JPH01295514A - Edge mode ceramic filter - Google Patents

Abstract

PURPOSE:To improve the characteristic and yield of the edge mode ceramic filter by providing a groove to nearly a midposition of a front end face of a drive electrode of a rectangular piezoelectric ceramic plate so as to lower the resonance frequency of the edge mode vibration. CONSTITUTION:A groove 6 is provided nearly to the center of the front end face of a drive electrode of a rectangular piezoelectric ceramic plate. The groove 6 is provided to lower the resonance frequency. Thus, the center frequency is adjusted by varying the depth of the groove or the substantial inner diameter by means of groove making or the like. Figure (b) shows a surface diagram of a drive section of the edge mode ceramic filter in the center frequency of 455kHz using the piezoelectric ceramic substrate, 3.1mm wide, 0.2mm thick and 0.9mm long, and figure (b) illustrates a measurement of a varied resonance frequency with respect to the depth of the groove in case of adjusting the resonance frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic filter structure in which the center frequency of the ceramic filter can be adjusted using edge mode vibration in which vibration energy is concentrated at the longitudinal ends of a thin rectangular piezoelectric ceramic plate.

Edge mode vibration is a vibration mode in which vibration energy is concentrated at the ends of an elastic rectangular plate, and its resonance frequency frFi is determined by the sound velocity v6, which is a material constant of the rectangular plate, and the width dimension W of the rectangular plate, and is determined by the following equation. Given.

Therefore, when increasing the resonance frequency f, the width dimension W
Adjustment can be easily made by making the value smaller. On the other hand, as a method of adjusting the resonance frequency fr to a low value, in the case of a vibration mode called bulk wave vibration such as longitudinal vibration or bending vibration of a general mechanical vibrator, a method of cutting down the vibration node part is a method.

Alternatively, there is a known method of lowering the resonant frequency by adding mass to the antinode of vibration, but in edge mode vibration, there are no nodes of vibration in the strict sense, and adding mass is a technique. It is difficult to apply conventional methods due to the technical difficulties involved. Therefore.

The method used was to set the resonant frequency low in advance and then adjust the resonant frequency upward.

An object of the present invention is to provide a device that utilizes edge mode vibration.

The present invention provides an edge mode ceramic filter in which a drive electrode is provided at one longitudinal end of a rectangular piezoelectric ceramic plate, and the drive electrode is extended onto the ceramic plate at the other end to form an external connection terminal. The center frequency f of the ceramic filter can be lowered by providing a groove in the approximate center of the front end surface of the drive electrode of the rectangular piezoelectric ceramic plate to lower the resonant frequency of edge mode vibration.

This makes it possible to lower the

The present invention will be described in detail below with reference to the drawings.

Figure 1 shows an example of the electrode configuration of a three-terminal ceramic filter constructed using edge mode vibration.
As shown in the figure, drive electrodes 2, 3, and 4 are provided on both sides of the surface end of the rectangular piezoelectric ceramic plate 10 and at the center position, and each drive electrode 2, 3, and 4 is extended to the other end of the piezoelectric ceramic plate 1. An input terminal 2', a ground terminal 3', and an output terminal 4' are provided as connection terminals with external lead terminals. Further, as shown in FIG. 1(b), on the back surface of the piezoelectric ceramic plate 1, there are drive electrodes 2.3 and 3 on the front surface.
Two floating electrodes 5 and 5' are provided at positions opposite to each other.

FIG. 2 is an electrical equivalent circuit of the three-terminal ceramic filter shown in FIG. If the electrode configuration is symmetrical as shown in FIG. 1, the filter will be symmetrical. In addition, in the symmetrical three-terminal ceramic filter represented by the equivalent circuit in FIG. 2, the center frequency is f. is the output terminal P, -
Input end with P2 open! , -I is known to match the resonant frequency fr when viewed as a two-terminal piezoelectric vibrator.

Therefore, instead of measuring the center frequency fo of the ceramic filter, it is sufficient to measure the resonance frequency fr of the two-terminal vibrator with the output end open, as described above.

Generally speaking, AM Silradio 455K, which is the most commonly used method, is used to reduce the center frequency variation of ceramic filters.
For Hz ceramic filters, an accuracy of ±I KHz is required. On the other hand, considering the variations in the piezoelectric material and the variations due to machining, the resonant frequency of the piezoelectric vibrator in the unadjusted state is ±5 with respect to the average of 455KHz.
It is unavoidable that it varies by about KHz. therefore.

In order to reduce this variation, it is necessary to adjust the resonance frequency.

The present invention provides an edge mode ceramic filter in which a drive electrode is provided at one longitudinal end of a rectangular piezoelectric ceramic plate, and the drive electrode is extended onto the ceramic plate at the other end to serve as an external connection terminal. The rectangular piezoelectric ceramic plate is characterized in that a groove is provided at approximately the center of the front end surface of the drive electrode.

By providing this groove, the width W in the above equation (1) becomes substantially wider, and the resonant frequency becomes lower. Therefore, the center frequency can be adjusted by changing the depth or substantial inner diameter of the groove by drilling or the like.

Figure 3 (,) shows a width of 3.1 m+ and a thickness of 0.9 m according to the present invention.
2 fights, length 9. A surface view of the driving part of an edge mode ceramic filter with a center frequency of 455 KHz made using an OTM piezoelectric ceramic substrate is shown, and Figure 3 (b) shows the depth of the groove and the amount of change in the resonant frequency when the resonant frequency is adjusted. This figure shows the measured values that indicate .

The grooves were bored using a GC grindstone with a thickness of about 0.6 wx and a tip shape with a radius of curvature of about 0.3 rIrx. Therefore, the groove width changes depending on the groove depth, and the groove depth is 0.
．． At 1■, the maximum groove width was about 0.5 m.

As shown in Figure 3(b), the width is only 0.5+m.

The resonant frequency is approximately 12KH due to the groove 6 with a depth of 0.1 ms.
It is understood that the resonant frequency adjustment method of the present invention is very effective as a method for lowering the resonant frequency.

Furthermore, in the adjustment range of fr shown in accordance with the present invention.

The results of measuring the capacitance ratio, 'mechanical Q' and free capacitance, which are other important characteristics of a piezoelectric vibrator, showed only changes within the measurement error range, except for an approximately 5% increase in the capacitance ratio.

As described above, according to the present invention, the resonant frequency can be easily lowered without changing other basic characteristics, and the resonant frequency can be increased by reducing the width, which is conventionally done. Combining this method with the method greatly contributes to improving the characteristics and yield of edge mode ceramic filters.

[Brief explanation of the drawing]

Figure 81 (,) shows a front view of an edge mode three-terminal ceramic filter, and (b) shows a back view. 2 shows a driving electrode portion of the ceramic filter equivalent to the ceramic filter of FIG. 1, and FIGS. 3(a) and 3(d) show characteristic diagrams obtained by the adjustment method according to the present invention. In the figure, l: ceramic plate 2, 3.4: drive electrode. 2' Two-person electrode, 3': Ground electrode. 4': Output electrode, 6: Groove. Figure 1 (Q) Figure 2 Figure 3 (α) Groove', length d (TrLrrL) Figure 3 (b)

Claims (1)

[Claims] 1) In the edge mode ceramic filter, a drive electrode is provided at one end in the length direction of a rectangular piezoelectric ceramic plate, and the drive electrode is extended onto the ceramic plate at the other end to serve as an external connection terminal. An edge mode ceramic filter characterized in that a groove is provided on the front end surface of a drive electrode of a rectangular piezoelectric ceramic plate.