JPS6365707A - Sealing for piezoelectric filter - Google Patents

Abstract

PURPOSE:To meet the requirements of assuring a guaranteed attenuation by approaching an electrode split part of a filter of a conductor seal guide wall to a filter element surface more than the other parts. CONSTITUTION:Recessed parts 8, 9 are provided to a guide wall facing a prescribed region along a common bus bar or an electrode split part of seal guides 6, 7 containing a double mode piezoelectric filter element 4 or a double mode SAW filter element 5. Then the electric lines of force between polarized electrodes or close IDTs are absorbed to a guide wall to be grounded to reduce the equivalent capacitance Cp. In requiring the guaranteed attenuation more than the attenuation gradient, only the seal guides 6, 7 have only to be changed without changing the filter element. Thus, it is possible to meet the requirements of assuring the guaranteed attenuation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the shape of a sealed tube of a piezoelectric filter, in particular a sealed tube of a multimode filter.

(Prior art) Multi-mode, especially dual-mode crystal filters have traditionally been used as IF filters in communication devices, but due to structural reasons, filters that tend to generate attenuation bodies and have a steep attenuation slope are required. This is convenient in some cases, but when a sufficient guaranteed attenuation amount is required, it is necessary to use a method such as widening the gap between the divided electrodes.

However, using the above-mentioned method requires changing the design of the filter element, which is not only extremely troublesome but also has the disadvantage that it often leads to deterioration of spurious characteristics.

(Object of the Invention) The present invention provides a sealed tube that can meet the requirements for ensuring guaranteed attenuation without relying on the above-mentioned design changes of the filter element when changing the characteristics of a multimode piezoelectric filter. The purpose is to provide.

(Summary of the Invention) In order to achieve the above objects, the sealed tube of the present invention has a multi-mode piezoelectric filter or a multi-mode SAW housed therein.
A tube wall facing a predetermined area centered on the electrode divided portion of the filter or the common busper is configured to be closer to the surface of the filter element than other tube walls.

(Examples) The present invention will be described in detail below by way of examples shown in the drawings.

In order to facilitate understanding of the present invention, the characteristics of a dual-mode piezoelectric filter and a dual-mode SAW filter to which the present invention is applied will be briefly explained before describing embodiments.

FIG. 2 is a diagram showing the characteristics of a dual mode piezoelectric filter. As is well known, the dual-mode piezoelectric filter has one divided section on a piezoelectric substrate such as crystal.

The passband is determined based on two different frequencies generated by the acoustic coupling of both electrodes, and its schematic structure and characteristics are as shown in FIG. 2 (al).

However, in actual filters, as shown in FIG. 2B, an equivalent capacitance Cp generally exists between the divided electrodes, and the existence of this Cp generates an attenuation pole and deteriorates the guaranteed attenuation amount. In order to deal with this, conventional techniques such as widening the gap between the divided electrodes have been used to meet the demand for ensuring a guaranteed attenuation amount, which is quite cumbersome as described above.

A similar problem occurs with dual mode SAW filters such as the one shown in FIG. That is, the dual mode SAW filter has a pair of I
The DT electrodes 3, 3 are placed close to each other, and both IDTs utilize two different frequencies generated based on the acoustic coupling between the poles 3, 3. It uses the same principle as the aforementioned dual mode piezoelectric filter. This is because it is a thing.

In order to solve this problem, in the present invention, as shown in Fig. A recess 8 or 9 is provided in the tube wall facing a predetermined area along the buspar to bring the recess 8 or 9 close to the filter element 4 or 5.

By doing so, lines of electric force between the divided electrodes or between adjacent IDTs are absorbed by the grounded tube wall, and as a result, the equivalent capacitance Cp decreases.

Therefore, the attenuation pole generated by the capacitance Cp becomes close to non-pole, and at the same time, the guaranteed attenuation amount improves, so if the guaranteed attenuation amount is required rather than the attenuation slope, it is sufficient to change only the sealing tube without changing the filter element. Therefore, it is extremely efficient.

Only the case where the tube wall is recessed is described above, and the present invention is not necessarily limited to this.9 For example, a metal piece may be attached to a desired position on the inner wall of the sealed tube, or a conductive An adhesive may be laminated.

Finally, experimental data showing the effect of using the sealed tube of the present invention is shown in FIG.

(Effects of the Invention) Since the present invention is configured and functions in nine different ways as explained above, there is no need to make any special design to the elements of the dual mode piezoelectric filter or the dual mode SAW filter, and therefore spurious characteristics etc. It is extremely effective in ensuring guaranteed attenuation characteristics without deteriorating the characteristics.

[Brief explanation of drawings]

FIGS. 1(a) to 1(d) are a perspective view, an AA sectional view, a partially cutaway view, a BB sectional view, and a BB sectional view, respectively, of an embodiment of the sealed tube according to the present invention. Figure 2 (at and (bl) are diagrams showing different characteristics of the dual mode piezoelectric filter, respectively; Figure 3 is a plan view showing the configuration of the dual mode SAW filter;
FIG. 4 (al and (bl) are diagrams respectively showing the characteristics of a dual mode piezoelectric filter using a conventional sealed tube and the results of a comparative experiment using the sealed tube of the present invention. 4... ......Multiple (double) mode piezoelectric filter. 5...Multiple (double) mode piezoelectric filter. 6.7......Sealed tube, 8,9・-・
・・・・・・Concavity. Patent applicant: Toyo Tsushinki Co., Ltd. 3rdfXJ Atsushi lfrEJ

Claims (1)

[Claims] The part of the conductor-sealed tube wall housing the multi-mode piezoelectric filter or the multi-mode SAW filter that faces the electrode-divided part of the piezoelectric filter or a predetermined area centered on the common busper of the SAW filter is A sealed tube for a piezoelectric filter, characterized in that a portion thereof is closer to the surface of the filter element.