JPS6334348Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to the structure of a surface acoustic wave device, and particularly to a surface acoustic wave device suitable for use as a duplexer or the like.

A surface acoustic wave device excites surface acoustic waves by providing interdigitated electrodes on a piezoelectric substrate. The surface acoustic waves excited by the interdigitated electrodes propagate in a direction perpendicular to the longitudinal direction of the electrode fingers of the interdigitated electrodes, but surface acoustic waves with a different propagation direction are excited at the ends of the electrodes. be done. The propagation direction of this surface acoustic wave has a certain angle from the direction perpendicular to the longitudinal direction of the electrode fingers, and the frequency is also different from the center frequency determined by the spacing between the electrode fingers.

This phenomenon is due to the following reasons. When a surface acoustic wave is excited by a crossed comb electrode, the propagation direction of the surface acoustic wave is determined by components in a direction perpendicular to and parallel to the longitudinal direction of the electrode fingers of the crossed comb electrode. In a normal crossed comb electrode, most of the components are in the perpendicular direction, so the propagation occurs in a direction perpendicular to the longitudinal direction of the electrode fingers, but at the ends, the parallel component becomes stronger, so the propagation direction is different. Therefore, by combining the orthogonal component and the parallel component, surface acoustic waves of any frequency can be propagated at a certain angle from a direction perpendicular to the longitudinal direction of the electrode fingers.

The inventor considered making use of the above-mentioned phenomenon to make the interdigitated comb-shaped electrodes feature periodicity, and devised a method to thereby form a periodic wave source and intensify surface acoustic waves propagating in different directions. When the interdigitated electrodes are given periodicity, the component of the surface acoustic wave in the direction parallel to the longitudinal direction of the electrode fingers becomes stronger at a specific frequency.
This makes use of the fact that surface acoustic waves of that frequency propagate in a fixed direction different from that of the center frequency.

There are the following methods to give periodicity to the electrodes. The intersecting comb electrodes are divided in parallel and a plurality of intersecting comb electrodes are arranged in the longitudinal direction of the electrode fingers, thereby providing a wave source having a period in the longitudinal direction. Each intersecting comb-shaped electrode becomes an electrode that excites surface acoustic waves with a center frequency determined by the spacing between the electrode fingers, but as a collection of these, a wave source with a certain width is repeatedly arranged. Become.

As described above, when an input electrical signal is applied to the interdigitated interdigitated electrodes having periodicity, a surface acoustic wave is excited.
The center frequency is determined by the spacing between the electrode fingers of the interdigitated electrode, but surface acoustic waves with a frequency different from the center frequency are generated from each section of the intersected interdigitated electrode, and the propagation direction of the surface acoustic wave of the center frequency It propagates in a certain direction different from that of

In this way, a surface acoustic wave of a specific frequency can be propagated in a specific direction by a periodic wave source, but by appropriately selecting the period of the surface acoustic wave wave source, the frequency and propagation direction can be changed. can be taken arbitrarily. This can be used to extract or remove signals of specific frequencies.

The object of the present invention is to utilize the above-mentioned principle to obtain a device with high utility value as a duplexer, etc., using a surface acoustic wave device that has not existed in the past.

A surface acoustic wave device according to the present invention will be explained according to the drawings.

FIG. 1 is a partial plan view showing an embodiment of the present invention. Although only input electrodes are shown, in an actual device, the substrate has a wide area and includes output electrodes at predetermined positions. Cross-comb electrodes 24a to 24h are arranged in parallel on a piezoelectric substrate 21. That is, all electrode fingers are connected to the pads of the input electrodes. Cross-comb electrodes 24a-24
d have opposite widths W ₁ of the same electrode fingers,
The width W ₂ of the crossed comb-shaped electrodes 24e to 24h
It is made to be different. As a result, the portions of the crossed comb electrodes 24a to 24d and the crossed comb electrode 24e
The period between 24h and 24h is different from each other.

Although the electrodes (wave sources) have periodicity due to the interdigitated electrodes 24a to 24h, they do not have a single period but a portion of the electrodes 24a to 24d and the electrode 24e.
Portions with different periods are formed in the portion from 24h to 24h. The center frequency is the same throughout, but
Due to the different periods, surface acoustic waves of a frequency different from the center frequency propagating from the electrodes 24a to 24d at a constant angle from a direction perpendicular to the longitudinal direction of the electrode fingers, and the surface acoustic waves of the electrodes 24e to 24h. Surface acoustic waves having a frequency different from the center frequency are excited from each part, which propagate at a constant angle from a direction perpendicular to the longitudinal direction of the electrode fingers. The two types of surface acoustic waves differ in frequency and propagation direction. This is because the two parts have different periodicities, so the components in the two directions appear differently, and as a result, the frequencies and propagation directions differ.

Although the output electrodes are not shown in FIG. 1, the piezoelectric substrate 21 extends not only in a direction perpendicular to the longitudinal direction of the electrode fingers of the interdigitated electrodes 24 but also on both sides thereof. Two or more output electrodes are formed at predetermined positions in a direction different from the propagation direction of the surface acoustic wave of the center frequency.

When a signal of each frequency is applied to the input signal, each surface acoustic wave having a different center frequency, frequency, and propagation direction excites the surface acoustic wave of that frequency in a predetermined direction. This direction of propagation is determined by the spacing between the electrode fingers of the interdigitated electrodes and the period.

The present invention is not limited to the above example, and can be modified in various ways, such as changing the period in three or more ways. Furthermore, the center frequency of the intersecting comb electrodes may be changed for each intersecting comb electrode. In this way, surface acoustic waves with different frequencies can be excited in different directions and converted into electrical signals at the output electrode.

The surface acoustic wave device according to the present invention can be used as a duplexer, etc. As shown in FIG. 2, the output electrode 2 is oriented at a predetermined angle from the direction perpendicular to the longitudinal direction of the electrode fingers of the interdigitated electrode 25 with respect to the input electrode 25.
6, 27 are provided. The output electrode 26 is provided in a direction having an angle of θ ₁ from the propagation direction of the surface acoustic wave at the center frequency, and the output electrode 27 is provided in a direction having an angle of θ ₂ from the propagation direction of the surface acoustic wave of the center frequency. The output electrode 26 and the output electrode 27 are designed to respond only to predetermined surface acoustic waves of different frequencies.

In this way, since the output electrode can be provided in the propagation direction of the surface acoustic wave having a certain frequency different from the center frequency to receive the surface acoustic wave, a highly accurate surface acoustic wave device with good selectivity can be obtained. It is also possible to increase the change in the period of the input electrode and provide a correspondingly large number of output electrodes to extract each frequency component. Conversely, it is also possible to remove surface acoustic waves of a certain frequency, and by combining these, various devices can be created.

In this way, the surface acoustic wave device according to the present invention can not only provide periodicity to the wave source, but also change the frequency characteristics by varying the periodicity. Furthermore, this can be achieved only by the structure and arrangement of the electrodes without the need for multiple devices. Therefore, it also has the advantage of being easy to manufacture and miniaturized.

[Brief explanation of the drawing]

FIG. 1 is a partial plan view of an embodiment of the present invention, and FIG. 2 is a plan view of another embodiment of the present invention. 21...Piezoelectric substrate, 24...Cross comb electrode, 2
5... Input electrode, 26, 27... Output electrode.

Claims (1)

[Scope of utility model registration request] In a surface acoustic wave device having a periodic wave source consisting of a plurality of intersecting comb electrodes formed by dividing intersecting comb electrodes in parallel, the electrode fingers of the plurality of intersecting comb electrodes forming a part of the intersecting comb electrodes constituting the periodic wave source are opposed to each other. an elastic surface whose width is different from the opposing widths of the electrode fingers of a plurality of interdigitated electrodes in other parts, and whose center frequency propagates in a direction perpendicular to the longitudinal direction of the electrode fingers determined by the spacing of the electrode fingers; 1. A surface acoustic wave device that excites surface acoustic waves having two or more frequencies different from waves in a direction different from the propagation direction of the surface acoustic waves having the center frequency.