitive coupling and inductive coupling between the first and second pattern electrodes 16a and 16b. In addition, its attenuation characteristics (frequency
FIG. 7 (B) shows the band-pass filter having attenuation poles on both sides of the pass band. The pass bandwidth of the filter is
It can be adjusted by changing the distance d between a and 16b. When the distance d is reduced, the pass bandwidth is widened, and when it is increased, the pass bandwidth is narrowed.

[0005]

By the way, the filter characteristic used in the RF circuit of the mobile communication device ideally passes only the band used for communication without loss and infinite attenuation in other bands. Is to have quantity. However, since such a filter cannot be realized, it is necessary to optimize the filter characteristics according to the system and the circuit configuration. F that uses different frequencies for transmission and reception
In a communication system using the DD system, each of the transmission and reception filters constituting the duplexer requires a particularly large attenuation in the other frequency band. Also, in a communication system using the TDD system that switches between transmission and reception at high speed, it is general to use a local oscillator set to an oscillation frequency separated by a desired frequency above or below a communication band, The filter used in such an RF circuit particularly requires an attenuation on the oscillation frequency side of the local oscillator. As a practical example, T
In the case of the PHS of the DD system, the communication frequency is 1.9 GHz,
Since the frequency of the local oscillator is set near 1.65 GHz, the image is generated near 1.4 GHz. Therefore, a filter that can obtain a sufficient amount of attenuation in a wide range of about 1.4 to 1.7 GHz on the low frequency side of the reception frequency of 1.9 GHz is required.

In the conventional dielectric band-pass filter shown in FIG. 7, when the distance d between the pattern electrodes 16a and 16b is reduced in order to increase the pass band width, the coupling capacitance between these pattern electrodes is reduced. Ingredients increase,
CX will increase. This widens the passband, but at the same time the attenuation pole moves away from the passband. Conversely, when the interval d between the pattern electrodes 16a and 16b is increased to reduce the pass band width, the attenuation pole approaches the pass band. Therefore, it is impossible to widen the pass band width and bring the attenuation pole close to the pass band even if the distance d is adjusted. In order to satisfy such requirements,
Although it is necessary to increase the M-coupling by bringing the electrodes near the ground close to each other, this is extremely difficult, as is clear from the structure of the conventional example shown in FIG. Further, in order to widen the pass band, it is necessary to increase CX as described above.
Even if CX is formed on the same plane as in the structure of FIG. 6, a very large CX cannot be obtained because the facing area between the electrodes is small. Therefore, when the conventional dielectric band-pass filter is applied to a device in which the frequency of the local oscillator is lower than the communication band, sufficient attenuation characteristics cannot be obtained in the low band outside the pass band, The reliability of the equipment was not sufficient. The present invention has been made in view of such problems of the conventional example, and an object of the present invention is to provide a small-sized multilayer band-pass filter having good attenuation characteristics over a wide frequency range in a low band outside a pass band. It is.

[0007]

In order to achieve the above object of the present invention, an input electrode, an output electrode,
And a laminated dielectric band-pass filter having an external ground electrode on the outside, the first and second internal ground electrodes connected to the external ground electrode, and the first and second internal grounds inside. First and second pattern electrodes provided on the same plane between the electrodes and forming first and second resonators together with the first and second internal ground electrodes; A first electrode and a second electrode, wherein the extraction electrode is connected to the input electrode, the extraction electrode of the second pattern electrode is connected to the output electrode, and the short-circuit ends of the first and second pattern electrodes are connected to the external ground electrode. And the third internal electrode provided between the first and second internal ground electrodes and the third internal electrode provided between the first and second internal ground electrodes. Pattern of electricity And a third pattern electrode whose short-circuited end is connected to the external ground electrode and is electromagnetically coupled to the first and second pattern electrodes, between the input electrode and the output electrode. To form a first, third, and second three-element resonator that is electromagnetically coupled to
In addition, the first resonator and the second resonator are electromagnetically jump-coupled.

In the dielectric band-pass filter of the present invention, the open ends of the first and second pattern electrodes are folded toward the short-circuit ends of these pattern electrodes.
The open end of the third pattern electrode is divided into two parts and folded symmetrically toward the short-circuit end, and the electromagnetic coupling between the first pattern electrode and the second pattern electrode and the first pattern electrode are formed.
Also, in the electromagnetic coupling between the second pattern electrode and the third pattern electrode, the capacitive coupling is configured to be dominant over the inductive coupling, so that it is good over a wide range of frequencies in the lower low band outside the pass band. A high attenuation characteristic can be obtained. Further, the dielectric band-pass filter of the present invention further comprises at least one line on the symmetry axis of the first and second pattern electrodes.
By providing an electrode electrically connected to the two external electrodes, it is possible to suppress jumping electromagnetic coupling between these pattern electrodes. Still further, the dielectric bandpass filter of the present invention is further provided between the first and second pattern electrodes and the first internal ground electrode so as to partially overlap with the pattern electrodes, and And an internal ground electrode connected to an external ground electrode on the side opposite to the short-circuited end of the second pattern electrode.
It is preferable that the characteristic impedance of the resonator can be adjusted.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an embodiment of a laminated dielectric band-pass filter according to the present invention will be described. FIG.
1A is a perspective view of a dielectric bandpass filter of the present invention, and FIG. 1B is an exploded perspective view thereof. In the figure, D1 to D6 are first to sixth dielectric substrates (hereinafter, substrates D1 to D6), which are sequentially stacked. Substrate D
Internal ground electrodes G1 and G2 are formed on the upper surface (front surface) of each of the substrates D1 and D5. These internal ground electrodes are provided on the entire substrate surface except for the central portion of a pair of short edges of the substrates D1 and D5. Across, is formed. An internal ground electrode G3 for impedance adjustment is formed on a part of the upper surface of the substrate D2. First and second pattern electrodes P1 and P2 are formed on the upper surface of the substrate D3, and third pattern electrodes P3 are formed on the upper surface of the substrate D4. No electrodes are formed on the lower surfaces (back surfaces) of the substrates D2 to D6, and the substrate D6 is for protection.

The first and second pattern electrodes P1 and P2 on the substrate D3 are formed symmetrically as a whole,
In each of the pattern electrodes, the substrate D3 is located approximately from the center.
The extraction electrodes ps1 and ps2 reaching the short edge of the substrate D3 are formed, and one end reaches the one long edge of the substrate D3 to form a short-circuit end (ground end). In addition, the third pattern P3 is formed in a substantially T-shaped symmetrical left and right shape, and the center end thereof reaches one long edge of the substrate D4 to form a short-circuit end. No extraction electrode is formed on the third pattern electrode P3. These first to third pattern electrodes, together with the first and second internal ground electrodes, are the first to third 1/1/3.
A four-wavelength resonator is formed. The details of the first to third pattern electrodes and the resonators formed thereby are shown in FIG.
This will be described in further detail below with reference to FIG.

After laminating these substrates D1 to D6,
As shown in FIG. 1A, external ground electrodes G4 and G5 are formed from both long edges on the lower surface of the substrate D1 to both long edges on the upper surface of the substrate D6. An input electrode S1 and an output electrode S2 are formed at the center of each of the two short edges from both short edges on the upper surface of the substrate D6. The external ground electrode G5 is connected to the substrates D1, D2, D
5, are connected to the internal ground electrodes G1, G2, G3 on
On the other hand, the external ground electrode G4 is connected to the internal ground electrodes G1 and G2 on the substrates D1 and D5.
3, also connected to the short-circuited ends of the first to third pattern electrodes P1 to P3 on D4. The input electrode S1 and the output electrode S
2 is connected to the extraction electrodes ps1 and ps2 on the substrate D3, respectively.

FIGS. 2A and 2B show substrates D3 and D3.
4 is an enlarged view of the first to third pattern electrodes P1 to P3 on FIG. First and second pattern electrodes P1, P
2 are formed symmetrically as described above, and together with the internal ground electrodes G1 and G2 (FIG. 1), the first and second 1 /
A four-wavelength resonator is configured. Third pattern electrode P3
Is a third quarter with internal ground electrodes G1 and G2.
It constitutes a wavelength resonator. FIG. 3 shows an equivalent circuit diagram of the dielectric band-pass filter of FIG. 1, and includes first to third pattern electrodes P1 to P3 and an internal ground electrode G.
The portions of the first to third resonators respectively constituted by 1 and G2 are surrounded by rectangular chain lines with P1 to P3. Therefore, after this, the first to third resonators also become P1
ＰP3.

First and second pattern electrodes P1, P2
Are open ends (portions A1 and A1) as shown in FIG.
The interval a in 2) is smaller than the interval c between the central portions C1 and C2,
Further, the interval b between the short-circuit ends (portions B1 and B2) is set to be smaller than the interval c. As shown in FIG. 2 (B), the third pattern electrode P3 has an open end divided into two parts and is bent at about 180 ° toward the short-circuit end to form open end portions D and F. I have. E is a short-circuit end. The first and third pattern electrodes P1 and P3 are configured such that the portions A1 and B1 and the portions D and E are capacitively and inductively coupled, respectively, as shown in the equivalent circuit of FIG. A bond CX13 and an inductive bond M13 are formed. Similarly, an electromagnetic capacitive coupling CX23 and an inductive coupling M23 are formed between the second and third pattern electrodes P2 and P3. Also, the first and second pattern electrodes P1, P2
Between the capacitive coupling CX12 and the inductive coupling M12.
Is formed. C1 and C2 are capacitance components formed between the first and second pattern electrodes P1 and P2 and the first and second internal ground electrodes G1 and G2, and C31 and C32 are the third components. Is formed between the pattern electrode P3 and the first and second internal ground electrodes G1 and G2.

As is apparent from FIG. 3, in the dielectric band-pass filter of the present invention, three resonators P1 to P3 formed by three pattern electrodes are provided between input / output terminals S1 and S2. Thus, a three-stage filter is constructed. Therefore, the attenuation can be increased as compared with the conventional two-stage dielectric band-pass filter including two resonators. At this time, in the dielectric band-pass filter of the present invention, although the number of layers is increased as compared with the conventional example, the mounting area of the chip is not increased. Can be improved. Further, in the dielectric band-pass filter of the present invention, jumping couplings CX12 and M12 are formed between the first and second resonators P1 and P2, thereby splitting the attenuation pole into two. And a greater attenuation can be obtained.

The degree of frequency separation between the two attenuation poles can be controlled by changing the size of the jump couplings CX12 and M12. That is, if you want to separate the attenuation poles,
The jump coupling may be increased by bringing the first and second pattern electrodes close to each other. The opposite is true when the attenuation poles are required to be close to each other. By increasing the distance a (FIG. 2) between the portions A1 and A2, the amount of coupling between them can be reduced.
As another method for reducing the amount of jump coupling, as shown in FIG. 4, first and second pattern electrodes P on a substrate D3 are used.
At least one end may be connected to the external ground electrode G5 and the electrode P4 may be arranged on the axis of symmetry between P1 and P2.
When such an electrode P4 is provided, jumping coupling between the first and second resonators P1 and P2 formed by these patterns is reduced. According to this method, since the planar area of the element is not increased, the demand for miniaturization is satisfied. Therefore, when it is necessary to change the jump coupling between the first and second resonators, FIG.
May be adjusted, or the length and width of the electrode P4 may be adjusted by providing an electrode P4 as shown in FIG. Of course, both adjustment methods may be employed.

The internal ground electrode G3 of the dielectric band-pass filter shown in FIG. 1 is for matching the characteristic impedance of the first to third resonators P1 to P3. In other words, as shown in FIG. 2B, the third pattern electrode P3 has an open end which is divided into right and left parts D
And F, the characteristic impedance of the third resonator tends to be low. For this reason, the internal ground electrode G3 is not provided on the substrate D2 on the lower surface side of the substrate D3 for the first and second resonators P1 and P2, but on the third resonator P3 side.
Provided on the first and second resonators P1, P2
2 can be reduced. Thereby, the characteristic impedances of the three resonators can be matched. One end of the internal ground electrode G3 is connected to the external ground electrode G as shown in FIG.
5 and the other end is an external ground electrode G
It is preferable that the first and second pattern electrodes 4 and 4 are not connected to each other and have an open end and partially overlap the first and second pattern electrodes. When the characteristic impedances of the three resonators are substantially the same, it is needless to say that the internal ground electrode G3 does not need to be provided.

The impedance of the third resonator can be increased even if the distance between the third pattern electrode P3 and the internal ground electrode G2 is increased. Also, the first
When the width near the open ends of the second pattern electrodes P1 and P2 is increased, the impedance of the first and second resonators can be reduced. Therefore, the impedance matching of the first to third resonators can be performed by this, but from the viewpoint of miniaturization, it is preferable to provide the internal ground electrode G3 for impedance adjustment. Even if the positions of the signal extraction electrodes ps1 and ps2 on the substrate D3 are changed, the characteristic impedance of the first and second resonators P1 and P2 can be adjusted.

FIG. 5 is a graph showing the results of experimentally fabricating a dielectric bandpass filter of the present invention and testing its attenuation characteristics. As shown in the graph, the experimental example of the present invention has a bandwidth of about 10% centering on 1.9 GHz and a bandwidth of 1.4 to 1.7 GHz.
A large amount of attenuation is obtained within the range. On the other hand, in the conventional example shown in FIG. 6, as shown in FIG. 7B, the bandwidth is about 5% centering on 3.0 GHz, and the range of large attenuation is 2.7. It is about 2.8 GHz. Therefore, according to the present invention, compared to the conventional example,
It can be seen that the bandwidth is doubled and the range where the amount of attenuation is large is greatly widened. And, as described above, P
In the HS, the communication frequency is around 1.9 GHz, and the image occurs around 1.4 GHz when the local oscillation frequency is around 1.65 GHz. However, if the band pass filter of the present invention is used, the local oscillation frequency and The image frequency can be sufficiently attenuated.

The above description has been given with reference only to the preferred embodiment of the present invention, and it goes without saying that various modifications and changes are possible. For example, the shapes of the first to third pattern electrodes are not limited to those of FIG. 2 and can be changed as appropriate. The material and size of the dielectric substrate and the material of the electrodes may be appropriately selected according to the electrical characteristics of the filter, the mounting space, and the like. Moreover,
At the time of manufacturing, electrodes for a plurality of elements are formed on a substrate, the obtained substrate is laminated, cut into one element, and an external electrode is formed on each element to form a plurality of elements at the same time. good.

[Brief description of the drawings]

FIGS. 1A and 1B show the configuration of a dielectric bandpass filter of the present invention, in which FIG. 1A is a perspective view and FIG. 1B is an exploded perspective view.

FIG. 2 is an explanatory diagram showing an enlarged display of first to third pattern electrodes provided in the dielectric bandpass filter of the present invention shown in FIG.

FIG. 3 is a circuit diagram showing an equivalent circuit of the dielectric bandpass filter of the present invention shown in FIG.

FIG. 4 is a diagram illustrating a state in which the dielectric band-pass filter of the present invention shown in FIG. 1 includes first and second pattern electrodes.
It is explanatory drawing which shows the example in which the electrode for reducing the amount of jump coupling was provided.

FIG. 5 is a graph showing an attenuation characteristic and a return loss characteristic of the dielectric bandpass filter of the present invention.

FIG. 6 is an exploded perspective view showing a configuration of a conventional dielectric bandpass filter.

FIG. 7 is a graph showing an equivalent circuit, attenuation characteristics, and return loss characteristics of the conventional dielectric bandpass filter shown in FIG.

Claims (4)

[Claims] 1. A laminated dielectric band-pass filter having an input electrode, an output electrode, and an external ground electrode on the outside, wherein a first and a second internal ground electrode connected to the external ground electrode are provided therein. And provided on the same plane between the first and second internal ground electrodes, together with the first and second internal ground electrodes.
And first and second pattern electrodes forming a second resonator, wherein the extraction electrode of the first pattern electrode is connected to the input electrode, and the extraction electrode of the second pattern electrode is connected to the output electrode. Between the first and second pattern electrodes, wherein the short-circuited ends of the first and second pattern electrodes are connected to an external ground electrode; and between the second internal ground electrode and the first and second pattern electrodes. And a third pattern electrode constituting a third resonator together with the first and second internal ground electrodes, the short-circuited end of which is connected to the external ground electrode, and A first, a third, and a second third electrode, which are electromagnetically coupled between an input electrode and an output electrode in order from a third pattern electrode electromagnetically coupled to the pattern electrode;
A first resonator and a second resonator.
Wherein the resonators are electromagnetically jump-coupled. 2. The dielectric band-pass filter according to claim 1, wherein the open ends of the first and second pattern electrodes are folded back toward the short-circuited ends of the pattern electrodes, and the third pattern electrode is provided. Open end is divided into two parts and folded symmetrically toward the short-circuited end, electromagnetic coupling between the first pattern electrode and the second pattern electrode, and the first and second pattern electrodes A dielectric bandpass filter characterized in that capacitive coupling prevails over inductive coupling in the electromagnetic coupling between the dielectric bandpass filter and the third pattern electrode. 3. The dielectric bandpass filter according to claim 2, wherein said filter is further electrically connected to at least one external ground electrode on the axis of symmetry of said first and second pattern electrodes. A dielectric bandpass filter comprising an electrode for suppressing jumping electromagnetic coupling between these pattern electrodes. 4. The dielectric band-pass filter according to claim 1, wherein said filter further comprises a first electrode and a second electrode disposed between said first and second pattern electrodes and said first internal ground electrode. A dielectric, provided with an internal ground electrode for impedance adjustment, provided so as to partially overlap the electrode, and connected to an external ground electrode opposite to the short-circuited end of the first and second pattern electrodes. Body bandpass filter.