JPH06334477A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To facilitate high frequency processing of an asymmetry filter by realizing the characteristic of the asymmetry filter in the surface acoustic wave filter using an interdigital electrode surface acoustic wave converter comprising electrode fingers of lambda/2 period. CONSTITUTION:An output side surface acoustic wave converter 12 is made up of a set electrode surface acoustic wave converter 13 comprising electrodes at an interval of lambda/2 obtained by extracting even number order of weighted data of sampling of a lambda/4 sampling to obtain a desired frequency characteristic and up of a set electrode surface acoustic wave converter 14 comprising electrodes at an interval of lambda/2 obtained by extracting odd number order of weighted data of sampling of a lambda/4 sampling to obtain a desired frequency characteristic. Then the set electrode surface acoustic wave converter 13 and the set electrode surface acoustic wave converter 14 are arranged in parallel with respect to the propagation direction of a surface acoustic wave by selecting a center distance (d) of the surface acoustic wave in the propagation direction as an odd number of multiple of lambda/4.

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 filter, and more particularly to a method of realizing an asymmetrical filter characteristic of a surface acoustic wave filter using a combined electrode type surface acoustic wave converter.

[0002]

2. Description of the Related Art Conventionally, in order to realize an asymmetric filter characteristic in a surface acoustic wave filter, sampling weights of λ / 4 intervals (λ: wavelength of a surface acoustic wave) for obtaining a desired filter characteristic are weighted on a piezoelectric substrate. One of the input-side surface acoustic wave converter and the output-side surface acoustic wave converter arranged in the above. FIG. 2 is a plan view showing a main part of an example of a conventional surface acoustic wave filter. The input side surface acoustic wave converter 21 shown in FIG. 7A is composed of split electrodes with normal type weighting at λ / 2 intervals. The output side surface acoustic wave converter 22 shown in FIG. 7B is composed of electrodes weighted by sampling at λ / 4 intervals. The frequency characteristics of the input surface acoustic wave converter 21 are symmetrical. The frequency characteristics of the output-side surface acoustic wave converter 22 are asymmetric because the sampling weighting at λ / 4 intervals is applied. The filter characteristic is the product of the frequency characteristics of the input side surface acoustic wave converter 21 and the output side surface acoustic wave converter 22.
Thereby, an asymmetric filter characteristic can be realized in the surface acoustic wave filter.

[0003]

However, in this conventional surface acoustic wave filter, either one of the input side surface acoustic wave converter and the output side surface acoustic wave converter is weighted by sampling at λ / 4 intervals. Therefore, λ / 4
Since it is necessary to form the electrode fingers at a cycle of λ / 2, there is a problem that it is difficult to increase the frequency as compared with a surface acoustic wave filter using a combined electrode type surface acoustic wave converter that can be configured with electrode fingers having a λ / 2 cycle. It was

The present invention has been made to solve the above problems, and an object of the present invention is to provide an elastic surface using a combined electrode type surface acoustic wave transducer which can be constituted by electrode fingers of λ / 2 period. The purpose of the wave filter is to realize an asymmetric filter characteristic and facilitate the high frequency operation of the asymmetric filter.

[0005]

In order to achieve such an object, the present invention provides one of the input side surface acoustic wave converter and the output side surface acoustic wave converter with a desired frequency characteristic. A first group electrode type surface acoustic wave transducer composed of electrodes weighted at λ / 2 intervals, which is an odd number extracted from the weighted data of sampling at λ / 4 intervals, and an even number of the weighted data is extracted. And a second group electrode type surface acoustic wave converter composed of electrodes weighted at λ / 2 intervals, the first group electrode type surface acoustic wave converter and the second group electrode type surface acoustic wave. The surface acoustic wave converter is arranged parallel to the surface acoustic wave propagation direction, with the center-to-center distance in the surface acoustic wave propagation direction being an odd multiple of λ / 4.

[0006]

Therefore, according to the present invention, for example, the input side surface acoustic wave converter is composed of the assembled electrodes which are weighted by the normal type in the λ / 2 interval, and the output side surface acoustic wave converter is constituted by the first and second. If it is configured with the combined electrode type surface acoustic wave converter, the frequency characteristics of the input side surface acoustic wave converter are made symmetric, the frequency characteristics of the output side surface acoustic wave converter are made asymmetric, and λ / 2 cycle An asymmetric filter characteristic can be realized in a surface acoustic wave filter using a combined electrode type surface acoustic wave converter that can be configured by electrode fingers.

[0007]

EXAMPLES The present invention will now be described in detail based on examples. FIG. 1 is a plan view showing a main part of an embodiment of the present invention. The input side surface acoustic wave converter 11 shown in FIG.
It is composed of a pair of electrodes with normal type weighting of / 2 interval. Output side surface acoustic wave converter 12 shown in FIG.
Is a first group electrode type surface acoustic wave converter 13 composed of electrodes weighted at λ / 2 intervals by extracting odd-numbered sampling weighted data at λ / 4 intervals for obtaining desired frequency characteristics. , A second group electrode type surface acoustic wave converter 14 which is composed of weighted electrodes at even intervals of λ / 2, which is an even number extracted from the weighting data.

In the output side surface acoustic wave converter 12, the assembled electrode type surface acoustic wave converters 13 and 14 have a period of λ / 2.
Of the same plurality of electrode fingers (3) are arranged in an even number, and the center-to-center distance c between adjacent paired electrodes is an odd multiple of λ / 4 (7λ in the embodiment). / 4)
Stipulated in. Further, the first group electrode type surface acoustic wave converter 13 and the second group electrode type surface acoustic wave converter 14 are
They are arranged parallel to the propagation direction A of the surface acoustic wave, and the center-to-center distance d in the propagation direction of the surface acoustic wave is set to an odd multiple of λ / 4 (λ / 4 in the embodiment) and electrically parallel to each other. It is connected. With such a configuration, the frequency characteristic of the output surface acoustic wave converter 12 becomes asymmetric.

That is, in this embodiment, the frequency characteristics of the input surface acoustic wave converter 11 are symmetrical, and the frequency characteristics of the output surface acoustic wave converter 12 are asymmetric. The filter characteristic is the product of the frequency characteristics of the input side surface acoustic wave converter 11 and the output side surface acoustic wave converter 12. This allows
An asymmetric filter characteristic can be realized in a surface acoustic wave filter using a combined electrode type surface acoustic wave converter that can be configured with electrode fingers of λ / 2 period.

In the above-described embodiment, the paired electrode type surface acoustic wave converter 13 and the paired electrode type surface acoustic wave converter 1 are used.
Although 4 and 4 are connected in parallel, they may be connected in series. Further, in the above-described embodiment, the output-side surface acoustic wave converter 12 side is configured by two combined electrode type surface acoustic wave converters, but the input-side surface acoustic wave converter 11 side is two. It may be configured by the combined electrode type surface acoustic wave converter.

[0011]

As is apparent from the above description, according to the present invention, one of the input side surface acoustic wave converter and the output side surface acoustic wave converter has a λ / 4 for obtaining a desired frequency characteristic. Λ / 2, which is an odd-numbered sample of weighting data for interval sampling, and λ / 2, which is a first set electrode type surface acoustic wave transducer composed of electrodes that are weighted at intervals, and λ / A second electrode group-type surface acoustic wave converter composed of electrodes weighted at two intervals, and a first electrode group-type surface acoustic wave converter and a second electrode group.
And the paired electrode type surface acoustic wave converter are arranged parallel to the surface acoustic wave propagation direction with the center-to-center distance in the surface acoustic wave propagation direction being an odd multiple of λ / 4. , The input-side surface acoustic wave converter is composed of a pair of electrodes with normal type weighting at λ / 2 intervals, and the output-side surface acoustic wave converter is composed of first and second paired electrode-type surface acoustic wave converters. If so, the frequency characteristics of the input side surface acoustic wave converter are made symmetrical, the frequency characteristics of the output side surface acoustic wave converter are made asymmetric, and a combined electrode type surface acoustic wave that can be configured with electrode fingers of λ / 2 period is used. In the surface acoustic wave filter using the converter, the asymmetric filter characteristic can be realized, and the asymmetric filter can be easily increased in frequency.

[Brief description of drawings]

FIG. 1 is a plan view showing a main part of an embodiment of the present invention.

FIG. 2 is a plan view showing a main part of an example of a conventional surface acoustic wave filter.

[Explanation of symbols]

 Reference Signs List 11 input-side surface acoustic wave converter 12 output-side surface acoustic wave converter 13 first set electrode type surface acoustic wave converter 14 second set electrode type surface acoustic wave converter

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[Procedure amendment]

[Submission date] April 22, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

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[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

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[0005]

In order to achieve such an object, the present invention provides one of the input side surface acoustic wave converter and the output side surface acoustic wave converter with a desired frequency characteristic. A first group electrode type surface acoustic wave converter composed of electrodes weighted at λ / 2 intervals, which is an odd number extracted from sampling weighted data at λ / 4 intervals, and an even number of the weighted data is extracted. And a second group electrode type surface acoustic wave converter composed of electrodes weighted at λ / 2 intervals, the first group electrode type surface acoustic wave converter and the second group electrode type surface acoustic wave. The surface acoustic wave converter is arranged parallel to the propagation direction of the surface acoustic wave with the center distance in the propagation direction of the surface acoustic wave being an odd multiple of λ / 4. Further, the combined electrode type surface acoustic wave converter has a period λ /
2 sets of electrodes that have the same plurality of electrode fingers as one set
It is configured by arranging several electrodes, and the distance between the centers of adjacent electrode pairs is
It is set to an odd multiple of λ / 4. Also,
One set electrode type surface acoustic wave transducer and second set electrode type elastic table
The surface wave converter is electrically connected in parallel. Well
And a first set electrode type surface acoustic wave converter and a second set electrode type
A surface acoustic wave converter that is electrically connected in series.
It

Claims (1)

[Claims] 1. A surface acoustic wave filter configured by disposing an input side surface acoustic wave converter and an output side surface acoustic wave converter on a piezoelectric substrate, wherein the input side surface acoustic wave converter and the output side surface acoustic wave filter are provided. Either one of the surface wave converters obtains the desired frequency characteristic λ
(Λ: wavelength of surface acoustic wave) / 4 first set electrode type surface acoustic wave converter composed of electrodes weighted at λ / 2 intervals by extracting odd-numbered sampling weighting data at / 4 intervals, Λ extracted from the even-numbered weighting data
A second group electrode type surface acoustic wave converter composed of electrodes weighted with a / 2 interval, the first group electrode type surface acoustic wave converter and the second group electrode type surface acoustic wave transducer. A surface acoustic wave filter, wherein the surface acoustic wave converter is arranged parallel to the surface acoustic wave propagation direction with the center-to-center distance in the surface acoustic wave propagation direction being an odd multiple of λ / 4. .