JPS63212212A - Ladder type piezoelectric ceramic filter - Google Patents

Abstract

PURPOSE:To improve the heat resistance of the titled filter considerably by making the direction of polarization of a series resonator constant. CONSTITUTION:The series resonator 1 used for the ladder type ceramic filter is connected in series so that the direction of polarization of the piezoelectric substrate 4 is made constant and the polarized direction is arranged. In order to make the direction of polarization of the series resonator 1 constant, based on the entire face electrode 5 or the partial electrode 6 as a reference, the resonators are arranged in contrast to the size of the electrodes, the direction of polarization is made in series by having only to arrange the direction of the electrode in assembling the ladder type piezoelectric ceramic filter, the selection is facilitated and the loss of polarization of the series resonator due to external temperature change is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a ladder-type piezoelectric ceramic filter constructed using a plurality of series resonators and parallel resonators.

<Conventional technology and its problems> In general, multi-element type ladder type ceramic filters are
As shown in Fig. 2, a plurality of series resonators 1 formed by providing electrodes on both sides of a piezoelectric substrate using ceramic are connected in series, and between each series resonator 1 and between the series resonator and the output terminal. The parallel resonators 2 formed in the same manner as the series resonators are connected to each other, and in the case shown in the figure, it is a three-stage ladder type filter.

The series resonator 1 and the parallel resonator 2 as described above are formed by providing electrodes on both sides of a substrate made of ceramic, applying polarization between both electrodes of the substrate, and imparting piezoelectricity to the substrate. As shown in the figure, each circuit is provided with a braking chamber 13.

By the way, the filter characteristics of a ladder-type piezoelectric ceramic filter are determined by the ratio of the damping capacity of the series resonator 1 and the parallel resonator 2. Therefore, the damping capacity 3 of the series resonator 1 becomes a problem.
is made smaller than the damping capacity 3 of the parallel resonator 2.

In order to obtain the above-mentioned difference in damping capacity 3, as shown in FIG. It has a structure in which the electrodes are partial electrodes 6, and during assembly, the series resonators 1 are randomly connected and used without specifying the direction of polarization.

When a completed ladder-type piezoelectric ceramic filter like the one above is subjected to a thermal shock test of -55°C + 85°C for several dozen cycles, a phenomenon occurs in which the polarization of the resonator is removed. It has been found that this phenomenon occurs more easily in the series resonator 1.

The cause of the above phenomenon of polarization is that the series resonator 1
This is because the polarization directions of the resonators are random, and as a result of thermal shock tests, there is a problem in that polarization often occurs, especially in series resonators using ceramic materials with low QM.

This invention was made to solve the above-mentioned problems, and is a ladder-type piezoelectric ceramic that is useful when it is necessary to use a material with low GM and without the phenomenon of depolarization caused by a thermal shock test. The purpose is to provide filters.

Means for Solving the Problems> In order to solve the above problems, the present invention has a structure in which the polarization direction of the piezoelectric substrate in each series resonator is constant.

Effect〉 If the polarization direction is made constant based on either the entire surface electrode or the partial electrode when polarization is imparted in the manufacturing process of series resonators, the polarization direction of all series resonators will be aligned when connected in series, which will prevent thermal shock. It is possible to prevent the occurrence of a phenomenon in which polarization is removed even if a test is performed.

<Example> Hereinafter, an example of the present invention will be described based on FIG. 1.

Note that the same parts as in FIGS. 2 and 4 will be described using the same reference numerals.

As shown in FIG. 1, the series resonators 1 used in the configuration of the ladder-type piezoelectric ceramic filter are connected in series so that the polarization direction of the piezoelectric substrate 4 is constant and the polarization directions are aligned.

In order to make the polarization direction of the series resonator 1 constant, it is sufficient to use either the entire electrode 5 or the partial electrode 6 as a reference and compare the size of the electrode.When assembling the ladder type piezoelectric ceramic filter, In this case, simply by aligning the electrodes, the polarization directions become serial, making the separation process easier.

In addition, the polarization direction of the series resonator 1 may be either ten polarity or negative polarity on the input side as shown in Figure 1, and the polarization direction of the other resonator All you have to do is place the .

<Effects> As described above, according to the present invention, since the polarization direction of the series resonators in the ladder-type piezoelectric ceramic filter is made constant, it is possible to prevent the phenomenon in which the series resonators become polarized due to external temperature changes. This is particularly effective when it is necessary to use ceramic materials with low QM.

Incidentally, the following table shows the results of thermal shock tests on the ceramic filter of this invention and the conventional ceramic filter.

The test conditions were 50 cycles of -55°C to 185°C.

As is clear from the above test results, by making the polarization direction of the series resonators constant, the heat resistance strength of the filter can be significantly improved.

[Brief explanation of the drawing]

Fig. 1 is an equivalent circuit diagram of a filter according to the present invention, Fig. 2 is an equivalent circuit diagram showing a conventional filter, Fig. 3 is an equivalent circuit diagram of a resonator, and Fig. 4 is a perspective view of a series resonator. . 1...Series resonator 2...Parallel resonator 4
...Piezoelectric substrate 5...Full surface electrode 6...
・Partial electrode

Claims (1)

[Claims] In a ladder-type piezoelectric ceramic filter constructed by connecting a plurality of series resonators and parallel resonators formed by providing electrodes on both sides of a ceramic piezoelectric substrate in a ladder shape, the polarization direction of the piezoelectric substrate in each series resonator A ladder type piezoelectric ceramic filter characterized by a constant value.