Acoustic wave filter

Abstract

To secure attenuation characteristics in a band at a higher side than a pass band.SOLUTION: An acoustic wave filter comprises: a series arm connected between an input end and an output end; a plurality of series arm resonators provided in the series arm; a plurality of parallel arms connected between the series arm and a reference potential; and a plurality of parallel arm resonators provided in the plurality of parallel arms. The plurality of parallel arm resonators have the same electrostatic capacitance; inductance between the plurality of parallel arm resonators and the reference potential is 1 nH or less; and the remaining inductance excluding maximum inductance in the inductance is varied equal to or less than 2 / 3 of the maximum inductance.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to acoustic wave filters. [Background technology]

[0002] Conventionally, various surface acoustic wave filters have been proposed, in which a series arm resonator made of a surface acoustic resonator is inserted in a series arm between an input terminal and an output terminal, and a parallel arm resonator made of a surface acoustic resonator is inserted in a parallel arm configured between the series arm and a ground potential. Surface acoustic wave filters having a ladder circuit configuration are suitable for use as bandpass filters because of their low loss and wide band, and are widely used as bandpass filters for mobile phones (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-314372 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional acoustic wave filters, the attenuation characteristics in a band higher than the passband may decrease.

[0005] The present disclosure provides an acoustic wave filter capable of ensuring attenuation characteristics in a band higher than a pass band. [Means for solving the problem]

[0006] The first aspect is a series arm connected between the input end and the output end; a plurality of series arm resonators provided in the series arm; a plurality of parallel arms connected between the series arm and a reference potential; a plurality of parallel arm resonators provided in each of the plurality of parallel arms, the parallel arm resonators have the same capacitance, an inductance between each of the parallel arm resonators and the reference potential is 1 nH or less; In the acoustic wave filter, the remaining inductances excluding the maximum inductance among the respective inductances vary within ⅔ or less of the maximum inductance.

[0007] A second aspect is the acoustic wave filter of the first aspect, The capacitance of each of the parallel arm resonators may be greater than the capacitance of each of the series arm resonators.

[0008] A third aspect is the acoustic wave filter of the first or second aspect, When the capacitance of each of the parallel arm resonators is Cp and the capacitance of each of the series arm resonators is Cs, Cp / Cs may be 2 or more.

[0009] A fourth aspect is the acoustic wave filter of any one of the first to third aspects, The plurality of series arm resonators may have the same capacitance.

[0010] A fifth aspect is an acoustic wave filter according to any one of the first to fourth aspects, The parallel arm resonators include a first parallel arm resonator connected to the input end or the output end; The amplifier may further include a second parallel arm resonator connected between adjacent series arm resonators among the plurality of series arm resonators.

[0011] A sixth aspect is the acoustic wave filter of the fifth aspect, The second parallel arm resonator may include a plurality of parallel arm resonators connected in parallel to each other.

[0012] A seventh aspect is the acoustic wave filter of any one of the first to sixth aspects, The plurality of series arm resonators may include a plurality of series arm resonators connected in series between adjacent parallel arms of the plurality of parallel arms. Effect of the Invention

[0013] The present disclosure can ensure attenuation characteristics in a band higher than the passband. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating an example of a circuit configuration of an acoustic wave filter according to a first embodiment. [Diagram 2] FIG. 13 illustrates an example of a circuit configuration of an acoustic wave filter according to a second embodiment. [Diagram 3] 4 is a diagram illustrating an example of pass characteristics of the acoustic wave filter according to the first embodiment. FIG. [Figure 4] 13 is a diagram illustrating an example of pass characteristics of the acoustic wave filter according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0016] Fig. 1 is a diagram illustrating an example of a circuit configuration of an acoustic wave filter according to a first embodiment. An acoustic wave filter 101 illustrated in Fig. 1 is a bandpass filter having a ladder-type circuit configuration in which a plurality of resonators are connected in a ladder shape. An example of the acoustic wave filter 101 is a SAW (Surface Acoustic Wave) filter.

[0017] The acoustic wave filter 101 includes a series arm 21, a plurality of series arm resonators 31, 32, 33, 34, a plurality of parallel arms 41, 42, 43, 44, and a plurality of parallel arm resonators 51, 52, 53, 54. The series arm 21, the plurality of series arm resonators 31, 32, 33, 34, the plurality of parallel arms 41, 42, 43, 44, and the plurality of parallel arm resonators 51, 52, 53, 54 are formed on, for example, a piezoelectric substrate (not shown).

[0018] The series arm 21 is connected between the input terminal 11 and the output terminal 12. The series arm 21 is a transmission path for a signal from the input terminal 11 to the output terminal 12.

[0019] A plurality of series arm resonators 31, 32, 33, 34 (hereinafter also referred to as "series arm resonators 31, etc.") are provided in the series arm 21. The plurality of series arm resonators 31, etc. are connected in series in the series arm 21 connecting the input terminal 11 and the output terminal 12. The series arm resonator 31 is connected to the input terminal 11. The series arm resonator 34 is connected to the output terminal 12.

[0020] The multiple parallel arms 41, 42, 43, 44 (hereinafter also referred to as "parallel arms 41, etc.") are connected between the series arm 21 and a reference potential 13. The reference potential 13 is, for example, a ground potential. The parallel arm 41 is provided between the reference potential 13 and a connection point between the adjacent series arm resonators 31, 32. The parallel arm 42 is provided between the reference potential 13 and a connection point between the adjacent series arm resonators 32, 33. The parallel arm 43 is provided between the reference potential 13 and a connection point between the adjacent series arm resonators 33, 34. The parallel arm 44 is provided between the reference potential 13 and a connection point between the series arm resonator 34 and the output end 12.

[0021] A plurality of parallel arm resonators 51, 52, 53, 54 (hereinafter also referred to as "parallel arm resonators 51, etc.") are provided in each of the parallel arms 41, 42, 43, 44. The parallel arm resonator 51 is provided in the parallel arm 41, the parallel arm resonator 52 is provided in the parallel arm 42, the parallel arm resonator 53 is provided in the parallel arm 43, and the parallel arm resonator 54 is provided in the parallel arm 44. The parallel arm resonators 51, etc. are formed to have the same electrostatic capacitance.

[0022] The parallel arm resonator 54 is an example of a first parallel arm resonator connected to the output terminal 12. The parallel arm resonators 51, 52, and 53 are each an example of a second parallel arm resonator connected between adjacent series arm resonators of the multiple series arm resonators 31, etc. For example, the parallel arm resonator 51 is connected between the adjacent series arm resonators 31 and 32.

[0023] For example, each of the multiple series arm resonators 31 etc. and the multiple parallel arm resonators 51 etc. has an interdigital transducer (hereinafter, referred to as "IDT") and a pair of reflectors provided on both sides of the IDT. When a SAW excited in both directions from the IDT is reflected by the pair of reflectors, a standing wave of the SAW is formed, and a resonance phenomenon occurs.

[0024] The multiple series arm resonators 31 etc. and the multiple parallel arm resonators 51 etc. are formed so that the anti-resonance frequency of the parallel arm 41 etc. matches the resonance frequency of the series arm 21. This provides filter characteristics in which the passband is near that frequency, the stopband on the lower side of the passband is near the anti-resonance frequency of the series arm 21, and the stopband on the higher side of the passband is near the resonance frequency of the parallel arm 41 etc.

[0025] The plurality of series arm resonators 31 etc. and the plurality of parallel arm resonators 51 etc. have parameters such as capacitance adjusted so that they have a passband in a predetermined frequency band. Examples of the predetermined frequency band include the UHF (Ultra High Frequency) band, the SHF (Super High Frequency) band, and the EHF (Extremely High Frequency) band. A specific example of the predetermined frequency band is Sub-6 at 6 GHz or less. Examples of the Sub-6 band include the n77 band (3300 MHz-4200 MHz), the n78 band (3300 MHz-3800 MHz), and the n79 band (4400 MHz-5000 MHz). The predetermined frequency band is not limited to these bands.

[0026] The acoustic wave filter 101 is formed such that inductances 61, 62, 63, 64 between the parallel arm resonators 51, 52, 53, 54 and the reference potential 13 vary within a range greater than 0 and equal to or less than 1 nH. The inductances 61, 62, 63, 64 are generated by, for example, an inductance component of a bonding wire electrically connecting each of the parallel arm resonators 51, 52, 53, 54 to an electrode pad connected to the reference potential 13.

[0027] The acoustic wave filter 101 is formed so that the remaining inductances 61, 62, 63, and 64, excluding the maximum inductance, vary within ⅔ or less of the maximum inductance. In the example shown in Fig. 1, when the inductance 61 is at its maximum value, the remaining inductances 62, 63, and 64 are adjusted to vary within a range greater than 0 and ⅔ or less of the inductance 61.

[0028] The inductance that takes the maximum value is not limited to the inductance 61 provided in the parallel arm 41 having the smallest number of series arm resonators between it and the input terminal 11, but may be any one of the other inductances 62, 63, and 64. Furthermore, the inductance that takes the maximum value is literally only one of the multiple inductances 61, 62, 63, and 64.

[0029] In addition, "varying within 2 / 3 or less of the maximum inductance" does not necessarily mean that the remaining inductances, excluding the maximum inductance, are all different, and may include the same value. For example, when inductance 61 is the maximum, if inductances 62, 63, and 64 are 2 / 3 or less of inductance 61, inductance 62 has a different value from inductances 63 and 64, but inductances 63 and 64 may have the same value.

[0030] The acoustic wave filter 101 has electrical characteristics in which the parallel arm resonators 51 etc. have the same capacitance, the inductances 61, 62, 63, and 64 are 1 nH or less, and the remaining inductances excluding the maximum inductance among the inductances vary within ⅔ or less of the maximum inductance. By having such electrical characteristics, the acoustic wave filter 101 can ensure attenuation characteristics in a band higher than the pass band.

[0031] The attenuation in the stop band having a higher frequency than the pass band is more susceptible to the influence of the inductance 61 and the like than the attenuation in the stop band having a lower frequency than the pass band. Therefore, by providing an inductance having a maximum value among the multiple inductances 61, 62, 63, and 64, a significant attenuation pole is formed in a band having a higher frequency than the pass band, and the attenuation in the stop band having a higher frequency than the pass band can be ensured. The remaining inductances excluding the maximum inductance among the multiple inductances 61, 62, 63, and 64 vary within ⅔ or less of the maximum inductance, so that the attenuation on the higher frequency side than the attenuation pole is stabilized. Therefore, by having the above-mentioned electrical characteristics, the acoustic wave filter 101 can ensure the attenuation characteristics in the band higher than the pass band.

[0032] When the capacitance Cp of each of the parallel arm resonators 51 etc. is larger than the capacitance Cs of each of the series arm resonators 31 etc., the attenuation in the stopbands on the high frequency side and the low frequency side of the passband in the acoustic wave filter 101 can be increased.

[0033] The overall attenuation of the acoustic wave filter 101 is determined by the ratio of the capacitance Cp of each of the parallel arm resonators 51, etc. to the capacitance Cs of each of the series arm resonators 31, etc. The larger Cp / Cs is, the greater the attenuation is. For example, when Cp / Cs is 2 or more, the attenuation in the stopband with a higher frequency than the passband and the attenuation in the stopband with a lower frequency than the passband are increased. There is no particular upper limit to Cp / Cs, but in order to prevent the acoustic wave filter 101 from becoming large, Cp / Cs is, for example, 10 or less.

[0034] The series arm resonators 31, 32, 33, and 34 have the same capacitance, but may have different capacitances in order to finely adjust the attenuation characteristics of the acoustic wave filter 101.

[0035] Fig. 2 is a diagram showing an example of a circuit configuration of an acoustic wave filter according to a second embodiment. In the second embodiment, the description of the configuration, operation, and effects similar to those of the first embodiment will be omitted by incorporating the above description. An acoustic wave filter 102 shown in Fig. 2 is a bandpass filter having a ladder circuit configuration in which a plurality of resonators are connected in a ladder shape.

[0036] The acoustic wave filter 102 includes a series arm 21, a plurality of series arm resonators 31, 32, and 33, a plurality of parallel arms 41, 42, 43, and 44, and a plurality of parallel arm resonators 51, 52, 53, and .

[0037] A plurality of series arm resonators 31, 32, and 33 (hereinafter also referred to as "series arm resonators 31, etc.") are provided in the series arm 21. The plurality of series arm resonators 31, etc. are connected in series in the series arm 21 connecting between the input terminal 11 and the output terminal 12. The series arm resonator 31 is connected to the input terminal 11. The series arm resonator 33 is connected to the output terminal 12.

[0038] The multiple series arm resonators 31 etc. include multiple series arm resonators connected in series between adjacent parallel arms of the multiple parallel arms 41 etc. The series arm resonator 31 includes multiple series arm resonators 31a, 31b connected in series between adjacent parallel arms 41, 42. The series arm resonator 32 includes multiple series arm resonators 32a, 32b connected in series between adjacent parallel arms 42, 43. The series arm resonator 33 includes multiple series arm resonators 33a, 33b connected in series between adjacent parallel arms 43, 44.

[0039] The multiple parallel arms 41, 42, 43, 44 (hereinafter also referred to as "parallel arms 41, etc.") are connected between the series arm 21 and a reference potential 13. The reference potential 13 is, for example, a ground potential. The parallel arm 41 is provided between the reference potential 13 and a connection point between the input end 11 and the series arm resonator 31. The parallel arm 42 is provided between the reference potential 13 and a connection point between the adjacent series arm resonators 31, 32. The parallel arm 43 is provided between the reference potential 13 and a connection point between the adjacent series arm resonators 32, 33. The parallel arm 44 is provided between the reference potential 13 and a connection point between the series arm resonator 33 and the output end 12.

[0040] The parallel arm resonators 51 and 54 are an example of a first parallel arm resonator connected to the input terminal 11 or the output terminal 12. The parallel arm resonator 51 is connected to the input terminal 11. The parallel arm resonator 54 is connected to the output terminal 12. The parallel arm resonators 52 and 53 are each an example of a second parallel arm resonator connected between adjacent series arm resonators of the multiple series arm resonators 31, etc. For example, the parallel arm resonator 52 is connected between adjacent series arm resonators 31 and 32.

[0041] The parallel arm resonator 52 includes a plurality of parallel arm resonators 52a and 52b connected in parallel to each other. The parallel arm resonator 53 includes a plurality of parallel arm resonators 53a and 53b connected in parallel to each other.

[0042] The multiple parallel arm resonators 51, 52a, 52b, 53a, 53b, and 54 (hereinafter also referred to as "parallel arm resonators 51, etc.") are formed to have the same electrostatic capacitance.

[0043] The acoustic wave filter 102 has electrical characteristics in which the parallel arm resonators 51 etc. have the same capacitance, the inductances 61, 62, 63, 64 are 1 nH or less, and the remaining inductances excluding the maximum inductance among the inductances vary within ⅔ or less of the maximum inductance. By having such electrical characteristics, the acoustic wave filter 102 can ensure attenuation characteristics in a band higher than the pass band.

[0044] 3 is a diagram showing an example of the pass characteristic of the acoustic wave filter according to the first embodiment. Pass characteristic 101a shows a case where inductances 61, 62, 63, and 64 are all set to 0 nH in the configuration of FIG. 1 (Comparative Example 1). Pass characteristic 101b shows a case where inductances 61, 62, 63, and 64 are all set to 0.7 nH in the configuration of FIG. 1 (Comparative Example 2). Pass characteristic 101c shows a case where one of inductances 61, 62, 63, and 64 in the configuration of FIG. 1 is set to 0.7 nH and the remaining three inductances are varied around 0.3 nH (0.25 nH, 0.3 nH, and 0.35 nH) (Example 1). Pass characteristic 101d shows a case where, in the configuration of Fig. 1, two of inductances 61, 62, 63, and 64 are varied around 0.7 nH (0.68 nH, 0.72 nH) and the remaining two inductances are varied around 0.3 nH (Comparative Example 3). Pass characteristic 101e shows a case where, in the configuration of Fig. 1, one of inductances 61, 62, 63, and 64 is set to 1.2 nH and the remaining three inductances are varied around 0.3 nH (0.25 nH, 0.3 nH, 0.35 nH) (Comparative Example 4).

[0045] 1 of Comparative Examples 1 to 4 and Example 1, the parameters such as capacitance of the multiple series arm resonators 31 etc. and the multiple parallel arm resonators 51 etc. are adjusted so that they have a passband of 4800 MHz to 4900 MHz included in the n79 band. Specifically, the capacitance Cs of each of the series arm resonators 31 etc. is 4.64×10 -13 F, and the capacitance Cp of each of the parallel arm resonators 51, etc. is set to 9.28×10 -13 It is set to F.

[0046] Pass characteristic 101c (first embodiment) indicates that the acoustic wave filter 101 has electrical characteristics in which multiple parallel arm resonators 51 etc. have the same capacitance, inductances 61, 62, 63, and 64 are 1 nH or less, and the remaining inductances excluding the maximum inductance among the inductances vary within 2 / 3 or less of the maximum inductance.

[0047] In the case of the pass characteristic 101c (Example 1), an attenuation pole is formed in the stopband on the high frequency side of the passband. In addition, in the case of the pass characteristic 101c (Example 1), the attenuation amount on the high frequency side of the attenuation pole is stabilized compared to the pass characteristic 101b (Comparative Example 2), the pass characteristic 101d (Comparative Example 3), and the pass characteristic 101e (Comparative Example 4). In particular, in the pass characteristic 101d (Comparative Example 3) in which the two inductances vary around 0.7 nH, the remaining inductances excluding the maximum inductance include values ​​exceeding 2 / 3 of the maximum inductance, so that the attenuation amount on the high frequency side of the attenuation pole is reduced.

[0048] 4 is a diagram showing an example of the pass characteristic of the elastic wave filter according to the second embodiment. Pass characteristic 102a shows a case where inductances 61, 62, 63, and 64 are all set to 0 nH in the configuration of FIG. 2 (Comparative Example 5). Pass characteristic 102b shows a case where inductances 61, 62, 63, and 64 are all set to 0.55 nH in the configuration of FIG. 2 (Comparative Example 6). Pass characteristic 102c shows a case where one of inductances 61, 62, 63, and 64 in the configuration of FIG. 2 is set to 0.55 nH and the remaining three inductances are varied around 0.3 nH (0.25 nH, 0.3 nH, and 0.35 nH) (Example 2). Pass characteristic 102d shows a case where, in the configuration of Fig. 2, two of inductances 61, 62, 63, and 64 are varied around 0.55 nH (0.53 nH, 0.57 nH) and the remaining two inductances are varied around 0.3 nH (Comparative Example 7). Pass characteristic 102e shows a case where, in the configuration of Fig. 2, one of inductances 61, 62, 63, and 64 is set to 1.2 nH and the remaining three inductances are varied around 0.3 nH (0.25 nH, 0.3 nH, 0.35 nH) (Comparative Example 8).

[0049] 2 of Comparative Examples 5 to 8 and Example 2, the parameters such as capacitance of the multiple series arm resonators 31 etc. and the multiple parallel arm resonators 51 etc. are adjusted so that they have a passband of 4800 MHz to 4900 MHz included in the n79 band. Specifically, the capacitance Cs of each of the series arm resonators 31a, 31b, 32a, 32b, 33a, and 33b is 6.56×10 -13 F, and the capacitance Cp of each of the parallel arm resonators 51, 52a, 52b, 53a, 53b, and 54 is set to 6.56×10 -13 F. In other words, the combined capacitance of each of the series arm resonators 31, 32, and 33 is set to 3.28×10 -13 F, and the combined capacitance of each of the parallel arm resonators 52 and 53 is set to 13.12×10 -13 It is set to F.

[0050] Pass characteristic 102c (Example 2) indicates that the acoustic wave filter 102 has electrical characteristics in which the parallel arm resonators 51 etc. have the same capacitance, the inductances 61, 62, 63, and 64 are 1 nH or less, and the remaining inductances excluding the maximum inductance among the inductances vary within 2 / 3 or less of the maximum inductance.

[0051] In the case of the pass characteristic 102c (Example 2), an attenuation pole is formed in the stopband on the high frequency side of the passband. In addition, in the case of the pass characteristic 102c (Example 2), the attenuation amount on the high frequency side of the attenuation pole is stabilized compared with the pass characteristic 102b (Comparative Example 6), the pass characteristic 102d (Comparative Example 7), and the pass characteristic 102e (Comparative Example 8). In particular, in the pass characteristic 102d (Comparative Example 7) in which the two inductances vary around 0.7 nH, the remaining inductances excluding the maximum inductance include values ​​exceeding 2 / 3 of the maximum inductance, so that the attenuation amount on the high frequency side of the attenuation pole is reduced.

[0052] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0053] For example, the acoustic wave filter is not limited to a SAW filter, and may be a filter having another structure, such as a BAW (Bulk Acoustic Wave) filter.

[0054] Furthermore, the number of series arm resonators connected in series between the input terminal 11 and the output terminal 12 is not limited to three or four and may be two or more. The number of parallel arms is not limited to four and may be three or more. For example, in the configuration shown in Fig. 1, the series arm resonators 31 and 32, the parallel arm 41, the parallel arm resonator 51, and the inductance 61 may be deleted. For example, in the configuration shown in Fig. 1, the series arm resonator 31, the parallel arm 41, the parallel arm resonator 51, and the inductance 61 may be deleted, and the series arm resonator 34, the parallel arm 44, the parallel arm resonator 54, and the inductance 64 may be deleted. [Explanation of symbols]

[0055] 11 Input terminal 12 Output terminal 13 Reference potential 21 Series Arm 31, 32, 33, 34 Series arm resonators 41, 42, 43, 44 Parallel arms 51, 52, 53, 54 Parallel arm resonators 61, 62, 63, 64 Inductance 101,102 Elastic wave filters

Claims

1. a series arm connected between the input end and the output end; a plurality of series arm resonators provided in the series arm; a plurality of parallel arms connected between the series arm and a reference potential; a plurality of parallel arm resonators provided in each of the plurality of parallel arms, the parallel arm resonators have the same capacitance, an inductance between each of the parallel arm resonators and the reference potential is 1 nH or less; An elastic wave filter, wherein the remaining inductances excluding a maximum inductance among the respective inductances vary within 2 / 3 or less of the maximum inductance.

2. The acoustic wave filter according to claim 1 , wherein a capacitance of each of the parallel arm resonators is greater than a capacitance of each of the series arm resonators.

3. When the capacitance of each of the parallel arm resonators is Cp and the capacitance of each of the series arm resonators is Cs, The acoustic wave filter according to claim 2 , wherein Cp / Cs is 2 or greater.

4. The acoustic wave filter according to claim 3 , wherein the plurality of series arm resonators have the same capacitance.

5. The parallel arm resonators include a first parallel arm resonator connected to the input end or the output end; The acoustic wave filter according to claim 1 , further comprising: a second parallel arm resonator connected between adjacent series arm resonators among the plurality of series arm resonators.

6. The acoustic wave filter according to claim 5 , wherein the second parallel arm resonator includes a plurality of parallel arm resonators connected in parallel to each other.

7. The acoustic wave filter according to claim 6 , wherein the plurality of series arm resonators include a plurality of series arm resonators connected in series between adjacent parallel arms of the plurality of parallel arms.

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