JP5363821B2 - Surface acoustic wave filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave (SAW) filter capable of sharpening shoulder characteristics without enlarging a substrate area. <P>SOLUTION: A SAW filter 10 includes a piezoelectric substrate 11, slanted electrode fingers 12-15, a first reflector group 16 and a second reflector group 17. Between the slanted electrode fingers 12 and 13 and the slanted electrode fingers 14 and 15, there are provided the first reflector group 16 including a plurality of reflectors 16a and the second reflector group 17 including a plurality of reflectors 17a. The first reflector group 16 is configured to reflect SAWs of a frequency component lower than a lower-side frequency of a passband just by a predetermined frequency, and the second reflector group 17 is configured to reflect SAWs of a frequency component higher than a higher-side frequency of the passband just by a predetermined frequency. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a surface acoustic wave filter used, for example, in a mobile communication device.

  Conventionally, as this type of surface acoustic wave filter, an oblique electrode on the input side having a plurality of oblique electrode fingers that input an electric signal and generate a surface acoustic wave on a piezoelectric substrate and a surface acoustic wave are received. Output-side oblique electrodes having a plurality of oblique electrode fingers that are converted into electrical signals, and each of the input-side and output-side oblique electrode fingers has an interval between adjacent electrode fingers, the propagation direction of the surface acoustic wave What is formed so that it may change in the direction orthogonal to (for example, refer patent document 1) is known.

  In a surface acoustic wave filter, in order to suitably separate signals whose frequencies are close to each other, a steep filter characteristic in which the amount of attenuation suddenly increases from the signal pass band to the stop band is required. Therefore, for example, there is a method of increasing the number of diagonal electrode fingers in the input side and output side diagonal electrodes and steepening the frequency characteristics (hereinafter referred to as “shoulder characteristics”) of the rising and falling parts in the filter waveform. It is done. In this case, due to the increase in the number of pairs of diagonal electrode fingers, the diagonal electrode on the input side and the diagonal electrode on the output side are close to each other, and electromagnetic coupling occurs between them.

  Therefore, in the conventional device, if the shoulder characteristics are steep, it is necessary to suppress the electromagnetic coupling by separating the oblique electrode on the input side and the oblique electrode on the output side from each other, which increases the area of the substrate. There was a problem that miniaturization could not be achieved.

JP 2002-057551 A

  The present invention has been made to solve the conventional problems, and an object of the present invention is to provide a surface acoustic wave filter capable of making the shoulder characteristics steep without increasing the area of the substrate.

A surface acoustic wave filter according to the present invention is a surface acoustic wave filter that passes an electric signal in a frequency range from a first frequency to a second frequency higher than the first frequency. The surface acoustic wave filter includes a piezoelectric substrate and a piezoelectric substrate on the piezoelectric substrate. A surface acoustic wave generating means for generating a surface acoustic wave corresponding to a frequency from the first frequency to the second frequency by inputting an electric signal formed thereon; and the surface acoustic wave generating means formed on the piezoelectric substrate. The surface acoustic wave receiving means that receives the generated surface acoustic wave and converts it into an electric signal, and the elasticity generated by the surface acoustic wave generating means between the surface acoustic wave generating means and the surface acoustic wave receiving means. and a surface acoustic wave reflecting means for reflecting a portion of the surface wave, the surface acoustic wave generating means includes a pair of product-side oblique electrode having a plurality of generation electrode fingers for generating the surface acoustic waves, prior to The generation-side oblique electrode is such that the electrode finger interval between adjacent generation electrode fingers gradually spreads along one direction orthogonal to the surface acoustic wave propagation direction, and the maximum and minimum electrode fingers The surface acoustic wave having the first and second wavelengths is generated at each position at intervals, and the surface acoustic wave receiving means has a pair of reception electrode fingers having a plurality of receiving electrode fingers for receiving the surface acoustic wave. Each of the reception side diagonal electrodes is such that the electrode finger spacing of the reception electrode fingers adjacent to each other gradually spreads along the one direction, and is the maximum and minimum electrode finger spacing. Receiving the surface acoustic waves of the first and second wavelengths generated by the generation-side oblique electrode at a position, and the surface acoustic wave reflecting means has a frequency that is determined in advance from the first frequency. Low frequency & What der which reflects the surface acoustic wave having a center frequency of at least one of the serial predetermined frequency by a frequency higher than the second frequency, a plurality of which are arranged along the propagation direction of the surface acoustic wave Each of the plurality of reflectors provided in the first reflector group includes at least one of a first reflector group and a second reflector group each including a reflector, and reflector intervals between reflectors adjacent to each other. Are arranged at intervals larger than half of the first wavelength, and the plurality of reflectors included in the second reflector group have reflector intervals between the reflectors adjacent to each other. It has the structure which is arrange | positioned by the space | interval smaller than half of the wavelength of this.

  With this configuration, in the surface acoustic wave filter of the present invention, the surface acoustic wave reflecting means has at least one of a frequency lower by a predetermined frequency than the first frequency and a frequency higher by a predetermined frequency than the second frequency. By reflecting the surface acoustic wave having a center frequency of, the shoulder characteristics can be made steep without increasing the area of the substrate.

Also, with this configuration, the surface acoustic wave filter of the present invention is such that the surface acoustic wave reflecting means reflects the surface acoustic wave having a frequency corresponding to at least one of the low band side and the high band side of the pass band. The shoulder characteristics can be made steep without increasing the area of the substrate.

  Furthermore, in the surface acoustic wave filter according to the present invention, the plurality of reflectors included in the first reflector group are respectively positioned at a position that is the maximum electrode finger interval of the generation-side oblique electrode and the reception-side oblique electrode. The plurality of reflectors provided in the second reflector group are arranged in a region overlapping a line segment connecting the position to be the maximum electrode finger interval, respectively, It has a configuration in which it is arranged in a region that overlaps a line segment connecting the position that becomes the minimum electrode finger interval and the position that becomes the minimum electrode finger interval of the reception-side oblique electrode.

  With this configuration, in the surface acoustic wave filter of the present invention, the first reflector group and the second reflector group can reflect the surface acoustic wave having a desired frequency component over a wider range.

  Furthermore, the surface acoustic wave filter of the present invention has a configuration in which the surface acoustic wave reflecting means is one in which the first reflector group and the second reflector group are electrically connected.

  With this configuration, the surface acoustic wave filter according to the present invention includes the first reflector group and the second reflector group in an integrated manner, and can reflect the surface acoustic wave over a wider range.

  Furthermore, the surface acoustic wave filter of the present invention has a configuration in which the surface acoustic wave reflecting means is grounded.

  With this configuration, the surface acoustic wave filter of the present invention can suppress electromagnetic coupling that occurs between the surface acoustic wave generating means and the surface acoustic wave receiving means.

  The present invention can provide a surface acoustic wave filter having the effect of making the shoulder characteristics steep without increasing the area of the substrate.

FIG. 1 is a diagram conceptually showing the structure of the surface acoustic wave filter in the first embodiment of the present invention. FIG. 2 is an explanatory diagram for the basic functions of the reflector according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating the principle of obtaining steep shoulder characteristics in the surface acoustic wave filter according to the first embodiment of the present invention. FIG. 4 is a diagram showing a simulation result of the surface acoustic wave filter according to the first embodiment of the present invention in comparison with a conventional one. FIG. 5 is a diagram conceptually showing the structure of the surface acoustic wave filter according to the second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, the configuration of the surface acoustic wave filter according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram conceptually showing the structure of a surface acoustic wave filter 10 in the present embodiment.

  As shown in FIG. 1, the surface acoustic wave filter 10 according to the present embodiment includes a piezoelectric substrate 11, oblique electrode fingers 12 to 15 formed of a metal thin film having the same film thickness on the piezoelectric substrate 11, and a first reflector group. 16 and the second reflector group 17. In FIG. 1, in order to make the configuration easy to understand, there are four electrode fingers for the oblique electrode fingers 12 and 14 and three electrode fingers for the oblique electrode fingers 13 and 15.

The piezoelectric substrate 11 is made of a ferroelectric piezoelectric material such as lithium niobate, potassium niobate, lithium tantalate, or langasite. In the present embodiment, the piezoelectric substrate 11 is configured by a 128-degree Y-cut LiNbO ₃ single crystal substrate and has a rectangular shape as shown in FIG. Hereinafter, the long side direction and the short side direction of the piezoelectric substrate 11 are referred to as a horizontal direction and a vertical direction, respectively.

  The oblique electrode fingers 12 and 13 are formed on the piezoelectric substrate 11 by a metal thin film made of, for example, an AlCu alloy, and are arranged so that the electrode fingers are alternately adjacent to each other. The oblique electrode fingers 12 and 13 are connected to an electric signal source (not shown) such that the oblique electrode finger 13 is on the ground side, for example, and an electric signal is input from the electric signal source. The oblique electrode fingers 12 and 13 constitute a surface acoustic wave generating means according to the present invention, and each electrode finger included in the oblique electrode fingers 12 and 13 constitutes a generated electrode finger according to the present invention.

  Further, in the diagonal electrode fingers 12 and 13, the distance between the adjacent electrode fingers is formed so as to increase in the vertical direction, and the diagonal electrode fingers 12 and 13 are respectively connected to the electrode finger end portions 12a and 13a. Have. Here, as shown in the drawing, a surface acoustic wave having a wavelength of λ1 is generated on the electrode finger end portion 13a side, and the electrode finger intervals of the oblique electrode fingers 12 and 13 on the line segment A are respectively λ1. On the other hand, a surface acoustic wave having a wavelength of λ2 is generated on the electrode finger end portion 12a side, and the electrode finger interval between the oblique electrode fingers 12 and 13 on the line segment B is λ2. That is, in the diagonal electrode fingers 12 and 13, the electrode finger interval changes from the maximum interval λ1 to the minimum interval λ2. Note that λ1 corresponds to the first wavelength according to the present invention, and λ2 corresponds to the second wavelength according to the present invention.

  On the other hand, the oblique electrode fingers 14 and 15 are configured similarly to the oblique electrode fingers 12 and 13, respectively. That is, the oblique electrode fingers 14 and 15 are formed on the piezoelectric substrate 11 by a metal thin film of, for example, an AlCu alloy, and are arranged so that the respective electrode fingers are alternately adjacent. In addition, the oblique electrode fingers 14 and 15 are connected to the ground side, for example, so that the oblique electrode fingers 15 receive surface acoustic waves, convert them into electric signals, and output the converted electric signals. The oblique electrode fingers 14 and 15 constitute a surface acoustic wave receiving means according to the present invention, and each electrode finger included in the oblique electrode fingers 14 and 15 constitutes a reception electrode finger according to the present invention.

  Further, in the diagonal electrode fingers 14 and 15, the distance between the adjacent electrode fingers is formed to increase as it goes upward in the vertical direction, and the diagonal electrode fingers 14 and 15 are respectively connected to the electrode finger end portions 14a and 15a. Have. In addition, a surface acoustic wave having a wavelength of λ1 is received on the electrode finger end portion 15a side, and the electrode finger interval between the oblique electrode fingers 14 and 15 on the line segment A is λ1. On the other hand, a surface acoustic wave having a wavelength of λ2 is received on the electrode finger end portion 14a side, and the distance between the electrode fingers of the oblique electrode fingers 14 and 15 on the line segment B is λ2. That is, also in the oblique electrode fingers 14 and 15, the electrode finger interval changes between the maximum interval λ1 and the minimum interval λ2.

  In the above-described configuration, the oblique electrode fingers 12 and 13 receive an electric signal from an electric signal source (not shown), and out of the frequency components included in the electric signal, frequency components corresponding to the distance from the electrode finger interval λ1 to λ2 The surface acoustic wave is generated based on the piezoelectric effect by the piezoelectric substrate 11. Specifically, assuming that the frequency of the surface acoustic wave generated at the electrode finger interval λ1 is the first frequency and the frequency of the surface acoustic wave generated at the electrode finger interval λ2 is the second frequency, the oblique electrode fingers 12 and 13 Generates a surface acoustic wave corresponding to the frequency components from the first frequency to the second frequency among the frequency components included in the input electrical signal.

  The surface acoustic waves generated by the oblique electrode fingers 12 and 13 propagate along the surface of the piezoelectric substrate 11 and travel in the lateral direction, and are received by the oblique electrode fingers 14 and 15. The oblique electrode fingers 14 and 15 convert the received surface acoustic waves into electrical signals based on the piezoelectric effect by the piezoelectric substrate 11 and output electrical signals including frequency components from the first frequency to the second frequency. It has become.

  A first reflector group 16 and a second reflector group 17 are provided on the piezoelectric substrate 11 between the oblique electrode fingers 12 and 13 and the oblique electrode fingers 14 and 15. Hereinafter, the first reflector group 16 and the second reflector group 17 will be described in detail.

  A line segment A shown in FIG. 1 is a line segment that connects the electrode finger end portion 13a and the electrode finger end portion 15a, and a line segment B connects the electrode finger end portion 12a and the electrode finger end portion 14a. It is a line segment. For convenience, the line segment A and B are equally divided into six channels ch1 to ch6. The distance between the electrode fingers becomes narrower from ch1 to ch6, the surface acoustic wave having the lowest frequency propagates in ch1, and the surface acoustic wave having the highest frequency propagates in ch6.

  The first reflector group 16 and the second reflector group 17 are formed on the piezoelectric substrate 11 by a metal thin film made of, for example, an AlCu alloy, and reflect a surface acoustic wave having a predetermined frequency. The first reflector group 16 includes a plurality of reflectors 16a, and the second reflector group 17 includes a plurality of reflectors 17a. The reflector interval of each reflector 16a is 1/2 · λ3 and has a relationship of λ1 <λ3. Moreover, the reflector interval of each reflector 17a is 1/2 · λ4, and has a relationship of λ2> λ4. In addition, the 1st reflector group 16 and the 2nd reflector group 17 comprise the surface acoustic wave reflection means which concerns on this invention.

  Each of the plurality of reflectors 16a is formed across a vertical region of ch1 and a region protruding from the line segment A by a predetermined dimension in the vertical direction. Each of the plurality of reflectors 17a is formed across a vertical region of ch6 and a region protruding from the line segment B by a predetermined dimension downward in the vertical direction.

  With the above-described configuration, the first reflector group 16 reflects the surface acoustic wave having a frequency component lower than the first frequency by a predetermined frequency, and the second reflector group 17 is predetermined by the second frequency. A surface acoustic wave having a frequency component higher by the frequency is reflected.

  As a method of forming the oblique electrode fingers 12 to 15, the first reflector group 16, and the second reflector group 17 described above, for example, after forming a metal thin film on the piezoelectric substrate 11 by sputtering, a desired pattern is formed. It is formed by etching away unnecessary portions by the remaining photolithographic technique.

  Next, functions of the reflectors 16a and 17a will be described with reference to FIGS.

  First, basic functions of a general reflector will be described with reference to FIG. As shown in FIG. 2 (a), in the configuration in which the reflector is not provided between the oblique electrode fingers 12 and 13 and the oblique electrode fingers 14 and 15, the insertion loss characteristic shown on the right in FIG. 2 (a) is obtained. It is done. On the other hand, as shown in FIG. 2B, when the reflector 18 is added, the signal of the frequency component corresponding to the width of the reflector 18 and the interval between the reflectors is reduced, and a notch filter can be configured. . The present applicant pays attention to this point, and as a result of examination, has come to solve the above-mentioned problems. Note that the present applicant has proposed a configuration in which a reflector is provided in Japanese Patent Laid-Open No. 61-289714.

  Next, the principle of obtaining steep shoulder characteristics in the surface acoustic wave filter 10 according to this embodiment will be described with reference to FIG.

  FIG. 3A conceptually shows a composite surface wave 21 of surface acoustic waves generated by the oblique electrode fingers 12 and 13. The composite waveform 21 of the surface acoustic wave is obtained by combining the components of the surface acoustic wave generated in each of the regions ch1 to ch6 (see FIG. 1), and has a waveform rising portion 21a and a waveform falling portion 21b. Including.

FIG. 3B is an enlarged view of the rising portion 21a of the waveform, and is generated corresponding to the electrode finger interval λ1 among the surface acoustic waves generated by the oblique electrode fingers 12 and 13 (see FIG. 1). the center frequency of the surface acoustic wave is shown in f _L was.

Of the surface acoustic wave generated by the oblique electrode fingers 12 and 13, to represent the center frequency of the reflected wave first reflector group 16 (see FIG. 1) is reflected by f _N, a notch around the frequency f _N A filter is generated. FIG. 3 (c), the center frequency f _N of the notch characteristic 22 by the notch filter, an example which is set to a lower side by a predetermined frequency higher than the frequency f _L. Here, the frequencies f _L and f _N are determined in correspondence with the electrode finger interval λ1 and the reflector interval 1/2 · λ3 in FIG. 1, respectively, and are set through simulations and experiments in advance. It is preferable to do this.

  FIG. 3D shows a state where the rising portion 21 c is newly generated by the combined waveform 21 of the surface acoustic wave and the notch characteristic 22. As shown in the figure, the newly generated rising part 21c is steeper than the original rising part 21a.

  Therefore, the surface acoustic wave filter 10 according to the present embodiment can make the shoulder characteristics on the low band side of the pass band steep.

  The above description relates to the low band side of the passband of the surface acoustic wave filter 10, but on the high band side, the electrode finger interval λ2 and the reflector interval 1/2 · λ4 in FIG. 1 are set to desired values. By setting, a steep shoulder characteristic can be obtained as in the low frequency side.

  Therefore, the surface acoustic wave filter 10 in the present embodiment can make the shoulder characteristics of at least one of the low band side and the high band side of the pass band steep.

  In the above-described configuration, the film thicknesses of the first reflector group 16 and the second reflector group 17 and the film thicknesses of the oblique electrode fingers 12 to 15 are the same. Either one or both of the film thicknesses of the device group 16 and the second reflector group 17 can be made thicker or thinner than the film thicknesses of the oblique electrode fingers 12 to 15. However, since the surface acoustic wave speed decreases as the thickness of the reflector increases, it is not preferable to change only the thickness of the reflector. In consideration, it is preferable to change the reflector interval at the same time so that the center frequency of the notch characteristic becomes a desired frequency. Further, instead of the first reflector group 16 and the second reflector group 17, a groove as a grating structure may be provided in these regions by, for example, ion etching or ion implantation.

  Next, the effect by the surface acoustic wave filter 10 in this embodiment is demonstrated based on a simulation result. Table 1 shows the simulation conditions of the surface acoustic wave filter 10. As design target values, the center frequency of the pass band is 174 MHz and the bandwidth of the pass band is 22 MHz.

In Table 1, the propagation distance refers to the distance indicated by the arrow in FIG. 1, and the opening length refers to the distance between the electrode finger end 12a and the electrode finger end 13a (between the line segments A and B) in FIG. The length of Λ represents the wavelength of the surface acoustic wave. Further, the lower electrode design frequency (161.55 MHz) corresponds to the frequency f _L in FIG. 3, and the lower reflector design frequency (160.8 MHz) corresponds to the frequency f _N in FIG. Although omitted in FIG. 3, the high-frequency electrode design frequency is 186.66 MHz, and the high-frequency reflector design frequency is 188.0 MHz.

  4 and Table 2 show the simulation results of the surface acoustic wave filter 10 in comparison with the conventional one.

  As shown in FIG. 4, according to the surface acoustic wave filter 10 of the present embodiment, a shoulder characteristic steeper than that of the conventional one is obtained. Specifically, as shown in Table 2, the surface acoustic wave filter 10 has a 1 dB in a 3 dB bandwidth that is 3 dB lower than the passband level and a 40 dB band that is 40 dB lower than the passband level. In terms of width, the bandwidth is as narrow as 4 MHz. Further, regarding the ratio of the 40 dB bandwidth to the 3 dB bandwidth, the surface acoustic wave filter 10 is about 10% narrower than the conventional one, and it can be seen that the shoulder characteristics are improved.

  Next, the operation of the surface acoustic wave filter 10 in this embodiment will be described with reference to FIG. In the following description, it is assumed that the surface acoustic wave filter 10 is configured on the assumption of the simulation conditions described above.

  When the oblique electrode fingers 12 and 13 input electrical signals, the piezoelectric substrate 11 vibrates due to the piezoelectric effect, and surface acoustic waves corresponding to the electrode finger interval from the maximum interval λ1 to the minimum interval λ2 are generated. That is, the oblique electrode fingers 12 and 13 generate surface acoustic waves having a passband center frequency of 174 MHz and a passband design frequency of 161.55 MHz to 186.66 MHz. This surface acoustic wave propagates on the surface of the piezoelectric substrate 11 and travels in the lateral direction.

  The reflector 16 a of the first reflector group 16 reflects a low frequency component having a center frequency of 160.8 MHz among the surface acoustic waves propagating on the surface of the piezoelectric substrate 11.

  The reflector 17 a of the second reflector group 17 reflects a high frequency component having a center frequency of 188.0 MHz among the surface acoustic waves propagating on the surface of the piezoelectric substrate 11.

  As a result, the oblique electrode fingers 14 and 15 had surface acoustic waves from which frequency components having center frequencies of 160.8 MHz and 188.0 MHz were removed, that is, the shoulder characteristics on the low frequency side and high frequency side became steep. The surface acoustic wave is received by the piezoelectric effect of the piezoelectric substrate 11 and converted into an electrical signal and output.

  As described above, according to the surface acoustic wave filter 10 in the present embodiment, the reflector 16a of the first reflector group 16 among the surface acoustic waves generated by the oblique electrode fingers 12 and 13 has a predetermined low frequency side. Since the surface acoustic wave component of the center frequency is reflected and the reflector 17a of the second reflector group 17 reflects the surface acoustic wave component of the predetermined high frequency side center frequency, the area of the substrate is increased. The shoulder characteristics can be made steep.

  Therefore, the surface acoustic wave filter 10 according to the present embodiment can be suitably applied as a surface acoustic wave filter for a mobile communication device such as a mobile phone that requires downsizing of the device.

  In the first embodiment, the surface acoustic wave filter 10 has been described by taking as an example a configuration including both the first reflector group 16 and the second reflector group 17, but the present invention is limited to this. Instead, one of the first reflector group 16 and the second reflector group 17 may be provided, and a configuration suited to the application can be taken. For example, the configuration in which the surface acoustic wave filter 10 includes only the first reflector group 16 as a reflector can be applied to an apparatus that requires steep shoulder characteristics only on the low frequency side of the pass band. Also, with this configuration, unnecessary signal components on the low frequency side, such as side lobes, can be removed with a simple configuration.

  Moreover, in 1st Embodiment, although the several reflector 16a was arrange | positioned in the area | region which overlaps with the line segment A, and the example made to protrude outside the line segment A was demonstrated, this invention is limited to this. Instead, for example, the plurality of reflectors 16a may be provided so as to be accommodated in the vertical region (within the entire width) of ch1, and may not be projected outside the line segment A. Similarly, the plurality of reflectors 17a may be provided so as to be accommodated in the vertical region of ch6 and may not protrude outside the line segment B.

  Further, in the first embodiment, the example in which the plurality of reflectors 16a are arranged in the direction orthogonal to the traveling direction of the surface acoustic wave has been described, but the present invention is not limited to this, and the elastic surface It is good also as a structure inclined only by the predetermined angle with respect to the advancing direction of a wave. The same applies to the plurality of reflectors 17a.

  In the first embodiment, the plurality of reflectors 16a and 17a may be connected to the ground. With this configuration, the surface acoustic wave filter 10 is preferable because it can suppress electromagnetic coupling between the oblique electrode fingers 12 and 13 and the oblique electrode fingers 14 and 15.

  Further, in the first embodiment, the oblique electrode fingers 12 to 15 have been described by taking the so-called single electrode as an example, but the present invention is not limited to this, and for example, a so-called double electrode, floating Similar effects can be obtained with an electrode-type unidirectional electrode, a distributed acoustic reflection-type unidirectional electrode, and the like.

(Second Embodiment)
Next, a second embodiment of the surface acoustic wave filter according to the present invention will be described.

  In the first embodiment described above, the reflector 16a of the first reflector group 16 and the reflector 17a of the second reflector group 17 are individually configured as shown in FIG. The configuration is as shown in FIG.

  That is, the surface acoustic wave filter 30 shown in FIG. 5 has an integrated reflector 31 connected to the ground, and the integrated reflector 31 electrically connects the plurality of reflectors 31a and the plurality of reflectors 31a. The connection part 31b, the some reflector 31c, and the connection part 31d which electrically connects the some reflector 31c are provided. In addition, about the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  Each of the plurality of reflectors 31a is obtained by extending the reflector 16a in the first embodiment to the line segment B side, and similarly to the reflector 16a, the surface acoustic wave having a low frequency component in the pass band is received. It is designed to reflect. Further, the plurality of reflectors 31c are obtained by extending the reflector 17a in the first embodiment to the line segment A side, and like the reflector 17a, surface acoustic waves having a low frequency component in the pass band are generated. It is designed to reflect. Further, the plurality of reflectors 31a and the plurality of reflectors 31c are electrically connected as shown in the vicinity of the centers of the line segments A and B.

  As described above, the surface acoustic wave filter 30 is provided with the reflector 31a and the reflector 31c over a wider range than in the first embodiment, so that the desired frequency components of the low-frequency side and the high-frequency side of the pass band can be obtained. The surface acoustic wave can be reflected more reliably, and the shoulder characteristics can be made steep without increasing the area of the substrate.

  In addition, since the surface acoustic wave filter 30 includes the integrated reflector 31 connected to the ground, electromagnetic coupling between the oblique electrode fingers 12 and 13 and the oblique electrode fingers 14 and 15 can be suppressed.

  In the second embodiment, the example in which the integrated reflector 31 is connected to the ground has been described. However, the present invention is not limited to this, and the integrated reflector 31 is not connected to the ground. Also good.

  As described above, the surface acoustic wave filter according to the present invention has an effect that the shoulder characteristics can be sharpened without increasing the area of the substrate, and is used as a surface acoustic wave filter for mobile communication devices and the like. Useful.

DESCRIPTION OF SYMBOLS 10 Surface acoustic wave filter 11 Piezoelectric substrate 12-15 Diagonal electrode finger 12a, 13a, 14a, 15a Electrode finger edge part 16 1st reflector group 16a Reflector 17 2nd reflector group 17a Reflector 18 Reflector 21 Surface acoustic wave 21a, 21c Waveform rising portion 21b Waveform falling portion 22 Notch characteristics 30 Surface acoustic wave filter 31 Integrated reflector 31a, 31c Reflector 31b, 31d Connection portion

Claims (4)

A surface acoustic wave filter that passes an electrical signal in a frequency range from a first frequency to a second frequency higher than the first frequency,
A piezoelectric substrate, surface acoustic wave generating means for generating a surface acoustic wave according to a frequency from the first frequency to the second frequency by inputting an electric signal formed on the piezoelectric substrate, and on the piezoelectric substrate A surface acoustic wave receiving means that receives the surface acoustic wave generated by the surface acoustic wave generating means and converts the surface acoustic wave into an electrical signal; and the elasticity between the surface acoustic wave generating means and the surface acoustic wave receiving means. A surface acoustic wave reflecting means for reflecting a part of the surface acoustic wave generated by the surface wave generating means,
The surface acoustic wave generation means includes a pair of generation side oblique electrodes having a plurality of generation electrode fingers for generating the surface acoustic wave,
The generation-side oblique electrode is such that the electrode finger interval between adjacent generation electrode fingers gradually spreads along one direction perpendicular to the propagation direction of the surface acoustic wave, and the maximum and minimum electrodes Generating surface acoustic waves of the first and second wavelengths at respective positions to be a finger interval;
The surface acoustic wave receiving means includes a pair of reception-side oblique electrodes having a plurality of reception electrode fingers for receiving the surface acoustic wave,
The reception-side oblique electrodes are formed such that electrode finger intervals of adjacent reception electrode fingers gradually spread along the one direction, and are at the maximum and minimum electrode finger intervals at the generation side. Receiving the surface acoustic waves of the first and second wavelengths generated by the oblique electrodes;
The surface acoustic wave reflecting means reflects a surface acoustic wave having a center frequency at least one of a frequency lower by a predetermined frequency than the first frequency and a frequency higher by a predetermined frequency than the second frequency. what der which comprises at least one of the first reflector group and the second reflector group including the plurality arranged along the propagation direction of a surface acoustic wave reflector, respectively,
The plurality of reflectors included in the first reflector group are arranged such that reflector intervals between adjacent reflectors are larger than half of the first wavelength, respectively.
The plurality of reflectors included in the second reflector group are characterized in that the reflector intervals of the reflectors adjacent to each other are arranged at intervals smaller than half of the second wavelength. Surface acoustic wave filter. Each of the plurality of reflectors included in the first reflector group has a position that becomes the maximum electrode finger interval of the generation side oblique electrode and a position that becomes the maximum electrode finger interval of the reception side oblique electrode. It is placed in the area that overlaps the connected line segments,
Each of the plurality of reflectors included in the second reflector group has a position that becomes the minimum electrode finger interval of the generation-side oblique electrode and a position that becomes the minimum electrode finger interval of the reception-side oblique electrode. The surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is disposed in a region overlapping the connected line segments . 3. The surface acoustic wave according to claim 1, wherein the surface acoustic wave reflecting means is one in which the first reflector group and the second reflector group are electrically connected. 4. filter. The surface acoustic wave filter according to claim 1, wherein the surface acoustic wave reflecting means is grounded .

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