JPH06104682A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To reduce a loss due to 2-way performance of a surface acoustic wave, to improve the in-band characteristic and to make the size small by adopting apodized electrodes for input or output side electrodes at both ends of a substrate. CONSTITUTION:For example, an apodized interdigital electrode 4 is adopted for input side electrodes only at both ends and a similar interdigital electrode 4 to that of a conventional device is adopted for other electrodes. Thus, a multiple reflection of a surface acoustic wave is minimized between the input side electrode 2 and the output side electrode 3 attended with ununiformity of the electrodes and the insertion loss is reduced while suppressing fluctuation of a loss due to an in-band ripple. The power of the surface acoustic wave is concentrated onto the middle of the surface acoustic wave device and the power is small at both ends. Thus, the power of the surface acoustic wave leaked to the outside of the input side electrode 2 or the output side electrode 3 placed at both ends is reduced. Since the power of the electric signal inputted to an input terminal 5 is outputted efficiently to the output terminal 6, the insertion loss is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device that uses the propagation characteristics of surface acoustic waves to pass or delay signals.

[0002]

2. Description of the Related Art Conventionally, as a method of realizing a low-loss surface acoustic wave device, a plurality of input electrodes for converting an input electric signal into a surface acoustic wave and, conversely, converting a surface acoustic wave into an output electric signal. A so-called multi-electrode configuration in which a plurality of output electrodes are alternately arranged on the piezoelectric substrate along the surface acoustic wave propagation direction is often used.

[0003] FIG. 3 shows, for example, the document Mayion Lewis, AIE Proceeding 1982, Ultrasonics Symposium, page 12 (Meirio
n Lewis IEEE Proc., 1982 Ultrasonics Symposium, p.
12 is a configuration diagram showing the conventional surface acoustic wave device shown in FIG. 12), in which reference numeral 1 is a piezoelectric substrate which is a substrate for propagating surface acoustic waves, and an input electric signal is applied to the surface of the piezoelectric substrate. There are provided five input-side electrodes 2 for converting the surface acoustic waves into four and four output-side electrodes 3 for converting the surface acoustic waves into output electric signals. These electrodes 2 and 3 are arranged alternately along the surface acoustic wave propagation direction.

Further, each of the input side electrode 2 and the output side electrode 3 is composed of one interdigital electrode 4. Further, all the input side electrodes 2 are connected to one common input side terminal 5, and all the output side electrodes 3 are connected to one common output side terminal 6.

Next, the operation will be described. FIG. 3 shows the case where the input side electrode 2 is located at the outermost side. However, in such a surface acoustic wave, the reciprocity theorem in the electric circuit network theory is generally established, so that the input side terminal 5 and the output side terminal 6 are Even if they are connected in reverse, the pass characteristics are exactly the same.

That is, even when the output electrode 3 is located on the outermost side, the same pass characteristic is exhibited. Therefore, here, as shown in FIG. 3, the case where the input side electrode 2 is located on the outermost side will be described.

Each of the five input-side electrodes 2 is composed of the same one interdigital electrode 4. Therefore, when an input electric signal is applied to the input side terminal 5, the input side terminal 5
The electric power supplied to the input electrodes 2 is equally distributed to the input-side electrodes 2 by 1/5 and converted into surface acoustic waves. The surface acoustic waves thus excited propagate toward both sides of each input-side electrode 2, are transmitted to the output-side electrode 3, and are converted into an electric signal again here, and are transmitted from the output-side terminal 6 to the electric signal. It is output as a signal.

At this time, the surface acoustic wave propagated from the outermost input side electrode 2 toward both ends of the piezoelectric substrate 1 is
It is not received by the output electrode 3. Therefore, a total of one-fifth of the electric power directed to both ends of the piezoelectric substrate 1 is discarded, and only the remaining four-fifth of the electric power is output.
It will be taken out from.

The insertion loss in this case is 0.97 decibel, and this insertion loss is a loss caused by the surface acoustic wave propagating in both directions. In general, if the total number of the input side electrodes 2 and the output side electrodes 3 is N, then the loss caused by the above-described bidirectionality of the surface acoustic wave is −10 × log (( N-1) / (N +
1)) Become decibel. Therefore, the insertion loss can be reduced by increasing the numbers of the input side electrodes 2 and the output side electrodes 3.

[0010]

Since the conventional surface acoustic wave device is constructed as described above, if the loss caused by the bidirectionality of the propagation of the surface acoustic wave is made sufficiently small, the input side It is necessary to make the number of electrodes 2 and the number of output side electrodes 3 very large, and therefore, on the surface of the piezoelectric substrate 1,
Since a large number of input side electrodes 2 and output side electrodes 3 are arranged, there is a problem that the size of the piezoelectric substrate 1 becomes large.

The invention of claim 1 has been made in order to solve the above-mentioned problems, and it is possible to reduce the loss due to the bidirectionality of the surface acoustic wave, improve the in-band characteristics, and reduce the size. An object is to obtain a surface acoustic wave device that can be realized.

It is an object of the present invention to provide a surface acoustic wave device capable of suppressing multiple reflections of surface acoustic waves between electrodes and reducing insertion loss by reducing non-uniform portions of electrode fingers. And

[0013]

A surface acoustic wave device according to a first aspect of the present invention includes a substrate for propagating a surface acoustic wave, and an input provided on the substrate for converting an input electric signal into a surface acoustic wave. A side electrode and an output side electrode that is alternately arranged on the substrate in the propagation direction of the surface acoustic wave together with the input side electrode, and that converts the surface acoustic wave excited by the input side electrode into an output electric signal. The input-side electrodes or output-side electrodes arranged at both ends of the substrate are apodized electrodes.

The surface acoustic wave device according to the invention of claim 2 is
A substrate for propagating surface acoustic waves, and provided on the substrate,
An input side electrode for converting an input electric signal into a surface acoustic wave and the input side electrode are alternately arranged on the substrate in the propagation direction of the surface acoustic wave, and are excited by the input side electrode to output the surface acoustic wave. An output side electrode for converting into an electric signal is provided, and the crossing width of the interdigital electrode of the input side electrode or the output side electrode arranged at both ends of the substrate is made shorter than the crossing width of other electrodes, and tilted. It was made.

[0015]

Since the input side electrode or the output side electrode at both ends of the substrate in the invention of claim 1 is an apodized type electrode, the electric impedance of each of these electrodes becomes high, so that only a small current flows there. First, the electric power of the surface acoustic wave to be excited is reduced, the electric power leaking to the outside is suppressed, and the size and the loss can be reduced without increasing the number of electrodes. Further, by reducing the non-uniform portion of the electrode fingers, multiple reflection of surface acoustic waves can be minimized, loss variation due to ripples in the band can be suppressed, and insertion loss can be reduced.

According to the second aspect of the present invention, the input side electrodes or the output side electrodes at both ends of the substrate are formed by making the crossing width of the interdigital electrodes shorter than the crossing width of the other electrodes and inclining them. The power leaked to the outside is reduced, and the structure can be made smaller and the loss can be reduced. Further, it is possible to reduce the non-uniform portion of the electrode fingers, suppress the loss fluctuation due to multiple reflection of surface acoustic waves and ripples in the band, and reduce the insertion loss.

[0017]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a substrate that propagates surface acoustic waves as a piezoelectric substrate, 2 is an input side electrode, 3 is an output side electrode,
4 is a comb-shaped electrode of the input side electrode 2 and the output side electrode 3,
Reference numeral 5 is an input side terminal, and 6 is an output side terminal. Then, only the input side electrodes 2 at both ends are constituted by apodized electrodes arranged along the wavefront direction of the surface acoustic wave, and the other input side electrodes 2 and output side electrodes 3 are the same as in the conventional example of FIG. It is composed of a comb-shaped electrode 4.

The cause of the loss is that the input side electrodes 2 on both ends are
Since the electric power of the surface acoustic wave leaks to the outside of, the loss can be considerably suppressed even by making the intensity of the surface acoustic wave excited from the input side electrodes 2 at both ends smaller than the other.

In this embodiment, only the input-side electrodes 2 at both ends are composed of the apodized interdigital electrodes 4, and the other interdigital electrodes 4 are the same as those in the conventional example. The multiple reflection of the surface acoustic wave between the electrodes 2 and 3 can be minimized, and the insertion loss can be reduced while suppressing the loss fluctuation due to the ripple in the band to be small.

Next, the operation will be described. First, in this surface acoustic wave device, the electric power of the surface acoustic wave is concentrated in the central part, and the electric power becomes small at both ends. Therefore, the electric power of the surface acoustic wave leaking to the outside of the input-side electrode 2 (or the output-side electrode 3) located at both ends can be suppressed to be small.

Therefore, since the electric power of the electric signal inputted to the input side terminal 5 can be efficiently outputted to the output side terminal 6, the insertion loss can be made smaller than that of the conventional surface acoustic wave device. Further, the number of input-side electrodes 2 and output-side electrodes 3 required to obtain the same insertion loss can be reduced, and a surface acoustic wave device smaller than the conventional one can be obtained.

Further, the input side electrode 2 and the output side electrode 3
Therefore, it is not necessary to reduce the aperture length, and it is easy to match with an external circuit without increasing the insertion loss due to the surface acoustic wave diffraction.

Example 2. FIG. 2 is a block diagram showing another embodiment of the present invention. This embodiment is different from that shown in FIG. 1 in that only the input side electrodes 2 at both ends have a short cross width of the interdigital electrodes 4 arranged along the wavefront direction of the surface acoustic wave, and the surface acoustic wave is reduced. Is evenly distributed and further inclined.

Therefore, also in this embodiment, the loss can be reduced by suppressing the leakage of the surface acoustic wave.
It is possible to suppress multiple reflection of surface acoustic waves between electrodes,
Further, it is possible to suppress the loss variation due to the ripple in the band and reduce the insertion loss.

[0025]

As described above, according to the first aspect of the invention, the substrate for propagating the surface acoustic wave, and the input side electrode provided on the substrate for converting the input electric signal into the surface acoustic wave. An output side electrode that is alternately arranged on the substrate together with the input side electrode in the propagation direction of the surface acoustic wave, and that converts the surface acoustic wave excited by the input side electrode into an output electric signal. Since the input side electrode or the output side electrode arranged at both ends of the is an apodized type electrode, the electric power of the surface acoustic wave excited is reduced, the electric power leaked to the outside is suppressed, and the number of electrodes is not increased. By reducing the size and reducing the loss, and by reducing the non-uniform parts of the electrode fingers,
There is an effect that the multiple reflection of the surface acoustic wave is minimized, the loss fluctuation due to the ripple in the band is also suppressed, and the insertion loss can be reduced.

According to the second aspect of the present invention, a substrate for propagating a surface acoustic wave, an input side electrode provided on the substrate for converting an input electric signal into a surface acoustic wave, and the substrate are provided on the substrate. Output side electrodes, which are alternately arranged in the propagation direction of the surface acoustic wave together with the input side electrodes and convert the surface acoustic waves excited by the input side electrodes into output electric signals, are arranged at both ends of the substrate. Since the crossing width of the interdigital electrode of the input side electrode or the output side electrode is made smaller than the crossing width of the other electrode and is inclined, the electric power leaked to the outside of each of these electrodes is reduced. In addition to the effect of reducing the size and the loss, it is possible to reduce the insertion loss by reducing the non-uniform portion of the electrode fingers, suppressing the loss fluctuation due to the multiple reflection of surface acoustic waves and the ripple in the band.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a surface acoustic wave device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a surface acoustic wave device according to another embodiment of the present invention.

FIG. 3 is a configuration diagram showing a conventional surface acoustic wave device.

[Explanation of symbols]

 1 Piezoelectric substrate (substrate) 2 Input side electrode 3 Output side electrode 4 Interdigital electrode

Claims (2)

[Claims] 1. A surface acoustic wave propagating substrate, an input side electrode provided on the substrate for converting an input electric signal into a surface acoustic wave, and the surface acoustic wave together with the input side electrode on the substrate. A surface acoustic wave device alternately arranged in a propagation direction of the output side electrode for converting a surface acoustic wave excited by the input side electrode into an output electric signal, wherein the surface acoustic wave device is arranged at both ends of the substrate. A surface acoustic wave device characterized in that an input side electrode or an output side electrode is an apodized type electrode. 2. A surface acoustic wave propagating substrate, an input side electrode provided on the substrate for converting an input electric signal into a surface acoustic wave, and the surface acoustic wave together with the input side electrode on the substrate. A surface acoustic wave device alternately arranged in a propagation direction of the output side electrode for converting a surface acoustic wave excited by the input side electrode into an output electric signal, wherein the surface acoustic wave device is arranged at both ends of the substrate. A surface acoustic wave device, characterized in that a crossing width of a comb-shaped electrode of an input side electrode or an output side electrode is made smaller than a crossing width of another electrode and is inclined.