JP2714189B2 - Surface acoustic wave filter and communication device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface acoustic wave propagating on a substrate, in which the electrode finger crossing width of all the counter electrode finger pairs of the IDT weighted to the electrode finger crossing width is determined. The present invention relates to a surface acoustic wave filter that is longer than the center wavelength of the surface acoustic wave and suppresses generation of diffracted waves.

[Conventional technology]

Conventionally, in order to avoid the occurrence of diffracted waves at locations where the electrode finger crossing width of the weighted interdigital electrodes is short, the counter electrode, for example, disclosed in Japanese Patent Application Laid-Open No. A technique has been used in which a plurality of counter electrode portions formed by serially connecting floating intermediate electrodes obtained by dividing into two or three or more pieces are connected in parallel. The above technology is
There is an advantage that the distribution of the electrode strength becomes substantially uniform in the length direction of the counter electrode.

[Problems to be solved by the invention]

However, the above-described conventional technique has a problem that as the number of divisions increases, the intersection width also becomes smaller and is affected by the diffraction effect.

The present invention solves the problems of the prior art as described above,
It is an object of the present invention to provide a surface acoustic wave filter that suppresses the effect of a diffraction effect generated at a place where the electrode finger crossing width is small.

[Means for solving the problem]

In order to achieve the above object, in the present invention, when a desired surface acoustic wave excitation intensity is to be excited by a pair of counter electrode fingers at a position in the surface wave propagation direction of the electrode weighted to the electrode finger crossing width, When the electrode finger crossing width is shorter than the center wavelength of the surface wave propagating above, the electrode at that position is divided into two in a direction perpendicular to the surface wave propagation direction, and the electrode finger crossing of each part is performed. The width is longer than the center wavelength of the surface acoustic wave, is excited by voltages of opposite phases, and is formed so that the difference between the electrode finger intersection widths is equal to the narrow intersection width, and the surface acoustic wave propagating on the substrate All desired surface acoustic wave excitation intensities are obtained only by the counter electrode pair finger having the electrode finger crossing width longer than the center wavelength of.

[Action]

According to the above, the sum of the strengths of the surface acoustic waves in the direction perpendicular to the electrode fingers excited in each of the two divided portions is a pair of undivided opposed electrode fingers shorter than the center wavelength of the surface acoustic wave. The intensity of the surface acoustic wave in the direction perpendicular to the electrode finger excited at the intersection is equal to the intensity of the surface acoustic wave, and the electrode finger intersection width of each of the divided parts is generally much longer than when not divided, so the diffraction effect Can be suppressed very well.

〔Example〕

FIG. 1 is a schematic plan view of the first embodiment of the present invention. A piezoelectric substrate 1 is made of a single crystal of lithium niobate that transmits a 128-degree rotated Y-axis and cuts an X-axis. On this substrate 1, an input interdigital electrode 2 and an output interdigital electrode 3 are arranged. Are divided into two interdigital transducers 4 and 5 of a portion A which becomes the narrow intersection width in the conventional interdigital transducer;
The other portion B is formed from the interdigital electrodes 6. On both sides of the input / output electrodes 2 and 3, that is, on both ends of the substrate 1,
A sound absorbing material 7 is applied to suppress unnecessary reflected waves from the end face of the substrate. Terminals 8, 8 'are input terminals, and terminals 9, 9' are output terminals. The central electrode bus bars 10, 11 forming the interdigital electrodes 4, 5 are connected to output terminals 9 ', 9, respectively. The center frequency of this filter is 36.15MHz,
The number of pairs of output interdigital electrodes 3 is 57.5 pairs and the maximum aperture length is 1300.
μm, the number of pairs of input interdigital electrodes 2 is 8.5, and the maximum aperture length is 2000 μm. Surface acoustic wave propagation direction x of interdigital transducer 4 (bus bar 10) and interdigital transducer 5 (bus bar 11)
Electrode finger cross widths w ₁ and w ₂ at any position x ′
Are longer than the center wavelength w _{s of the} surface acoustic wave propagating in the substrate 1, the lower interdigital electrode 5 provides an excitation intensity in phase with the desired surface acoustic wave, and the upper interdigital electrode 4 provides an excitation intensity in opposite phase. . The difference in length of the cross width w ₁ of the cross width w ₂ and the upper interdigital electrode 4 of the lower interdigital electrode 5 is equal to cross width in the case of not conventional split. The surface acoustic waves excited by the vertically interdigitated interdigital electrodes 4 and 5 have opposite phases, and the desired surface acoustic wave excitation intensity is set to be longer than the center wavelength of the surface acoustic wave propagating through the substrate. Since it can be realized with a long length, the diffraction effect can be suppressed.

FIG. 2 shows a conventional example in which the same surface acoustic wave excitation intensity can be obtained. The same parts as those in FIG. 1 are denoted by the same reference numerals. The narrow intersection A shown in the figure causes unnecessary diffraction waves.

FIG. 3 shows a plan view of the second embodiment of the present invention. The bus bars 10 'and 11' at the center of the portion A are both connected to the output terminal 9 ', and the electrode fingers connected to these buses are connected to the output terminal 9', respectively.
And intersects with the electrode fingers of the interdigital electrodes 4 'and 5' connected to. Since the electric field between the electrode fingers of the interdigital electrodes 4 'and 5' becomes opposite in phase at the same position in the surface acoustic wave propagation direction x,
The same effect as in the first embodiment can be obtained. Further, since the central bus bars 10 'and 11' have the same potential, unnecessary surface acoustic waves can be prevented from being excited between them.

FIG. 4 is a plan view of a third embodiment of the present invention. In this embodiment, the central busbars 10 ', 11' of the second embodiment are replaced by a single busbar 12. By doing so, the same effects as in the second embodiment can be obtained, the number of wirings can be reduced, and the manufacturing process can be improved. Further, the degree of freedom in selecting the cross width of the interdigital transducers forming the portion A is increased.

FIG. 5 is a schematic plan view of an output electrode according to a fourth embodiment of the present invention. In section B, the interdigital electrodes 14 and 15 connected to the output terminal 9 form counter electrodes with the interdigital electrode 13 connected to the central output terminal 9 '. IDT 13,14
The electric field between the electrode fingers of the interdigital electrodes 13 and 15 has the same phase at the same position in the surface acoustic wave propagation direction x, and the surface acoustic waves excited at the intersections of the respective opposed electrode pairs have the same phase. For this reason, the same effect as in the third embodiment can be obtained by appropriately selecting the cross width of each counter electrode to be larger than the center wavelength of the surface acoustic wave transmitted through the substrate 1. Further, since the central bus bar is common to the entire output electrode, the wiring process is simplified as compared with the third embodiment.

FIG. 6 is a plan view of an output electrode according to a fifth embodiment of the present invention. In the case of the fourth embodiment, the interdigital electrodes 13 and 14, 15 are replaced with split-connect type interdigital electrodes 13 ', 14', and 1 '.
5 '. As a result, the same effect as that of the fourth embodiment can be obtained, and since the additional electrode finger is of a split connect type, the crossing width of each counter electrode can be selected independently, so that the degree of freedom of design increases.

FIG. 7 shows an output electrode according to a sixth embodiment of the present invention. The electrode fingers extending from the interdigital electrode 16 connected to the output terminal 9 and the interdigital electrode 17 connected to the output terminal 9 ′ are electrode fingers 18.
And 19, it is bent by half the center wavelength of the surface wave in the surface wave propagation direction in the middle of the direction perpendicular to the surface wave propagation direction. The electrode fingers 18 and 19 is formed in a cross section at position x _1, x _2, x ₃ and position x _2, x _3, x ₄ respectively SAW propagation axis x. IDT at position x ₃
The electric field due to the intersection between the electrode finger 18 extending from 16 and the electrode finger 19 extending from the interdigital electrode 17 and the electric field due to the intersection between the electrode finger 20 extending from the interdigital electrode 16 and the electrode finger 19 extending from the interdigital electrode 17 are: , has a reverse phase with each other, since the surface acoustic wave the phase of the excitation at each intersection are opposite phases, position bending of the electrode fingers 19 and 20 suitably, cross two places at position x ₃ By selecting the portion to be larger than the center wavelength of the surface acoustic wave propagating through the substrate, it is possible to realize a cross width capable of suppressing diffraction, and the same effect as in the first embodiment can be obtained. Further, the power distribution in the direction perpendicular to the surface acoustic wave propagation direction is also continuous, and better frequency characteristics can be obtained. In addition, the wiring routing process is simple, the effect of direct waves is suppressed, and the manufacturing process is simplified.

FIG. 8 is a block diagram of an output electrode according to the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 50-24050. This electrode has the advantage that the power intensity distribution is almost uniform in the direction perpendicular to the surface acoustic wave propagation direction x, but there is a problem that as the number of divisions increases, the cross width becomes smaller and the diffraction effect occurs. . Further, since the floating electrode 21 exists, it is difficult to calculate a potential of the floating electrode to give a desired surface acoustic wave excitation intensity.

FIG. 9 is a plan view of an output electrode according to a seventh embodiment of the present invention. In the portion C surrounded by the broken line, when the excitation intensity of the surface acoustic wave transmitted through the substrate 1 is to be excited by a pair of counter electrode fingers, the electrode finger crossing width is larger than the center wavelength of the surface wave and is twice or less. Part. In the portion C, the crossing portion formed by the interdigital electrodes 13 and 15 has the same surface acoustic wave excitation strength and electrode finger crossing width as in the case of a pair of counter electrode fingers. Further, the electrode fingers all have a common potential between the interdigital electrodes 13 and 14, and do not excite surface acoustic waves. As a result, the degree of freedom in selecting the divided electrode portion is increased, and the manufacturing process and the wiring process are simplified.

Further, if the surface acoustic wave filter of the present invention, in which the out-of-band is suppressed by suppressing the diffraction effect as shown in each of the above embodiments, is used for communication equipment, the S / N ratio is improved, and the degree of noise suppression is improved. I do.

〔The invention's effect〕

As described above, according to the present invention, even a portion where the desired surface acoustic wave excitation intensity is small can be realized only by an excitation source having an electrode finger cross width longer than the wavelength of the surface acoustic wave propagating on the substrate. Since the diffraction effect can be suppressed, the effect of improving the frequency characteristics of the element can be obtained. In the embodiment, the degree of suppression outside the band is improved by 5 dB as compared with the conventional example.

[Brief description of the drawings]

1 is a diagram of a first embodiment of the present invention, FIG. 2 is a diagram of a conventional example, FIG. 3 is a diagram of a second embodiment, FIG. 4 is a diagram of a third embodiment, and FIG. FIG. 6 is an output electrode diagram of the fifth embodiment, FIG. 7 is an output electrode diagram of the sixth embodiment, FIG. 8 is a diagram of an example of an improved conventional technique, and FIG. 9 is a diagram of the seventh embodiment. It is an output electrode diagram. 1 ... Piezoelectric substrate, 2 ... Input interdigital electrode, 3,3 '...
... Output interdigital electrodes, 4, 5... Divided interdigital electrodes at positions where the surface acoustic wave excitation intensity is low, 6... Interdigital electrodes at positions where the surface acoustic wave excitation intensity is high, 7. ′
…… Input terminal, 9,9 ′ …… Output terminal, 10,10 ′, 11,11 ′, 1
2 busbar 13,13 ', 14,14', 15,15 ', 17 ... interdigital electrode, 18,19,20 ... electrode finger, 21 ... floating electrode, A ...
... A portion where the crossover width becomes shorter than the center wavelength of the surface wave when excited by one electrode finger pair, B. a portion where the crossover width becomes longer than the center wavelength of the surface wave when excited by one electrode finger pair, x... Direction axis, x ₁ , x ₂ , x ₃ , x ₄ ... Position on x axis.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Jun Yamada 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Home Appliance Research Laboratory, Hitachi, Ltd.

Claims (9)

(57) [Claims] 1. A surface acoustic wave filter in which a plurality of interdigital electrodes used for input or output are provided on a piezoelectric substrate, and the electrode finger intersection width of at least one of the electrodes is weighted. When trying to excite the wave excitation intensity with a pair of normal counter electrode fingers, the electrode finger cross width is small and the cross width is narrow, and two points in the direction perpendicular to the surface wave propagation direction at the position where the diffraction effect is affected. A surface wave excitation point is provided, and the electrode finger intersection width of each part is longer than the center wavelength of the surface wave, and each part is excited in opposite phase, and the difference of each electrode finger intersection width becomes a desired surface acoustic wave excitation intensity. A surface acoustic wave filter having a portion formed as described above. 2. When a desired surface acoustic wave excitation intensity is to be excited by a pair of normal counter electrode fingers at a position of an electrode weighted with the electrode finger cross width, the electrode finger cross width becomes small and becomes narrow. In the case where the diffraction effect is exerted, the electrode at that position is provided with an electrode finger that is bent in the middle by a half wavelength of the center wavelength of the surface wave in the direction of propagation of the surface wave, and each of the portions is divided into two by the bent portion. 2. The elasticity according to claim 1, wherein the electrode finger crossing width is longer than the center wavelength of the surface wave, is excited in opposite phases, and the difference between the respective crossing widths is equal to the narrow crossing width. Surface wave filter. 3. A method for obtaining a desired excitation intensity of an electrode weighted with an electrode finger intersection width, wherein a plurality of adjacent continuous positions which should have the narrow intersection width have a surface at a center in a direction perpendicular to the surface acoustic wave propagation direction. An interdigitated electrode divided into two by an electrode finger common bus extending in the wave propagation direction is arranged, and the electrode finger intersection width of each of the divided portions is longer than the center wavelength of the surface wave, and they are excited in opposite phases. 2. The surface acoustic wave filter according to claim 1, further comprising a portion formed such that a difference between the electrode finger cross widths is equal to the narrow cross width. 4. The surface acoustic wave according to claim 3, wherein the outermost electrode finger common bus has the same potential over the entire length of the electrode in the surface acoustic wave propagation direction weighted to the electrode finger crossing width. filter. (5) When a desired excitation intensity is to be obtained with a pair of opposed electrode fingers, at a position where the electrode finger intersection width is longer than twice the center wavelength of the surface wave, each of the divided portions is provided with a respective electrode. The finger crossing width is longer than the center wavelength of the surface, and the sum of the crossing widths of the respective parts is equal to the required width in the case of a pair of opposing electrode fingers, and they are connected in parallel and are excited in the same phase, respectively. At a position where the electrode finger cross width is longer than the surface acoustic wave center wavelength and equal to or less than twice when the desired excitation intensity is to be obtained with the counter electrode finger, each of the divided portions is one of the above pair of counter electrode fingers. The same electrode finger cross width and the same phase are excited, and the other part eliminates the electrode finger crossing and the surface wave is not excited. (C) When a desired excitation intensity is obtained with a pair of opposing electrode fingers, At positions where the finger crossing width is equal to or smaller than the center wavelength of the surface wave, Or width is longer than the center wavelength of the surface wave,
4. The surface acoustic wave filter according to claim 3, wherein the surface acoustic wave filters are excited so as to be excited in opposite phases, respectively, so that a difference between the respective intersection widths is equal to the narrow intersection width. 6. An interdigital transducer having the configuration according to claim 3, wherein (a) when an attempt is made to obtain a desired excitation intensity with a pair of opposing electrode fingers, the electrode finger crossing width is larger than twice the center wavelength of the surface wave. In the position where the distance is also longer, each of the divided portions has a crossover width of each electrode finger longer than the center wavelength of the surface, and the sum of the crossover widths of each portion is 1
4. The surface acoustic wave filter according to claim 3, wherein the width is equal to a required width in the case of a pair of counter electrode fingers, and each is connected in parallel and excited in the same phase. 7. An interdigital transducer having the configuration according to claim 3, wherein (b) when an attempt is made to obtain a desired excitation intensity with a pair of opposing electrode fingers, the electrode finger crossing width is longer than the surface wave center wavelength. In the position where the width is equal to or less than twice, each of the divided portions is excited in the same phase at the same electrode finger crossing width as in the case of the pair of counter electrode fingers in one portion, and eliminates the electrode finger crossing in the other portion to reduce the surface wave. The surface acoustic wave filter according to claim 3, wherein the surface acoustic wave filter is excited. 8. The surface acoustic wave filter according to claim 1, wherein the interdigital transducer is of a split connector type. 9. A communication device using the surface acoustic wave filter according to any one of claims 1 to 8.