JPH066171A - Surface elastic wave filter - Google Patents

Abstract

PURPOSE:To obtain the surface acoustic wave filter with a low loss and high selectively by implementing weighing so as not to increase an insertion loss concerning to the multi-electrode type surface acoustic wave filter used for a communication equipment or the like. CONSTITUTION:At least one of plural interdigital electrode finger pairs 11, 12 being components of a multi-electrode type surface acoustic wave filter lets all crossing lengths equalize and at least one electrode finger pair is made up of regular electrode fingers 13 and divided electrode fingers 14 divided on the way of a crossing length. Thus, the surface acoustic wave filter with an excellent outside band characteristic is obtained without increase in the insertion loss due to weighing.

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 used for mobile communication equipment and the like.

[0002]

2. Description of the Related Art With the development of mobile communication devices, it has been required to miniaturize and improve the performance of various parts constituting the devices. The surface acoustic wave filters used in the above are also required to be further miniaturized and have higher performance. In addition, the reduction of insertion loss is the most important issue in this high performance, and in order to solve this, multi-electrode configuration in which input electrodes and output electrodes are alternately arranged is often used. There is.

A conventional multi-electrode type surface acoustic wave filter will be described below. FIG. 2 is a chip pattern showing the structure of a conventional multi-electrode type surface acoustic wave filter. In FIG. 2, 1 is an input electrode finger pair, 2 is an output electrode finger pair, 3 is an input terminal, and 4 is an output terminal.

In the conventional surface acoustic wave filter configured as described above, the surface acoustic waves excited by the electric signal from the input terminal 3 into all the electrode fingers of the input electrode finger pair 1 are arranged at both ends thereof. The mechanical vibration is propagated in the direction of the output electrode finger pair 2 and is converted into an electric signal and output to the output terminal 4 to perform out-of-band attenuation in the frequency characteristic.

[0005]

However, in the above-described conventional surface acoustic wave filter, the input / output electrode pair fingers 1 and 2 are all formed of regular electrodes in order to prevent an increase in insertion loss. It was not possible to obtain sufficient out-of-band attenuation. Further, in order to improve this and obtain a sufficient amount of out-of-band attenuation, the lengths of the electrode fingers forming the electrode finger pairs 1 and 2 are partially changed, that is, when a so-called apodization weighting is applied, a cross length direction is obtained. There is a problem that the structure becomes non-uniform and the insertion loss increases.

The present invention solves the above problems, and an object of the present invention is to provide a multi-electrode surface acoustic wave filter having a low insertion loss and good out-of-band characteristics.

[0007]

In order to solve this problem, in the surface acoustic wave filter of the present invention, at least one of a plurality of comb-shaped electrode finger pairs forming a multi-electrode surface acoustic wave filter is The crossing lengths of the electrode fingers are the same, and at least one electrode finger pair is formed by combining a normal type electrode finger and a split electrode finger divided in the middle of the crossing length.

[0008]

With this configuration, the split electrode fingers and the normal type electrode fingers divided in the middle of the cross length have different electric fields, so that apodized weighting is performed and spurious out of the band is suppressed. To be done. However, unlike the apodized weighting, the insertion loss does not increase due to the uniform configuration in the cross length direction.
Therefore, a surface acoustic wave filter having a low insertion loss and excellent out-of-band characteristics can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave filter according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a chip pattern diagram showing the structure of the surface acoustic wave filter in the embodiment. In FIG. 1, 11 is an input terminal 10.
The pair of comb-shaped electrode fingers on the input side connected to the output terminal 12 is the output terminal 1
The output-side comb-shaped electrode finger pair connected to the reference numeral 5, 13 is a normal-type electrode finger forming the output-side comb-shaped electrode finger pair 12, and 14 is a divided electrode finger similarly divided in the middle of the intersecting length. In the case of the example, a five-electrode configuration in which two comb-shaped electrode finger pairs are combined on the input side and three comb-shaped electrode finger pairs are combined on the output side,
In the comb-shaped electrode finger pair 12 on the output side, both ends of the comb-shaped electrode finger pair 12 arranged at the center are divided into two at the center to provide the divided electrode fingers 14.

The operation of the surface acoustic wave filter of the present invention constructed as above will be described. The surface acoustic wave excited by the electric signal that has entered the comb-shaped electrode finger pair 11 on the input side has the comb-shaped electrode finger pair 1 on the output side provided on both sides.
The mechanical vibration of the surface acoustic wave, which propagates in the two directions, is converted into an electric signal. At this time, in the comb-shaped electrode finger 12 on the output side arranged in the center, the divided electrode fingers 14 at both ends are divided into two parts, and thus 1 / th of the normal type electrode finger 13 is provided.
Only the electric field of 4 is applied, and the frequency characteristics are substantially apodized, and it is possible to realize the frequency characteristics with excellent out-of-band characteristics as compared with the configuration of the comb-shaped electrode finger pair using only the normal type electrode fingers 13. Becomes Moreover, since the configuration is uniform in the cross length direction, the insertion loss does not increase unlike apodization weighting.

In the above embodiment, the divided electrode finger 14 is applied only to the output-side comb-shaped electrode finger pair 12 arranged at the center, but the input-side comb-shaped electrode finger pair 11 or the output-side comb-shaped electrode finger pair 12 is used. When applied to all of the above, it is more effective in improving the out-of-band characteristics.

In the above embodiment, the divided electrode finger 14 is divided into two parts, but it goes without saying that another divided form or a combination thereof may be used.

[0013]

As described above, the surface acoustic wave filter according to the present invention is capable of preventing the increase of insertion loss while improving the out-of-band attenuation in the configuration of the multi-electrode type comb-shaped electrode finger pair. There is a great value.

[Brief description of drawings]

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

FIG. 2 is a chip pattern diagram showing a configuration of a conventional multi-electrode type surface acoustic wave filter.

[Explanation of symbols]

 10 Input Terminals 11 Comb-shaped Electrode Finger Pairs on Input Side 12 Comb-shaped Electrode Finger Pairs on Output Side 13 Normal Type Electrode Fingers 14 Split Electrode Fingers Divided in the Midway of Crossing 15 Output Terminals

Claims (1)

[Claims] 1. All or more comb-shaped electrode fingers formed by normal-shaped electrode fingers having the same length are arranged in parallel in the propagation direction of a surface acoustic wave, and these comb-shaped electrode finger pairs are alternately arranged. At least one of the pair of comb-shaped electrode fingers has the same crossing length of all the electrode fingers and is divided from the normal type electrode fingers in the middle of the crossing length. A surface acoustic wave filter formed by combining electrode fingers.