JP2002300002A - High frequency ladder type piezoelectric filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ladder piezoelectric filter easily assembled with a structure of low profile and a desired filter characteristic at a high frequency region. SOLUTION: The ladder type piezoelectric filter is configured with a serial and parallel combination of series resonators S1 , S2 and parallel resonators P1 , P2 . Each of the resonators is formed by concentrically placing a center electrode and an outer electrode on one side of a piezoelectric ceramic substrate and placing a common electrode on the other side, and oppositely polarizing the center electrode region and the outer electrode region. The center electrode 2a and the outer electrode 2b of the parallel resonators only are electrically connected. As the configuration of the series resonators S1 , S2 and the parallel resonators P1 , P2 , the center electrodes and the common electrodes are connected as required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ladder-type piezoelectric filter used for a radio communication device such as a portable mobile radio device and a car telephone.

[0002]

2. Description of the Related Art Conventionally, most of such ladder type piezoelectric filters are designed to operate at a response frequency of 455 KHz. Such a filter is configured as a ladder type by combining a thick and small-capacity piezoelectric resonator having a resonance frequency of 455 KHz and a thin and large-capacity piezoelectric resonator having an anti-resonance frequency of 455 KHz in series and parallel, respectively. I have.

Recently, there has been a demand for a ladder-type piezoelectric filter which operates in a high frequency region and is as thin as possible, as a filter for a radio communication device for an automobile telephone. However, in order to meet this demand based on the conventional configuration, the dimensions of the piezoelectric resonator must be very thin compared to 5 mm for 455 KHz, making it virtually impossible to construct a device. Met.

Therefore, a resonator is provided in which a center electrode and an outer electrode are provided concentrically on one surface of a piezoelectric ceramic substrate, a common electrode is provided on the other surface, and the center electrode region and the outer electrode region are polarized in the same direction. As a series resonator, a center electrode and an outer electrode are provided concentrically on one surface of a piezoelectric ceramic substrate, a common electrode is provided on the other surface, and the center electrode region and the outer electrode region are polarized in opposite directions. A ladder circuit that can be used in the high-frequency region by using a plurality of piezoelectric resonators with resonance and anti-resonance frequencies of 1 MHz or higher using the second harmonic by using Type piezoelectric filters have been proposed.

[0005]

By the way, in such a ladder type piezoelectric filter which has been conventionally proposed, the series resonator connects the center electrode and the outer electrode on the same surface to the input / output line sequentially. Therefore, in the case of a ladder-type piezoelectric filter that stores each resonator in a case in a stacked state, it is necessary to make necessary electrical connections while ensuring electrical insulation between the center electrode and the outer electrode. There is a problem that the structure of the terminal plate becomes complicated, it is difficult to stably secure the conductive path, and a product defect due to a short circuit easily occurs.

Accordingly, an object of the present invention is to provide a ladder-type piezoelectric filter which can be formed thin in structure and is easy to assemble, and has desired filter characteristics in a high frequency region.

[0007]

In order to achieve the above object, a ladder-type piezoelectric filter according to the present invention comprises a first piezoelectric ceramic substrate and a center formed on a first surface of the piezoelectric ceramic substrate concentrically. A plurality of series resonators comprising an electrode, an outer electrode, and a common electrode formed on the other surface, wherein a plurality of series resonators are provided in which the center electrode region and the outer electrode region are polarized in directions opposite to each other; A center electrode and an outer electrode formed concentrically on one surface of the piezoelectric ceramic substrate and electrically connected to each other, and a common electrode formed on the other surface, and the center electrode region and the outer electrode region are arranged in opposite directions. A plurality of polarized parallel resonators are provided, the center electrode of one series resonator is connected to one of the input / output pads, and the center electrode of another series resonator is connected to the other of the input / output pads. The common electrodes of the parallel resonators are connected to each other and connected to the center electrode of one parallel resonator, the center electrode of another series resonator is connected to the center electrode of another parallel resonator, and the common electrode of each parallel resonator is connected. It is characterized by being connected to each other and grounded.

[0008] In one embodiment of the present invention, the first piezoelectric ceramic substrate provided with each series resonator can be formed thicker than the second piezoelectric ceramic substrate provided with each parallel resonator.

In another embodiment of the present invention, the electrode area of each parallel resonator can be made wider than the electrode area of each series resonator.

With the above configuration, the filter can be made thinner and desired filter characteristics can be obtained. That is, as shown in FIG. 1 of the accompanying drawings, the center electrode region and the outer electrode region are polarized in directions opposite to each other,
Examination of the relationship between the frequency and the amount of attenuation reveals that the third harmonic mode shows a larger amount of attenuation than the fundamental mode as shown in FIG. In connection with this, the following table shows an example of measurement of the element thickness, the fundamental mode, and the third harmonic mode. Element thickness 210 μm 165 μm 107 μm 80 μm Fundamental wave 10 MHz 13 MHz 20 MHz 26.7 MHz Third harmonic 30 MHz 39 MHz 60 MHz 80 MHz

In this type of ladder filter, it is necessary to increase the ratio between the capacity of the series resonator and the capacity of the parallel resonator in order to increase the amount of attenuation in the stop band. Therefore, according to the present invention, in the series resonator, since the center electrode and the outer electrode are electrically insulated, the capacitance between the center electrode and the common electrode and the capacitance between the outer electrode and the common electrode become equivalently in series. The capacitance is apparently small, and the capacitance between the center electrode and the common electrode and the capacitance between the center electrode and the common electrode and the capacitance between the outside electrode and the common electrode of the parallel resonator are electrically connected to the center electrode and the outer electrode. Since they are equivalently in parallel and their capacitance is apparently large, a required capacitance ratio can be obtained.

As described above, the center electrode region and the outer electrode region are polarized in opposite directions, and only the parallel resonator is electrically connected to the center electrode and the outer electrode to secure a large capacitance ratio. By connecting the series resonator and the parallel resonator in series and parallel by connecting to the center electrode and the common electrode respectively by configuring the series resonator and the parallel resonator, the ladder having the desired filtering characteristics can be obtained. Type piezoelectric filter can be provided. In this configuration, the series resonator and the parallel resonator are connected to the center electrode and the common electrode on the front and back surfaces, respectively, so that the electrical connection can be easily performed in a stacked state. it can.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIGS. 3 to 5 show a ladder-type piezoelectric filter according to an embodiment of the present invention. Reference numeral 1 denotes a first piezoelectric ceramic substrate provided with two series resonators S ₁ and S _{2. 1, S 2}
Is a rectangular annular groove 1 on one surface of the first piezoelectric ceramic substrate 1.
The center electrode 1a and the outer electrode 1b are formed concentrically via the line d, and the common electrode 1c is formed on the other surface. The center electrode region 1a and the outer electrode region 1b are polarized in opposite directions. That is, in the reverse polarization, a predetermined high DC electric field in the forward direction is applied between the center electrode 1a and the common electrode 1c, and a predetermined high DC electric field in the reverse direction is applied between the outer electrode 1b and the common electrode 1c. The application is performed.

Reference numeral 2 denotes a second piezoelectric ceramic substrate provided with two parallel resonators P ₁ and P ₂ , and the second piezoelectric ceramic substrate 2 is formed thinner than the first piezoelectric ceramic substrate 1. ing. Thus, by further reducing the thickness of the parallel resonators P ₁ and P ₂ to be smaller than that of the series resonators S ₁ and S ₂ , the capacitance ratio increases, and the attenuation of the stop band can be increased. Each parallel resonator P ₁ , P ₂
Represents a rectangular annular groove 2 on one surface of the second piezoelectric ceramic substrate 2.
The center electrode region 2a and the outer electrode region 1b are formed concentrically via the center electrode 2d and the common electrode 2c formed on the other surface. Polarized in the opposite direction. After the polarization, the center electrode 2a and the outer electrode 2b are electrically connected by a conductive bridge 2e formed by solder, conductive adhesive, metal deposition, or the like.

As shown in FIGS. 4 and 5, the series resonator formed on the first piezoelectric ceramic substrate 1 and the series resonator formed on the second piezoelectric ceramic substrate 2 are interposed via the spacer frame 3. A top end plate 4 is laminated on the first piezoelectric ceramic substrate 1, and a bottom end plate 5 is laminated below the second piezoelectric ceramic substrate 2. The spacer frame 3 each resonator _{S 1, S 2, P 1} , two so as not to interfere with vibration of the _{P 2} of the window portion 3a, and a 3b. The top end plate 4 and the bottom end plate 5 are provided with two concave portions 4a, 4b and 5a, respectively, so as not to hinder the vibration of each resonator.
5b. In FIG. 5, 6 is an input / output pad, and 7 is a ground pad.

[0016] In the above configuration, in a mounted state of each member, the center electrode 1a of the series resonator S _1, S ₂ is connected to the output pad 6 through the respective connection conductor 1e, the parallel resonator P ₂ The center electrode 2a is connected to the input / output pad 6 via the connection conductor 2e. Common electrode 1c of the series resonator S _1, S ₂ are connected via the relay connection terminal 1f (FIG. 4), the series resonator S _1, S ₂ by sled are connected in series. Common electrode 1c of the series resonator S _1, S ₂ is the through-hole printing connected via the connection conductor 2g to the central electrode 2a of the parallel resonator P _1. The connection conductor 1e connected to the center electrode 1a of the series resonators S ₁ and S ₂ and the connection conductor 2g connected to the center electrode 2a of the parallel resonator P ₂ are connected to each other by through-hole printing.

The common electrode 2c of the parallel resonators P ₁ and P ₂
Are connected to the ground pad 7 by the connection conductor 2f, and each is connected in parallel. By attaching the top end plate 4 and the bottom end plate 5, a ladder type piezoelectric filter is formed.

[0018] Figure 6, in this way an equivalent circuit diagram of a ladder type piezoelectric filter shown in FIGS. 3 to 5 constructed, one of the center electrode 1a of the series resonator S ₁ is connected to an input terminal T ₁ , the common electrode 1c of the resonator S ₁ is connected to a common electrode 1c of the other series resonators S _2, the center electrode 1a of the other resonator S ₂ is connected to the output terminal T _2. The outer electrodes 1b of the series resonators S ₁ and S ₂ are floating.

[0019] One of the center electrode 2a of the parallel resonator P ₁ is connected between the common electrode 1c of the series resonator S _1, S _2, also the center electrode 2a of the other parallel resonators P ₂ are other resonator S
It is connected to the center electrode 1a and the output terminal T ₂ of the _2. Common electrode 2c of both the parallel resonator P _{1, P 2} is connected to the ground line E.

FIGS. 7 and 8 show series resonators and parallel resonators according to another embodiment of the present invention. In this embodiment, as shown in FIGS. 7 and 8B, FIG. To
The first piezoelectric ceramic substrate 1 and the second piezoelectric ceramic substrate 2 are formed to have the same thickness, and FIGS.
(A), the electrode region of each parallel resonator is configured to be wider than the electrode region of each series resonator so as to obtain a required capacitance ratio. Note that FIGS. 7 and 8B
In, the arrow indicates the polarization direction.

In each of the illustrated configurations, the series resonator and the parallel resonator are respectively provided on the front and back surfaces thereof with the center electrode 1.
a, 2a and the common electrodes 1c, 2c, respectively, so that they can be easily connected electrically in a laminated state, and a ladder-type piezoelectric filter having the illustrated laminated structure can be easily formed. become. In addition, the above-described series resonator S and parallel resonator P have exactly the same shape and polarization direction, which facilitates the polarization processing.

[0022]

As described above, in the high frequency ladder type piezoelectric filter according to the present invention, the first piezoelectric ceramic substrate has the center electrode and the center electrode formed concentrically on one surface of the piezoelectric ceramic substrate. A plurality of series resonators comprising an outer electrode and a common electrode formed on the other surface, wherein the center electrode region and the outer electrode region are polarized in directions opposite to each other are provided, and each of the series resonators is provided on the second piezoelectric ceramic substrate. A center electrode and an outer electrode formed concentrically on one surface of a piezoelectric ceramic substrate and electrically connected to each other, and a common electrode formed on the other surface, and the center electrode region and the outer electrode region are arranged in opposite directions to each other. Providing a plurality of polarized parallel resonators,
The center electrode of one series resonator is connected to one of the input / output pads, the center electrode of another series resonator is connected to the other of the input / output pads, the common electrode of each series resonator is connected to each other, and one Connect the center electrode of another parallel resonator to the center electrode of another parallel resonator, connect the center electrode of another series resonator to the center electrode of another parallel resonator,
Since the common electrodes of the respective parallel resonators are connected to each other and grounded, the filter itself can be reduced in thickness and desired filtering characteristics can be obtained in a high frequency range.

Further, in the laminated state, the electrical connection is facilitated, and since the polarization forms of the series resonator and the parallel resonator used are equal, the polarization process can be performed uniformly, and the manufacturing is easy. Becomes

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a resonator used in the present invention.

FIG. 2 is a graph showing a relationship between impedance and frequency of a resonator.

FIG. 3 is an exploded perspective view of a ladder-type piezoelectric filter according to the present invention.

FIG. 4 is an enlarged vertical sectional side view of the ladder type piezoelectric filter shown in FIG. 3;

5 is a perspective view of the ladder-type piezoelectric filter shown in FIG.

FIG. 6 is an equivalent circuit diagram of a ladder type piezoelectric filter according to the present invention.

7A and 7B show a series resonator S of a ladder-type piezoelectric filter according to another embodiment of the present invention, wherein FIG. 7A is a plan view and FIG. 7B is a side view.

8A and 8B show a parallel resonator P of a ladder type piezoelectric filter according to another embodiment of the present invention, wherein FIG. 8A is a plan view and FIG. 8B is a side view.

[Explanation of symbols]

1: First piezoelectric ceramic substrate provided with two series resonators 1a: Center electrode of series resonator 1b: Outer electrode of series resonator 1c: Common electrode of series resonator 2: Two parallel resonators provided Second piezoelectric ceramic substrate 2a: center electrode of parallel resonator 2b: outer electrode of parallel resonator 2c: common electrode of parallel resonator

Claims (3)

[Claims] A first piezoelectric ceramic substrate includes a center electrode and an outer electrode formed concentrically on one surface of the piezoelectric ceramic substrate, and a common electrode formed on the other surface. A plurality of series resonators whose outer electrode regions are polarized in directions opposite to each other are provided, and are formed on the second piezoelectric ceramic substrate concentrically on one surface of the piezoelectric ceramic substrate and electrically connected to each other. A plurality of parallel resonators comprising a center electrode and an outer electrode, and a common electrode formed on the other surface, wherein the center electrode region and the outer electrode region are polarized in directions opposite to each other are provided, and a center electrode of one series resonator is provided. Connected to one of the input / output pads, the center electrode of another series resonator is connected to the other of the input / output pads, the common electrode of each series resonator is connected to each other, and connected to the center electrode of one parallel resonator. ,another Connect the center electrode of the series resonator to the center electrode of another parallel resonator,
A high frequency ladder type piezoelectric filter wherein common electrodes of respective parallel resonators are connected to each other and grounded. 2. The high frequency device according to claim 1, wherein the first piezoelectric ceramic substrate provided with each series resonator is thicker than the second piezoelectric ceramic substrate provided with each parallel resonator. Ladder type piezoelectric filter. 3. The high frequency ladder type piezoelectric filter according to claim 1, wherein an electrode area of each parallel resonator is wider than an electrode area of each series resonator.