JPH10341133A - Monolithic filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent vibrating characteristic without losing piezoelectric vibration performance and to set a termination impedance over a wide variety by forming input output electrodes to one side of a piezoelectric substrate opposite to each other and introduced diagonally and providing a common electrode introduced to each diagonal angle opposed to the input output electrodes and adjacent diagonally to the other side. SOLUTION: A support electrode 12 is formed respectively to each corner in a package 11 while being in continuity with at least three mount electrodes formed to be mounted on a printed circuit board at an outer bottom side of the box shaped package 11. On the other hand, a piezoelectric substrate such as a crystal substrate 13 is contained along an inner side bottom side of the package 11. Then input and output electrodes are formed to the lower side of the crystal substrate 13 opposed to each other at a prescribed interval so as to be introduced to each corner on diagonal lines opposed to each other. Furthermore, a common electrode opposed to the input and output electrodes on the upper side so as to be introduced to each corner adjacent to each corner to which the input and output electrodes are introduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic filter capable of coping with a wide range of impedances without deteriorating characteristics due to lead-out of electrodes.

[0002]

2. Description of the Related Art Recently, a plurality of electrode pairs are provided on a piezoelectric plate,
There is known a monolithic filter in which the vibration modes are coupled by bringing the electrode pairs closer to each other to generate acoustic coupling. Since this monolithic filter does not require external elements such as a transformer and can be constituted by only one piezoelectric substrate, it is compact, lightweight, has high stability, is inexpensive, and has an IF filter for various wireless devices. Widely used for

On the other hand, recent electronic devices are desired to be small and lightweight, and are required to automate an assembling process. Therefore, surface-mounted electronic components are frequently used. Therefore, there is a tendency that a monolithic filter used in such electronic equipment is required to be a surface mount type. FIG. 3 is a plan view showing an example of a surface-mounted monolithic filter using a quartz plate as a piezoelectric plate.
This shows a state where the lid is removed.

That is, a quartz plate 2 on which electrodes are formed is housed in a box-shaped ceramic container 1. An input electrode and an output electrode are formed on the lower plate surface of the quartz plate 2 with a predetermined gap, and are led out to the plate surface end in opposite directions. A common electrode 3 is formed on the upper plate surface of the quartz plate so as to face the input electrode and the output electrode, and is led out to the end of the plate surface in a direction perpendicular to the lead-out direction of the input / output electrodes. This has the advantage that each electrode can be led out to the outside at the shortest distance.

A holding electrode 4 is formed at a predetermined position in the container 1 corresponding to the lead-out end of each electrode of the quartz plate 2, and the holding electrode 4 is formed on the outer bottom surface of the container 1. It is made to conduct to the mounting electrode which does not.
Then, the lead-out end of each electrode of the quartz plate 1 is connected to the holding electrode 4.
For example, they are fixed and held by a conductive adhesive and are electrically connected. By the way, in such a monolithic filter, the height dimension of the electrode (h in the figure)
When the value of is increased, the terminal impedance decreases, and when the value is decreased, the terminal impedance increases.

In such a filter, it is not preferable that the distance between the common electrode and the lead-out end is too small, because the dispersion of the conductive adhesive applied to the lead-out end causes a variation in filter characteristics. Therefore, the common electrode needs to be formed with an appropriate gap from the leading end. For this reason, if the width of the quartz plate is constant, the height of the quartz plate is limited, thereby restricting the terminal impedance as a filter from being too low.

Further, the inventors fix the lead-out end of the common electrode with a conductive adhesive, so that the quartz plate 1 is mechanically fixed at the central side, thereby suppressing piezoelectric vibration. And found that the vibration characteristics deteriorated. For this reason, as shown in the graph of temperature characteristic shown in Fig.
The original temperature characteristic was a flat cubic curve as shown by the curve A, but the characteristic of having a large temperature gradient as shown by the curve B by fixing the center side of the quartz plate is disadvantageous. is there.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and does not impair piezoelectric vibration.
It is an object of the present invention to provide a monolithic filter capable of obtaining good vibration characteristics and setting a wide range of terminal impedance.

[0009]

According to a first aspect of the present invention, there is provided a rectangular piezoelectric plate, input / output electrodes formed on one surface of the piezoelectric plate and led to opposite diagonals, respectively, and the piezoelectric plate. And a common electrode formed on the other plate surface facing the input / output electrode and extending to each diagonal adjacent to the diagonal from which the input / output electrode is derived. The piezoelectric plate according to claim 1 is characterized in that the piezoelectric plate is quartz, and the piezoelectric plate according to claim 1 is housed in a box-shaped ceramic container,
A feature is a surface-mounted monolithic filter in which each electrode of the piezoelectric plate is fixed and held by a conductive adhesive to a holding electrode formed in the container and is electrically connected.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing an example of a surface-mounted monolithic filter of the present invention, with a lid removed. For example, at least three mounting electrodes (not shown) used for mounting on a printed board are formed on the outer bottom surface of the box-shaped container 11 made of ceramic and having an opening on the upper surface.

Then, the container 11 is electrically connected to the mounting electrode.
The holding electrode 12 is formed at each corner of the inside.
On the other hand, the piezoelectric plate 13 is housed along the inner bottom surface of the container 11. The piezoelectric plate 13 is, for example, a quartz plate 13 obtained by cutting a crystal of artificial quartz into a plate shape at a predetermined angle with respect to a crystal axis.

The lower plate surface of the quartz plate 13, that is, the plate surface facing the inner bottom surface of the container 11, is shown in a perspective view, for example, in FIG. Thus, the input electrode 14a and the output electrode 14b are formed.
A common electrode 14c is formed on the upper plate surface of the quartz plate 12, that is, the plate surface facing the opening of the container 11, for example, as shown in FIG.

That is, the input electrode 14a and the output electrode 14a formed opposite to each other on the lower plate surface with a predetermined gap are 14b.
Are derived to opposite diagonals, that is, corners on opposite diagonals. Further, the common electrode 12c formed on the upper plate surface so as to face the input electrode 14a and the output electrode 14b is led to each corner adjacent to the corner from which the input electrode 14a and the output electrode 14b are led. I have to.

In this manner, each electrode 1 of the quartz plate 13 is
4 a, 14 b, 14 c can be electrically connected to the respective corners of the container 11 by, for example, a conductive adhesive.
There can be a distance to b, 14c that does not adversely affect the characteristics. In particular, it is possible to separate the common electrode 14c from the lead-out end thereof, and it is possible to prevent deterioration of characteristics due to the conductive adhesive applied to the lead-out end.

Since the plate surface of the quartz plate 13 can be used effectively when the electrodes are led out, the terminal impedance of the filter can be reduced by, for example, increasing the height of the electrodes, and the filter design can be reduced. In this case, there is an advantage that the selection range of the termination impedance can be widened.

The present invention is not limited to the above embodiment. For example, in the above embodiment, a surface mount type filter has been described. However, the present invention is also applicable to a filter which is housed in a metal container and leads electrodes through lead terminals. Of course, it can be applied and the same effect can be obtained.

[0017]

The present invention is embodied in the form described above and has the following effects. Since the portion fixed by the conductive adhesive is far from the center of the piezoelectric plate, the piezoelectric vibration is not suppressed, whereby good vibration characteristics can be obtained, and the terminal impedance can be set in a wide range. A monolithic filter can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of a monolithic filter according to an embodiment of the present invention, showing a state in which a lid is removed.

FIGS. 2A and 2B are plan views showing electrode shapes of the filter shown in FIG. 1, wherein FIG. 2A is a perspective view of an input / output electrode, and FIG.

FIG. 3 is a plan view showing an example of a conventional monolithic filter, with a lid removed.

FIG. 4 is a graph illustrating a change in temperature characteristics due to an adhesive.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Container 12 Holding electrode 13 Piezoelectric plate 14a, 14b Input / output electrode 14c Common electrode

Claims (3)

[Claims] 1. A rectangular piezoelectric plate, input / output electrodes formed on one plate surface of the piezoelectric plate and led to opposite diagonals, and the input / output electrodes on the other plate surface of the piezoelectric plate. And a common electrode formed to face each diagonal adjacent to the diagonal from which the input and output electrodes are formed facing each other. 2. The monolithic filter according to claim 1, wherein the piezoelectric plate is made of quartz. 3. The piezoelectric plate according to claim 1, wherein the piezoelectric plate is housed in a box-shaped ceramic container, and each electrode of the piezoelectric plate is fixed to a holding electrode formed in the container with a conductive adhesive. A monolithic filter characterized by holding and electrically conducting.