JP2004007094A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device wherein a frequency region providing a greater attenuation is extended without increasing the insertion loss. <P>SOLUTION: The surface acoustic wave device has: a plurality of serial arm resonators 54 to 56 connected in series and placed between an input terminal IN and an output terminal OUT; and a plurality of parallel arm resonators 57 to 60 placed in parallel between the serial arm resonators and ground terminals GND. The anti-resonance frequencies of all the parallel arm resonators 57 to 60 are selected nearly equal to each other, and the resonance frequency of the parallel arm resonators 57, 58 resonate at the resonance frequency different from the other parallel arm resonators 58, 59. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface acoustic wave device used for a band-pass filter of a wireless communication circuit such as a mobile communication device, and in particular, a ladder-type filter formed by connecting a plurality of surface acoustic wave resonators in a ladder form. The present invention relates to a surface acoustic wave device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, surface acoustic wave devices used as high-frequency band filters in mobile communication devices have been known. For example, Japanese Patent Publication No. 56-19765 discloses a surface acoustic wave device in which a plurality of surface acoustic wave resonators are formed on a piezoelectric substrate to form a ladder-type filter circuit.
[0003]
FIG. 9 shows a circuit configuration of a general surface acoustic wave device represented by the above-mentioned prior art. In the surface acoustic wave device 510, surface acoustic wave resonators 530, 540, 550, 525, 535, 545, 555 are connected to each other in a ladder (ladder) form. Also, a specific electrode structure of the resonators 530, 540,... Is shown in FIG.
[0004]
FIG. 10 is a plan view schematically showing only the electrode portion of the one-port type surface acoustic wave resonator 700. The resonator 700 has a structure in which reflectors 720 and 730 are arranged on both sides of an interdigital transducer (hereinafter, IDT) 710 arranged in the center. The IDT 710 has a structure in which a comb-shaped electrode 710a and a comb-shaped electrode 710b mesh with each other. The surface wave excited by the IDT 710 of the resonator 700 having such a structure is reflected by the reflectors 720 and 730 to generate a standing wave, and the standing wave is confined between the reflectors 720 and 730 and the resonator is closed. 700 operates as a resonator having a high Q factor. As is well known, in the impedance characteristics of the resonator 700, there are a resonance frequency at which the impedance is very low and an anti-resonance frequency at which the impedance is very high.
[0005]
As shown in FIG. 9, the resonators 530, 540,... Of the surface acoustic wave device 510 are connected in series between the input terminal 570 and the output terminal 580. (Hereinafter, each of these resonators is referred to as a “series arm resonator”). Resonators 525, 535, 545, and 555 are connected in parallel between the series and the ground terminal (hereinafter, each of the resonators is referred to as a "parallel arm resonator"). The series arm resonators 530, 540, and 550, and the parallel arm resonators and 525, 535, 545, and 555 are alternately connected between input and output. One set of the series arm resonator 530 and the parallel arm resonator 525 constitutes a one-stage SAW filter.
[0006]
Since all of the series arm resonators 530, 540, 550 and the parallel arm resonators 525, 535, 545, 555 have the above-described predetermined impedance characteristics, the resonance frequency of the series arm resonators 530, 540, 550 and the parallel arm By substantially matching the anti-resonance frequency of the resonators 525, 535, 545, 555, the input / output impedance is matched with the characteristic impedance to form a pass band.
[0007]
Also, near the resonance frequency of the parallel arm resonators 525, 535, 545, and 555, the impedance becomes very low, and an attenuation pole on the lower frequency side than the pass band is formed. In the vicinity of the anti-resonance frequency, the impedance becomes very high, and an attenuation pole on the higher frequency side than the pass band is formed. FIG. 11A shows the impedance characteristics of the series arm resonators 530, 540, and 550 and the parallel arm resonators 525, 535, 545, and 555, and FIG. 11B shows the transmission characteristics of the filter obtained by combining these. Show.
[0008]
However, in such a ladder-type filter, although the amount of attenuation at the attenuation pole is large, the amount of attenuation decreases rapidly away from the attenuation pole, and the frequency range where the amount of attenuation is large is narrow. Therefore, improvement is required.
[0009]
As a method for solving this problem, in order to enlarge the region where the attenuation is large in the stop band on the lower frequency side than the pass band, if the electrode finger pitch of some parallel arm resonators is different from that of other parallel arm resonators, In order to expand the region where the attenuation is large in the stop band on the higher frequency side than the passband, the electrode finger pitch of some series arm resonators is made different from that of other series arm resonators, and the attenuation poles are dispersed. There is a way to make it happen.
[0010]
[Problems to be solved by the invention]
For example, in the surface acoustic wave device 510 of FIG. 9, the electrode finger pitch of two parallel arm resonators 525 and 555 among the plurality of parallel arm resonators 525 to 555 is changed to the electrode finger pitch of the other parallel arm resonators 535 and 545. By making the pitch wider than the pitch, the resonance frequency fr ₂ of the parallel arm resonators 525 and 555 is shifted to a lower frequency side than the resonance frequency fr ₁ of the other parallel arm resonators 535 and 545 as shown in FIG. The attenuation pole existing on the lower frequency side than the pass band on the transmission characteristic of the filter can be dispersed, and the frequency region where the amount of attenuation is large can be expanded. However, the anti-resonance frequency fa ₂ of the parallel arm resonators 525 and 555 is simultaneously shifted from the anti-resonance frequency fa _{1 of the} other parallel arm resonators 535 and 545 to a lower frequency side. As shown, there is a problem that the insertion loss of the pass band increases. In this example, as can be seen from FIG. 4 (b), the insertion loss on the high frequency side of the pass band is significantly deteriorated.
[0011]
Similarly, in the series arm resonators 530 to 550, by making the electrode finger pitch of some series arm resonators wider or narrower than the electrode finger pitch of other series arm resonators, the resistance of some series arm resonators is reduced. By making the resonance frequency different from the anti-resonance frequency of the other series arm resonators, the attenuation pole existing on the higher frequency side than the pass band on the transmission characteristics of the filter can be dispersed, and the area where the attenuation is large can be expanded. At the same time, the resonance frequency also changes, so that the insertion loss in the pass band also deteriorates.
[0012]
In order to solve this problem, Japanese Patent Application Laid-Open No. H11-55067 discloses that in some parallel arm resonators, the length of a wire for connecting the parallel arm resonator to a reference potential is reduced by using another parallel arm resonator. A method is disclosed in which the inductance value of the wire itself is made different by making it different, and the attenuation pole in the stop band on the lower frequency side than the pass band is dispersed to widen the frequency region where the attenuation is large. According to this, since only the resonance frequency is changed without changing the anti-resonance frequency of the parallel arm resonator, the attenuation pole existing in the stop band on the lower frequency side than the pass band without deteriorating the insertion loss of the pass band. Is dispersed, and the frequency region where the attenuation is large can be expanded.
[0013]
However, in this method, it is necessary to increase the length of the wire and the electrode area, and it is difficult to apply the method to a SAW filter for a mobile communication device that is required to have a small size and a low profile. Further, at present, a surface acoustic wave filter in which a surface acoustic wave element is flip-chip mounted on a package in order to meet a demand for miniaturization has become mainstream, but it is impossible to apply the technology of the above-mentioned publication to this. .
[0014]
The present invention has been devised in view of the above-described problems, and while maintaining the insertion loss in the pass band, in the stop band on the low frequency side and the high frequency side of the pass band, the frequency range where the amount of attenuation is large is set. It is an object of the present invention to provide a surface acoustic wave device that can be widened and can be reduced in size at the same time.
[0015]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, according to the first aspect of the present invention, two comb-shaped electrodes composed of a common electrode and a plurality of electrode fingers are arranged on a piezoelectric substrate such that the plurality of electrode fingers mesh with each other. A plurality of surface acoustic wave resonators comprising an interdigital transducer formed as described above and a pair of reflectors formed so as to sandwich the interdigital transducer, an input terminal, an output terminal, a ground terminal, and connecting these A surface acoustic wave device having a wiring pattern
The plurality of surface acoustic wave resonators, a plurality of series arm resonators arranged and connected in series between an input terminal and an output terminal, and an input terminal side or an output terminal side of each series arm resonator and a ground terminal. And a plurality of parallel arm resonators disposed between the plurality of parallel arm resonators. The resonance frequencies of at least one parallel arm resonator among the plurality of parallel arm resonators are set while substantially matching the anti-resonance frequencies of all the parallel arm resonators. A surface acoustic wave device characterized in that the frequency is different from the resonance frequency of another parallel arm resonator.
[0016]
According to the second aspect of the present invention, the resonance frequency of at least one parallel arm resonator among the parallel arm resonators is substantially the same as the antiresonance frequency of all the parallel arm resonators. The anti-resonance frequency of at least one of the series arm resonators is different from the resonance frequency of the arm resonator, and the resonance frequencies of all the series arm resonators are substantially matched. A surface acoustic wave device characterized by being different from the anti-resonance frequency of the series arm resonator.
[0017]
According to the third aspect of the present invention, the anti-resonance frequency of at least one of the series arm resonators is set to be equal to the other series arm resonators while the resonance frequencies of all the series arm resonators are substantially matched. Provided is a surface acoustic wave device characterized by having a different antiresonance frequency from the arm resonator.
[0018]
In the fourth and fifth aspects of the present invention, the width of the electrode fingers of the surface acoustic wave resonator is L, and the distance between adjacent electrode fingers is S, which is derived from the equation (D = L / (L + S)). The metallization ratio D is different between the at least one parallel arm resonator and the other parallel arm resonator and / or at least one series arm resonator and the other series arm resonator And a surface acoustic wave device characterized in that the surface acoustic wave device is different from the above.
[0019]
In the inventions according to claims 6 and 7, the thickness of the electrode fingers of the surface acoustic wave resonator is made different from each other so that the distance between the at least one parallel arm resonator and the other parallel arm resonator is increased. A surface acoustic wave device is provided that is different and / or different between at least one series arm resonator and the other series arm resonator.
[Action]
According to the configuration of the present invention, while making the anti-resonance frequencies of all the parallel arm resonators substantially coincide with each other, the resonance frequency of at least one parallel arm resonator among the plurality of parallel arm resonators becomes the other parallel arm resonance. The resonance frequency of the filter is different from that of the filter, so that the transmission loss of the filter does not increase the insertion loss in the pass band, but disperses the attenuation pole present in the stop band on the lower frequency side than the pass band, resulting in a large amount of attenuation. The frequency range can be expanded.
[0020]
Similarly, according to the present invention, the anti-resonance frequency of at least one series arm resonator among the plurality of series arm resonators is changed while the resonance frequencies of all the series arm resonators are substantially matched. Different from the anti-resonance frequency of the series arm resonator of the above, the transmission characteristics of the filter, without increasing the insertion loss in the pass band, disperse the attenuation pole present in the stop band on the higher frequency side than the pass band, The frequency range in which the amount of attenuation is large can be expanded.
[0021]
By combining them in the same manner, the attenuation pole existing in the stop band on the lower frequency side than the pass band is dispersed, and at the same time, the attenuation pole existing in the stop band on the higher frequency side is dispersed. Can be expanded.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a surface acoustic wave device according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a structure of a surface acoustic wave device according to an embodiment of the present invention, and FIG. 2 is an enlarged view of a parallel arm resonator for explaining a characteristic portion of the present invention.
[0023]
In FIG. 1, a surface acoustic wave device A includes a plurality of series arm resonators 54, 55, 56 connected in series between an input terminal (IN) and an output terminal (OUT). GND), a plurality of parallel arm resonators 57, 58, 59, and 60 are connected in parallel.
[0024]
The series arm resonators 54, 55, 56 and the parallel arm resonators 57, 58, 59, 60 all have IDTs 54a to 60a at the center on the main surface of the piezoelectric substrate 1, and have reflectors 54b, 54c on both sides thereof. 55b, 55c... 60b, 60c are formed.
[0025]
The piezoelectric substrate 1 is made of quartz, lithium niobate, lithium tantalate, lithium tetraborate, or the like, which is cut into a rectangular shape so as to have a predetermined cut angle and a predetermined propagation direction.
The IDTs 54a to 60a and the reflectors 54b to 60c on both sides thereof are made of, for example, an aluminum thin film and have a thickness of about 0.2 μm and are formed in a predetermined pattern. The electrode finger width and the electrode finger interval of the IDTs 54a to 60a and the reflectors 54b to 60c on both sides thereof are, for example, approximately λλ with respect to the wavelength λ of the surface acoustic wave.
[0026]
The IDTs 54a to 56a are connected in series from the input terminal (IN) and connected to the output terminal (OUT) to form a series. Further, one side of the IDTs 57a to 60a is connected in series through the reflectors 57b, 58c, 59c, and 60b, and the other side is connected to a ground terminal (GND) by the reflectors 57c, 58b, 59b, and 60c, and is connected in parallel. Is formed.
[0027]
In the present embodiment, of the parallel arm resonators 57 to 60, the difference between the resonance frequency and the antiresonance frequency of the parallel arm resonators 57 and 60 is different from the resonance frequency of the other parallel arm resonators 58 and 59 and the antiresonance. It is different from the frequency.
Hereinafter, the electrode structure of the IDTs 54a to 60a will be described. 2A and 2B show the structures of the IDTs 57a to 60a of the parallel arm resonators 57 to 60. 2A is an enlarged view of a main part of the IDTs 58a and 59a, and FIG. 2B is an enlarged view of a main part of the IDTs 57a and 60a. In particular, in FIG. 2, the electrode finger width is described as L, the electrode finger spacing is described as S, and the total length of the electrode finger width L and the electrode finger spacing S is described as the electrode finger pitch P.
[0028]
In the present embodiment, the characteristic point is that the resonance frequency of at least one of the parallel arm resonators is different from the resonance frequency of the other arm while the anti-resonance frequencies of all the parallel arm resonators are substantially matched. It is different from the resonance frequency of the parallel arm resonator.
[0029]
As a specific means, for example, the metallization ratio D, which is the ratio of the electrode finger width L to the electrode finger pitch P, is changed while the electrode finger pitch P remains unchanged. This metallization ratio is represented by the following equation.
D = L / (L + S)
In the figures, the IDTs 58a and 59a are designed to have a metallization ratio of 0.35 as shown in FIG. Further, the IDTs 57a and 60a are designed to have a metallization ratio of 0.65 as shown in FIG. The thickness of the IDTs 54a to 60a is designed to be constant.
[0030]
As described above, by making the metallization ratio D of some of the parallel arm resonators 57 and 60 different from the metallization ratio D of the other parallel arm resonators 58 and 59, some of the parallel arm resonators 57 and 60 are made. The difference between the resonance frequency and the anti-resonance frequency of the parallel arm resonators 58 and 59 is made different from the difference between the resonance frequency and the anti-resonance frequency of the other parallel arm resonators 58 and 59. By increasing (or decreasing) the electrode finger pitch of the resonators 57 and 60, the impedance characteristics of some of the parallel arm resonators 57 and 60 are shifted to a lower frequency side (or to a higher frequency side) on the frequency axis, and The anti-resonance frequency of the parallel arm resonators 57 and 60 is substantially equal to the anti-resonance frequency of the other parallel arm resonators 58 and 59. In this way, the resonance frequency of some parallel arm resonators can be made different from the resonance frequency of the other parallel arm resonators while the anti-resonance frequencies of all the parallel arm resonators 57 to 60 are substantially matched. . As a result, the attenuation pole existing in the stop band on the lower frequency side than the pass band can be dispersed without increasing the insertion loss in the pass band in the transmission characteristics of the filter, and the frequency region where the amount of attenuation is large can be expanded.
[0031]
Similar effects can be obtained also when the metallization ratio D in some of the series arm resonators among the series arm resonators 54 to 56 is changed. For example, by making the metallization ratio D of some series arm resonators 55 different from the metallization ratio D of the other series arm resonators 54 and 56, the resonance frequency and the anti-resonance frequency of some series arm resonators 55 are obtained. Is made different from the difference between the resonance frequency and the anti-resonance frequency of the other series arm resonators 54 and 56, and then the electrode finger pitch of some series arm resonators 55 is changed without changing the metallization ratio D. By increasing (or decreasing) the impedance characteristics of some series arm resonators 55, the impedance characteristics of some series arm resonators 55 are shifted to a lower frequency side (or to a higher frequency side) on the frequency axis, and the resonance frequency of some series arm resonators 55 is changed to other frequencies. And the resonance frequency of the series arm resonators 54 and 56 of FIG. In this way, the anti-resonance frequency of some series arm resonators can be made different from the anti-resonance frequency of other series arm resonators while keeping the resonance frequencies of all series arm resonators 54 to 56 substantially matched. It is. As a result, in the transmission characteristics of the filter, the attenuation pole existing in the stop band on the higher frequency side than the pass band can be dispersed without increasing the insertion loss in the pass band, and the frequency region where the attenuation is large can be expanded.
[0032]
In addition, by combining these, the attenuation pole existing in the stop band on the low frequency side from the pass band is dispersed, and at the same time the attenuation pole existing in the stop band on the high frequency side is dispersed, so that both the low frequency side and the high frequency side are dispersed. It is possible to widen the frequency range where the amount of attenuation is large in the stop band.
[0033]
In the above-described embodiment, in the surface acoustic wave device A, the difference between the resonance frequency and the antiresonance frequency of some surface acoustic wave resonators is determined by comparing the difference between the resonance frequency and the antiresonance frequency of the other surface acoustic wave resonators. The difference is realized by changing the metallization ratio of the surface acoustic wave resonator. This is because, as shown in FIG. 7, by changing the metallization ratio of the electrode fingers, Δf, which is the difference between the resonance frequency and the anti-resonance frequency of the surface acoustic wave resonator, changes. However, the present invention is not limited to this. As shown in FIG. 8, in the surface acoustic wave resonator A, the difference between the resonance frequency and the antiresonance frequency can be obtained by changing the electrode thickness of some surface acoustic wave resonators. Changes, and a similar effect can be obtained.
[0034]
Specifically, by making the electrode finger thickness of some parallel arm resonators thicker than the electrode finger thickness of other parallel arm resonators, the resonance frequency of some parallel arm resonators and the anti-resonance The difference from the frequency is made different from the difference between the resonance frequency and the antiresonance frequency of the other parallel arm resonators, and then the electrode finger pitch of some parallel arm resonators is increased without changing the metallization ratio D (or ), The impedance characteristic of some parallel arm resonators is shifted to a lower frequency side (or higher frequency side) on the frequency axis, and the anti-resonance frequency of some parallel arm resonators is shifted to other parallel arm resonances. To approximately match the anti-resonance frequency of the vessel. In this way, the resonance frequencies of some parallel arm resonators can be made different from the resonance frequencies of the other parallel arm resonators while the anti-resonance frequencies of all the parallel arm resonators are made substantially equal. In a series arm resonator, the difference between the resonance frequency and the antiresonance frequency can be changed in the same manner.
[0035]
Still another method is to make the electrode material and piezoelectric material of some surface acoustic wave resonators different from those of other surface acoustic wave resonators, so that the difference between the resonance frequency and the anti-resonance frequency can be reduced by another surface acoustic wave resonator. It can be different from a resonator.
[0036]
【Example】
(Experimental example 1)
In order to demonstrate the effect of the present invention, a surface acoustic wave device A shown in FIG. 1 was manufactured. Specifically, it was manufactured with the following dimensions. In FIG. 3, the metallization ratio of the parallel arm resonators 57 and 60 is 0.65, the metallization ratio of the other parallel arm resonators 58 and 59 is 0.35, and the metallization of the series arm resonators 54 to 56 is shown. The impedance characteristic of each resonator when the ratio is set to 0.5 is shown. In FIG. 3, the vertical axis represents impedance (Ω), and the horizontal axis represents frequency (MHz).
[0037]
As shown in the drawing, while the anti-resonance frequencies fa of the parallel arm resonators 57 and 60 and the parallel arm resonators 58 and 59 are substantially matched, the resonance frequency fr ₂ of the parallel arm resonators 57 and 60 and the parallel arm resonator It can be seen that the resonance frequencies fr _{1 of} 58 and 59 are different.
(Experimental example 2)
FIG. 4A shows the transmission characteristics of the filter by the surface acoustic wave device A of FIG. 1 using the series arm resonators 54 to 56 and the parallel arm resonators 57 to 60 described above. As a comparative example, by setting the electrode finger pitch of the parallel arm resonators 525 and 555 of the surface acoustic wave device 510 of FIG. 9 larger than the electrode finger pitch of the other parallel arm resonators 535 and 545, the frequency is lower than the pass band. The transmission characteristics of the surface acoustic wave filter when the attenuation poles on the side are dispersed are also shown. FIG. 4B is an enlarged view of the vicinity of the pass band in FIG. The vertical axis of the figure is the attenuation (dB), and the horizontal axis is the frequency (MHz).
[0038]
According to FIG. 4A, in both the present invention and the comparative example, by dispersing the attenuation pole in the stop band on the lower frequency side than the pass band, the frequency region where the attenuation is large can be expanded. Looking at (b), it can be seen that in the comparative example, the insertion loss in the vicinity of 1970 to 1990 MHz, which is on the higher side of the passband, increases compared to the present invention, and does not satisfy the insertion loss standard.
[0039]
In this comparative example, the resonance frequency is shifted from fr ₁ to fr ₂ as shown in FIG. 12 by widening the electrode finger pitch of some of the parallel arm resonators 525 and 555. As described above, the anti-resonance frequency shifts from fa ₁ to fa ₂ , which increases the insertion loss in the pass band.
[0040]
On the other hand, in the present invention, as shown in FIG. 3, since the anti-resonance frequencies fa of all the parallel arm resonators 57 to 60 are substantially matched, the insertion loss around 1970 to 1990 MHz, which is on the high frequency side of the pass band. Does not increase.
(Experimental example 3)
In the above-described Experimental Example 1, an example was shown in which the metallization ratio of the parallel arm resonator was increased. However, FIGS. 5 and 6 show the characteristics of the resonator and the filter when the metallization ratio of the series arm resonator was changed. .
[0041]
In the surface acoustic wave device A of FIG. 1, the metallization ratio of the series arm resonator 55 is 0.65, the metallization ratio of the other series arm resonators 54 and 56 is 0.35, and the metallization of the parallel arm resonator is All ratios were 0.5. FIG. 5 shows the frequency characteristics of each resonator, and FIG. 6 shows the transmission characteristics of the filter in that case. FIG. 6 shows a comparative example in which the electrode finger pitch of the series arm resonator 540 is smaller than the electrode finger pitch of the other series arm resonators 530 and 550 in the surface acoustic wave device 510 of FIG. The transmission characteristics of the filter when the attenuation pole on the side is dispersed are also shown.
[0042]
As shown in FIG. 5, by setting the metallization ratio of the series arm resonator 55 to 0.65 and the metallization ratio of the other series arm resonators 54 and 56 to 0.35, the resonance of the series arm resonator 55 the difference between the frequencies fr and the antiresonant frequency fa ₂ be different from the difference between the resonance frequency fr and the antiresonance frequency fa ₁ other series arm resonators 54 and 56, and thereby the resonance frequency fr coincide with other series arm resonator it is thus possible to vary the anti-resonant frequency fa ₁ anti-resonance frequency fa ₂ and other series arm resonators 54 and 56 of the series arm resonators 55 a resonant frequency fr while allowed to substantially coincide.
[0043]
As a result, as shown in FIG. 6, an attenuation pole corresponding to the anti-resonance frequency fa ₁ is formed near 1930 MHz in a stop band on the higher frequency side than the pass band, and an attenuation pole corresponding to the anti-resonance frequency fa ₂ is formed near 1946 MHz. By dispersing the attenuation poles in this manner, the frequency range where the amount of attenuation is large can be expanded. Since the resonance frequencies of all the series arm resonators are substantially the same, the insertion loss of the pass band does not increase unlike the comparative example.
[0044]
【The invention's effect】
According to the configuration of the present invention, the resonance frequency of at least one parallel arm resonator is made different from the resonance frequency of another parallel arm resonator while keeping the anti-resonance frequencies of all the parallel arm resonators substantially the same, And / or by making the anti-resonance frequency of at least one series arm resonator different from the anti-resonance frequency of another series arm resonator while keeping the resonance frequencies of all series arm resonators substantially matched. In the transmission characteristics of (1), the attenuation pole can be dispersed and the frequency region where the amount of attenuation is large can be expanded without increasing the insertion loss of the pass band.
[Brief description of the drawings]
FIG. 1 is a plan view of a surface acoustic wave device according to the present invention.
FIGS. 2A and 2B are enlarged views of a main part of an IDT of a parallel arm resonator.
FIG. 3 is a diagram illustrating impedance characteristics of a surface acoustic wave resonator according to the present invention.
4A is a diagram illustrating transmission characteristics of surface acoustic wave filters according to the present invention and a comparative example, and FIG. 4B is an enlarged diagram near a pass band in FIG.
FIG. 5 is a diagram illustrating impedance characteristics of each resonator according to the second embodiment of the present invention.
FIG. 6A is a diagram illustrating transmission characteristics of a surface acoustic wave filter according to a second embodiment of the present invention and a comparative example, and FIG. 6B is an enlarged view of the vicinity of the pass band in FIG.
FIG. 7 is a diagram illustrating a change in Δf due to a change in the metallization ratio of the surface acoustic wave resonator.
FIG. 8 is a diagram showing a change in Δf due to a change in electrode thickness of the surface acoustic wave resonator.
FIG. 9 is a diagram showing a circuit configuration of a conventional surface acoustic wave device.
FIG. 10 is a schematic diagram for explaining a conventional surface acoustic wave resonator.
11A is a diagram illustrating impedance characteristics of respective resonators in a conventional general surface acoustic wave filter, and FIG. 11B is a diagram illustrating transmission characteristics of a conventional general surface acoustic wave filter. is there.
FIG. 12 is a diagram illustrating impedance characteristics of a conventional parallel arm resonator.
[Explanation of symbols]
A: Surface acoustic wave device 1: Piezoelectric substrates 54 to 56: Series arm resonators 57 to 60: Parallel arm resonator 61: Input terminal 62: Output terminal

Claims (7)

An interdigital transducer formed by arranging two comb-shaped electrodes each composed of a common electrode and a plurality of electrode fingers on a piezoelectric substrate so that the plurality of electrode fingers mesh with each other, and sandwiching the interdigital transducer. A plurality of surface acoustic wave resonators comprising a pair of reflectors, an input terminal, an output terminal, a ground terminal, and a wiring pattern connecting these,
The plurality of surface acoustic wave resonators, a plurality of series arm resonators arranged in series between an input terminal and an output terminal, and an input terminal side or an output terminal side of each series arm resonator and a ground terminal. And a plurality of parallel arm resonators disposed between the plurality of parallel arm resonators. The resonance frequencies of at least one parallel arm resonator among the plurality of parallel arm resonators are set while substantially matching the anti-resonance frequencies of all the parallel arm resonators. A surface acoustic wave device having a frequency different from a resonance frequency of another parallel arm resonator. While making the resonance frequencies of all of the series arm resonators substantially the same, the anti-resonance frequency of at least one of the series arm resonators is different from the anti-resonance frequency of the other series arm resonators. The surface acoustic wave device according to claim 1, wherein An interdigital transducer formed by arranging two comb-shaped electrodes each composed of a common electrode and a plurality of electrode fingers on a piezoelectric substrate so that the plurality of electrode fingers mesh with each other, and sandwiching the interdigital transducer. A plurality of surface acoustic wave resonators comprising a pair of reflectors, an input terminal, an output terminal, a ground terminal, and a wiring pattern connecting these,
The plurality of surface acoustic wave resonators, a plurality of series arm resonators arranged in series between an input terminal and an output terminal, and an input terminal side or an output terminal side of each series arm resonator and a ground terminal. And a plurality of parallel arm resonators arranged between
While making the resonance frequencies of all of the series arm resonators substantially the same, the anti-resonance frequency of at least one of the series arm resonators is different from the anti-resonance frequency of the other series arm resonators. A surface acoustic wave device. Assuming that the electrode finger width of the surface acoustic wave resonator is L and the interval between adjacent electrode fingers is S, the metallization ratio D derived from the equation (D = L / (L + S)) is equal to the at least one parallel arm resonance. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is different from the other parallel arm resonator. Assuming that the electrode finger width of the surface acoustic wave resonator is L and the distance between adjacent electrode fingers is S, the metallization ratio D derived from the equation (D = L / (L + S)) is equal to the at least one series arm resonance. 4. The surface acoustic wave device according to claim 2, wherein the surface acoustic wave device is different from the other series arm resonator. The thickness of an electrode finger of the surface acoustic wave resonator is different between the at least one parallel arm resonator and the other parallel arm resonator. Surface acoustic wave device. The electrode finger of the surface acoustic wave resonator has a different thickness between the at least one series arm resonator and the other series arm resonator. Surface acoustic wave device.

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