JPS598422A - Piezoelectric longitudinal oscillation multistage narrow band filter element - Google Patents

Abstract

PURPOSE:To obtain a monolithic piezoelectric longitudinal oscillation multistage narrow band filter element, by adhering plural sets of electrodes on both sides of a single longitudinal oscillation piezoelectric substrate so as to invert alternately the phase for attaining a 4-terminal element oscillated in the double harmonic mode. CONSTITUTION:Electrodes 2-4 and 2'-4' are adhered to two parts of the longitudinal oscillation piezoelectric element board 1 as if it were bisected along the direction of socillation so as to invert the phase of both parts. In the oscillating mode of the oscillation having the constitution in this way, since the right half is oscillated to be shrinked by taking a point 9 being a node as a boundary when the left half from the center is extended to both sides by taking a point 8 being a node as a boundary at a moment as shown in the arrow in Figure, this oscillation corresponds to the 2nd order longitudinal oscillation mode. The resonance frequency of both of the said oscillating parts if the same and the value is about twice the generated resonance frequency is the said electrodes are adhered to the piezoelectric element board having a size shown in Figure. That is, the multisatge connection filter equivalent to the two-stage connection of oscillators resonated at a double harmonic of the basic frequency of the piezoelectric element boards of the same size is obtained with a single oscillator.

Description

DETAILED DESCRIPTION OF THE INVENTION Conventionally, relatively low frequencies (50 KHz-I MHz)
□ As a filter element in the band, a multi-stage vertically connected vibrator that utilizes the longitudinal vibration of a piezoelectric plate is used.

However, since all of these systems involve a predetermined number of individually manufactured oscillators housed in appropriate packages and electrically connected, they are unable to keep up with the trend toward smaller and cheaper peripheral circuits. There was a problem.

The present invention has been made in view of the above-mentioned problems, and consists of a plurality of sets of electrodes attached to both sides of a single longitudinally vibrating piezoelectric substrate so that the phases are alternately reversed, thereby vibrating in a harmonic mode. It is an object of the present invention to provide a monolithic pressure '41 oscillation multi-stage narrow band filter element whose pass band is determined by the effective resonance characteristics including the vibrator and peripheral circuits by using it as a terminal element.

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

FIG. 1 is an external view of a general piezoelectric longitudinal vibrator. That is,
Separate electrodes 2 and 3 are attached to one surface of the X-plate crystal or ceramic plate 1 with lines serving as nodes of vibration as boundaries, and electrodes 4 are attached to the other surface of the entire surface, and leads 5, 6 and 4 are attached on the lines serving as nodes of vibration, respectively. 7 is bonded.

By doing so, the two vibrators vibrate as if expanding and contracting in the longitudinal direction in the figure, and the fundamental frequency depends on the material and dimensions of the piezoelectric plate 1, but it is a relatively low resonance frequency. If used as an equivalent circuit, it can be expressed by an equivalent circuit as shown in FIG.

It is clear that such a single-stage filter generally has a very narrow passband width and does not have sufficient attenuation.

In order to obtain the desired amount of attenuation, conventionally, such vibrators were connected in series in multiple stages, making it difficult to miniaturize the circuit and reduce the cost, as described above.

In order to solve this problem, the following measures are taken in the present invention.

FIG. 3 is a side view of a multi-stage connected filter element according to the present invention.

That is, as if dividing the longitudinally vibrating piezoelectric element plate 1 into two equal parts along the excitation direction, electrodes 2 and 3 similar to the vibrator shown in FIG.
and 4) 2', 3' and 4' are attached so that the phases of the two are reversed.

In this case, the electrodes 3 and 3' may be connected by, for example, applying a conductive adhesive to the side surface of the piezoelectric plate 1, or
A vapor deposition method using a mask may also be used.

As shown by the arrows in the figure, the vibration mode of a vibrator with such a configuration extends from the center to both sides at a point 8, where the left half is a node, and when the right half reaches point 9, which is a node. (Since it vibrates twice, it corresponds to the second-order longitudinal vibration mode.)

Furthermore, the resonant frequencies of both the vibrating parts are the same, and the value of the resonant frequency is i if the electrodes as shown in FIG.
Needless to say, it will double.

A multistage filter equivalent to the one described above can be obtained with a single oscillator.

Figure 4 is an equivalent circuit when the resonator shown in Figure 3 is used as a filter, and its passband and damping characteristics are as follows.
The result will be as shown in the figure.

FIG. 5 is a diagram showing the results of an experiment using a two-stage connected filter as shown in FIG.
An attenuation of about 60 dB was obtained.

Incidentally, in such a narrow band filter, the temperature characteristic becomes a problem, but the temperature-frequency characteristic of the X-plate crystal is a quadratic curve with the apex temperature at room temperature.

Since its secondary temperature coefficient is about 0.034 PPM/C'', no particular problem arises under the conditions of use in wiring.

Next, the practical structure of the multistage connection filter according to the present invention will be explained.

In recent years, piezoelectric vibrators have been developed into shapes that are easy to store in flat packages, in order to facilitate miniaturization and automation of manufacturing processes, and to be able to be handled in the same way as J) IP such as ICs and LSIs. structure is required.

In parts 11 to 14, the base plate 1 and the frame 10 surrounding it are integrally joined at a joining part with a sufficiently small cross-sectional area, and slits 15 and 15 are formed in the other parts. ．． - Said board 1 by...
If the above-mentioned sleeve) 15, 15. If ceramics are used, the necessary electrodes 2, 3 and 4 as well as 2/, a/ and 4' are attached as shown in the figure, and the lead electrodes are connected to the vibration nodes 11 to 4'. 14
It extends to the end of the frame 10 through the connecting portion at 2 and is connected to a lead terminal of the package (not shown). At this time, it is clear that if the 1° vibrator frame is mechanically connected to the lead terminal at the same time, it will significantly contribute to automation of the manufacturing process and reduction of the number of man-hours.

Note that the connection with the electrode 3 and the electrode 3' on the back side is made using the frame l.
Since the conductive adhesive 16 can be attached along the outer side of O or by vapor deposition, no special technique is required for manufacturing.

Although only a two-stage connected monolink filter has been described above, the present invention is not necessarily limited to this, and it is also possible to use a third-order harmonic to create a three-stage filter, if necessary. However, if the number of connected stages is further increased, the one-pass band width becomes too narrow, causing a practical problem.

Needless to say, it has its own limits.

Since the present invention is constructed and functions as described above, it exhibits a remarkable effect in producing a seven-nolithic multi-stage connected filter at an extremely low cost and in a small size.

[Brief explanation of drawings]

FIG. 1 is an external view of a general piezoelectric vibrator, FIG. 2 is an equivalent circuit diagram of a filter using this, and FIG. 3 is a side view of a two-stage connection filter according to the present invention. FIG. 4 is an equivalent circuit diagram thereof, FIG. 5 is a diagram showing one experimental data thereof, and FIG. 6 is a plan view showing an embodiment of the structure of a two-stage connected filter according to the present invention. 1...Longitudinal vibrating piezoelectric plate, 2 (2'), 3 (
3') and 4 (4')... Electrode patent applicant Toyo Tsushinki Co., Ltd.

Claims (1)

[Claims] By attaching multiple sets of electrodes to both sides of a single longitudinally vibrating piezoelectric element plate so that their phases are alternately reversed to form a four-terminal element, and by utilizing the harmonic vibration of the element, steep P-wave characteristics can be obtained. A piezoelectric longitudinal vibration multi-stage narrowband filter element characterized in that: