JPS6324708A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain a band-pass filter having a desired frequency characteristics, by arranging a dot shape structure which makes an surface acoustic wave having a prescribed frequency reflect and scatter at a prescribed position between a pair of electrodes. CONSTITUTION:A scattered reflector 42 that is the dot shape structure arranged along the propagating direction of the surface acoustic wave, is formed at the prescribed position between an input electrode 20, and an output electrode 22. The surface acoustic wave passing each of channels A, B, C,... is synthesized and outputted if no scattered reflector 42 exists. However, for example, in case of arranging the scattered reflector 42 on the channel C, the surface acoustic wave passing the channel C is prevented from arriving at the output electrode 22 because it is reflected and scattered, and as a result, an output signal OUT has the frequency characteristic in which the surface acoustic wave in the neighborhood of a center frequency is missing.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a surface acoustic wave filter, and particularly to a surface acoustic wave filter that can extract signals having desired frequency characteristics.

(Prior Art) FIG. 6 shows an example of a surface acoustic wave filter according to the prior art. In this filter, an input electrode and an output electrode 22 are formed on the surface of a piezoelectric body 40. The input electrode has two common electrodes 24a and 24b, and the common electrode 2I4a has a plurality of electrode fingers 26a formed in a comb-teeth shape, the tips of which gradually approach each other toward the other common electrode 24b. has been done. On the other hand, the common electrode 24b has a plurality of electrode fingers 26 whose tips gradually widen toward the common electrode 24a.
b is formed in a comb-teeth shape. These electrode fingers 26a, 26b are arranged so as to mesh with each other. Note that the output electrode n has a pair of common electrodes 28a, 28b in the same manner as in the case of adding input electrodes, and electrode fingers 30a, 30 formed on these common electrodes 28a, 28b.
b are arranged in the same state as the input electrodes 20, respectively.

It is known that the frequency characteristic of the output signal OUT obtained by the filter 6 configured in this manner has a substantially rectangular shape as shown in FIG. Here, in Fig. 7, the width a
is the pass frequency bandwidth obtained by filter rotation,
The width a is determined by the maximum and minimum spacing between the plurality of electrode fingers 26a and 26b or 30a and 30b.

(Problem to be solved by the invention) However, the output signal O obtained from this filter 6
The frequency characteristics of the UT are simple and approximately rectangular, and in order to obtain an output signal with the desired complex frequency characteristics, a plurality of input electrodes 20 and output electrodes with different frequency characteristics are placed on the surface of the piezoelectric body 4. It was necessary to arrange a pair of and combine their output signals. Therefore, there is a drawback that the configuration of the filter becomes complicated and large. Additionally, in order to obtain an output signal with desired frequency characteristics, it is conceivable to combine the filter 6 with a filter consisting of a coil, a capacitor, etc., but the disadvantage is that the configuration becomes more complicated as it requires external electrical components. There is.

In order to eliminate such drawbacks, a grading structure that reflects a portion of one surface acoustic wave was disposed at a predetermined location between a pair of electrodes formed on the surface of a piezoelectric material, as disclosed in patents in the Showa era. No. 130,679 of 1960.

(Means for Solving the Problems) The present invention has been made in order to solve the above-mentioned drawbacks, and it is possible to use at least one of a pair of electrodes formed on the surface of a piezoelectric material using 8 surface acoustic wave waves. In a surface acoustic wave filter composed of comb-like electrodes that gradually expand and approach in a direction perpendicular to the propagation direction of It is equipped with dot-shaped structures that allow

(Embodiment) FIG. 1 is a plan view showing an embodiment of a surface acoustic wave filter according to the present invention, in which the surface acoustic wave filter is shown at the top, four
is a piezoelectric body, and 20 is an input electrode.

n is an output electrode, 24a, 24b, 28i, 28
b is a common electrode, 26a, 26b, 30a,
30b is an electrode finger, and 42 is a scattering reflector. Piezoelectric body 4
A pair of input and output electrodes made of a thin metal film or the like are formed on the surface of the substrate 0 by vapor deposition or the like. The input electrode 20 includes a common electrode 24a having a plurality of comb-shaped electrode fingers 26a, and a plurality of comb-shaped electrode fingers 26a.
and a common electrode 24b having a common electrode 24b.

These electrode fingers 26a, 26b are arranged so as to mesh with each other. In this case, the tips of one of the plurality of electrode fingers 26a gradually approach the common electrode 24b, and the tips of the other plurality of electrode fingers 26b approach the common electrode 24b.
It is formed so that it gradually expands toward a. The output electrode η is composed of a common electrode 28a having a plurality of electrode fingers 30a and a common electrode 28b having a plurality of electrode fingers 30b, and is arranged on the surface of the piezoelectric body 4 in the same shape as the input electrode. will be established.

These electrode fingers 26a, 26b, 30a and 30b are.

It is arranged to be oriented in a direction substantially perpendicular to the propagation direction T of the surface acoustic wave between the input electrode and the output electrode 22.

On the other hand, at a predetermined position between the input electrode 22 and the output electrode 22, there is a scattering reflector which is a dot-shaped structure oriented in a direction perpendicular to the propagation direction T of the surface acoustic wave and arranged along the propagation direction T. A body 42 is formed.

This scattering reflector 42 is made of the same metal thin film as the input electrode and the output electrode n, and is preferably formed by vapor deposition or the like at the same time as these electrode marks 22.

Various dot shapes can be considered for the dot-like structure forming the scattering reflector 42, such as a square shape and a circular shape. FIG. 2 is a diagram showing an example of the dot shape of the dot structure. In Fig. 2, the propagation direction T of one surface acoustic wave is
The distance between the dots of the scattering reflector 42 is kept constant,
If the wavelength is set to an integral multiple of the % wavelength of the surface acoustic wave, the efficiency of 1 reflection and scattering becomes the best.

Furthermore, as shown in FIG. 2, if the shape of the dot is inclined from a direction perpendicular to the propagation direction T of the surface acoustic wave, the surface acoustic wave reflected by the scattering reflector 42 can be transmitted to the input electrode 20. It would be possible to remove one of the causes of deterioration of the frequency characteristics without receiving signals.

(for production) In FIG. 1, the common electrode 24a of the input electrodes 20.

When an input signal IN is applied between 24b and 24b, the piezoelectric body 4 vibrates due to the piezoelectric effect, and the vibration propagates on the surface of the piezoelectric body 4 as an elastic wave and reaches the output electrode n. Here, the frequency band of the surface acoustic wave propagated to the output electrode n is
As previously mentioned.

A plurality of electrode fingers 2 in the input electrode hole and the output electrode 22
Depending on the maximum and minimum spacing of 6a and 26b or 3Qa and 30b. When the propagation region of the surface acoustic wave between the input electrode hole and the output electrode n is divided into a plurality of channels parallel to the propagation direction T as shown in Fig. 1, each channel A, B, C, D ,・・・・・・
In this case, surface acoustic waves having normal frequency distributions with different center frequencies are propagated. Each of these channels A, B, C
.

If the scattering reflector 42 is not present, the frequency characteristics of the output signal OUT obtained by converting the surface acoustic waves passing through the channels A, . The surface acoustic waves passing through B, C, D, . . . are synthesized, resulting in the characteristics shown in FIG.

However, in this embodiment, a scattering reflector 42 is disposed, for example, in the channel C between the input type pole mark and the output electrode n. Therefore, the surface acoustic waves passing through this channel C are reflected and scattered by the scattering reflector 42 and do not reach the output electrode 22, and the output signal OUT obtained from the output electrode n is at the center corresponding to the channel C. The surface acoustic waves near the frequency will have a missing frequency characteristic.

FIG. 3 shows the frequency characteristics at this time.

b indicates the reflected frequency stopband. A frequency characteristic having such a frequency stop band can be effectively utilized as a notch filter for removing an audio signal in the video band of a television signal, for example.

(Other Embodiments) FIG. 4 is a plan view showing another embodiment of the surface acoustic wave filter according to the present invention, and 2 indicates the surface acoustic wave filter,
4 is a piezoelectric body, 20 is an input electrode 22 is an output electrode, 44
, 46 are scattering reflectors. The structure of the input electrode hole and the output electrode 22 is the same as that shown in FIG. In FIG. 4, between the input electrode 20 and the output electrode n, a scattering reflector 44 is provided between channels in different propagation regions of surface acoustic waves.
, 46 are arranged. In this embodiment, two nearby elastic surface waves with different frequencies are reflected and scattered by the scattering reflectors 44 and 46, respectively.
A frequency characteristic having two frequency stopbands c and d as shown in FIG. 5 can be obtained.

(Effects of the Invention) According to the present invention, a pair of electrodes of a surface acoustic wave filter are constructed of comb-shaped electrodes that gradually expand and approach each other along a direction perpendicular to the propagation direction of surface acoustic waves. By arranging a dot-shaped structure that reflects and scatters a portion of one surface acoustic wave at a predetermined location between the two, it is possible to remove signals of any frequency, thereby creating a bandpass filter that has desired frequency characteristics. There are advantages that can be obtained.

Further, the scattering reflector having a dot-shaped structure can be manufactured simultaneously with the input electrode and the output electrode by vapor deposition, etc., so the manufacturing cost is low and there is no need to add any external electrical parts.

It has advantages such as being able to realize a filter with complex frequency characteristics.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an embodiment of the surface acoustic wave filter according to the present invention, FIG. 2 is a diagram showing an example of the dot shape of the dot-shaped structure according to the present invention, and FIG. 3 is similar to FIG. FIG. 4 is a plan view showing another embodiment of the surface acoustic wave filter according to the present invention, and FIG. 5 is a frequency characteristic diagram of the filter shown in FIG.
1 is a frequency characteristic diagram of the filter shown in FIG. 1, and FIG. 6 is a plan view of a surface acoustic wave filter according to the prior art. FIG. 7 is a frequency characteristic diagram of the filter shown in FIG. 6. 1, 2.6...filter, 4...piezoelectric body, 20...
- Input electrode, 22. ,,output electrode, 24a, 24b
, 28a, 28b... common electrode + 26a +2
6b, 30a, 30b...electrode fingers. 42, 44, 46... scattering reflector.

Claims (2)

[Claims] (1) At least one of the pair of electrodes formed on the surface of the piezoelectric body is formed into a comb-shaped electrode that gradually expands and approaches along the direction orthogonal to the propagation direction of the surface acoustic wave, and A surface acoustic wave filter for extracting a signal having a characteristic, characterized in that a dot-shaped scattering reflector that reflects and scatters surface acoustic waves of a predetermined frequency is disposed at a predetermined location between the pair of electrodes. filter. (2) A surface acoustic wave filter characterized in that the dot-shaped scattering reflectors according to claim 1 are arranged at an angle from a direction perpendicular to the propagation direction of surface acoustic waves.