JP3371562B2 - Surface acoustic wave filter - Google Patents

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 transversal surface acoustic wave filter.

[0002]

2. Description of the Related Art In a transversal type surface acoustic wave filter, generally, a surface acoustic wave converter (I) in which positive and negative interdigital electrodes are interdigitated with each other on a surface of a piezoelectric substrate.
DT) provided two, one for input and the other for output, the surface acoustic wave excited by the voltage signal input to the input converter is converted into a voltage signal by the output converter and externally It is designed to output to.

By the way, in this type of surface acoustic wave filter, conventionally, the insertion loss is large due to the bidirectional loss of each converter, and even if 100% conversion is performed in each converter, a loss of 6 db is achieved. Although it has been unavoidable, loss has been recently reduced by using a unidirectional converter.

Various methods are known for imparting unidirectionality to the surface acoustic wave converter. Among them, the floating method which positively utilizes the reflection of the excited surface acoustic wave in the electrode is known. A unidirectional converter using electrodes is a unidirectional converter based on another method in that unidirectionality can be obtained with a relatively simple structure without the need for an external phase shifter. Excellent for vessels.

In a unidirectional surface acoustic wave converter using a floating electrode, a plurality of electrode fingers are arrayed at intervals λ ₀ corresponding to the center frequency, respectively, between positive and negative interdigital electrodes. , A structure in which floating electrodes are provided at positions deviated from the center position between them is used. As the floating electrodes, there are an open type in which each floating electrode is not short-circuited with other floating electrodes and, for example, two adjacent floating electrodes. A short-circuit type in which floating electrodes are short-circuited with a connecting electrode or a combination of these has been proposed (Japanese Patent Laid-Open No. 61-691).
No. 6).

[0006]

By the way, in the transversal type surface acoustic wave filter, in order to obtain a desired band characteristic, it is necessary to weight the input transducer. That is, in this type of filter, depending on the specifications of the frequency band, as shown in FIG. 9, the positive and negative interdigital transducers 11 and 1 of the input converter 1 are provided.
It is necessary to sequentially change the overlapping width of the electrode fingers of No. 2 in the arrangement direction of the electrode fingers, and in order to invert the phase of the elastic wave in the transducer 1 if necessary, one electrode finger of one polarity is used. , Two electrodes are continuously formed at an interval of 1/2 of the regular interval λ ₀ , and the electrode fingers of the other polarity are formed at an interval of 3/2 of λ _{0 with} the two electrode fingers sandwiched therebetween. It is necessary to provide the so-called phase inversion unit T.

Conventionally, a surface acoustic wave filter using a transducer in which floating electrodes are arranged so as to have unidirectionality and which is weighted as described above has not been put into practical use. No detailed reports have been made on specific examples of how to arrange the floating electrode or how to handle the floating electrode in the presence of the phase inversion part.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a surface acoustic wave filter having a low insertion loss and a good frequency characteristic by imparting directionality and weighting using a floating electrode.

[0009]

In order to achieve the above object, the surface acoustic wave filter of the present invention (first invention) is input on a piezoelectric substrate as illustrated in FIG. 1 which is an embodiment drawing. Surface acoustic wave converters 1 and 2 for output and output
In the surface acoustic wave filter provided with, the input transducer 1 is weighted by sequentially changing the overlapping width of the positive and negative interdigital electrodes 11 and 12 in the arrangement direction of the electrode fingers. While applying, the electrode fingers of the positive and negative interdigital electrodes 11 and 12 are arranged so that the elastic wave excited by the input signal to the input transducer 1 is directed to the output transducer 2. It is characterized by adopting a unidirectional converter in which the floating electrode 3 is formed at a position where the center position between them is displaced.

As illustrated in FIG. 3, the overlapping width of each electrode finger of the positive / negative interdigital transducers 11 and 12 of the input converter 1 has a plurality of peak portions P in the arrangement direction A of the electrode fingers. When weighted so as to change sequentially, the area inside the envelope connecting the tips of the positive and negative electrode fingers (hatched portion),
An area A formed by an area (cross hatching area) within a line L drawn from each peak point Pa in each peak portion P toward the output transducer 2 side in a direction orthogonal to each electrode finger.
At i, the floating electrode 3b is formed in such a positional relationship that the elastic wave excited by the signal input to the input transducer is directed to the output transducer 2, while the area A other than the area Ai is formed.
At o, it is desirable to form the floating electrode 3c in such a positional relationship that the elastic wave excited by the signal input to the input transducer 1 goes to the side opposite to the output transducer 2.

Here, the floating electrode 3 has a length substantially equal to the length of the adjacent electrode fingers as shown in FIG. 1, and only in the overlapping portion of the positive and negative interdigital electrodes 11 and 12. The floating electrode 3a may have a length equal to each overlapping width so as to have unidirectionality (see FIG. 2).

In this case, among the electrode fingers of the positive and negative interdigital transducers 11 and 12 of the input side converter 1, the electrode fingers except the longest electrode finger 11a and 12a having the maximum overlapping width. It is more preferable to form the dummy electrodes 13 connected to the electrodes of opposite polarities so as to fill the voids generated at the tips of the respective electrode fingers on the extension of (FIG. 4).
reference).

Further, as another configuration (second invention) of the present invention for achieving the above object, as illustrated in FIG.
Positive and negative interdigital electrodes 11 and 12 each having a plurality of electrode fingers formed on a piezoelectric substrate with a constant space λ ₀ therebetween.
A surface acoustic wave in which two transducers 1 and 2 for input and output are arranged, which are surface acoustic wave transducers (21, 22) facing each other so as to overlap each other in the arrangement direction of the electrode fingers. In the filter, the input converter 1
The overlapping widths of the electrode fingers of the negative interdigital electrodes 11 and 12 are weighted so as to sequentially change in the arrangement direction of the electrode fingers, and the positive / negative interdigital shape is formed at the position where the overlapping width is the shortest. Two electrodes are formed on either side of the electrode at a distance of 1/2 of the distance λ ₀ , and the other side is sandwiched between the two electrode fingers at an interval of 3/2 of the distance λ _0. Two phase inversion parts T are formed, and floating electrodes 3f are formed between the electrode fingers of the input converter 1 at positions displaced from the center position between the electrodes.
The floating electrode 3f is a short-circuit type floating electrode in which two adjacent electrodes are connected to each other at each one end by a connecting electrode 4, and the connecting position of each two floating electrodes by the connecting electrode 4 is set. , And is reversed by sandwiching the phase inversion part T from one end side to the other end side.

Here, in addition to the above-mentioned configuration, between the electrode fingers of the input converter 1, in addition to the short-circuit type floating electrode 3f, an open type floating electrode 5 not connected thereto is provided. It may be formed (see FIG. 6).

In addition, the positive and negative electrodes 11 of the input converter 1,
In the vicinity of the tip of each electrode finger except the longest electrode fingers 11a and 12a in which the mutual overlapping width of the 12 electrode fingers is maximum,
It is desirable to provide a dummy electrode 13 or 6 connected to the electrode of the opposite pole or the floating electrode on the extension of each electrode finger so as to fill the void generated at these tip portions (see FIGS. 7 and 8).

In addition to each of the above-mentioned constitutions of the present invention,
As the output converter 2, the positive and negative interdigital transducers 21 and 22 are arranged between the electrode fingers and between the electrodes based on a positional relationship having a directionality opposite to that of the input converter 1. It is desirable to employ a unidirectional converter in which the floating electrode 7 is formed at a position displaced from the center position of.

[0017]

[Function] The positive / negative interdigital transducers 11 of the input converter 1,
Weighting is performed by sequentially changing the overlapping width of each electrode finger of 12 with a plurality of peak portions P in the arrangement direction of the electrode fingers, and the envelope connecting the tips of these electrode fingers is formed into an appropriate shape. A desired filter characteristic can be obtained by. By using such an input transducer 1 as a unidirectional transducer using the floating electrode 3, the surface acoustic wave excited by the pair of electrode fingers can be exclusively propagated to the output transducer 2 side. Therefore, it is possible to achieve desired band characteristics and simultaneously improve characteristics such as reduction of insertion loss and suppression of in-band ripple.

Further, when the overlapping width of the positive and negative interdigital electrodes 11 and 12 of the input converter 1 is changed sequentially with a plurality of peak portions P in the arrangement direction of the electrode fingers, the positive and negative Area inside the envelope connecting the tips of the electrode fingers and the respective peak points Pa at the respective peak portions P.
From the input transducer 1 to the output transducer 2 side, the elastic wave excited by the input transducer 1 is generated only in the area Ai including the area within the line L drawn in the direction orthogonal to the electrode fingers. When the floating electrode 3b is formed in such a positional relationship that it is directed toward, and in the area Ao other than the area Ai, the floating electrode 3c is formed in such a positional relationship that it has the opposite directionality, each electrode in the input converter 1 is formed. The main signal generated in the overlapping portion of the fingers is not blocked in the propagation path toward the output converter 2, and unnecessary vibration can be propagated to the opposite side as much as possible. , The relative attenuation of unnecessary vibration becomes larger.

Further, by making the length of each floating electrode only at the portion where the positive and negative electrode fingers overlap, that is, only at the portion surrounded by the envelope connecting the tips of the respective electrode fingers, the floating electrode 3a. By providing, it becomes possible to give directionality to the main signal generated in the portion where the electrode fingers overlap each other, and as a result, it is possible to increase the relative attenuation amount of unnecessary vibration.

In such a structure, a void-like region where no electrodes exist at all is formed at the tip of each electrode finger except the longest one. By filling the formed voids with the dummy electrodes 13 connected to the electrodes of opposite polarities, the regularity in the converter 1 is not disturbed, and the disturbance of the reflection of signals in the converter 1 can be prevented. In addition, the directivity of the main signal can be provided.

By using a short-circuit type floating electrode in the input converter 1, not only the mass effect of the floating electrode but also the electric field effect are combined, so that the directionality of the propagating surface acoustic wave becomes more remarkable. Is known to be
FIG. 5 shows that the short circuit type floating electrode is applied to a converter having a phase inversion part T by taking advantage of the superiority of the floating electrode.
2 is another configuration (second invention) of the present invention illustrated in FIG.

The phase inversion part T is one pole side in the converter 1 which is composed of positive and negative interdigital electrodes 11 and 12 in which a plurality of electrode fingers are formed at regular intervals of the central wavelength λ _0. the spacing of the electrode fingers lambda _0/2 by forming the two continuous of the electrode fingers of the other pole sides of the electrode fingers of consecutive two Part 3
lambda _0/2 of it is obtained by forming at intervals, in such a phase inversion unit T, as applied to the normal type transducer, two each on one side of the floating electrode between the electrode fingers It is not possible to simply provide a conventional short-circuit type floating electrode that is connected at the end of the. Therefore, in such an electrode finger configuration, when the floating electrodes 3f are arranged between the respective electrode fingers, and two of them are connected at the end portions by the connecting electrodes 4 to provide a short-circuit type floating electrode, phase inversion is performed. On both sides of the section T, the connection ends of the floating electrodes 3f by the connection electrodes 4 are inverted from one end side to the other end side. Thereby, in the phase inversion part T, the spatial phase matching of the short-circuit type floating electrode can be achieved.

In such a combination of the phase inversion part T and the short circuit type floating electrode, if the open type floating electrode 5 is provided between the electrode fingers in addition to the short circuit type floating electrode 3f, the direction of the surface acoustic wave is generated. The sex becomes more prominent.

Further, even in the converter 1 which is weighted as described above and is provided with the directivity by the short-circuit type floating electrode, the positive and negative electrode fingers are not overlapped at a portion where the overlapping width of the electrode fingers is narrow. There is a void in the tip where no electrode exists.
Or by filling with 6 or 6, the regularity in the converter 1 is not broken, and the disturbance of the reflection of the signal in the converter 1 can be prevented. However, in this case, since the dummy electrode 6 formed in the portion where the connecting electrode 4 is present cannot be connected to the electrode having the opposite polarity, only the mass effect is used as the floating electrode.

In each of the above-mentioned configurations, the floating electrode 7 is arranged between the electrode fingers of the output converter 2 in such a positional relationship that it has a directionality opposite to that of the input converter 1. Thus, if unidirectionality is given, the passage loss of the surface acoustic wave excited by the input converter 1 can be reduced, and the insertion loss can be further reduced.

[0026]

FIG. 1 is a schematic diagram showing the electrode structure of the first embodiment of the present invention. An input transducer 1 and an output transducer 2 are formed on the surface of a piezoelectric substrate. Both the input converter 1 and the output converter 2 are arranged so that the positive and negative interdigital electrodes 11, 12 or 21, 22 each consisting of a plurality of electrode fingers are overlapped with each other. It is a so-called interdigital transducer (IDT). Then, the input signal to the filter is supplied to the positive interdigital transducer 11 of the input converter 1, and the output signal is taken out from the positive interdigital transducer 21 of the output converter 2.

The input converter 1 is weighted according to the so-called apodization method, in which the overlapping width of each electrode finger of the positive and negative interdigital transducers 11 and 12 sequentially changes in the arrangement direction of the electrode fingers. , And a phase inversion unit T. That is, the positive and negative comb-shaped electrodes 11 and 12 basically have electrode fingers formed at intervals equal to the wavelength (center wavelength) λ ₀ corresponding to the center frequency of the pass band of the filter. and with which, in the portion where the overlapping width of each other is minimized, the electrode fingers of one electrode side are contiguous two at intervals of lambda _0/2, across the two electrode fingers, the other electrode side of the electrode fingers are provided at intervals of 3 [lambda] _0/2.

Further, between the positive and negative electrode fingers of the input transducer 1, a length equivalent to that of each electrode finger is provided at a position deviated from the center position of each electrode to the output transducer 2 side. Is provided with a floating electrode 3 having positive and negative interdigital electrodes 1
The phases of the surface acoustic waves excited by 1 and 12 and the phase of the surface acoustic waves reflected by the floating electrode 3 are in the same phase in the direction toward the output converter 2 side and opposite in the opposite direction. The floating electrodes 3 are arranged in such a positional relationship that they are in phase. Due to the presence of the floating electrode 3, the input converter 1 is a unidirectional converter whose excitation wave is directed to the output converter 2 side.

On the other hand, the output converter 2 is a normal type IDT, and the above-mentioned input converter 1 is provided between the respective electrode fingers.
The floating electrode 7 is provided so as to have a directionality opposite to that of. That is, the floating electrode 7 of the output converter 2 is
The positive and negative interdigital transducers 21 and 22 are arranged at positions displaced from the center position between the electrode fingers to the input transducer 1 side, and the surface acoustic waves coming from the input transducer 1 are mainly subjected to voltage. It can be converted into a signal.

According to the above-described embodiments, most of the surface acoustic waves adjusted to have a desired frequency band characteristic by weighting the input transducer 1 are directed to the output transducer 2 side due to the presence of the floating electrode 3. In the output converter 2, only the main signal propagating from the input converter 1 is converted into a voltage signal by the presence of the floating electrode 7, and unnecessary vibration reflected at the end portion of the substrate is converted into a voltage signal. A surface acoustic wave filter that does not undergo conversion, has a low insertion loss, and has excellent band characteristics.

FIG. 2 is a schematic diagram showing the essential electrode structure of the second embodiment of the present invention, in which only the input converter 1 is extracted and shown. The feature of the second embodiment lies in the length of the floating electrode 3a provided in the input converter 1, the pattern of the positive / negative interdigital electrodes 11, 12 itself, and the floating electrode 3a for each electrode finger. Positional relationship in the electrode finger array direction,
The configuration of the output converter 2 (not shown in FIG. 2) is exactly the same as that of FIG.

In the second embodiment, the floating electrode 3a in the input converter 1 has substantially the same width as the overlapping width of the positive / negative interdigital transducers 11 and 12, and the positive / negative interdigital transducers. The directionality of the floating electrode 3a is given only in the region surrounded by the envelope connecting the tips of the electrode fingers of the strip electrodes 11, 12.

In this type of weighted transducer, a surface acoustic wave serving as a main signal is excited inside a portion where the electrode fingers overlap each other, in other words, inside an envelope connecting the tips of the electrode fingers. Therefore, according to the floating electrode 3a as described above, only the directivity of the main signal is emphasized, and the relative attenuation amount of the unwanted vibration component wave (unwanted signal) with respect to the main signal can be increased. Compared with the configuration, there is an advantage that spurious can be suppressed low.

FIG. 3 is an explanatory view of the third embodiment of the present invention.
(A) is a schematic diagram showing the electrode configuration, and (B) is a diagram showing a conceptual diagram and an operation explanatory diagram of the input converter 1 together.

In the third embodiment, the pattern of the positive / negative interdigital transducers 11 and 12 themselves of the input converter 1,
The structure of the output converter 2 is the same as that of the previous examples, but the floating electrode in the input converter 1 is provided with directivity opposite to each other in the two regions Ai and Ao in the converter 1. Therefore, two types of floating electrodes 3b and 3c having different positional relationships from each other are provided for each electrode finger.

That is, the overlapping width of the input transducer 1 changes sequentially while having a plurality of peak portions P in the arrangement direction of the electrode fingers, and the overlap width of the inside of the envelope connecting the tips of the positive and negative electrode fingers is increased. A region (hatched portion) and a region (cross hatched portion) inside a line L drawn from the upper and lower peak points Pa in each peak portion P toward the output converter 2 in a direction orthogonal to each electrode finger. The floating electrode 3b for directing the surface acoustic wave excited by the signal input to the output transducer 2 side is provided in the area Ai combined with the area Ai, and the floating electrode 3b is provided in the other area Ao. A floating electrode 3c is provided to have a reverse directionality. Specifically, the floating electrode 3b in the area Ai has the same positional relationship as the floating electrode 3 or 3a in FIGS.
The floating electrode 3c inside is placed at a position deviated from the center position of each electrode finger in the opposite direction to the above.

According to the configuration of the third embodiment, in the excitation region of the main signal wave, which is inside the envelope connecting the tips of the electrode fingers, it faces the output converter 2 side as in the example of FIG. The directionality is imparted, and the directionality in the same direction is imparted even in a region where the main signal wave propagates even outside the envelope, in a region shown by cross hatching in FIG. As a result, reflection or the like does not occur on the entire propagation path of the surface acoustic wave. In addition, the area A excluding the area Ai that combines the main signal wave excitation area and its propagation area as described above.
At o, the floating electrode 3c gives a direction opposite to that of the floating electrode 3c.
The unnecessary signal wave generated in the area other than the propagation area of the main signal wave propagates in the direction opposite to that of the output converter 2.
The relative attenuation amount of the unnecessary signal can be further increased as compared with the above example, and the spurious reduction effect is further enhanced.

FIG. 4 is a schematic view of the essential electrode structure showing only the input converter 1 of the fourth embodiment of the present invention. The feature of the fourth embodiment is that, in addition to the structure of the third embodiment, positive / negative interdigital transducers 11 and 12 of the input converter 1 are provided.
The dummy electrode 13 (shown in black in the figure) connected to the electrode of the opposite polarity is formed so as to fill the void portion which is the nonexistent portion of the electrode generated at the tip of each electrode finger.

When the input transducer 3 is weighted based on, for example, the apodization method, as is clear from FIG. 3 of the above example, the longest positive / negative electrode finger ( In the tip parts of the electrode fingers excluding the electrode finger corresponding to the peak point Pa in the maximum peak part P in FIG.
A void portion is formed in which neither electrode exists. Therefore,
In the fourth embodiment, among the positive and negative electrode fingers, a dummy electrode 13 connected to an electrode having a polarity opposite to that of the electrode finger is formed on the extension of each electrode finger except the longest electrode fingers 11a and 12a. It is provided.

Between the electrode fingers of the positive / negative interdigital transducers 11 and 12, as in the example of FIG. 3, the output converter 2 is provided in the area Ai defined in FIG. 3 (B). The floating electrode 3b for giving the directionality toward the side and the floating electrode 3c for giving the directionality opposite to this are arranged in the other area Ao, and each dummy electrode 13 also has a floating electrode 3d in the area Ai, which has the same positional relationship as that of the floating electrode 3b, and therefore has a directionality toward the output converter 2.
Inside, in the same positional relationship as the floating electrode 3c,
Therefore, the floating electrode 3e for providing the direction opposite to the output converter 2 is arranged adjacently.

According to such a configuration, the input converter 1
The regularity of the electrode pattern in the inside is not broken, and the periodicity of the electrode arrangement on the propagation path of the main signal in the region Ai is maintained in addition to the effect of the third embodiment described above.
The disturbance of the internal reflection of the signal is suppressed and the area Ao
Since the periodicity of the electrode arrangement on the propagation path of the unnecessary signal in the inside is maintained, the unnecessary signal is less likely to be diffracted or multiply reflected in the converter 1, and only the main signal is emphasized in the output converter 2. Therefore, the band characteristic is further propagated than in the third embodiment,
The attenuation characteristic of the unnecessary signal is improved.

FIG. 5 is a schematic diagram showing the essential electrode structure of the fifth embodiment of the present invention, in which only the input converter 1 is extracted and shown. The fifth and subsequent embodiments correspond to the second invention.

In the fifth embodiment, the pattern of the positive / negative interdigital transducers 11 and 12 of the input converter 1 and the configuration of the output converter 2 (not shown in FIG. 4) are the first. As in the third embodiment, a so-called short-circuit type floating electrode is used as the floating electrode to be provided with directivity to the input converter 1, and the short-circuiting type floating electrode is used as described below. The arrangement of the connecting electrodes 4 for forming is characteristic.

That is, the surface acoustic wave excited by the converter 1 is directed to the output converter 2 side between the electrode fingers of the positive and negative interdigital transducers 11 and 12 of the input converter 1. The floating electrodes 3f arranged in such a positional relationship are connected to each other by two electrodes adjacent to each other via the connecting electrode 4 to form a short-circuit type floating electrode. Then, the connecting portion of each floating electrode 3f by the connecting electrode 4 is vertically inverted with the phase inversion portion T of the input converter 1 interposed therebetween.

According to the fifth embodiment, a filter having a desired band characteristic can be obtained by weighting including the phase inversion section T, and at the same time, the input converter 1 is constituted by the short-circuit type floating electrode including the phase inversion section T. Since the directivity can be given to the input electrodes 1, the directivity is given not only by the mass effect of the individual floating electrodes 3f but also by the electric field effect, and the directivity of the input converter 1 becomes more remarkable.

FIG. 6 is a schematic view of the essential electrode construction showing an input converter 1 according to a sixth embodiment of the present invention. The feature of the sixth embodiment is that, in addition to the short circuit type floating electrode in which two floating electrodes 3f are connected by the connecting electrode 4, the short circuit type floating electrode is opened between the positive and negative electrode fingers. This is because the floating electrode 5 of the mold is provided. The combination of the floating electrode of the short circuit type and the floating electrode of the open type improves the periodicity of the electrode arrangement to reduce the influence of diffraction and multiple reflection, and at the same time, the directionality is improved. It will be remarkable.

FIG. 7 is an explanatory view of the seventh embodiment of the present invention.
(A) is a schematic diagram of a main part electrode structure which extracts and shows only the input converter 1, and (B) is a partially enlarged view thereof.
Like the sixth embodiment, the seventh embodiment is characterized in that a short-circuit type floating electrode formed by connecting the floating electrodes 3f by the connecting electrode 4 and an open type floating electrode 5 are used together.
The dummy electrode 13 or 6 connected to the electrode of the opposite polarity or the floating electrode is provided with the void generated at the tip of the positive / negative electrode finger caused by weighting the input converter 1 (these are shown in FIG. 7A). In black).

In the example of FIG. 7, the dummy electrode 6 is a part of the short-circuit type floating electrode as shown in FIG.
However, as shown in FIG. 8, it may be connected to the open floating electrode 5.

According to the configurations shown in FIGS. 7 and 8, both positive and negative interdigital electrodes 11, which are generated by weighting,
The voids formed at the tips of the electrode fingers of 12 are the dummy electrodes 1
By being filled with 3 or 6, the periodicity of the electrode arrangement in the transducer 1 is maintained, and as in the example shown in FIG. 4, the multiple reflection of surface acoustic waves and the diffraction phenomenon of the surface acoustic wave in the transducer 1 are maintained. The suppression effect is improved. Note that, in the example of FIG. 7 or FIG. 8, the dummy electrode 6 in the portion where the connecting electrode 4 is present has no electric field effect because the polarity is not given unlike the dummy electrode 13 illustrated in FIG. However, the effect of suppressing the multiple reflection and diffraction phenomenon can be expected sufficiently by the mass effect alone.

In each of the above embodiments, a method based on the apodization method is adopted as a method for weighting the input converter 1, but the present invention is not limited to this and, for example, tilts can be used. It goes without saying that any method can be adopted as long as it is a method of performing weighting by sequentially changing the overlapping width of the electrode fingers, such as a type weighting method.

[0051]

According to the present invention, the weight is given by sequentially changing the overlapping width of the electrode fingers of the input transducer, and by providing the floating electrode in the input transducer, the desired weight is obtained. The surface acoustic wave excited in the state where the frequency band characteristic is given can be directed exclusively to the output converter, and the improvement of the frequency band and the reduction of the insertion loss can be achieved at the same time.

Further, when the length of the floating electrode provided in the input transducer is adapted to the overlapping width of each electrode finger so that the directivity is obtained only within the overlapping width, It is possible to give directionality to only the signal component in an emphasized manner, and it is possible to increase the relative attenuation amount of the unnecessary signal component. Further, in the area Ai which is the propagation path of the surface acoustic wave of the main signal, the directionality toward the output transducer side is provided, and in the other areas Ao, the directionality opposite to this is provided. Based on each area Ai and Ao
By taking into account the position of each floating electrode within, the relative attenuation of the unwanted signal is further increased. Then, in the configuration in which the directions of the floating electrodes in the two regions are reversed, the void portions which do not exist in the electrodes, which are generated at the tips of the electrode fingers of the positive and negative interdigital electrodes by weighting, have opposite polarities. If a floating electrode is arranged adjacent to the dummy electrode so as to have the same directionality as the above according to each area, it will be filled with a dummy electrode connected to the electrode of Therefore, unnecessary elastic waves due to multiple reflection, diffraction, etc. are less likely to be generated, spurious is improved, and unnecessary signal component attenuation effect is improved.

When the input converter is weighted including the phase inversion part T, the floating electrodes arranged between the electrode fingers on one side and the other side across the phase inversion part T are connected by connecting electrodes. By reversing the ends, it is possible to combine the converter having the phase inversion section T and the short-circuit type floating electrode, and a filter having desired band characteristics and having remarkable directivity is realized.

Also in this case, the weighting is positive or
By filling the void portion generated at the tip of the negative electrode finger with the dummy electrode connected to the floating electrode, it is expected that spurious emission will be improved and unnecessary signal components will be attenuated by suppressing multiple reflection and diffraction.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an electrode configuration of a first embodiment of the present invention.

FIG. 2 is a schematic diagram of an essential electrode configuration showing an input converter 1 extracted from a second embodiment of the present invention.

3A and 3B are explanatory diagrams of a third embodiment of the present invention, in which FIG. 3A is a schematic diagram showing the electrode configuration, and FIG. 3B is a conceptual diagram of the overall configuration of the input converter 1 and an operation explanatory diagram. Diagram shown together

FIG. 4 is a schematic diagram of an essential electrode configuration showing only an input converter 1 according to a fourth embodiment of the present invention.

FIG. 5 is a schematic diagram of a main part electrode configuration showing only an input converter 1 of a fifth embodiment of the present invention.

FIG. 6 is a schematic diagram of an essential electrode configuration showing only an input converter 1 of a sixth embodiment of the present invention.

7A and 7B are explanatory views of a seventh embodiment of the present invention, in which FIG. 7A is a schematic view of the essential electrode configuration showing only the input converter 1 and FIG. 7B is a partially enlarged view thereof.

FIG. 8 is an explanatory diagram of a modified example of the seventh embodiment.

FIG. 9 is a schematic diagram showing an example of electrode configuration of an input transducer of a conventional surface acoustic wave filter with weighting.

[Explanation of symbols]

1 Input converter 11 Positive interdigital transducer 12 Negative interdigital transducer 13 Dummy electrode 2 Output converter 21 Positive interdigital transducer 22 Negative interdigital transducer 3, 3a, 3b, 3c, 3d, 3e, 3f , 5 Floating electrode 4 Connection electrode 6 Dummy electrode P Overlap width peak part Pa Peak point T Phase inversion part

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-5-63488 (JP, A) JP-A-6-237139 (JP, A) JP-A 52-149459 (JP, A) JP-A 60- 123123 (JP, A) European Patent Application Publication 533431 (EP, A 1) (58) Fields searched (Int.Cl. ⁷ , DB name) H03H 9/145

Claims (8)

(57) [Claims] 1. Elasticity in which positive and negative interdigital electrodes having a plurality of electrode fingers formed at regular intervals on a piezoelectric substrate are arranged to face each other so as to overlap each other in the arrangement direction of each electrode finger. In a surface acoustic wave filter including two transducers for input and output, which are surface acoustic wave transducers, in the transducer for input, the electrode fingers of the positive and negative interdigital transducers overlap each other. There are multiple widths in the array direction of the electrode fingers.
Is weighted so that it changes sequentially with the peak part of, and between the electrode fingers of the positive and negative interdigital electrodes, a floating electrode is formed at a position where the center position between the electrodes is shifted. Is a sex converter, and the floating electrode is
The area inside the envelope connecting the tips of the electrode fingers and each peak
From each peak point in
With the area inside the line drawn in the direction orthogonal to each electrode finger toward
Is the bullet excited by the signal input to the input transducer.
Formed in a positional relationship such that the sex wave is directed to the output converter
And the area other than that area is converted for the input.
The elastic wave excited by the signal input to
A surface acoustic wave filter characterized in that the surface acoustic wave filter is formed so as to face the opposite side of the converter . 2. The floating electrodes formed between the electrode fingers of the positive and negative interdigital transducers of the input converter have a length substantially equal to that of the electrode fingers adjacent to each other. The surface acoustic wave filter according to claim 1, which is characterized in that. 3. A floating electrode formed between the electrode fingers of the positive and negative interdigital transducers of the input converter is unidirectional only at the overlapping portion of the electrode fingers of the positive and negative interdigital transducers. The surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter has a length equal to each overlapping width so as to have a property. 4. An extension of each electrode finger of the positive and negative electrodes of the input transducer except for the longest electrode finger having the maximum overlapping width with each other. 2. A dummy electrode connected to an electrode of opposite polarity is formed so as to fill the void formed at the tip, 2.
The surface acoustic wave filter according to 2 or 3 . 5. A piezoelectric substrate having a constant spacing λ _0.
Open and open to form a plurality of electrode fingers. Positive and negative interdigital electrodes are arranged opposite to each other so that they overlap each other in the arrangement direction of each electrode finger. In the surface acoustic wave filter provided with the transducer, the overlapping width of each electrode finger of the positive / negative interdigital transducers of the input transducer is weighted so as to sequentially change in the arrangement direction of the electrode fingers. In addition, at the location where the overlapping width is the shortest, one of the positive and negative interdigital electrodes is formed with a half interval of the above interval λ ₀ , and the other side is formed. Two phase inversion parts are provided with an interval of 3/2 of the above-mentioned interval λ ₀ sandwiching two electrode fingers, and each electrode finger is provided between the electrode fingers of the input converter. To the position shifted from the center position between Floating electrodes are formed, and each of the two floating electrodes is a short-circuit type floating electrode in which two adjacent electrodes are connected to each other by a connecting electrode at each one end, and two floating electrodes are formed by the connecting electrodes. The surface acoustic wave filter, wherein the connection positions of the electrodes are reversed from one end side to the other end side across the phase inversion part. 6. Between the electrode fingers of the input converter, in addition to the short-circuit type floating electrodes connected by two by the connecting electrode, there are open type floating electrodes not connected to these. It is formed, The surface acoustic wave filter of Claim 5 characterized by the above-mentioned. 7. The tip of each of the electrode fingers of the positive and negative electrodes of the input transducer is extended on the electrode fingers except the longest electrode finger having the maximum overlapping width. 7. The surface acoustic wave filter according to claim 5 , wherein a dummy electrode connected to either the electrode of the opposite polarity or the floating electrode is formed so as to fill the void generated in the above. 8. The output converter shifts a center position between the electrode fingers of the positive and negative interdigital transducers so as to have a directionality opposite to that of the input converter. characterized in that the unidirectional transducer floating electrode is formed at a position, the surface acoustic wave filter according to claim 3, 4, 5, 6 or 7.