JP5365406B2 - Elastic wave filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an elastic wave filter excelling in symmetry of an attenuation characteristics when viewing a low-frequency side and a high-frequency side from the central frequency of a passing frequency band, in an elastic wave filter wherein input-side and output-side IDT electrodes parts are each formed into a tapered shape. <P>SOLUTION: In the tapered IDT electrode part formed so that an arrangement pattern of electrode fingers 15 is expanded from one-side bus bar 14a toward the other-side bus bar 14b, both ends of the one-side bus bar 14a are extended in the extending direction of the bus bar 14a to form second extension parts 32; the other-side bus bar 14b is extended from both ends thereof toward the tip sides of the second extension parts 32 to form first extension parts 31; the arrangement pattern of the electrode fingers 15 is continuously extended between the first extension parts 31 and the second extension parts 32; and a high-frequency-side logarithm N<SB>H</SB>and a low-frequency-side logarithm N<SB>L</SB>are set to satisfy 0.96&times;(N<SB>L</SB>/N<SB>H</SB>)&lt;f<SB>L</SB>/f<SB>H</SB>&lt;1.04&times;(N<SB>L</SB>/N<SB>H</SB>). In this case, N<SB>H</SB>is a logarithm of the electrode finger in a region nearest to the one-side bus bar 14a; N<SB>L</SB>is a logarithm of the electrode finger in a region nearest to the other-side bus bar 14b in a part interposed between the extension parts of the other-side bus bar 14b; and f<SB>H</SB>and f<SB>L</SB>are a high-frequency-side frequency and a low-frequency-side frequency of the pass band of the elastic wave filter, respectively. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an acoustic wave filter, for example, a (SAW: Surface Acoustic Wave) filter.

The SAW device uses surface acoustic waves, and an electrode part called IDT (interdigital transducer) is arranged on a piezoelectric substrate as an input side electrode and an output side electrode along the propagation direction of the elastic wave. Electric-mechanical mutual conversion between an electric signal and an elastic wave is performed between two electrode portions to give frequency selection (band filter) characteristics. A SAW filter, which is one of SAW devices, is used as a panda-pass filter for various communication devices such as mobile phones that have been improved in function and size. Along with this, there is a demand for a wide pass frequency band and a steep attenuation characteristic. Further, when the center frequency in the pass frequency band of the filter is f ₀ , it is required that the attenuation characteristics are as symmetrical as possible when the low frequency side and the high frequency side are viewed from the center frequency f ₀ .

  As a technique for widening the pass frequency band as described above, for example, a method using the following filter is known. As shown in FIG. 7, this filter is configured so that the width dimension and the distance dimension of the electrode finger 102 and the reflective electrode 107 increase from the bus bar 101 on one side (back side) toward the bus bar 101 on the other side (near side). The tapered IDT electrode 103 is arranged as an input-side IDT electrode 104 and an output-side IDT electrode 105 along the elastic wave propagation direction. For example, a rectangular metal film (shield electrode) is provided between the electrodes 104 and 105. 106) is arranged. A sound absorbing material (not shown) for absorbing an elastic wave propagating to the end region is disposed in the end region of the piezoelectric substrate 100 on the side of the IDT electrodes 104 and 105.

  In this filter, λ in FIG. 7 is a periodic unit that is repeated at a predetermined interval according to the width dimension and interval dimension of the electrode finger 102 and the reflective electrode 107 so as to correspond to the wavelength of the propagating elastic wave, and the propagation of the elastic wave Propagating from the elastic wave of the short wavelength wavelength track (propagation path) to the elastic wave of the long wavelength wavelength wave from the bus bar 101 on one side to the bus bar 101 on the other side so as to have a constant period along the direction. In other words, the pass frequency band is widened.

At this time, as shown in FIG. 8, the frequency corresponding to the low frequency side track in the pass frequency band of the filter is f _low , the frequency corresponding to the high frequency side track is f _high , and these frequencies f _low If the passbands (main lobes) formed at f _high and df _high are df _low and df _high , respectively, in the above filter, the specific bands (df _low / f _low and df _high / f _low ) are equal, The absolute bands (df _low and df _high ) become wider on the high frequency side. Therefore, the attenuation characteristic obtained by this filter has a gentle attenuation curve on the high frequency side than on the low frequency side, for example, as shown schematically in FIG. Therefore, good symmetry cannot be obtained with respect to the attenuation characteristics when the low frequency side and the high frequency side are viewed from the center frequency f ₀ in the pass frequency band. FIG. 8 schematically shows characteristics obtained in the low frequency side track and the high frequency side track of the filter.

Further, in this filter, in order to set a wide pass frequency band, for example, when the difference of the cycle unit λ between the _low frequency f _low and the high frequency f _high is set to be large, the high frequency is further increased. Since the absolute band of f _high becomes wider than the absolute band of the _low frequency f _low , the symmetry of the attenuation characteristic is further deteriorated.

In Patent Document 1, the number of pairs of electrode fingers having a _high frequency f _high is set higher than that of the _low frequency f _low to flatten the band characteristics, and the low frequency bus bar is used as an elastic wave propagation region. Although it has been described a technique that suppresses unnecessary reflection of elastic waves to reduce ripples by stretching, and to obtain good group delay characteristics by eliminating the path difference of elastic waves in each track. No consideration has been given to the symmetry of.

JP-A-61-288508 (page 2, lower left column, lines 2 to 14, line 1)

  The present invention has been made in view of such circumstances, and an object thereof is to provide a steep attenuation characteristic and a pass frequency band in an elastic wave filter in which an input side IDT electrode portion and an output side IDT electrode portion are configured in a tapered shape. It is an object of the present invention to provide an elastic wave filter having good symmetry of attenuation characteristics when the low frequency side and the high frequency side are viewed from the center frequency.

The elastic wave filter of the present invention is
In the acoustic wave filter in which the input-side IDT electrode part and the output-side IDT electrode part are arranged apart from each other in the propagation direction of the elastic wave on the piezoelectric substrate,
A pair of bus bars formed so as to be parallel to each other, and a group of electrode fingers that are alternately extended from each of the pair of bus bars and formed in a comb-teeth shape. The tapered IDT electrode portion formed so that the gap region of the pair extends from one bus bar to the other bus bar of the pair of bus bars constitutes at least one of the input side IDT electrode portion and the output side IDT electrode portion. And
Extending both ends of one bus bar in the tapered IDT electrode portion in a direction in which the bus bar extends;
Extending from both ends of the other bus bar toward the distal end side of the extended portion of the one bus bar to form an extended portion;
Continuously extending an arrangement pattern of electrode fingers formed between the pair of bus bars between the extended portion of the one bus bar and the extended portion of the other bus bar;
The number of electrode fingers in the region closest to the one bus bar is _NH , and the number of electrode fingers in the region closest to the other bus bar is N _L in the region sandwiched between the extension portions of the other bus bar. When the high-frequency side frequency and the low band side frequency pass band of each f _H, and f _L,
0.96 × (N _L / N _H ) <f _L / f _H <1.04 × (N _L / N _H )

The input-side IDT electrode part and the output-side IDT electrode part are both configured by the tapered IDT electrode part,
The number of pairs of electrode fingers _NH in the region closest to the one bus bar of the input side IDT electrode portion and the portion sandwiched between the extended portions of the other bus bar of the input side IDT electrode portion are the closest to the other bus bar. The number N _{L of the} electrode fingers in the near region is set to N _HI and N _LI , respectively, and the number N _{H of the} electrode fingers in the region closest to the one bus bar of the output-side IDT electrode unit and the output IDT electrode unit When the number N _{L of the} electrode fingers in the region closest to the other bus bar is N _HO and N _{LO in the} region sandwiched between the extension portions of the other bus bar ,
It is preferable that 0.98 × (N _HO / N _LO ) <(N _HI / N _LI ) <1.02 × (N _HO / N _LO ).

The present invention relates to an input-side IDT electrode section and a tapered IDT electrode section formed so that the width of the electrode fingers and the space between the electrode fingers expand from one bus bar to the other bus bar of the pair of bus bars. In the acoustic wave filter that constitutes at least one of the output side IDT electrode part, and the input side IDT electrode part and the output side IDT electrode part are arranged on the piezoelectric substrate so as to be separated from each other in the propagation direction of the elastic wave, the tapered IDT An extension portion is formed by extending both ends of one bus bar in the electrode portion in the extending direction of the bus bar, and extending from both ends of the other bus bar toward the distal end side of the extension portion of the one bus bar. Formed between the pair of bus bars between the extension portion of the one bus bar and the extension portion of the other bus bar. And and to extend the arrangement pattern of the electrode fingers in succession, further the logarithm of the electrode finger in the area closest to the one bus bar N _H, on the other bus bar at a site flanked by extension of the other bus bar Assuming that the number of electrode fingers in the nearest region is N _L , and the high frequency and low frequency of the passband of the acoustic wave filter are f _H and f _L , respectively, 0.96 × (N _L / N _H ) < f _L / f _H <1.04 × (N _L / N _H ) is set. Therefore, the attenuation characteristic on the high frequency side becomes almost as steep as the attenuation characteristic on the low frequency side, so that the attenuation characteristic when looking at the low frequency side and the high frequency side from the center frequency of the pass frequency band is good. Symmetry can be obtained.

It is a top view which shows an example of the elastic wave filter which concerns on embodiment of this invention. It is the top view which expanded a part of above-mentioned elastic wave filter. It is a top view which shows typically the method of designing said filter. It is a schematic diagram which shows a mode that an elastic wave propagates in the above-mentioned elastic wave filter. It is a characteristic view which shows typically the characteristic acquired about the above-mentioned elastic wave filter. It is a characteristic view which shows typically the characteristic acquired about the above-mentioned elastic wave filter. It is a top view which shows the conventional elastic wave filter. It is the schematic which shows the characteristic in the conventional elastic wave filter. It is a characteristic view which shows typically the characteristic acquired in the conventional elastic wave filter.

An elastic wave filter according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. The elastic wave filter of the present invention includes an input-side tapered IDT electrode portion 12 and an output-side tapered IDT electrode portion 13 that are provided at intervals along the propagation direction of the elastic wave. It is arranged on a piezoelectric substrate 11 such as LiNbO ₃ ). Between these IDT electrode portions 12 and 13, for example, a shield electrode (square metal film) 17 is disposed. A sound absorbing material (damper) (not shown) for absorbing unnecessary elastic waves propagating to the end region via the IDT electrode portions 12 and 13 is provided in the end region of the piezoelectric substrate 11 in the elastic wave propagation direction. Is arranged. Further, the shield electrode 17 is schematically shown. 1 and 2, the electrode portions 12 and 13 and the shield electrode 17 are hatched so as to be easily distinguished from the region of the piezoelectric substrate 11. The same applies to the following figures.

  The input-side tapered IDT electrode section 12 includes a bus bar 14a on one side and a bus bar 14b on the other side formed on the back side and the near side so as to be parallel to each other along the propagation direction of elastic waves, and these bus bars. Electrode fingers 15 and reflective electrodes 16 extending from each of 14a and 14b so as to be alternately comb-shaped are provided. The electrode fingers 15 and the reflective electrodes 16 are formed such that the width dimension and the interval dimension of each of the electrode fingers 15 and the reflection electrodes 16 increase from the bus bar 14a on one side toward the bus bar 14b on the other side. A pair of electrode fingers 15, 15 formed adjacent to each other from each of 14 a, 14 b and one reflective electrode 16 extending from the bus bar 14 a so as to be adjacent to these electrode fingers 15, 15 make one set. Thus, they are arranged so as to be repeated periodically along the propagation direction of the elastic wave at a predetermined cycle unit λ.

  In this filter, an elastic wave having the same length as the period unit λ propagates. Accordingly, when the track that is the propagation path of the elastic wave is Tr, in a direction orthogonal to the propagation direction of the elastic wave, the cycle unit λ is narrower from Tr1 to Tr2 that extends from the rear bus bar 14a to the front bus bar 14b. Will be formed. In FIG. 1, the width dimensions of the electrode fingers 15 and the reflective electrodes 16 are drawn as constant for simplification of illustration.

  The bus bar 14a on one side is connected to the input port 21, and the bus bar 14b on the other side is grounded. Also, the other side of the bus bar 14b on the other side extends from the other side of the bus bar 14b on the other side in the length direction (acoustic wave propagation direction) so as to go around the region where the electrode fingers 15 and the reflective electrodes 16 are formed from both sides. The first extending portions 31 are formed so as to extend substantially perpendicular to the bus bar 14a side and so that the front end portions thereof are close to the bus bar 14a on the one side. Therefore, the region where the electrode finger 15 and the reflective electrode 16 are formed is formed (enclosed) by the first extension portions 31 and 31 and the pair of bus bars 14a and 14b so as to be substantially rectangular. )

  Here, it is known that the acoustic wave has a difference in propagation speed between a region where the electrode film is formed (for example, the first extension portion 31) and a region where the electrode film is not formed (on the piezoelectric substrate 11). ing. Therefore, the first extension portions 31, 31, as will be described later, can obtain a good group delay characteristic from the track Tr 1 to the track Tr 2, that is, the elastic wave is input to the tapered IDT electrode portion on the input side. The width dimension is adjusted in the direction orthogonal to the propagation direction of the elastic wave so that the delay time from the output from 12 to the output side tapered IDT electrode portion 13 reaches from the track Tr1 to the track Tr2. Has been. In this example, the width of the first extended portions 31 is gradually narrowed from the other bus bar 14b toward the first bus bar 14a.

  Here, a method of designing the IDT electrode unit 12 will be described with reference to FIG. First, in the IDT electrode portion 12 in which the electrode fingers 15 and the reflective electrodes 16 are formed between the bus bars 14a and 14b as shown in FIG. 11A, as shown in FIG. Both end portions in the length direction are extended in the direction in which the bus bar 14a extends to form second extension portions 32, 32. Next, the electrode fingers 15 and the reflective electrodes 16 are formed so that the arrangement pattern of the electrode fingers 15 and the reflective electrodes 16 on the center side is continuously extended in the second extending portions 32 and 32. Then, as shown in FIG. 3C, from the other side of the bus bar 14b to the tip of the second extension portions 32 and 32, the region where the electrode fingers 15 and the reflective electrodes 16 are formed is substantially rectangular. On the other hand, the above-described first extended portions 31 are formed at substantially right angles. Also, between the first extension portion 31 and the second extension portion 32, the electrode fingers 15 and the reflective electrodes 16 extending from the second extension portion 32 do not interfere with the first extension portion 31. The tip portions of the electrode fingers 15 and the reflective electrodes 16 are formed up to a region close to the first extension portion 31, and the acoustic waves are excited by crossing the electrode fingers 15 extending from the second extension portion 32. Thus, the electrode fingers 15 are arranged so as to extend from the first extension portion 31 toward the second extension portion 32.

Thus, the arrangement pattern of the electrode fingers 15 and the reflective electrodes 16 is continuously extended from the center portion side between the first extension portion 31 and the second extension portion 32. Therefore, the number of pairs of electrode fingers 15 in the region corresponding to the high frequency on the one side closest to the bus bar 14a is N _H , and the other side bus bar 14b is the most sandwiched between the first extension portions 31 and 31. When the logarithm of the electrode finger 15 in the region corresponding to the adjacent low frequency is N _L , the high frequency log N _H is larger than the low frequency log N _L. At this time, whereas the frequency respectively corresponding to the track Tr2 track Tr1 and the other side of the bus bar 14b on the side of the bus bar 14a f _H, when the f _L, the electrode fingers 15 and the reflective electrode 16 as described above is formed between since forming the region on the substantially rectangular, a high-frequency side frequency f _H and the low-frequency side frequency f _L and the high frequency side log N _H and the low frequency side log N _L, the following equation (1 ) Is set such that the high-frequency logarithm _NH and the low-frequency logarithm _NL are set.
0.96 × (N _L / N _H ) <f _L / f _H <1.04 × (N _L / N _H ) (1)
That is, when a region where the electrode fingers 15 and the reflective electrode 16 is formed is formed into a substantially rectangular, the ratio of the high band side frequency f _H and the low-frequency side frequency _{f L (f L / f H} ), the high frequency side pairs N The ratio (N _L / N _H ) between _H and the low-frequency logarithm N _L is approximately equal.

  Next, the output side taper type IDT electrode part 13 will be described. The output side taper type IDT electrode part 13 is configured in the same manner as the above input side taper type IDT electrode part 12, and as shown in FIG. In addition, a bus bar 14c on one side and a bus bar 14d on the other side are provided. The bus bar 14c on one side is disposed on the back side in FIG. 1 and connected to the output port 22, and the bus bar 14d on the other side is disposed on the near side and grounded. Similarly to the input-side tapered IDT electrode portion 12, the output-side tapered IDT electrode portion 13 has a constant period unit λ along the propagation direction of the elastic wave, and the one-side bus bar 14c to the other-side bus bar. The electrode fingers 15 and the reflective electrodes 16 are provided so that the periodic unit λ becomes an array pattern extending from Tr1 to Tr2 toward 14d. In the output side tapered IDT electrode portion 13, the reflective electrode 16 is connected to the other bus bar 14d.

  And the 1st extension part 31 and 31 extended at a substantially right angle toward the bus bar 14c of the one side from the other side bus bar 14d so that the area | region in which these electrode fingers 15 and the reflective electrode 16 were formed may be enclosed from both sides. Is formed. Further, second extension portions 32, 32 are formed at both ends along the length direction from the bus bar 14c on one side, and a central portion is provided between the first extension portion 31 and the second extension portion 32. The electrode fingers 15 and the reflective electrodes 16 are formed so that the arrangement pattern of the electrode fingers 15 and the reflective electrodes 16 on the side is continuously extended.

Also in the output side tapered IDT electrode portion 13, the high-frequency side frequency f _H and the low-frequency side frequency f _L and the high frequency side log N _H and above equation between the low-frequency log N _L (1) The electrode finger 15, the reflective electrode 16, the first extension portion 31, and the second extension portion 32 are formed so that this relationship is established. At this time, the high frequency side log N _H and the low frequency side log N _L at the output side tapered IDT electrode 13, a high-frequency logarithmic N _H and the low frequency side log N _L of the input side tapered IDT electrode 12 Each is roughly equal. That is, the logarithm N _H on the high frequency side and the logarithm N _L on the low frequency side in the input side tapered IDT electrode portion 12 are respectively N _HI and N _LI , and the logarithm N _H on the high frequency side in the output side tapered IDT electrode portion 13. When the logarithm N _L on the low frequency side is N _HO and N _LO , the IDT electrode portions 12 and 13 are formed so that the following formula (2) is established.
0.98 × (N _HO / N _LO ) <(N _HI / N _LI ) <1.02 × (N _HO / N _LO ) (2)

  In such an acoustic wave filter, when a frequency signal is input to the input-side tapered IDT electrode portion 12 via the input port 21, a surface acoustic wave (SAW) is generated. The elastic wave propagates in the forward and reverse directions in the track Tr in which the periodic unit λ corresponding to the wavelength length is formed in the input side tapered IDT electrode portion 12. In each track, the acoustic wave propagates from the input-side tapered IDT electrode portion 12 toward the output-side tapered IDT electrode portion 13 (passes through a region between the electrode fingers 15 and 15 intersecting each other). As a result, the elastic wave having a wavelength corresponding to each periodic unit λ is gradually strengthened, or the elastic wave having a wavelength different from each periodic unit λ is gradually weakened. Therefore, the main lobe (absolute band), which is the pass band, becomes narrower in each track as it propagates toward the output-side tapered IDT electrode portion 13. Thereafter, for example, the elastic wave is taken out through the output port 22 in the output side tapered IDT electrode section 13, and is subjected to mechanical-electrical mutual conversion and taken out as an electric signal.

At this time, as described above, the high frequency side log N _H is made larger than the low frequency logarithm N _L , and these logarithms N _L and N _H are set as in the above-described equation (1). because, in the high band side frequency f _H, as shown in FIG. 4, the absolute bandwidth df H _(main lobe) is reduced, further absolute bandwidth df _H of approximately the same bandwidth and the absolute bandwidth df _L lower frequency It becomes. Therefore, as schematically shown in FIG. 5, the attenuation characteristic obtained in this filter is such that the attenuation characteristic on the high frequency side becomes as steep as the attenuation characteristic on the low frequency side, and the center frequency in the pass frequency band is f _0. when the attenuation characteristic of the low frequency side and high frequency side becomes the center frequency substantially symmetrical when viewed around the f _0. Further, as described above, the width dimension of the first extension portion 31 is adjusted in the direction orthogonal to the propagation direction of the elastic wave, and the input side tapered IDT electrode portion 12 is changed to the output side tapered IDT electrode portion 13. Since the arrival delay time is uniform in each track Tr, good group delay characteristics can be obtained. When the attenuation characteristic shown in FIG. 5 is shown in FIG. 6 together with the attenuation characteristic in the conventional filter shown in FIG. 9, as described above, in the present invention, the attenuation characteristic on the high frequency side is the conventional filter. It can be seen that the attenuation is steeper and the symmetry of the attenuation characteristics on the low frequency side and the high frequency side is improved. The elastic wave propagating to the left side from the input side tapered IDT electrode part 12 and the elastic wave propagating to the right side from the output side tapered IDT electrode part 13 are absorbed by a sound absorbing material (not shown).

According to the above-described embodiment, the tapered IDT electrode portion formed so that the width and the interval region of the electrode finger 15 and the reflection electrode 16 are widened from the one side bus bar 14a toward the other side bus bar 14b. At least one of the tapered IDT electrode portion 12 and the output-side tapered IDT electrode portion 13 is configured, and the input-side tapered IDT electrode portion 12 and the output-side tapered IDT electrode portion 13 are separated from each other in the elastic wave propagation direction. In the acoustic wave filter disposed on the piezoelectric substrate 11, the second extension portion 32 is formed by extending both ends of the bus bar 14a on one side of the tapered IDT electrode portion in the direction in which the bus bar 14a extends, The first extension portion is extended from both ends of the bus bar 14b on the side toward the distal end side of the second extension portion 32. 31 is formed, and the arrangement pattern of the electrode fingers 15 and the reflective electrodes 16 is continuously extended between the first extension portion 31 and the second extension portion 32, and the equation (1) Thus, the high frequency side logarithm _NH and the low frequency side logarithm _NL are set. Therefore, since the attenuation characteristic on the high frequency side becomes steep like the attenuation characteristic on the low frequency side, the attenuation characteristic when the low frequency side and the high frequency side are viewed from the center frequency f ₀ of the pass frequency band is good. Symmetry can be obtained.

Further, for both the input side tapered IDT electrode portion 12 and the output side tapered IDT electrode portion 13, the first extension portion 31 and the second extension portion 32 are formed as described above, and these extension portions 31, 32, the arrangement pattern of the electrode fingers 15 and the reflection electrodes 16 is formed so as to be continuously extended, and the high frequency side of each of the two IDT electrode portions 12 and 13 as shown in Expression (2). The logarithm _NH and the low-frequency log _NL are approximately equal. Therefore, it is possible to improve the attenuation characteristic on the high frequency side as compared with the case where only the high frequency side logarithm _NH and the low frequency side logarithm _NL are set as in Expression (1) for only one of the IDT electrode portions 12 and 13. As a result, the attenuation characteristic on the high frequency side can be made steeper, and thus a better symmetry can be obtained with respect to the attenuation characteristic.

  In the above example, both the input-side tapered IDT electrode portion 12 and the output-side tapered IDT electrode portion 13 are tapered IDT electrode portions, but only one of them may be a tapered IDT electrode portion. Further, the shield electrode 17 may not be disposed, or a grating reflector may be disposed in place of the shield electrode 17. Furthermore, the reflective electrode 16 may not be provided between the bus bars 14a and 14b, or the electrode fingers 15 and the reflective electrode 16 may be thinned out to form thinned electrodes. Furthermore, for example, two electrode fingers 15 may be alternately extended from each of the bus bars 14a and 14b to form split electrodes. Also in these cases, the upper limit value and the lower limit value of the ratios in the expressions (1) and (2) are set appropriately according to each filter, and the same effect can be obtained.

  Further, when the IDT electrode portions 12 and 13 are formed so that the arrangement pattern of the electrode fingers 15 and the reflective electrodes 16 spreads from the one side bus bar 14a (14c) to the other side bus bar 14b (14d), the above example Then, although the electrode finger 15 and the reflective electrode 16 are arranged linearly, they may be arranged in a curved shape or may be arranged in a staircase shape.

DESCRIPTION OF SYMBOLS 11 Piezoelectric substrate 12 Input side taper type IDT electrode part 13 Output side taper type IDT electrode part 14 Bus bar 15 Electrode finger 16 Reflective electrode 31 First extension part 32 Second extension part Tr Track N _H High frequency side logarithm _NL Low Logarithm side f _H High side frequency f _L Low side frequency

Claims (2)

In the acoustic wave filter in which the input-side IDT electrode part and the output-side IDT electrode part are arranged apart from each other in the propagation direction of the elastic wave on the piezoelectric substrate,
A pair of bus bars formed so as to be parallel to each other, and a group of electrode fingers that are alternately extended from each of the pair of bus bars and formed in a comb-teeth shape. The tapered IDT electrode portion formed so that the gap region of the pair extends from one bus bar to the other bus bar of the pair of bus bars constitutes at least one of the input side IDT electrode portion and the output side IDT electrode portion. And
Extending both ends of one bus bar in the tapered IDT electrode portion in a direction in which the bus bar extends;
Extending from both ends of the other bus bar toward the distal end side of the extended portion of the one bus bar to form an extended portion;
Continuously extending an arrangement pattern of electrode fingers formed between the pair of bus bars between the extended portion of the one bus bar and the extended portion of the other bus bar;
The number of electrode fingers in the region closest to the one bus bar is _NH , and the number of electrode fingers in the region closest to the other bus bar is N _L in the region sandwiched between the extension portions of the other bus bar. When the high-frequency side frequency and the low band side frequency pass band of each f _H, and f _L,
An elastic wave filter, wherein 0.96 × (N _L / N _H ) <f _L / f _H <1.04 × (N _L / N _H ). The input-side IDT electrode part and the output-side IDT electrode part are both configured by the tapered IDT electrode part,
The number of pairs of electrode fingers _NH in the region closest to the one bus bar of the input side IDT electrode portion and the portion sandwiched between the extended portions of the other bus bar of the input side IDT electrode portion are the closest to the other bus bar. The number N _{L of the} electrode fingers in the near region is set to N _HI and N _LI , respectively, and the number N _{H of the} electrode fingers in the region closest to the one bus bar of the output-side IDT electrode unit and the output IDT electrode unit When the number N _{L of the} electrode fingers in the region closest to the other bus bar is N _HO and N _{LO in the} region sandwiched between the extension portions of the other bus bar ,
The elastic wave filter according to claim 1, wherein 0.98 × (N _HO / N _LO ) <(N _HI / N _LI ) <1.02 × (N _HO / N _LO ).

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