JPS6313510A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain a surface acoustic wave filter with a low loss by designing the titled filter such that an electrode finger cross part of a 1st interdigital electrode group and a common meander electrode and an electrode finger cross part of a 2nd interdigital electrode group and the common meander electrode form one propagation line without any isolated or projecing part. CONSTITUTION:The 1st electrodes 1-1, 1-2, the 2nd electrodes 2-1, 2-2 and common meander electrodes 3-1, 3-2 are formed as the split form. In order to bring the cross width of electrode fingers of parts 15a-15e of the common meander electrode having one finger and of adjacent electrodes and the cross width of the electrode fingers of parts 16a-16c of the common meander electrode having three fingers and of adjacent electrodes on one propagation line, one of the electrode fingers of the adjacent split electrodes to the common meander electrode having one finger is cut off on its way and connected to the other electrode finger. Each two of the common meander electrodes 3-1, 3-2 is cut off on its way at the 1st and 2nd electrodes 1-1, 1-2, 2-1, 2-2 respectively. Since the cross parts exist on one and same propagation line, the conversion loss by two-way propagation is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a surface acoustic wave filter equipped with a unidirectional transducer, which is suitable for reducing loss.

[Conventional technology]

Conventionally, a surface acoustic wave filter equipped with a unidirectional transducer includes a first electrode forming a first interdigital electrode group, a common meander electrode, and a common meander electrode, as disclosed in Japanese Patent Application Laid-Open No. 51-138362. The distance between the second electrode and the common meandering electrode forming the two interdigital electrode groups is n±1/4.
(where n is an arbitrary integer), and the first . Surface waves are excited in both directions using a transducer in which a 90-degree phase shifter is connected between the second electrode group to provide an electrical phase difference and allow surface acoustic waves to propagate in only one direction. The conversion loss (3 dB) caused by this was improved.

However, as shown in FIG.
An intersection portion 17 that is an excitation source for the first electrode group formed by the electrode 6 and the common meander electrode 8, and an intersection portion 18 that is an excitation source for the second electrode group formed by the second electrode 7 and the common meander electrode 8 are on the same propagation path. Unnecessary intersection 19.20 because it does not exist
However, there is a problem in that surface waves that propagate in both directions deviate from the unidirectional condition, resulting in increased loss.

[Problem that the invention seeks to solve]

An object of the present invention is to solve the problems of the conventional surface acoustic wave filter using a unidirectional transducer, and to provide a surface acoustic wave filter with low loss.

[Means for solving problems]

In order to solve the above problems, in the present invention, the electrode finger crossing portion between the first interdigital electrode group and the common meander electrode, and the electrode finger crossing portion between the WfI2 interdigital electrode group and the common meander electrode are isolated. A single propagation path is formed without any protruding parts.

However, at the intersecting portion of the interdigital electrode group and the common meandering electrode, the wavelength at the desired in-band frequency is λ0, and the distance between the electrode fingers facing each other is +*.

For solid type electrode fingers, set it within approximately λ0/4, and for split type electrode fingers, set it within approximately λ, I/8.
・Ru.

Furthermore, when the cross width weighting is used to gradually change the length of the intersecting portion of the electrode fingers (i.e., the cross width), as in the case of electrodes, it is sufficient as long as there is no isolated protruding portion that deviates from this gradual change. In the case of split-type electrode fingers, when applying the present invention, the length of each pair of electrode fingers is changed according to the above principle.

[Effect]

If the intersection formed by the first electrode and the common meander electrode and the intersection formed by the second electrode and the common meander electrode form one propagation path without any isolated and protruding unnecessary parts, then The surface acoustic waves generated by the first interdigital electrode and the second interdigital electrode all interact to generate surface acoustic waves in one direction.

In addition, in the case of split electrodes, the excitation sources viewed in the forward direction are lined up at an interval of approximately V/2 fo (fo: center frequency determined by pitch, V: effective surface wave velocity), and it is difficult to eliminate omission of excitation sources. , above No. 1. The number of meander electrodes between the second interdigital electrodes can be repeatedly formed in the following manner: 1 and 3. In this electrode, the part consisting of one meandering electrode has an electrode width of λ
Since it is about o/8, there is little effect even if the electrode is made thinner.

Therefore, the first electrode near one meander electrode. By shortening the second electrode and conversely shortening the meander electrode side in a portion with three meander electrodes, the crossing portions can be provided on the same propagation path.

〔Example〕

FIG. 1 is a diagram showing a first embodiment of the present invention. A LiNbO3 substrate is used as the piezoelectric substrate 4, and the first
Electrodes (1-1, 1-N second electrodes (2-1, 2-2) and common meander electrodes (3-1, 3-2) are formed.

A 90 degree phase shifter (5-i) that satisfies the unidirectional condition.

5-2) to form a regular unidirectional transducer. The intersection width W was set to 1000 μm. The crossing width refers to the length of the electrode crossing portion. The intersecting width of the electrode fingers of a point with one common meander electrode finger (158 to 15e) and the electrodes on both sides of it, and the intersection width of the electrode fingers of a point with three common meander electrode fingers (18 to 160) and the electrodes on both sides thereof. Make sure that the intersecting widths of the electrode fingers are on the same propagation path.

In a place where there is one common meander electrode finger, one of the electrode fingers of the split electrodes on both sides of it is deleted midway, and the other one is removed.
Connect to the book's electrode finger. In locations where there are three common meander electrode fingers, the common meander electrode is placed first. 2 each on the second electrode side
Delete one book at a time.

This embodiment is a surface acoustic wave filter using a regular split type unidirectional transducer, and since there is an intersection on the same propagation path, conversion loss due to bidirectional propagation can be improved. Figure 1 shows two input and output electrodes.

FIG. 3 shows a second embodiment of the invention. This figure shows one of the input and output electrodes, the first electrode 9°, the second electrode 10. A common meander electrode 11 is provided and weighted in the cross width direction. In the transducer weighted in the cross-width direction, the shapes of the first electrode, the second electrode, and the common meander electrode are changed as in the first embodiment. According to the second embodiment, even when weighting is applied in the cross width direction, the conversion loss due to the bidirectional propagation at the unnecessary cross section described above can be completely improved.

FIG. 4 shows a third embodiment of the invention. This figure shows one of the input and output electrodes, the first electrode 12 and the second electrode 1 having split electrode fingers on the piezoelectric substrate.
3. A common meander electrode 14 is provided, which is weighted in the cross width direction. Of the three electrode fingers of the common meander electrode, the outer two electrode fingers were connected to the electrode fingers of the electrodes on both sides in a vertical pair.

According to this embodiment, even when weighting is applied in the intersection width direction, bidirectional propagation loss due to other intersection widths can be improved, and a portion of the common meander electrode in the surface acoustic wave propagation direction is omitted. There are many.

Since the ratio of the metalized portions of the electrodes to the non-metalized portions in the cross width direction is approximately uniform, the phase of one surface acoustic wave is also approximately uniform, and there is little deterioration in characteristics.

〔Effect of the invention〕

As described above, according to the present invention, a surface acoustic wave filter with reduced loss can be obtained by using a unidirectional transducer that eliminates bidirectional propagation loss at unnecessary intersections of electrode fingers.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the first embodiment of the present invention, Fig. 2 is a schematic diagram of a conventional unidirectional transducer, and Fig. 3 is a schematic diagram of the conventional unidirectional transducer.
FIG. 4 is a schematic diagram of a unidirectional transducer according to a third embodiment of the present invention. 1-1.1-2.6, 9.12...first electrode 2-1.
2-2.7, 10.13... Second electrode 3-1.3-2
．． 8,11.14...Common meander electrode 4...Piezoelectric substrate 5-1.5-2...Phase shifter 15&~15e...One location I of common meander electrode
Sa~16o...Three points 17 of common meander electrode
...First electrode group intersection 18...Second electrode group intersection

Claims (1)

[Claims] 1. First and second interdigital electrode groups are provided on a surface acoustic wave substrate including a piezoelectric material, and signals having an electrical phase difference are applied to these interdigital electrode groups, In a surface acoustic wave filter using a unidirectional transducer in which surface acoustic wave energy propagates more in one direction than in the opposite direction,
Assuming that the wavelength at the desired in-band frequency is λ_0, the interval between the electrode fingers of the first and second interdigital electrode groups and the adjacent and opposing common meander electrode is approximately within λ_0/4 in the case of solid electrode fingers; Approximately λ_ in the case of split-type electrode fingers
A surface acoustic wave filter characterized in that a unidirectional transducer is used in which the intersecting portions of electrode fingers set within 0/8 form one propagation path without isolated and protruding unnecessary portions. 2. In a surface acoustic wave filter using a unidirectional transducer consisting of split-type electrode fingers, each of which is formed into a set of two electrode fingers connected to the same electrode of the first and second interdigital electrode groups, one A combination consisting of a common meander electrode and adjacent first and second interdigital electrode group electrode fingers, and three common meander electrodes and adjacent first and second interdigital electrode group electrode fingers. There is at least one group consisting of a combination of the above, and the distance between the first or second electrode group electrode finger and the common meander electrode is approximately λ_0/8.
The common meander electrode shortens the electrode fingers of the first and second electrode groups on both sides of the book part until the crossing part reaches the desired length so that the crossing parts of the electrode fingers that are set within the same distance are on the same propagation path. and connects to another electrode finger of the same electrode, and furthermore, in the place where three common meander electrodes are adjacent in succession, the first and second
The surface acoustic wave filter according to claim 1, which uses a unidirectional transducer in which a common meander electrode adjacent to the electrode group electrode finger is shortened to a desired length.