JP2001168678A - Ladder filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small and staged ladder filter which is easily designed. SOLUTION: A unit is formed by inserting a metallic terminal plate 34 between the upper surface electrode of a bending resonator 61 becoming a serial resonator and the lower surface electrode of a bending resonator 71 becoming a parallel resonator for piling them. Two sets of these units are disposed planar on a substrate 32, and a metallic cover 33 is placed on the substrate 32 so as to cover these units. By the conductive pattern of the substrate 32, the lower surface electrode of the resonator 61 of the unit of the first stage is connected to an input terminal 44, the plate 34 of the unit of the first stage is connected to the lower surface electrode of the resonator 61 of the unit of the next unit, and the plate 34 of the unit of the next stage is connected to an output terminal 46. Further, the upper surface electrodes of the resonators 71 of the respective units are continued to each other with a cover 33.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ladder filter formed by connecting a series resonator and a parallel resonator in a ladder manner.

[0002]

2. Description of the Related Art FIG. 1 shows a two-stage ladder filter used for communication equipment and the like. In this ladder filter, two series resonators 3, 4 are connected in series between an input terminal 1 and an output terminal 2, and both series resonators 3, 4
The parallel resonator 5 is connected between the middle point and the ground, and the parallel resonator 6 is connected between the output terminal 2 and the ground.

A specific structure of a ladder filter conventionally used is shown in FIGS. 2A and 2B by a vertical sectional view and a horizontal sectional view. The ladder filter 11 includes an input terminal plate 12, a ground terminal plate 16, an output terminal plate 18, an internal connection terminal plate 14 bent in a U-shape, and a series resonator 3 and 4 using spread vibration. Piezoelectric resonators (hereinafter referred to as “spread resonators”) 13 and 19, and piezoelectric resonators (hereinafter referred to as “spread resonators”) 15 and 17 for parallel resonators 5 and 6 using spreading vibrations. The input terminal plate 12, the ground terminal plate 16 and the output terminal plate 18 are
a, 16a and 18a. Each of the expansion resonators 13, 15, 17, and 19 performs expansion vibration in which expansion in the outer peripheral direction and contraction in the central direction are repeated by application of a signal, and a node is provided at the center of each main surface. (Node) is located.

As shown in FIG. 2, these are an input terminal plate 12, a spread resonator 13, one electrode plate 14a of an internal connection terminal plate 14, a spread resonator 15, and a ground terminal plate 1.
6, the expansion resonator 17, the output terminal plate 18, the expansion resonator 19, and the other electrode plate 14b of the internal connection terminal plate 14 are stacked in this order, and the input terminal plate 12, the ground terminal plate 16, Terminal plate 18 and internal connection terminal plate 14
Each of the protrusions provided on the electrode plates 14a and 14b abuts on the central portion which is a node of each of the expansion resonators 13, 15, 17, and 19. Each of the lead legs 12a, 16 of the input terminal plate 12, the ground terminal plate 16, and the output terminal plate 18
The holes 18a and 18a are inserted into the holes of the bottom cover 21 and the holes are closed with the resin 22, and the case 20 is put thereon and sealed.

However, such a ladder filter not only has a complicated structure and is poor in assemblability, but also needs to be redesigned every time the number of stages is increased, and the design is troublesome. For example, a two-stage ladder filter and a three-stage ladder filter have completely different terminal structures (particularly, the structure of internal connection terminals). It was not possible to design a ladder filter with four or four stages, and it was necessary to redesign each time the number of stages was different.

FIG. 3A shows a structure of a spreading resonator used as a series resonator or a parallel resonator in the ladder filter as described above. FIG. 3B shows the directions of the polarization axis and the electric field axis. This extended resonator 7
The surface electrode 9 is provided on both front and back main surfaces of a single piezoelectric layer 8 having a square shape, and the entire piezoelectric layer 8 is polarized in a direction perpendicular to both main surfaces. Therefore, the direction (electric field axis) of the electric field applied between the surface electrodes 9 is also perpendicular to both main surfaces and parallel to the polarization axis. In such a spreading oscillator 7,
When a signal is applied between both surface electrodes 9, the piezoelectric layer 8 expands and contracts in the direction parallel to the two main surfaces in the outer peripheral direction.

In the extended resonator 7, the product of the length Ls of one side and the resonance frequency fr is substantially constant, and Ls × fr = As. Here, As is a constant (frequency constant),
As ≒ 2100 mmkHz. For example, to obtain a resonator having a resonance frequency fr = 450 kHz, the length of one side is Ls = 4.67 mm.

However, in the world of electronic components, lighter, thinner and shorter are being increasingly used, and it is difficult for such a spread resonator to meet not only the demand for size reduction and weight reduction but also cost reduction. Such dimensions were unacceptable.

FIG. 4 shows the attenuation characteristic of a two-stage ladder filter. As a characteristic of such a ladder filter, it is necessary to make the guaranteed attenuation Att. Shown in FIG. 4 as large as possible. The series resonator 3 in FIG.
4 is C1, C1 and the capacitance between terminals of the parallel resonators 5, 6 is C2, C2, the guaranteed attenuation Att. Of the two-stage ladder filter is Att. = 2 × 20 log (C2 / C1)... In order to increase the guaranteed attenuation Att., The capacitances C2 and C between the terminals of the parallel resonators 5 and 6 are set.
2, the capacitances C1, C1 between the terminals of the series resonators 3, 4 need to be reduced. However, in the case where the above-described extended resonators are used as the parallel resonators 5 and 6, the inter-terminal capacitance C2 is used for the following reason.
Was difficult to increase.

[0010] The extended resonator 7 shown in FIG.
The terminal-to-terminal capacitance Cs of the piezoelectric layer 2
Is the relative dielectric constant of ε and the thickness is t, Cs = (ε · ε₀・ Ls²) / T... Where ε₀Is the dielectric constant in vacuum,
ε₀= 8.854 × 10 ^-12It is.

When the resonance frequency fr of the expanding resonator 7 is determined, the length Ls of one side of the expanding resonator 7 is determined (see the above equation). Therefore, the terminal capacitance Cs is determined by the thickness t of the piezoelectric layer 2 and the relative dielectric constant. It is determined only by the ratio ε.

In order to increase the inter-terminal capacitance Cs of the spreading resonator 7, it is necessary to increase the relative permittivity ε of the piezoelectric layer 8 or reduce its thickness t. However, the relative permittivity ε of the piezoelectric layer 8 is a constant inherent to the material of the piezoelectric layer 8 and cannot be arbitrarily selected. Changing the piezoelectric material also affects other characteristics. In addition, when the thickness t of the piezoelectric layer 8 is reduced, the breaking strength is reduced, and the spreading resonator 7 is easily damaged, so that the selection range is limited.

Therefore, it has been difficult to obtain a resonator having a large capacitance between terminals, although a resonator having a large capacitance between terminals is required as a parallel resonator of a ladder filter. On the contrary, if a piezoelectric resonator having a small constant corresponding to the above-described constant Cs is developed and the piezoelectric resonator can be miniaturized, the capacitance between terminals becomes small as a result. As a result, the guaranteed attenuation of the ladder filter becomes worse.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and an object of the present invention is to make it possible to easily design each stage and to reduce the size of a small ladder. To provide a filter. Also,
A further object of the present invention is to provide a ladder filter having a large guaranteed attenuation and good characteristics.

[0015]

According to a first aspect of the present invention, there is provided a ladder filter comprising a conductive member disposed between one surface electrode of a series resonator utilizing bending vibration and one surface electrode of a parallel resonator utilizing bending vibration. A plurality of units stacked one on top of the other are arranged on a substrate and arranged in a plane, a lid having conductivity is placed on the substrate so as to cover these units, and a conductive pattern provided on the substrate and the lid form a cover. The other surface electrodes of the series resonators in the units subsequent to the first stage are electrically connected to the conductive members in the previous unit, and the other surface electrodes of the parallel resonators in each unit are electrically connected to each other.

A ladder filter according to a second aspect is the ladder filter according to the first aspect, wherein the series resonator and the parallel resonator are combinations of resonators having different numbers of internal electrodes, and the number of internal electrodes is large. A resonator is used as a parallel resonator, and a resonator having a small number of internal electrodes is used as a series resonator.

According to a third aspect of the present invention, in the ladder filter according to the first or second aspect, the other surface electrodes of the parallel resonators in each of the units are electrically connected to each other through the lid having a substantially whole surface. It was made.

[0018]

In the ladder filter according to the first aspect of the present invention, a plurality of units in which a series resonator and a parallel resonator are stacked with a conductive member interposed therebetween are arranged in a plane on a substrate. Are connected in ladder form. Therefore, when increasing the number of stages of the ladder filter, a unit is additionally provided on the substrate, and the other surface electrode of the series resonator in the unit (the surface electrode on the opposite side to the surface electrode in contact with the conductive member. , On the signal input side) with the conductive member (on the signal output side) in the preceding unit, and connect the other surface electrode (on the ground side) of the parallel resonator in this unit to the parallel resonator in the other unit. On the other hand, it suffices to conduct to the surface electrode. Therefore, the wiring pattern and the like can be formed by repeating a predetermined pattern, and the design can be easily performed when the number of stages of the ladder filter is increased. In particular, the same conductive member can be used in common even if the number of steps is different.

Since the series resonator and the parallel resonator in the ladder filter use bending vibration, the resonator size can be increased and can be made very small as compared with the resonator. In addition, since the units are connected to each other by the wiring pattern formed on the substrate and the lid, a wiring space for connecting the units by bonding wires or lead wires can be eliminated. As a result, a small ladder filter having a relatively small thickness can be manufactured.

In the ladder filter according to the present invention, a resonator having a large number of internal electrodes is used as a parallel resonator among resonators utilizing bending vibration, and a resonator having a small number of internal electrodes is a series resonator. , The capacitance between the terminals of the parallel resonator can be made larger than the capacitance between the terminals of the series resonator without making the parallel resonator too large or too thin, and the guaranteed attenuation of the ladder filter And filter characteristics can be improved.

In the ladder filter according to the third aspect, since the other surface electrodes of the parallel resonators in each unit are electrically connected to each other through the lid, a conductive pattern for electrically connecting the other surface electrodes of the parallel resonators is provided. Need not be provided on the substrate, and the conductive pattern on the substrate can be simplified. Therefore, even when the ladder filter is downsized, the pattern line width can be increased and the wiring resistance can be reduced. Moreover, since almost the entire surface of the lid has conductivity and is electrically connected to the other surface electrode of the parallel resonator at the ground potential, the lid has an electromagnetic shielding effect and has a high noise resistance ladder filter. Can be manufactured.

[0022]

(First Embodiment) FIG. 5 is a cross-sectional view of a ladder filter 31 according to an embodiment of the present invention.
3 is an exploded perspective view of the ladder filter 31. FIG. The ladder filter 31 is a two-stage filter, and is mainly composed of a substrate 32, two sets of units, and a lid 33.

In each unit, a metal terminal plate 34 is placed on a piezoelectric resonator (hereinafter, referred to as a bending resonator) 61 utilizing bending vibration, and a piezoelectric resonator utilizing bending vibration (hereinafter, bending resonance) is placed thereon. (Referred to as a child) 71. On the upper surface of the piezoelectric resonator 61, a conductive pillow 68 is formed near the node by applying and drying a conductive paste on the center of each side, and the metal terminal plate 34 is brought into contact with the conductive pillow 68. A vibration space is formed on the bending resonator 61 and between the surface electrode 62 on the upper surface of the bending resonator 61 and the metal terminal plate 34.
Similarly, on the upper and lower surfaces of the piezoelectric resonator 71, a conductive pillow 81 is formed near the node by applying and drying a conductive paste on the center of each side. Is placed on the metal terminal plate 34 so as to contact the upper surface of the metal terminal plate 34, and a vibration space is formed between the metal terminal plate 34 and the surface electrode 78 on the lower surface of the bending resonator 71. I have. Therefore, the surface electrode 62 on the upper surface of the bending resonator 61 and the bending resonator 7
The lower electrode 1 is electrically connected to the surface electrode 78 via the conductive pillows 68 and 81 to the metal terminal plate 34.

In this unit, the upper and lower bending resonators 71 and 61 are connected in a τ-shape to constitute one stage of a ladder filter.
Are used as series resonators, and the bending resonator 71 is used as a parallel resonator in the ladder filter 31. The surface electrode 66 on the lower surface of the bending resonator 61
Are the input terminals of the ladder-type circuit, the metal terminal plate 34 is the output terminal of the ladder-type circuit, and the surface electrode 72 on the upper surface of the bending resonator 71 is the ground terminal of the τ-type circuit. The metal terminal plate 34 has a bent end, and the bent resonator 61,
A bent portion 34b extends downward from an end of the flat plate portion 34a sandwiched between 71.

The lid 33 is large enough to cover the two units, and is made of a metal material, particularly a metal material having good conductivity such as aluminum.

FIGS. 7A, 7B and 7C are a plan view, a side view and a back view showing the structure of the substrate 32, respectively. The substrate 32 has a conductive pattern formed on the upper surface, the lower surface, and both side surfaces of the ceramic plate 35. The input terminal 44, the ground terminal 45, and the output terminal 46 are provided from both side surfaces to the upper and lower surfaces of the substrate 32, respectively. The input terminals 44 on both side surfaces are connected by a connection line 47 on the back surface, and the ground terminal 45 on both side surfaces. The output terminals 46 on both sides are connected by a connection line 49 on the back side.

Near the input terminal 44 on the upper surface of the substrate 32, a pad portion 36 for mounting the first stage unit and a terminal plate connection pad 37 for connecting the bent portion 34b of the metal terminal plate 34 are formed. A pad portion 38 for mounting the next unit and a terminal plate connection pad 39 for connecting the bent portion 34b of the metal terminal plate 34 are formed near the output terminal 46 on the upper surface of the substrate 32. Have been. The first-stage pad portion 36 is connected to the input terminal 44 by a lead-out line 40. The first-stage terminal plate connection pad 37 and the next-stage pad portion 38 are connected by a connection line 41, and the next-stage terminal is connected. The board connection pad 39 is connected to an output terminal 46 by a lead line 42. Further, on the upper surface of the substrate 32, the lid connection pads 43 extend from both ground terminals 45.

In mounting the unit on the substrate 32, first, a soldering resist ink 50 is applied to a region indicated by a diagonal broken line in FIG. At this time, both ends of the pad portions 36 and 38, a region excluding the periphery of the terminal plate connection pads 37 and 39, and a region excluding the periphery of the lid connection pad 43 are the openings 3 of the soldering resist ink 50 respectively.
6a, 38a, 37a, 39a and 43a are exposed.

Next, as shown in FIG. 9, an insulating adhesive 51 is printed around the upper surface of the substrate 32. The area where the insulating adhesive 51 is printed has substantially the same size as the lower surface of the lid 33. When the insulating adhesive 51 is applied, the insulating adhesive 51 is partially opened on the lid connection pad 43, and the lid connection pad 43 is exposed from the opening 52.

Subsequently, the soldering resist ink 50
And the pad portion 36 exposed from the insulating adhesive 51,
A conductive paste is applied to the terminal plate connection pad 37, the pad portion 38, the terminal plate connection pad 39, and the lid connection pad 43, and the conductive paste is formed as shown in FIG. At the same time, a conductive paste is applied and cured on the soldering resist ink 50 on both sides of the pad portion 36 and the pad portion 38 at the same time.
To form

When the substrate 32 is thus prepared, one unit is placed on the pad portion 36 and the conductive pillows 53 on both sides thereof, and the nodes of the lower bending resonator 61 are connected to the conductive pillows 53.
And a vibration space is formed between the lower surface of the bending resonator 61 and the substrate 32. Further, the tip of the bent portion 34 b of the metal terminal plate 34 sandwiched between the bent resonators 61 and 71 is pressed against the conductive pillow 53 of the terminal plate connection pad 37.

Similarly, the other unit is placed on the pad portion 38 and on the conductive pillows 53 on both sides thereof, and the nodes of the lower bending resonator 61 are supported by the conductive pillow 53 and the bending resonator 61 A vibration space is formed between the lower surface and the substrate 32.
The tip of the bent portion 34 b of the metal terminal plate 34 sandwiched between the bent resonators 61 and 71 is pressed against the conductive pillow 53 of the terminal plate connection pad 39.

After the two units have been mounted on the board 32, the board 32 is covered so as to cover both units.
A lid 33 on top of it, and attach the lower surface of the lid 33 to the insulating adhesive 5.
1 and the lid 33 is adhered to the substrate 32. At the same time, the lower surface of the lid 33 is pressed against the conductive pillow 53 in the opening 52, and the lid 33 is electrically connected to the ground terminal 45 via the conductive pillow 53 and the lid connection pad 43. The conductive pillow 81 on the upper surface of the bending resonator 71 above the unit also comes into pressure contact with the inner surface of the lid 33, and the surface electrode 72 on the upper surface of the bending resonator 71 is electrically connected to the ground terminal 45 via the lid 33.

As a result, the surface electrode 66 on the lower surface of the bending resonator 61 in the first stage unit is connected to the input terminal 44, and the surface electrode 72 on the upper surface of the bending resonator 71 is connected to the ground terminal 4.
5, the metal terminal plate 34 electrically connected to the surface electrode 62 on the upper surface of the bending resonator 61 and the surface electrode 78 on the lower surface of the bending resonator 71 is connected to the surface electrode 66 on the lower surface of the bending resonator 61 in the next unit. Further, the surface electrode 72 on the upper surface of the bending resonator 71 in the next unit is connected to the ground terminal 4.
The metal terminal plate 34 connected to the surface electrode 62 on the upper surface of the bending resonator 61 and the surface electrode 78 on the lower surface of the bending resonator 71 is connected to the output terminal 46. Thus, a two-stage ladder filter 31 as shown in FIG. 1 is completed.

According to the ladder filter having such a structure, when the ladder filter is to be expanded to, for example, a three-stage configuration or a four-stage configuration, the conductive pattern connected to the preceding stage as in the next conductive pattern on the substrate 32 in FIG. By adding a pattern, it is only necessary to increase the number of stages and mount the same unit, and a ladder filter having many stages can be easily designed.

Next, the bending resonator 61 used as a series resonator in the ladder filter will be described. FIG. 11A is a perspective view of the bending resonator 61. The bending resonator 61 is used in a frequency band of, for example, 300 kHz to 800 kHz. This bending resonator 6
1 is a two-layer ceramic piezoelectric layer 63 having a square shape,
The internal electrode 64 is sandwiched between the piezoelectric layers 63 and 65.
Surface electrodes 62 and 66 are respectively formed on both front and back main surfaces of a laminated body including the internal electrodes 5 and the internal electrodes 64. The piezoelectric layers 63 and 65 on both sides of the internal electrode 64 are subjected to polarization processing in a direction perpendicular to the main surface and in opposite polarization directions. Note that the polarization direction may be outward with the internal electrode 64 interposed therebetween, or may be inward with the internal electrode 64 interposed therebetween, as indicated by solid arrows in FIG. 11B.

Therefore, when a voltage is applied between both surface electrodes 62 and 66, an electric field is generated in the direction shown by the broken arrow in FIG. 11B, and the electric field direction and the polarization direction are generated inside one piezoelectric layer. Are in the same direction, and the piezoelectric layer contracts in the center direction, and in the other piezoelectric layer, the electric field direction and the polarization direction are opposite to each other, and the piezoelectric layer expands in the outer edge direction. As a result, when a signal (high-frequency electric field) is applied between both surface electrodes 62 and 66, both piezoelectric layers 63 and 65 both expand and vibrate to expand and contract in the outer edge direction and the center direction. Are inverted, so that as a whole FIG.
As shown in FIG. 1 (b), the bending resonator 61 bends and deforms so that both main surfaces alternately repeat irregularities (bending vibration).
The node 67 of this bending oscillator is located at the center of each side.

In such a bent resonator 61, the product of the length Lb of one side and the resonance frequency fr is substantially constant, and Lb × fr = Ab. Here, this frequency constant is Ab ≒ 430 mmkHz.

The frequency constant Ab of the bending resonator 61 is
It is about 0.3 times (= A) compared to the frequency constant As of the spreading resonator.
b / As), for the same resonance frequency fr,
The length Lb of one side of the bending resonator 61 is about 0.3 times the length Ls of one side of the expanding resonator. Therefore, when the bending resonator 61 is compared with the expanding resonator, the bending resonator 61 is about 1 / 3.3 or less of the expanding resonator and the area is about 1/10 in one side length. Therefore, if the resonance frequency fr is the same, the size of the resonator can be significantly reduced by using the bending resonator 61 as compared with the expansion resonator.

In this flexural resonator 61, if the length of one side is Lb, the relative permittivity of the piezoelectric layers 63 and 65 is ε, and the total thickness of each of the piezoelectric layers 63 and 65 is t, The inter-terminal capacitance Cb is represented by the following equation. _{Cb = (ε · ε 0 ·} Lb 2) / t ... represented by. Here, ε ₀ is a dielectric constant in a vacuum. Therefore, if the total thickness of the piezoelectric layer is equal to the length of one side,
The expanded resonator and the terminal capacitance become equal.

Next, the bent resonator 71 used as a parallel resonator will be described. FIGS. 12A and 12B are a perspective view and a sectional view of the bending resonator 71. FIG. The bent resonator 71 is composed of three square ceramic piezoelectric layers 7.
Two internal electrodes 74, 76 are sandwiched between 3, 75, 77, and surface electrodes 72, 7 are respectively provided on the front and back main surfaces of the laminated piezoelectric layers 73, 75, 77 and the internal electrodes 74, 76.
8 is formed. The central piezoelectric layer 75 is not polarized, and the piezoelectric layers 73 and 77 on both sides are subjected to polarization processing in a direction perpendicular to the main surface and in opposite polarization directions. The direction of the polarization axis is shown in FIG.
In (b), as shown by a solid line arrow, it may be inward with the center piezoelectric layer 75 interposed, or may be outward with the center piezoelectric layer 75 interposed.

Further, in the piezoelectric resonator 71,
Connection electrodes 80 are provided on both side surfaces. On the other hand, the connection electrode 80 is provided every other layer as the surface electrode 72 and the internal electrode 76.
Electrically insulated with the insulating material 7 formed on the side surface
9 is insulated from the intermediate internal electrode 74. The other connecting electrode 80 is electrically connected to the surface electrode 78 and the internal electrode 74 every other layer, and is insulated from the intermediate internal electrode 76 by an insulating material 79 formed on the side surface.

Therefore, both surface electrodes 72 and 78 are shown in FIG.
When a voltage is applied in the direction shown by the broken arrow in (b), the direction of the electric field and the direction of polarization are the same in one of the piezoelectric layers 73 and 77, and the piezoelectric layer becomes The piezoelectric layer contracts toward the center, and the direction of the electric field and the direction of polarization become opposite in the other piezoelectric layer, and the piezoelectric layer expands in the outer edge direction and undergoes bending vibration. The node of the bending resonator 71 is also located at the center of each side.

Even in such a bent resonator 71, the product of the length Lb of one side and the resonance frequency fr is substantially constant, and Lb × fr = Ab. Here, this frequency constant is Ab ≒ 430 mmkHz.

The frequency constant Ab of the bending resonator 71 is
It is about 0.3 times (= A) compared to the frequency constant As of the spreading resonator.
b / As), for the same resonance frequency fr,
The length Lb of one side of the bent resonator 71 is about 0.3 times the length Ls of one side of the expanding resonator. Therefore, when the bending resonator 71 is compared with the expanding resonator, the bending resonator 71 is about 1 / 3.3 or less of the expanding resonator and the area is about 1/10 in one side length. Therefore, if the resonance frequency fr is the same, the size of the resonator can be significantly reduced by using the bending resonator 71 as compared with the expansion resonator.

In the three-layered bending resonator 71, the length of one side is Lb, the relative permittivity of the piezoelectric layers 73, 75, 77 is ε, and the thickness of each of the piezoelectric layers 73, 75, 77. Are respectively ta, tb, and tc, the inter-terminal capacitance Cb is expressed by the following equation. _{Cb = (ε · ε 0 ·} Lb 2) (1 / ta + 1 / tb + 1 / tc) ... represented by. Here, ε ₀ is a dielectric constant in a vacuum.

Now, for the same piezoelectric material (having the same value of ε),
The dimensions are equal (Lb = Ls) and the thickness is equal (ta + tb +
tc = t) Comparing the expansion resonator and the bending resonator 71, the capacitance Cs between terminals of the expansion resonator is represented by the above equation. On the other hand, each piezoelectric layer 7 of the bending resonator 71
Assuming that the thicknesses of 3, 75 and 77 are equal (ta = tb = t
c = t / 3), and the inter-terminal capacitance Cb is given by the following equation. _{Cb = (ε · ε 0 ·} Lb 2) (9 / t) = 9Cs ... Thus, in the bending resonator 71, the same size, spread resonators of the same thickness (or bent resonator 61) in comparison with 9 times the inter-terminal capacitance can be obtained. Even if the thickness of the piezoelectric layers 73, 75, and 77 is reduced, they are laminated and the overall thickness does not change, so that sufficient strength can be provided.

Therefore, as the series resonator used in the ladder filter as shown in FIG.
1 and the bent resonator 71 is used as the parallel resonator, the guaranteed attenuation Att. Of the ladder filter 31 increases by 38.2 dB as represented by the following equation. ΔAtt. = 2 × 20 log (Cb / Cs) = 38.2 [dB] ... A method of selecting a material having a different dielectric constant ε or changing the thickness of the series resonator and the parallel resonator, which is a conventional technique. By combining the above, it becomes possible to design the capacity ratio and the guaranteed attenuation more widely.

Also, comparing the spread resonators having the same resonance frequency fr with the bent resonators 61 and 71 as described above, the area of the bent resonators 61 and 71 is about 1/10 (Lb ² =
Ls ^2/10). Therefore, the ladder filter 31 by the miniaturization of the bending resonator 61 and 71 can be downsized.

Further, since the units are connected by the conductive pattern provided on the substrate 32 and the lid 33, there is no need to provide a wiring space such as a bonding wire inside, and the ladder filter can be further reduced in size.

Further, in the ladder filter 31 of the present invention, since the unit in which the two bending resonators 61 and 71 are overlapped is arranged in a plane, the ladder filter 31 can be made relatively thin. it can.

[0052]

According to the ladder filter of the first aspect, the design can be easily performed when the number of filter stages is increased. Also, a relatively small thickness ladder filter can be manufactured.

According to the ladder filter of the second aspect, the terminal capacitance of the parallel resonator is made larger than the terminal capacitance of the series resonator without increasing the size of the parallel resonator or making it too thin. Thus, the guaranteed attenuation of the ladder filter can be increased, and the filter characteristics can be improved.

According to the ladder filter of the third aspect, even when the ladder filter is downsized, the pattern line width can be increased and the wiring resistance can be reduced. Moreover, since almost the entire surface of the lid has conductivity and is electrically connected to the other surface electrode of the parallel resonator at the ground potential, the lid has an electromagnetic shielding effect and has a high noise resistance ladder filter. Can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration of a ladder filter.

2A and 2B are longitudinal sectional views showing a specific structure of a conventional ladder filter, and FIG. 2B is a horizontal sectional view thereof.

FIG. 3A is a perspective view showing a structure of a conventional spread resonator, and FIG. 3B is a side view showing directions of a polarization axis and an electric field axis.

FIG. 4 is a diagram illustrating characteristics of the ladder filter of FIG. 1;

FIG. 5 is a cross-sectional view illustrating a structure of a ladder filter according to an embodiment of the present invention.

FIG. 6 is an exploded perspective view of the ladder filter.

FIGS. 7A, 7B, and 7C are a plan view, a side view, and a bottom view of a substrate used in the ladder filter according to the first embodiment.

FIG. 8 is a view showing an application area of a soldering resist ink on the substrate of the above.

FIG. 9 is a plan view of the substrate showing a state where a soldering resist ink and an insulating adhesive are applied.

FIG. 10 is a plan view of a substrate on which a conductive pillow is formed.

11A is a perspective view of a bending oscillator (series resonator) used in the ladder filter of FIG. 5, and FIG. 11B is a diagram illustrating a state of bending vibration.

12A and 12B are a perspective view and a cross-sectional view of a bending oscillator (parallel resonator) used in the ladder filter of FIG.

[Explanation of symbols]

 61 Bending Resonator (Series Resonator) 71 Bending Resonator (Parallel Resonator) 32 Substrate 33 Lid 34 Metal Terminal Plate 36, 38 Pad 37, 39 Terminal Plate Connection Pad 43 Lid Connection Pad 44 Input Terminal 45 Earth Terminal 46 Output Terminal 53, 68, 81 Conductive pillow

Claims (3)

[Claims] 1. A plurality of units stacked on a substrate with a conductive member sandwiched between one surface electrode of a series resonator using bending vibration and one surface electrode of a parallel resonator using bending vibration on a substrate. And a conductive lid provided on the substrate so as to cover these units, and the other surface electrode of the series resonator in the second and subsequent units by the conductive pattern and the lid provided on the substrate. A ladder filter, which is electrically connected to the conductive member in the unit at the preceding stage and the other surface electrodes of the parallel resonators in each unit are electrically connected to each other. 2. The series resonator and the parallel resonator are a combination of resonators having different numbers of internal electrodes. A resonator having a large number of internal electrodes is used as a parallel resonator, and a resonator having a small number of internal electrodes is used. The ladder filter according to claim 1, wherein the ladder filter is used as a series resonator. 3. The ladder filter according to claim 1, wherein the other surface electrodes of the parallel resonators in each of the units are electrically connected to each other through the lid having a substantially entire surface that is conductive.