JPS60180316A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain a desired frequency characteristic with less insertion losses and excellent shoulder characteristics without any external circuit by changing the length of an oblique electrode finger to apply weighting in a surface acoustic wave filter having respectively the oblique electrode finger at the transmission side or reception side or at both sides. CONSTITUTION:Transducers 4, 5 and common electrodes 41, 51 are provided on piezoelectric substrate 1. Captions 42, 52 are the oblique electrode fingers applied with weighting. As clearly shown in the figure, the weighting is applied by providing a change to the length of the electrode fingers prolonged from the common electrodes 41B, 51B of the lower part. Through the weighting above, the characteristics of the surface acoustic wave filter are improved and excellent band pass characteristics are obtained. Thus, the number of pairs at the high frequency side when the oblique electrode fingers are split by a channel in parallel with the direction of propagation T is increased, the input admittance of the transducers is controlled and the pass band characteristic is made flat.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave filter having diagonal electrode fingers, and more particularly to a surface acoustic wave filter having weighted diagonal electrode fingers.

Conventional broadband surface acoustic wave filters are realized by the apodization method or the method using dispersed electrodes. However, in either method, the insertion loss increases as the band becomes wider. Therefore, it has been difficult to achieve good characteristics with good shoulder characteristics and low insertion loss.

On the other hand, although the method using diagonal electrode fingers is suitable for widening the band, it has the drawback that the two-pass band characteristics are tilted depending on the balance of the input admittance of the electrodes. Figure 1 shows an example of a surface acoustic wave filter having conventional unweighted diagonal electrode finger transducers on the transmitting side A and the receiving side B, in which ■ is a piezoelectric substrate (piezoelectric thin film); .3 is Transgyzer.

21.31 is a common electrode, and 22.32 is a weighted image. Due to the inclination, the input loss increases in the high frequency range, and as a result, the passband characteristic becomes slanted, resulting in an I-circle.

The present invention solves the drawbacks of the prior art, and by weighting the diagonal electrode fingers, it is possible to maintain good shoulder characteristics in a wide band while improving the pass frequency band characteristics. This provides a surface acoustic wave filter that eliminates the slope, that is, has flattened characteristics.

Embodiments of the present invention shown in the drawings will be explained in detail below.

FIG. 2 shows a surface acoustic wave filter using diagonal electrode fingers according to an embodiment of the present invention.The arrangement is similar to that shown in FIG. 1, with transducers 4, 5, . A common electrode 41.51 is provided. 42.52 indicates weighted diagonal electrode fingers. As is clear from the figure, the lower common electrode 41B.

A weighted image is applied by varying the length of the electrode fingers extending from 51B. Due to such weight distortion, the characteristics of the surface acoustic wave filter shown in Fig. 1 are improved,
As shown in FIG. 4B, good passband characteristics can be obtained. This increases the logarithm on the high frequency side when the diagonal electrode fingers are divided into channels parallel to the propagation direction T.
The input admittance of the transuser can be controlled, and l
a Pass band characteristics can be flattened.

At this time, it is not necessary that the transmitting side A and receiving side B transusers have the same logarithm or weight function.

Next, if the frequency characteristics of the surface acoustic wave filter having diagonal electrode fingers shown in Fig. 4 become the pass band characteristics of the stone-climb as opposed to the stone-climb pass band characteristics shown in Fig. 4 (AIK), then Upper common electrodes 61A, 71 as shown in FIG.
By adding weight to the electrode fingers extending from A, the fourth
Good characteristics as shown in Figure (Bl) can be obtained.

This is the low frequency 1 when diagonal electrode fingers are divided into channels.
By increasing the logarithm of the channel of the jilj, the input atomicity of the transformer can be controlled and the two-pass band characteristics can be made even. Also in this case, the transmitter and receiver transducers do not need to have the same logarithm or weight function.

As explained above, the use of 9-weight (=j) diagonal electrode fingers makes it possible to achieve the desired frequency characteristics with low insertion loss and good shoulder characteristics without the need for an external circuit, compared to the conventional method when realizing a broadband filter. It has the advantage of being obtained in a simple way.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a conventional surface acoustic wave filter using oblique electrode fingers, FIGS. 2 and 3 are plan views showing each embodiment of the present invention, and FIG. teeth,
1A and 1B are graphs showing the frequency characteristics obtained by a conventional surface acoustic wave filter and the frequency characteristics obtained by the embodiment of the present invention shown in FIG. 1, respectively. ■ Piezoelectric substrate (piezoelectric thin film) + 2 + J + 4
+ 5 + 6 + 7・ Transgyzer, 21,
31, 41, 51, 61°7■... common electrode, 22,
32,42,52,62.72...Diagonal electrode finger, T...
・Propagation direction. Applicant: Japan Radio Co., Ltd.

Claims (1)

[Claims] In a surface acoustic wave filter having oblique electrode fingers on a transmitting side or a receiving side, or on each of them, on a piezoelectric substrate or a piezoelectric thin film. A surface acoustic wave filter having diagonal electrode fingers, characterized in that the length of the diagonal electrode fingers is changed to increase the weight, thereby flattening the passing frequency characteristic.