JPH09214281A - Surface elastic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently suppress a first side rope by executing weighting using a window function only on an external side from the center of one side electrode and using the electrode subjected to normal weighting or that near a normal type for the other side electrode. SOLUTION: An input-side electrode 11 is constituted by couples of comb-type electrodes which are arranged to face an aligning direction. Then, weighting using the window function is applied only to the external side from the center of the input-side electrode 11. The comb-type electrodes constituting the couples of the input-side electrode 11 are formed so that the length of parts facing the comb-type electrodes which are alternately arranged gradually become small, namely, the overlap of the crossing comb-type electrodes gradually becomes small as they go apart from the center of the input-side electrode 11. In the output-side electrode 12, normal weighting or that near the normal type is executed. The lengths of the parts facing the comb-type electrodes which are alternately arranged are constant.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a surface acoustic wave filter.

[0002]

2. Description of the Related Art This surface acoustic wave filter is composed of an input side electrode 1, an output side electrode 2 and reflectors 3 and 4 placed outside these electrodes 1 and 2, as shown in FIG. And are aligned. And the input side electrode 1
The output side electrode 2 is generally weighted by a cosine system in order to suppress the generation of side ropes and transverse modes of frequency characteristics. In FIG. 13, both the input side electrode 1 and the output side electrode 2 are combined comb-shaped electrodes facing each other, and 100% weighting (Hamming system) is further performed. In other words, the length of the facing portions of the comb electrodes forming the pair of electrodes is gradually reduced as the distance from the facing portions of the input side electrode 1 and the output side electrode 2 increases.

[0003]

SUMMARY OF THE INVENTION With such a configuration,
The first side rope on the low frequency side is not suppressed so much and remains as spurious. Further, the weighting method causes the impedance to become extremely high and makes it difficult to use as a filter.

[0004]

In order to solve such a problem, the input side electrode and the output side electrode are weighted differently. More specifically, one electrode is weighted only from the center to the outside using a window function, and the other electrode is a normal type or an electrode weighted close to the normal type. is there.

According to this structure, the first side rope can be efficiently suppressed, and the spurious generation as in the conventional case can be eliminated. Further, the extreme increase in impedance as in the conventional case is eliminated.

[0006]

FIG. 1 shows an embodiment of a surface acoustic wave filter of the present invention, in which an input side electrode 11, an output side electrode 12 arranged on the right side thereof, these electrodes 11,
And reflectors 13 and 14 placed on the outside of 12 and aligned. The input-side electrode 1 and the output-side electrode 2 have the structure characterized by the present invention, and have the following structure in order to suppress the side rope of the frequency characteristic.

First, the input-side electrode 11 is composed of a pair of comb-shaped electrodes which are arranged so as to face each other in the alignment direction as in the conventional case, and weighting using a window function is performed only from the center to the outside of the input-side electrode 11. Is being done. That is, the electrode halves on the side closer to the output side electrode 12 are of the regular type, and the lengths of the facing portions of the comb-shaped electrodes arranged alternately are constant. On the other hand, the electrode halves outside the center of the input-side electrode 11 are weighted using a window function (Hamming system), and a pair of input-side electrodes is formed as the distance from the center of the input-side electrode increases. The comb-shaped electrodes are formed such that the lengths of the opposed portions of the comb-shaped electrodes arranged alternately are gradually reduced, in other words, the overlapping of the comb-shaped electrodes intersecting each other is gradually reduced.

On the other hand, the output side electrodes 12 shown in FIG. 1 are all regular type, and the lengths of the opposing portions of the comb-shaped electrodes alternately arranged are constant. Further, in this embodiment, the number of comb electrodes is the same for both the input-side electrode 11 and the output-side electrode 12. In this example,
Of course, the canonical type includes those that are close to the canonical type and that exhibit the same characteristics as the canonical type.

2 to 8 show frequency characteristics when the above-described embodiment is used, where the horizontal axis represents frequency,
The vertical axis represents the amount of attenuation. 2 has a weight of 0% (normal type), FIG. 3 has a weight of 55%, FIG. 4 has a weight of 37.5%, FIG. 5 has a weight of 75%, and FIG. 6 has a weight of 43.75%. FIG. 7 shows the case where the weighting is 100%, and FIG. 8 shows the case where the weighting is 50%.

FIG. 9 shows the relationship between the weighting ratio and the minimum attenuation near the low-frequency side first side rope obtained from these characteristics. Here, the amount of attenuation represents the difference from the peak value in the pass band. From the characteristics of FIG. 9, it is understood that the attenuation amount of the low-frequency side first side rope appears larger than the other weightings in the weighting range of 43.75% to 55%.

FIGS. 10, 11 and 12 show another embodiment of the present invention. The difference between FIG. 10 and FIG. 1 is that the number of pairs of normal type or weighted comb type electrodes close to that is changed, and the length of the output side electrode 12 is made shorter than that of the input side electrode 11. , The number of pairs of comb-shaped electrodes forming the output side electrode is reduced. Even in this case, the effect of suppressing the first side rope can be obtained as in the configuration of FIG. In addition, FIG. 11 shows that the input side electrodes 11 in the configuration of FIG. 1 are weighted by the thinning method, and the pair of comb electrodes forming the input side electrodes are arranged so as to be thinned. Even in this case, the effect of suppressing the first side rope can be obtained as in the configuration of FIG.

FIG. 12 shows the configuration of FIG. 10 in which the weighting of the input side electrodes 11 is performed by the thinning method, and the pair of comb-shaped electrodes forming the input side electrodes are arranged to be thinned. Even in this case, the effect of suppressing the first side rope can be obtained as in the configuration of FIG.

Further, as shown in FIG. 10 or FIG. 12, the input / output impedance is almost the same by reducing the logarithm of the output side electrode rather than the input side electrode weighted from the center to the outside by using the window function. You can also

[0014]

As described above, when the surface acoustic wave filter according to the present invention is used, the first side rope can be suppressed more efficiently than in the conventional case, and the spurious generation as in the conventional case can be eliminated. In addition, one electrode is weighted only from the center to the outside using a window function, and the other electrode is a normal type or an electrode weighted close to it,
By reducing the logarithm of the weighted electrodes of the normal type or similar to that of the weighted electrodes,
Input and output impedance can be adjusted.

[Brief description of drawings]

FIG. 1 is an electrode layout showing an embodiment of a surface acoustic wave filter of the present invention.

FIG. 2 is a characteristic diagram showing frequency characteristics when the weighting of the input side electrode of the surface acoustic wave filter of FIG. 1 is set to 0%.

FIG. 3 is a characteristic diagram showing frequency characteristics when the weighting of the input side electrode of the surface acoustic wave filter of FIG. 1 is set to 55%.

FIG. 4 is a characteristic diagram showing frequency characteristics when the weighting of the input side electrode of the surface acoustic wave filter of FIG. 1 is set to 37.5%.

5 is a characteristic diagram showing frequency characteristics when the weighting of the input side electrode of the surface acoustic wave filter of FIG. 1 is set to 75%.

6 is a characteristic diagram showing frequency characteristics when the weighting of the input side electrode of the surface acoustic wave filter of FIG. 1 is set to 43.75%.

FIG. 7 is a characteristic diagram showing frequency characteristics when the weighting of the input side electrode of the surface acoustic wave filter of FIG. 1 is 100%.

8 is a characteristic diagram showing frequency characteristics when the weight of the input side electrode of the surface acoustic wave filter of FIG. 1 is set to 50%.

9 is a characteristic diagram showing a relationship between a weighting ratio of the surface acoustic wave filter of FIG. 1 and a minimum attenuation amount in the vicinity of a low-frequency side first side rope.

FIG. 10 is an electrode layout diagram showing another embodiment of the surface acoustic wave filter of the present invention.

FIG. 11 is an electrode layout diagram showing still another embodiment of the surface acoustic wave filter of the present invention.

FIG. 12 is an electrode layout diagram showing still another embodiment of the surface acoustic wave filter of the present invention.

FIG. 13 is an electrode layout diagram showing an example of a conventional surface acoustic wave filter.

[Explanation of symbols]

 1,11 Input side electrode 2,12 Output side electrode 3,4,13,14 Reflector

Claims (6)

[Claims] 1. In a surface acoustic wave filter in which the weights of an input side electrode and an output side electrode are different, weighting is performed using a window function only from the center to the outside of one electrode, and the other electrode is a normal one. A surface acoustic wave filter, characterized in that it uses electrodes that are weighted close to normal type or normal type. 2. The surface acoustic wave filter according to claim 1, wherein the weighting using the window function is a Hamming system. 3. The surface acoustic wave filter according to claim 1, wherein the weighting using the window function is performed by an apodization method. 4. The surface acoustic wave filter according to claim 1, wherein the weighting using the window function is performed by a thinning method. 5. The surface acoustic wave according to claim 1, wherein the output side electrode has a smaller number of logarithms of the output side electrode than the input side electrode weighted from the center to the outside by using a window function. filter. 6. The surface acoustic wave filter according to claim 1, wherein the weighting of the input side electrode weighted from the center to the outside by using the window function is 43.75% to 55%.