JPH04284015A - Ladder-type filter - Google Patents

Abstract

PURPOSE:To obtain the miniature ladder-type filter capable of constituting as an electronic equipment packageable on a plane. CONSTITUTION:First-third slits are formed while being extended from one edge to the inside, a piezoelectric substrate constitutes a turning fork-shaped oscillation part between the second and third slits, serial resonators 21 and 22 and parallel resonators 23 and 24 are composed of a tuning fork type piezoelectric resonator equipped with an oscillation electrode for oscillating the turning fork-shaped oscillation part of the piezoelectric substrate and for such a ladder- type filter 20, the serial resonators 21 and 22 and the parallel resonators 23 and 24 are laminated/integrated through cavity forming members 25-29 for securing the cavity so as not to interrupt the oscillation of the tuning fork- shaped oscillation part one and another.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ladder type filter, and more particularly to a ladder type filter in which a series resonator and a parallel resonator are constructed using tuning fork type piezoelectric resonators.

0002

2. Description of the Related Art An example of the structure of a conventional ladder type filter is shown in FIG. This ladder type filter is constructed using a plurality of piezoelectric resonators that utilize the spreading vibration mode of a square plate. That is, a four-element two-stage ladder filter shown in the circuit diagram of FIG. 3 is constructed using rectangular plate-shaped series resonators 1 and 2 and rectangular plate-shaped parallel resonators 3 and 4.

In FIG. 2, reference numeral 2a indicates an electrode formed on one main surface of the series resonator 2, and a similar electrode is formed on the other main surface of the series resonator 2. Similar electrodes are also formed on both main surfaces of the series resonator 1. On the other hand, the parallel resonators 3 and 4 have electrodes 3a on the entire surface of both main surfaces.
, 4a are formed. In addition, 5 to 11 indicate metal terminals, and the series resonators 1 and 2 and the parallel resonators 3 and 4 are shown in FIG.
They are used for mutual electrical connection as shown in the figure. The metal terminals 5 to 11, together with the series resonators 1 and 2 and the parallel resonators 3 and 4, are connected to a case 1 made of an insulating material.
It is stored in 2. Further, the upper opening 12a of the case member 12 is closed by a lid member (not shown) to form one ladder type filter component. In this case, the metal terminals 9 to 11 are pulled out of the case and used as connection terminals with the outside.

By the way, when driving the above-mentioned ladder type filter, it is necessary that the series resonators 1 and 2 and the parallel resonators 3 and 4 can vibrate in a desired manner while being housed in the case 12. That is, the vibration of each of the resonators 1 to 4 must not be hindered while housed in the case 12. Therefore, a so-called spring terminal having spring properties is used as the metal terminal 11 located at the end.

[0005]

[Problems to be Solved by the Invention] In the ladder type filter shown in FIG. 2, a spring terminal is used as the metal terminal 11 in order not to interfere with the vibration of the resonators 1 to 4 housed in the case 12. A considerable amount of unnecessary space is created, which tends to increase the overall size of the ladder filter. For example, in the illustrated two-stage ladder filter with built-in four elements, the dimensions when configured as a final ladder filter component are 7.0 mm x 8.0 mm.
The size was approximately 8.0 mm x thickness.

[0006] In recent years, like other electronic components, there has been a demand for ladder filters that are constructed as surface-mounted electronic components. Therefore, the purpose of the present invention is to
An object of the present invention is to provide a ladder filter that can be constructed as a surface-mounted electronic component and has a small overall shape.

[0007]

[Means for Solving the Problems] The present invention is a ladder type filter formed by connecting at least one series resonator and at least one parallel resonator, and is characterized by having the following configuration. That is, in the present invention, as a series resonator and a parallel resonator, second and third slits extend inward from one end edge of the piezoelectric substrate so as to sandwich a first slit extending inward from one end edge of the piezoelectric substrate. form the second,
A tuning fork type piezoelectric resonator is used in which a tuning fork-shaped vibrating section is formed between the third slits, and electrodes are formed on a piezoelectric substrate in order to vibrate the tuning fork-shaped vibrating section. Then, a plurality of tuning fork type piezoelectric resonators constituting a series resonator and a parallel resonator are stacked with a cavity forming material interposed therebetween to ensure a cavity that does not interfere with the vibration of each other's tuning fork shaped vibrating parts. are integrated.

[0008]

[Operation] Multiple tuning fork type piezoelectric resonators constructed using piezoelectric substrates are laminated and integrated through a cavity forming material, that is, because they are laminated and integrated without using spring terminals, the ladder The thickness of the mold filter component can be made very thin.

[0009]

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is an exploded perspective view showing the overall structure of a ladder type filter according to an embodiment of the present invention. In the ladder filter 20 of this embodiment, series resonators 21 and 22 and parallel resonators 23 and 24 are alternately stacked as shown in the figure.
A four-element, two-stage ladder filter is constructed. Figure 1
In, each series resonator 21, 22 and parallel resonator 23
, 24 are laminated with cavity forming members 25 to 27 interposed therebetween. Further, on the upper and lower sides of the laminate, similarly, cavity forming materials 28, 29 are provided.
The substrates 30a and 30b are stacked with each other interposed therebetween.

[0010] Spacers 31 to 34 having the same thickness as each resonator are arranged on the sides of each series resonator 21, 22 and parallel resonator 23, 24, respectively. next,
Details of the series resonators 21 and 22 and the parallel resonators 23 and 24 will be described with reference to FIGS. 4 to 9. As shown in an exploded perspective view in FIG. 4, the series resonator 21 is constructed by forming first to third slits 212 to 214 extending inward from one end edge of the piezoelectric substrate 211. Third
It has a structure in which a tuning fork-shaped vibrating part is formed between the slits 213 and 214. A vibrating electrode 215 is formed on the upper surface of the piezoelectric substrate 211 in the tuning fork-shaped vibrating section. Also,
As is clear from FIG. 6, which is an exploded view of only the electrodes formed on both main surfaces of the series resonator 21, a vibrating electrode 21 is also provided on the lower surface side of the piezoelectric substrate 211 so as to face the vibrating electrode 215.
6 is formed. Therefore, the vibrating electrodes 215, 216
By applying an alternating current voltage to the tuning fork-shaped vibrating part surrounded by the second and third slits 213 and 214, the tuning fork-shaped vibrating part is vibrated as a piezoelectric tuning fork.

Note that 217a and 217b indicate connecting conductive parts, and the connecting conductive parts 217a and 217b allow the vibrating electrodes 215 and 216 to connect to the terminal electrodes 218 and 21, respectively.
It is drawn out to 9. In the series resonator 21, the vibrating electrodes 215 and 216 formed on both main surfaces are led out to terminal electrodes 218 and 219 formed at different corner portions of the piezoelectric substrate 211, as is clear from FIGS. 4 and 6. ing.

Referring to FIG. 4, there is a gap 31a in front of the part where the tuning fork-shaped vibrating part of the series resonator 21 is formed.
A spacer 31 is placed between the two. gap 3
1a is provided so as not to hinder the vibration of the tuning fork-shaped vibrating section. The series resonator 21 and the spacer 31 are stacked with the parallel resonator 23 and the spacer 33 below, with a rectangular frame-shaped cavity forming member 25 interposed therebetween. The rectangular frame-shaped cavity forming member 25 has upper and lower series resonators 21 and parallel resonators 23.
It is provided to form a cavity that does not interfere with the vibration of the tuning fork-shaped vibrating part. The cavity forming material 25 can be constructed by applying an adhesive to the shape shown in the figure, or by using elastic rubber, synthetic resin, or the like molded into the shape of the rectangular frame shown in the figure. In any case, in order not to impede the vibration of the upper and lower tuning fork-shaped vibrating parts, it is necessary to have a predetermined thickness as shown in the figure.

The parallel resonator 23 has a structure in which first to third slits 232 to 234 are formed in a piezoelectric substrate 231, and vibrating electrodes 235 and 236 shown in FIG. 7 are formed on both main surfaces. The vibrating electrodes 235, 236 are led out to terminal electrodes 238, 239 by connecting conductive parts 237a, 237b, respectively. As is clear from FIGS. 4 and 7,
One terminal electrode 238 of the parallel resonator 23 is connected to the piezoelectric substrate 23
1 is formed at the center of the edge of the other terminal electrode 2.
39 is formed at one corner of the piezoelectric substrate 231.

FIGS. 5, 8 and 9 show details of the part where the series resonator 22 and parallel resonator 24 of FIG. 1 are stacked, and the upper series resonator 21 and parallel resonator 23 Figures 4, 6 and 7 used to explain
This is a diagram corresponding to . Therefore, the lower series resonator 22, parallel resonator 24, cavity forming material 27, and spacers 32, 34 will be given the same reference numbers as above, and detailed explanation thereof will be omitted.

The ladder type filter of this embodiment is constructed by laminating and integrating the constituent members shown in FIG. 1. That is, as shown in FIG. 10, the ladder type filter 20 of the embodiment is obtained by forming external electrodes 41 to 46 on both end surfaces of a stacked body 40 that is stacked and integrated. As is clear from FIGS. 6 to 9, the external electrode 41 is the terminal electrode 2 of the series resonator 21.
18, and the external electrode 42 is connected to the parallel resonator 23.
The external electrode 43 is connected to the terminal electrode 219 of the series resonator 21 and the terminal electrode 239 of the parallel resonator 23 . Similarly, the external electrode 44
is the terminal electrode 229 of the series resonator 22 and the parallel resonator 24
The external electrode 45 is connected to the terminal electrode 249 of the parallel resonator 24
The external electrode 46 is connected to the terminal electrode 228 of the series resonator 22 .

[0016] Therefore, by connecting the external electrodes 43 and 46 on the outer surface of the laminate 40 or outside, the ladder type filter shown in FIG. 11 is constructed. As is clear from FIG. 10, in the ladder type filter 20 of this embodiment, the series resonators 21 and 22 and the parallel resonators 23 and 24 are configured by tuning fork type piezoelectric resonators configured using a piezoelectric substrate. , and each resonator 21
24 have a structure in which they are laminated and integrated via the cavity forming members 25 to 27, so that the ladder filter can be configured as an ultra-thin component with a very small overall thickness. When a two-stage ladder filter 20 incorporating the four elements described above was actually manufactured, its dimensions were 6.2 x 5.0 x 2.0 mm. Therefore, it can be seen that the overall size is considerably smaller than the conventional ladder type filter shown in FIG. Moreover, since it can be electrically connected to the outside using the external electrodes 41 to 46 as described above, it can be seen that it can be provided as a chip type electronic component that can be surface mounted.

Note that in the above-mentioned embodiment, the series resonator 2
Although a case has been described in which a two-stage ladder filter is constructed using two parallel resonators, according to the present invention, one
It is possible to configure a ladder type filter having any number of stages as described above. FIG. 12 shows the attenuation-frequency characteristics of the ladder filter of the present invention. The characteristics shown by solid line A, broken line B and solid line C shown in FIG. 12 are 1st stage, 2nd stage and 4th stage, respectively.
This is the characteristic when a ladder type filter of stages (two two stages are connected) is configured. Note that the capacitance of the tuning fork type piezoelectric resonator used to configure each ladder type filter is as follows.

[0018] Series resonator...35pF, parallel resonator...35
0 pF. Moreover, the insertion loss of each ladder type filter showing the attenuation-frequency characteristics shown in FIG. 12 was as follows. 1-stage ladder filter (solid line A)...1.1 dB. Two-stage ladder filter (dashed line B)...2.1 dB. A four-stage ladder type filter (solid line C), which is a combination of two two-stage filters...4.2 dB.

Note that the tuning fork type piezoelectric resonator used in the present invention is not limited to one having the electrode structure described with reference to FIGS. 6 to 9. That is, as long as the piezoelectric substrate has a structure in which first to third slits are formed extending from one end edge of the piezoelectric substrate, and a tuning fork-shaped vibrating part is formed in the portion sandwiched between the second and third slits, other patterns may be used. Even those having a vibrating electrode can be used in the present invention.

[0020]

According to the present invention, a series resonator and a parallel resonator are constructed of tuning fork type piezoelectric resonators, and a plurality of tuning fork type piezoelectric resonators are laminated with a cavity forming material interposed therebetween.
The integrated design allows the overall dimensions of the ladder filter to be very small, particularly thin.

[0021] Furthermore, multiple tuning fork type piezoelectric resonators are laminated and
Since the structure is integrated, it is possible to provide a ladder filter as a chip-type electronic component that can be easily surface-mounted by adding external electrodes.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing the overall structure of a ladder filter according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view for explaining the structure of a conventional ladder type filter.

FIG. 3 is a diagram showing a conventional ladder filter circuit.

FIG. 4 is an exploded perspective view showing essential parts of the embodiment shown in FIG. 1;

5 is an exploded perspective view showing other main parts of the embodiment shown in FIG. 1. FIG.

FIG. 6 is a schematic exploded perspective view for explaining an electrode pattern of one series resonator.

FIG. 7 is a schematic exploded perspective view for explaining an electrode pattern of one parallel resonator.

FIG. 8 is a schematic exploded perspective view for explaining an electrode pattern of another series resonator.

FIG. 9 is a schematic exploded perspective view for explaining an electrode pattern of another parallel resonator.

FIG. 10 is an external perspective view showing the ladder type filter of the example.

FIG. 11 is a diagram showing a circuit of a ladder filter according to an embodiment.

FIG. 12 is a diagram showing attenuation vs. frequency characteristics of the ladder filter of the present invention.

[Explanation of symbols]

20... Ladder type filter 21, 22... Series resonators 23, 24... Parallel resonators 25 to 29... Cavity forming material 211, 221, 231, 241... Piezoelectric substrate 212, 2
22, 232, 242...first slit 213, 223
, 233, 243...second slit 214, 224, 2
34, 244...Third slit 215, 216, 225
, 226, 235, 236, 245, 246... vibrating electrode

Claims (1)

[Claims] 1. A ladder type filter comprising at least one series resonator and at least one parallel resonator connected, wherein the series resonator and the parallel resonator have a first slit extending inward from one end edge. A piezoelectric substrate has second and third slits extending inwardly from the one end edge so as to sandwich the piezoelectric substrate, and a tuning fork-shaped vibrating portion is formed between the second and third slits; The tuning fork type piezoelectric resonator has electrodes for vibrating the vibrating part, and the plurality of tuning fork type piezoelectric resonators constituting the series resonator and the parallel resonator are configured to vibrate each other's tuning fork-shaped vibrating part. A ladder type filter characterized in that the filter is laminated and integrated with a cavity forming material interposed therebetween to secure a cavity so as not to obstruct the flow.