JPH05299970A - Piezoelectric rudder filter - Google Patents

Abstract

PURPOSE:To make a device thin and compact by using a composite piezoelectric resonator in which plural piezoelectric oscillators are integrally constituted by forming electrodes in a piezoelectric element, for a serial oscillator and/or a parallel oscillator. CONSTITUTION:A composite piezoelectric resonator 20 is formed by integrally constituting two piezoelectric resonators 20a and 20b by forming an inside electrode 22 in a piezoelectric element 21. An electrode 41 is formed on one main face of the piezoelectric element 21, and an electrode 42 is formed on the other main face, and an electrode 43 electrically connected with the inside electrode 22 is formed on the side face. The other composite piezoelectric resonator 30 is formed by integrally constituting two piezoelectric resonators 30a and 30b by forming an inside electrode 32 in a piezoelectric element 31. Thus, both the composite piezoelectric resonators 20 and 30 are mechanically vibrated integrally, and electrically functioned as an independent resonator so that each rudder filter can the constituted. And also, a spring terminal is not necessitated between the piezoelectric resonators in the composite piezoelectric resonator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter utilizing a piezoelectric resonance phenomenon, and more particularly to a piezoelectric ladder filter constructed by connecting a series resonator and a parallel resonator by utilizing the piezoelectric lateral effect. Is.

[0002]

2. Description of the Related Art FIG. 1 is a circuit diagram showing a structure of a four-element two-stage ladder filter. Such a ladder filter can be used as a 455 kHz ladder filter, for example. As shown in FIG. 1, this four-element two-stage ladder filter includes series resonators 1 and 2 and a parallel resonator 3.
And 4. In the case of a resonator utilizing the piezoelectric lateral effect, generally, the spreading vibration mode of a thin square plate is used. Regarding the arrangement of the resonance frequencies of the series resonator and the parallel resonator, a good filter waveform can be obtained by increasing the resonance frequency of the series resonator to be near the anti-resonance point of the parallel resonator.

In this ladder filter, the amount of attenuation outside the pass band is uniquely determined by the capacitance ratio (capacitance ratio) of the series resonator and the parallel resonator. That is, in order to increase the amount of attenuation outside the pass band, the capacitance of the series resonator is reduced and the capacitance of the parallel resonator is increased. Specifically, the series resonator is designed to make the element as thick as possible to reduce the capacitance, and the parallel resonator is designed to make the element as thin as possible to increase the capacitance. FIG. 7 is an exploded perspective view for explaining the structure of a conventional ladder filter. This ladder filter includes series resonators 1 and 2 that use a spreading vibration mode of a square plate,
In addition, the parallel resonators 3 and 4 are used. Referring to FIG. 7, electrode 2a is provided on one main surface of series resonator 2.
Although not shown, a similar electrode is also formed on the other main surface side of the series resonator 2. Similar electrodes are 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 surfaces of both main surfaces.
And 4a are formed.

In order to electrically connect the series resonators 1 and 2 and the parallel resonators 3 and 4 to both, the metal terminals 5 to 11 are connected.
Is used. The metal terminals 5 to 11 are housed in a case 12 made of an insulating material together with the series resonators 1 and 2 and the parallel resonators 3 and 4. Further, the lid member (not shown) closes the upper opening 12a of the case 12 to form a ladder filter. In this case, the metal terminals 9 to 11 are drawn out of the case 12 and used as connection terminals with the outside.

When driving a ladder filter, the series resonators 1 and 2 and the parallel resonators 3 and 4 are
It is necessary to be able to vibrate in a desired manner while being housed in the case 12. That is, the vibration of each of the resonators 1 to 4 should not be hindered while being housed in the case 12. Therefore, as the metal terminal 11 located at the end,
A so-called spring terminal having a spring property is generally used.

[0006]

As described above, in the series resonator, the element is made as thick as possible to reduce the capacitance,
A parallel resonator is designed to have a thin element and a large electrostatic capacitance.
In practice, there are restrictions and the achievable capacity ratio is limited.
In recent years, in response to the downsizing of communication devices, there is an increasing demand for thinning and downsizing of ladder filters. In principle, the thicker the series resonator, the better. However, if the series resonator is too thick, the size of the component becomes large, and it is not possible to make the device thinner and smaller. Further, metal terminals for electrically connecting the respective elements are inserted between the elements, and the thickness of the metal elements is also a factor that hinders the thinning and downsizing of the ladder filter.

On the other hand, as for the parallel resonator, the thinner it is, the better, but there is a limit in terms of reliability such as impact resistance of parts. That is, an element that is too thin has a problem of being destroyed by a mechanical shock, and is usually 200 μm.
The degree is the limit. An object of the present invention is to provide a ladder filter that can be made thin and compact.

[0008]

A piezoelectric ladder filter of the present invention is a piezoelectric ladder filter constituted by connecting a series resonator and a parallel resonator, and at least one of the series resonator and the parallel resonator has a piezoelectric resonator. A feature is that a composite piezoelectric resonance element in which a plurality of piezoelectric resonators are integrally formed by forming electrodes in the body is used. In the present invention, the composite piezoelectric resonator element used for at least one of the series resonator and the parallel resonator is an integrally formed piezoelectric resonator utilizing the lateral effect. In the composite piezoelectric resonance element, series resonators or parallel resonators are integrated. As a method of integrating the resonators, there is a method of printing the internal electrode paste on a green sheet, stacking the pastes, and firing them to integrate them. Alternatively, the fired single-plate piezoelectric body may be adhered to be integrated.

[0009]

In the present invention, the composite type piezoelectric resonance element in which a plurality of piezoelectric resonators are integrally configured vibrate mechanically as one unit and are electrically independent so that each ladder filter is configured. Functions as a resonator. Further, in the present invention, since a plurality of piezoelectric resonators are integrally formed by forming electrodes in the piezoelectric element body, a conventional spring terminal is required between the piezoelectric resonators in the composite piezoelectric resonance element. No longer. For this reason, it can be made smaller than the shape of the entire conventional ladder filter. As for parallel resonators, a plurality of piezoelectric resonators are integrally configured, so even if the thickness of each piezoelectric resonator is reduced, the overall thickness is sufficient to maintain mechanical strength. have.
Therefore, the capacitance of the parallel resonator can be made larger than in the conventional case, and the amount of attenuation can be improved by increasing the capacitance ratio.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a block diagram showing an embodiment of a 4-element ladder filter according to the present invention. Referring to FIG. 2, the composite piezoelectric resonance element 10 includes two piezoelectric resonators 20 by forming an internal electrode 22 in a piezoelectric element body 21.
a and 20b are integrally configured. Piezoelectric resonator 2
0a constitutes the series resonator 1 of FIG.
b constitutes the series resonator 2 of FIG. An electrode 41 is formed on one main surface of the piezoelectric body 21, and an electrode 42 is formed on the other main surface.
Are formed. An electrode 43 electrically connected to the internal electrode 22 is formed on the side surface. Similarly, in the other composite type piezoelectric resonance element 30, the two piezoelectric resonators 30 are formed by forming the internal electrodes 32 in the piezoelectric body 31.
a and 30b are integrally formed. An electrode 44 is formed on one main surface of the piezoelectric body 31, and the electrode 44 is electrically connected to the electrode 42. Further, the electrode 45 formed on the other main surface of the piezoelectric body 31 extends from the side surface of the piezoelectric body 31 to the one main surface side and is electrically connected to the electrode 43. An electrode 46 is formed on the other side surface of the piezoelectric body 31, and the electrode 46 is electrically connected to the internal electrode 32.

The electrode 41 is connected to the IN terminal, and the electrode 42
And 44 are connected to the OUT terminal, and the electrode 32 is connected to the GND terminal. In FIG. 2, the arrows shown in the piezoelectric resonators indicate the piezoelectric resonators 20a, 20b, 30a and 3 respectively.
The polarization direction of 0b is shown. FIG. 3 is a block diagram according to the present invention.
It is a block diagram which shows the other Example of an element type ladder filter. With reference to FIG. 3, in this embodiment, two composite piezoelectric resonance elements 40 and 50 are used. In the composite type piezoelectric resonance element 40, by forming the internal electrode 42 in the piezoelectric element body 41, two series resonators 40a and 40 are provided.
b is integrated. An electrode 61 is formed on one main surface of the piezoelectric body 41, and an electrode 62 is formed on the other main surface. An electrode 63 is formed on the side surface of the piezoelectric body 41 so as to be electrically connected to the internal electrode 42.

The composite piezoelectric resonance element 50 includes a piezoelectric element 5
Two parallel resonators 50a and 50b are formed by forming the internal electrode 52 in 1. An electrode 64 is formed on one main surface of the piezoelectric body 51, and an electrode 65 is formed on the other main surface. A via hole connecting portion 53 is formed so as to penetrate from one main surface of the piezoelectric element body 51 to the other main surface thereof, and one end of the via hole connecting portion 53 is an electrode 67 formed on the one main surface side of the piezoelectric element body 51. , And the other end is connected to an electrode 65 formed on the other main surface side. Further, in the piezoelectric body 51, one end is electrically connected to the internal electrode 52, and the other end is electrically connected to the electrode 66 formed on the other main surface side.
4 are formed.

The electrode 62 of the composite piezoelectric resonance element 40 and the electrode 64 of the composite piezoelectric resonance element 50 are electrically connected, and these are connected to the OUT terminal. In addition, the electrode 63 of the composite piezoelectric resonance element 40 and the composite piezoelectric resonance element 5
The electrode 67 of 0 is electrically connected. An IN terminal is connected to the electrode 61, and a GND terminal is connected to the electrode 66. As in the embodiment of FIG. 3, via holes may be formed in the piezoelectric body to electrically connect the electrodes. FIG. 4 is a sectional view showing the structure of the 4-element ladder filter having the structure shown in FIG. The ladder filter having the circuit configuration shown in FIG. 2 can be obtained as a filter having a structure as shown in FIG. Referring to FIG. 4, composite piezoelectric resonance elements 20 and 30 are housed in exterior case 70.
A metal terminal 73, which serves as an IN terminal, is connected to the electrode 41 of the composite piezoelectric resonance element 20. Composite piezoelectric resonance element 2
A metal terminal 74 serving as an OUT terminal is provided between 0 and 30 and electrically connects the electrode 42 and the electrode 44. Further, the electrode 45 of the composite piezoelectric resonance element 30 has
A metal terminal 75 that serves as a GND terminal is provided. The metal terminals 73 to 75 are all spring terminals.

A conductive rubber sheet 76 for electrically connecting the electrodes 43 and 45 is provided between the electrodes 43 and 45. A conductive rubber sheet 77 for electrical connection is also provided between the electrode 46 and the metal terminal 75. A base plate 71 for closing the opening is provided at the opening of the outer case 70, and a sealing resin 72 is provided on the base plate 71 to provide the outer case 7.
The inside of 0 is sealed. The composite piezoelectric resonance element used for the ladder filter shown in FIG. 4 was manufactured as follows.

Compositional formula Pb (Zr _0.45 Ti _0.55 ) O ₃ +
A calcined powder of a piezoelectric ceramic represented by 0.5 wt% MnO ₂ was formed into a sheet by a usual doctor blade method. The sheet was punched into a predetermined size, the internal electrode paste was printed, and the stack was pressed to obtain a green compact.
The formed body was fired in an electric furnace at a temperature of 1200 to 1250 ° C. to obtain a laminated piezoelectric substrate. The size was determined from this substrate so that the frequency arrangement was optimum, and the substrate was cut into a square plate. External electrodes as shown in FIG. 2 and FIG.
An electric field of kv / mm was applied to carry out polarization treatment in the directions indicated by the arrows in FIGS. The composite piezoelectric resonance elements 1 and 30 were manufactured as described above. Figure 4
, The series resonators 20a and 20b are integrated as a composite piezoelectric resonance element 20, and the parallel resonator 30
By integrally using a and 30b as the composite piezoelectric resonance element 30, the number of metal terminals can be reduced as compared with the conventional case. Further, the thickness of the parallel resonator can be made thinner than before.

2 and 4 show a ladder filter having four elements, the present invention can be applied to a ladder filter having three or more elements. FIG. 5 is a circuit diagram showing the structure of a 5-element ladder filter. Referring to FIG. 5, in this ladder filter, series resonators 81, 82 and 83,
The parallel resonators 84 and 85 are connected in combination. FIG. 6 is a block diagram showing an embodiment of the 5-element ladder filter as shown in FIG. With reference to FIG. 6, the composite piezoelectric resonance element 90 integrates three series resonators 90a, 90b, and 90c by forming two internal electrodes 92 and 93 on a piezoelectric body 91. Piezoelectric body 9
An electrode 111 is formed on one main surface of the first electrode, and an electrode 113 is formed on the other main surface. An electrode 114 electrically connected to the internal electrode 92 is formed on the side surface of the piezoelectric body 91, and an electrode 112 electrically connected to the internal electrode 93 is formed on the other side surface.

Further, the composite type piezoelectric resonance element 100 is formed by forming the internal electrode 102 in the piezoelectric element body 101.
The two parallel resonators 100a and 100b are integrated. An electrode 115 is formed on one main surface of the piezoelectric body 101, and an electrode 116 is formed on the other main surface. In addition, an electrode 117 electrically connected to the internal electrode 102 is provided on the side surface.
Are formed. Electrode 11 of composite piezoelectric resonance element 90
4 and the electrode 115 of the composite piezoelectric resonance element 100 are electrically connected, and the electrode 112 of the composite piezoelectric resonance element 90 and the electrode 116 of the composite piezoelectric resonance element 100 are electrically connected. The electrode 111 is connected to the IN terminal, the electrode 113 is connected to the OUT terminal, and the electrode 117 is connected to the G terminal.
The ND terminal is connected.

Each resonator is polarized in the direction shown by the arrow in FIG. As shown in FIG. 6, in the resonator integrated according to the present invention, three resonators may be integrated, and the number of integrated resonators is not limited.
In the above embodiments, the piezoelectric element by the sheet stacking method in which the internal electrodes are formed by stacking the sheets on which the internal electrodes are stacked has been described as an example, but the present invention is not limited to this, for example, Alternatively, a composite piezoelectric resonance element may be used in which a plurality of piezoelectric resonators are integrated by bonding a fired single-plate piezoelectric body and providing electrodes between the piezoelectric bodies. Further, the piezoelectric body used in the present invention may be a single crystal piezoelectric body.

[0019]

According to the present invention, the composite piezoelectric resonance element is used for at least one of the series resonator and the parallel resonator. Since this composite type piezoelectric resonance element is composed of a plurality of piezoelectric resonance elements integrated with each other, it is less necessary to provide a spring terminal between the piezoelectric resonators as in the conventional case, and the spring type is more effective than the conventional piezoelectric ladder filter. It is possible to reduce the number of terminals. Therefore, the overall shape of the ladder filter can be made smaller than before. Further, since the plurality of piezoelectric resonators are integrally configured, even if the thickness of the parallel resonator is reduced, it is possible to obtain a sufficient mechanical strength as a whole. Therefore, the capacitance of the parallel resonator can be made larger than in the conventional case, the capacitance ratio can be increased, and the attenuation amount can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a four-element two-stage ladder filter.

FIG. 2 is a configuration diagram showing an embodiment of a four-element ladder filter according to the present invention.

FIG. 3 is a configuration diagram showing another embodiment of a four-element ladder filter according to the present invention.

FIG. 4 is a sectional view showing the structure of a 4-element ladder filter having the structure shown in FIG.

FIG. 5 is a circuit diagram showing a configuration of a 5-element ladder filter.

FIG. 6 is a configuration diagram showing an embodiment of a 5-element ladder filter according to the present invention.

FIG. 7 is an exploded perspective view for explaining the structure of a conventional ladder filter.

[Explanation of symbols]

20, 30, 40, 50, 90, 100 ... Composite piezoelectric resonance element 21, 31, 41, 51, 91, 101 ... Piezoelectric element body 20a, 20b, 30a, 30b, 40a, 40b, 5
0a, 50b, 90a, 90b, 90c, 100a, 1
00b ... Piezoelectric resonator 22, 32, 42, 52, 92, 102 ... Internal electrode

Claims (1)

[Claims] 1. A piezoelectric ladder filter configured by connecting a series resonator and a parallel resonator, wherein a plurality of piezoelectric elements are formed by forming electrodes in at least one of the series resonator and the parallel resonator in a piezoelectric element body. A piezoelectric ladder filter, wherein a composite piezoelectric resonance element having a resonator integrally formed is used.