Filter and filtering equipment

Abstract

The invention discloses a filter and filtering equipment, and is applied to the technical field of filtering, and surface acoustic wave resonators comprise a first surface acoustic wave resonator with the resonant frequency located at the low and medium frequency side of a passband and a second surface acoustic wave resonator with the resonant frequency located at the high and medium frequency side of the passband; the first surface acoustic wave resonator comprises a first interdigital electrode arranged on the surface of the substrate, and the second surface acoustic wave resonator comprises a second interdigital electrode arranged on the surface of the substrate; the first interdigital electrode has a first preset included angle, so that the insertion loss of the first surface acoustic wave resonator on the low-frequency side in a passband is smaller than that of the second surface acoustic wave resonator; and the second interdigital electrode has a second preset included angle, so that the insertion loss of the second surface acoustic wave resonator on the high-frequency side in the passband is smaller than that of the first surface acoustic wave resonator. The filter has relatively low insertion loss by pertinently optimizing the insertion loss of the surface acoustic wave resonators of which the resonant frequencies are positioned on different sides of the passband.

Description

Technical Field

[0001] The present invention relates to the field of filtering technology, and in particular to a filter and a filtering device. Background Art

[0002] Modern RF filters are generally based on the technical principles of surface acoustic waves or bulk acoustic waves, using a ladder or hybrid (ladder + coupled mode) architecture, and both architectures require the use of multiple series resonators or parallel resonator combinations. Generally speaking, the resonant frequency of the parallel resonator is located on the low- to medium-frequency side of the passband; the resonant frequency of the series resonator is located on the high- to medium-frequency side of the passband.

[0003] The resonator based on surface acoustic wave technology uses interdigital electrodes and reflective gratings to form a high-efficiency transducer. Usually, in order to obtain the maximum electromechanical coupling coefficient, the interdigital electrodes of the surface acoustic wave resonator are arranged perpendicular to the flat edge of the wafer.

[0004] In the prior art, the finger electrodes of all resonators are arranged in the same direction, and are generally arranged perpendicular to the flat edge of the wafer. At this time, the resonator can obtain the maximum electromechanical coupling coefficient, making it easy to realize a filter with a relatively large bandwidth. Although the resonator has obtained the maximum electromechanical coupling coefficient at this time, it is difficult to ensure that the Q value of the resonator in the effective range is very high, so the insertion loss of the designed filter is too large and difficult to meet the requirements. Therefore, how to provide a low insertion loss filter is an urgent problem that technicians in this field need to solve. Summary of the invention

[0005] An object of the present invention is to provide a filter with lower insertion loss; another object of the present invention is to provide a filtering device with lower insertion loss.

[0006] In order to solve the above technical problems, the present invention provides a filter, comprising a substrate, and a plurality of surface acoustic wave resonators formed based on interdigital electrodes arranged on the surface of the substrate;

[0007] The surface acoustic wave resonator comprises a first surface acoustic wave resonator having a resonance frequency located at the low-frequency side of the passband, and a second surface acoustic wave resonator having a resonance frequency located at the high-frequency side of the passband; the first surface acoustic wave resonator comprises a first interdigital electrode arranged on the surface of the substrate, and the second surface acoustic wave resonator comprises a second interdigital electrode arranged on the surface of the substrate;

[0008] The arrangement direction of the first interdigitated electrodes has a first preset angle with a direction perpendicular to the flat edge direction of the wafer used for the substrate, so that the insertion loss of the first surface acoustic wave resonator on the low-frequency side of the passband is smaller than that of the second surface acoustic wave resonator; the arrangement direction of the second interdigitated electrodes has a second preset angle with a direction perpendicular to the flat edge direction of the wafer used for the substrate, so that the insertion loss of the second surface acoustic wave resonator on the high-frequency side of the passband is smaller than that of the first surface acoustic wave resonator.

[0009] Optionally, the first surface acoustic wave resonator includes parallel resonators connected in parallel in the surface acoustic wave resonator.

[0010] Optionally, the plurality of parallel resonators in the first surface acoustic wave resonator have at least two different first preset angles.

[0011] Optionally, the second surface acoustic wave resonator includes a series resonator connected in series in the surface acoustic wave resonator.

[0012] Optionally, the plurality of series resonators in the second surface acoustic wave resonator have at least two different second preset angles.

[0013] Optionally, the first surface acoustic wave resonator further includes a first preset number of series resonators connected in series among the surface acoustic wave resonators; the second surface acoustic wave resonator includes a second preset number of series resonators connected in series among the surface acoustic wave resonators; the first preset number is less than the second preset number.

[0014] Optionally, the forked electrodes in the surface acoustic wave resonator are rotated clockwise relative to a direction perpendicular to the flat edge of the wafer used for the substrate to form the first surface acoustic wave resonator and the second surface acoustic wave resonator; or the forked electrodes in the surface acoustic wave resonator are rotated counterclockwise relative to a direction perpendicular to the flat edge of the wafer used for the substrate to form the first surface acoustic wave resonator and the second surface acoustic wave resonator.

[0015] Optionally, reflection gratings are provided at both ends of the interdigital electrodes along the arrangement direction of the interdigital electrodes.

[0016] Optionally, the angle value range of the first preset angle and the angle value range of the second preset angle do not exceed 20°.

[0017] Optionally, the first preset angle has an angle range of 0° to 6°, including the right endpoint value.

[0018] Optionally, the second preset angle has an angle range of 2° to 8°, including endpoint values.

[0019] Optionally, the substrate is a POI substrate.

[0020] Optionally, the thickness of the piezoelectric layer of the POI substrate is less than 1λ, where λ is the period length of the interdigital electrodes.

[0021] The present invention also provides a filtering device, comprising the filter as described in any one of the above items.

[0022] A filter provided by the present invention comprises a substrate, and a plurality of surface acoustic wave resonators formed based on interdigital electrodes arranged on the surface of the substrate; the surface acoustic wave resonators comprise a first surface acoustic wave resonator having a resonance frequency located at a low-frequency side of a passband, and a second surface acoustic wave resonator having a resonance frequency located at a high-frequency side of the passband; the first surface acoustic wave resonator comprises a first interdigital electrode arranged on the surface of the substrate, and the second surface acoustic wave resonator comprises a second interdigital electrode arranged on the surface of the substrate; the arrangement direction of the first interdigital electrode has a first preset angle with a direction perpendicular to a flat edge direction of a wafer used for the substrate, so that the insertion loss of the first surface acoustic wave resonator on the low-frequency side of the passband is smaller than that of the second surface acoustic wave resonator; the arrangement direction of the second interdigital electrode has a second preset angle with a direction perpendicular to a flat edge direction of a wafer used for the substrate, so that the insertion loss of the second surface acoustic wave resonator on the high-frequency side of the passband is smaller than that of the first surface acoustic wave resonator.

[0023] By making the arrangement direction of the forked electrodes in the surface acoustic wave resonator form a preset angle with the perpendicular direction of the flat edge direction of the wafer used for the substrate, the burrs in the real part characteristic curve of the admittance of the resonator can be effectively reduced, and the steepness near the passband of the resonator can be improved to increase the quality factor of the resonator; at the same time, by making the first surface acoustic wave resonator with a resonant frequency located on the low-frequency side of the passband and the second surface acoustic wave resonator with a resonant frequency located on the high-frequency side of the passband deflect at different angles, the insertion loss of the surface acoustic wave resonators with resonant frequencies located on different sides of the passband is optimized in a targeted manner, thereby effectively reducing the overall insertion loss of the filter, so that the filter has a lower insertion loss.

[0024] The present invention also provides a filtering device, which also has the above-mentioned beneficial effects and will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a structural schematic diagram of a filter in the prior art;

[0027] Figure 2 A schematic diagram of the structure of a filter provided by an embodiment of the present invention;

[0028] Figure 3 A schematic diagram of the structure of another filter provided by an embodiment of the present invention;

[0029] Figure 4 The real part characteristic curve of the admittance of the resonator at different transposition angles;

[0030] Figure 5 Q characteristic curves of the resonator at different transposition angles;

[0031] Figure 6 Insertion loss characteristic curve of the filter formed by different transposition angles;

[0032] Figure 7 It is the Q value curve of the conventional SAW device;

[0033] Figure 8 It is the Q value curve of POI-SAW device;

[0034] Fig. 9 is the lateral dispersion curve of the POI-SAW device when it is not rotating;

[0035] Fig.10 This is the lateral dispersion curve of the POI-SAW device when it is rotated 4°;

[0036] Fig.11 This is the lateral dispersion curve of the POI-SAW device when rotated 8°.

[0037] In the figure: 1. substrate, 2. transducer, 21. interdigitated electrodes, 22. reflection grating. DETAILED DESCRIPTION

[0038] The core of the present invention is to provide a filter. Figure 1 , Figure 1 Schematic diagram of the structure of the filter in the prior art. Figure 1 In the prior art, the arrangement direction of the interdigital electrodes 21 of all resonators is the same, and the arrangement direction of the interdigital electrodes 21 of the resonator is generally perpendicular to the flat edge direction of the wafer. At this time, the resonator can obtain the maximum electromechanical coupling coefficient, so it is easy to realize a filter with a relatively large bandwidth. At this time, although the resonator obtains the maximum electromechanical coupling coefficient, it is difficult to ensure that the Q value of the resonator in the effective range is very high, so the insertion loss of the designed filter is relatively large and difficult to meet the requirements.

[0039] The filter provided by the present invention comprises a substrate, and a plurality of surface acoustic wave resonators formed based on interdigital electrodes arranged on the surface of the substrate; the surface acoustic wave resonators comprise a first surface acoustic wave resonator having a resonance frequency located on the low-frequency side of a passband, and a second surface acoustic wave resonator having a resonance frequency located on the high-frequency side of the passband; the first surface acoustic wave resonator comprises a first interdigital electrode arranged on the surface of the substrate, and the second surface acoustic wave resonator comprises a second interdigital electrode arranged on the surface of the substrate; the arrangement direction of the first interdigital electrodes has a first preset angle with a direction perpendicular to the flat edge direction of a wafer used for the substrate, so that the insertion loss of the first surface acoustic wave resonator on the low-frequency side of the passband is smaller than that of the second surface acoustic wave resonator; the arrangement direction of the second interdigital electrodes has a second preset angle with a direction perpendicular to the flat edge direction of the wafer used for the substrate, so that the insertion loss of the second surface acoustic wave resonator on the high-frequency side of the passband is smaller than that of the first surface acoustic wave resonator.

[0040] By making the arrangement direction of the forked electrodes in the surface acoustic wave resonator form a preset angle with the perpendicular direction of the flat edge direction of the wafer used for the substrate, the burrs in the real part characteristic curve of the admittance of the resonator can be effectively reduced, and the steepness near the passband of the resonator can be improved to increase the quality factor of the resonator; at the same time, by making the first surface acoustic wave resonator with a resonant frequency located on the low-frequency side of the passband and the second surface acoustic wave resonator with a resonant frequency located on the high-frequency side of the passband deflect at different angles, the insertion loss of the surface acoustic wave resonators with resonant frequencies located on different sides of the passband is optimized in a targeted manner, thereby effectively reducing the overall insertion loss of the filter, so that the filter has a lower insertion loss.

[0041] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] Please refer to Figure 2 as well as Figure 3 , Figure 2 A schematic diagram of the structure of a filter provided by an embodiment of the present invention, Figure 3 A schematic diagram of the structure of another filter provided by an embodiment of the present invention.

[0043] See also Figure 2 as well as Figure 3In an embodiment of the present invention, a filter includes a substrate 1, and a plurality of surface acoustic wave resonators formed based on interdigital electrodes 21 arranged on the surface of the substrate 1; the surface acoustic wave resonator includes a first surface acoustic wave resonator having a resonance frequency located at a low-frequency side of a passband, and a second surface acoustic wave resonator having a resonance frequency located at a high-frequency side of the passband; the first surface acoustic wave resonator includes a first interdigital electrode arranged on the surface of the substrate 1, and the second surface acoustic wave resonator includes a second interdigital electrode arranged on the surface of the substrate 1; the arrangement direction of the first interdigital electrode has a first preset angle with a direction perpendicular to the flat edge direction of a wafer used for the substrate 1, so that the insertion loss of the first surface acoustic wave resonator on the low-frequency side of the passband is smaller than that of the second surface acoustic wave resonator; the arrangement direction of the second interdigital electrode has a second preset angle with a direction perpendicular to the flat edge direction of the wafer used for the substrate 1, so that the insertion loss of the second surface acoustic wave resonator on the high-frequency side of the passband is smaller than that of the first surface acoustic wave resonator.

[0044] The above-mentioned substrate 1 is a substrate 1 used for preparing the filter, and the material of the substrate 1 is usually the same as the material of the wafer used for preparing the functional chip including the filter. Since the wafer usually has a flat edge, the corresponding substrate 1 usually has a flat edge direction, that is, the direction represented by the flat edge and its extension line. In this embodiment, when the arrangement direction of the forked electrode 21 in the surface acoustic wave resonator is perpendicular to the flat edge direction of the substrate 1, it can have the maximum electromechanical coupling coefficient, but at this time the steepness on both sides of the passband and the smoothness of the real part of the admittance characteristic curve are insufficient, and the insertion loss and quality factor of the entire resonator are insufficient. The specific material of the above-mentioned substrate 1 can be set according to the actual situation, and is not specifically limited here.

[0045] The surface of the substrate 1 is provided with interdigital electrodes 21 as transducers 2, thereby forming a surface acoustic wave resonator. In this step, a total of multiple surface acoustic wave resonators are provided. In this embodiment, the surface acoustic wave resonator is specifically divided into a first surface acoustic wave resonator and a second surface acoustic wave resonator, wherein the resonant frequency of the first surface acoustic wave resonator is located on the medium and low frequency side of the passband, and the resonant frequency of the second surface acoustic wave resonator is located on the medium and high frequency side of the passband. The difference in the corresponding resonant frequency of the first surface acoustic wave resonator and the second surface acoustic wave resonator can be caused by the difference in the structure of the surface acoustic wave resonator itself, or it can be caused by the connection relationship between the surface acoustic wave resonators. It can be set according to actual conditions and is not specifically limited here. In this embodiment, the interdigital electrodes 21 of the first surface acoustic wave resonator are specifically first interdigital electrodes, and the interdigital electrodes 21 of the second surface acoustic wave resonator are specifically second interdigital electrodes. The first interdigital electrodes and the second interdigital electrodes are both arranged on the surface of the substrate 1.

[0046] The arrangement direction of the first interdigitated electrodes, i.e., the propagation direction of the surface acoustic wave in the first surface acoustic wave resonator, has a first preset angle with the perpendicular direction of the flat edge direction of the wafer used for substrate 1, i.e., the arrangement direction of the first interdigitated electrodes is not perpendicular to the flat edge direction of the wafer used for substrate 1; at the same time, the arrangement direction of the second interdigitated electrodes, i.e., the propagation direction of the surface acoustic wave in the second surface acoustic wave resonator, has a second preset angle with the perpendicular direction of the flat edge direction of the wafer used for substrate 1, i.e., the arrangement direction of the second interdigitated electrodes is also not perpendicular to the flat edge direction of the wafer used for substrate 1. The first preset angle of deflection and the second preset angle will make the insertion loss of the first surface acoustic wave resonator on the low-frequency side of the passband smaller than the insertion loss of the second surface acoustic wave resonator on the low-frequency side of the passband; at the same time, the insertion loss of the second surface acoustic wave resonator on the high-frequency side of the passband will be smaller than the insertion loss of the first surface acoustic wave resonator on the low-frequency side of the passband. Since the resonant frequency of the first surface acoustic wave resonator is located on the low-frequency side of the passband, and the resonant frequency of the second surface acoustic wave resonator is located on the high-frequency side of the passband, the above-mentioned deflection angle can specifically reduce the insertion loss of each surface acoustic wave resonator, thereby reducing the insertion loss of the filter as a whole and improving the quality factor of the filter.

[0047] In this embodiment, the interdigitated electrodes 21 in the surface acoustic wave resonator are rotated clockwise relative to the direction perpendicular to the flat edge direction of the wafer used for the substrate 1 to form the first surface acoustic wave resonator and the second surface acoustic wave resonator; or the interdigitated electrodes 21 in the surface acoustic wave resonator are rotated counterclockwise relative to the direction perpendicular to the flat edge direction of the wafer used for the substrate 1 to form the first surface acoustic wave resonator and the second surface acoustic wave resonator.

[0048] That is, the deflection of the first surface acoustic wave resonator and the second surface acoustic wave resonator in this embodiment can be obtained by deflecting the conventional surface acoustic wave resonator in a clockwise direction relative to the direction of the wafer flat edge used by the substrate 1, or can be obtained by deflecting the conventional surface acoustic wave resonator in a counterclockwise direction relative to the direction of the wafer flat edge used by the substrate 1. The above deflection direction is not specifically limited in the embodiment of the present invention, depending on the specific situation. Of course, in this embodiment, part of the surface acoustic wave resonator can be obtained by rotating clockwise, and the other part of the surface acoustic wave resonator can be obtained by rotating counterclockwise, that is, in this embodiment, the specific direction of the arrangement direction of the interdigital electrodes 21 in the first surface acoustic wave resonator and the second surface acoustic wave resonator is not specifically limited, depending on the specific situation.

[0049] In this embodiment, reflection gratings 22 are provided at both ends of the interdigital electrodes 21 along the arrangement direction of the interdigital electrodes 21. That is, in this embodiment, the transducer 2 of the surface acoustic wave resonator can be specifically formed by two reflection gratings 22 arranged along a preset direction, and the interdigital electrodes 21 located between the reflection gratings 22. The reflection gratings 22 are provided at both ends along the arrangement direction of the interdigital electrodes 21, and the reflection gratings 22 are specifically provided on the propagation path of the surface acoustic wave, so that the quality factor of the surface acoustic wave resonator can be effectively improved. The specific structure of the reflection grating 22 can refer to the prior art, and will not be repeated here.

[0050] In this embodiment, the angle value range of the first preset angle and the angle value range of the second preset angle are usually no more than 20°, so as to ensure that the surface acoustic wave resonator has an electromechanical coupling coefficient that meets the requirements.

[0051] A filter provided by an embodiment of the present invention can effectively reduce the burrs in the real part characteristic curve of the admittance of the resonator and improve the steepness near the passband of the resonator to increase the quality factor of the resonator by making the arrangement direction of the interdigitated electrodes 21 in the surface acoustic wave resonator form a preset angle with the perpendicular direction of the flat edge direction of the wafer used for the substrate 1; at the same time, by making the first surface acoustic wave resonator with a resonance frequency located on the low-frequency side of the passband and the second surface acoustic wave resonator with a resonance frequency located on the high-frequency side of the passband deflect at different angles, the insertion loss of the surface acoustic wave resonators with resonance frequencies located on different sides of the passband is targetedly optimized, thereby effectively reducing the overall insertion loss of the filter, so that the filter has a lower insertion loss.

[0052] The specific structure of a filter provided by the present invention will be described in detail in the following embodiments of the invention.

[0053] Please refer to Figures 4 to 6 , Figure 4 The real part characteristic curve of the admittance of the resonator at different transposition angles; Figure 5 Q characteristic curves of the resonator at different transposition angles; Figure 6 Insertion loss characteristic curve of the filter formed with different transposition angles.

[0054] Different from the above-mentioned invention embodiment, the embodiment of the present invention further defines the structure of the filter on the basis of the above-mentioned invention embodiment. The rest of the contents have been described in detail in the above-mentioned invention embodiment and will not be repeated here.

[0055] In this embodiment, the angle range of the first preset angle is 0° to 6°, including the right endpoint value. The angle range of the second preset angle is 2° to 8°, including the endpoint value. In this embodiment, for the surface acoustic wave resonator of the same structure, the angle of the second preset angle is usually greater than the angle of the first preset angle, that is, when the surface acoustic wave resonator is deflected, as the disk rotation angle increases, the performance of the resonator on the low-frequency side of the passband will be optimized first, and then the performance of the resonator on the high-frequency side of the passband will be optimized. According to the different structures of the surface wave resonator, the corresponding passbands are different, and the first preset angle and the second preset angle corresponding to the surface wave resonator of different types of structures will also be different. However, in general, in this embodiment, the angle range of the first preset angle is usually 0° to 6°, including the right endpoint value; and the angle range of the second preset angle is usually 2° to 8°, including the endpoint value, so as to achieve the purpose of optimizing the insertion loss of the surface acoustic wave resonator with a resonant frequency on different sides of the passband, thereby effectively reducing the insertion loss of the filter as a whole, so that the filter has a lower insertion loss effect.

[0056] For details, please refer to Figures 4 to 6 , Figures 4 to 6 The SAW resonator corresponding to the dashed line is a SAW resonator whose angle between the SAW resonator arrangement wind direction and the direction perpendicular to the wafer flat edge used by the substrate 1 is 4°; the SAW resonator corresponding to the solid line is a SAW resonator whose angle between the SAW resonator arrangement wind direction and the direction perpendicular to the wafer flat edge used by the substrate 1 is 6°. Figure 4 The dashed line in the middle is the real part of the admittance characteristic of the SAW resonator when the counterclockwise transposition angle is 4°, and the solid line is the real part of the admittance characteristic of the SAW resonator when the counterclockwise transposition angle is 6°. It can be seen that in the admittance characteristic between the resonant frequency (fs) and the upper edge of the stopband, the characteristics of the SAW resonator corresponding to 6° are obviously better than those corresponding to 4°. At some frequency points below the resonant frequency, the characteristics of the SAW resonator corresponding to 4° are better than those corresponding to 6°.

[0057] Figure 5 is the Q characteristic curve of different transposition angles. Figure 5 It can also be seen that the Q characteristics between the resonant frequency and the upper edge of the stopband, the characteristics of the SAW resonator corresponding to 6° are obviously better than those corresponding to 4°. And at some frequency points below the resonant frequency, the characteristics of the SAW resonator corresponding to 4° are better than those corresponding to 6°.

[0058] Figure 6The insertion loss comparison chart of filter characteristics designed for different transposition angles. The dotted line is the insertion loss of the surface acoustic wave device when the counterclockwise transposition angle is 4°, and the solid line is the insertion loss of the surface acoustic wave device when the counterclockwise transposition angle is 6°. It can be clearly seen that on the right side of the passband, the solid line is significantly better than the dotted line. On the left side of the passband, the dotted line is better than the solid line at some frequency points.

[0059] In an embodiment of the present invention, the first surface acoustic wave resonator includes parallel resonators connected in parallel in the surface acoustic wave resonator.

[0060] In this embodiment, a plurality of surface acoustic wave resonators are connected in parallel or in series, that is, the architecture adopted by the current filter usually needs to be implemented by a combination of multiple series resonators or parallel resonators. Generally speaking, the resonant frequency of the parallel resonator is located on the medium and low frequency side of the passband; the resonant frequency of the series resonator is located on the medium and high frequency side of the passband. Therefore, in this embodiment, the first surface acoustic wave resonator includes the parallel resonator connected in parallel in the above-mentioned surface acoustic wave resonator, that is, the parallel resonator will be identified as the first surface acoustic wave resonator in this embodiment, and it will be set to deflect the first preset angle relative to the vertical direction of the flat edge of the wafer used for the substrate 1, so that its insertion loss on the medium and low frequency side of the passband is less than that of the second surface acoustic wave resonator.

[0061] It should be noted that in this embodiment, the first preset angle is not only a fixed value, but is usually a range of values, that is, the above-mentioned first preset angle can have multiple different values. In this embodiment, the multiple parallel resonators in the first surface acoustic wave resonator can have at least two different first preset angles. That is, for the parallel resonator belonging to the first surface acoustic wave resonator, the above-mentioned angle formed by itself and the substrate can be specifically multiple angles. As long as the angle is within the value range of the first preset angle, the insertion loss of the first surface acoustic wave resonator on the low-frequency side of the passband can be smaller than that of the second surface acoustic wave resonator. In this embodiment, it is not required that the angle between the first surface acoustic wave resonator and the substrate be the same. Obviously, different first preset angles will optimize different frequencies. In this embodiment, multiple first preset angles can be determined specifically according to the specific characteristic curve of the surface wave resonator to optimize the performance of the filter at different frequencies. As for the series resonator, two solutions are specifically provided in this embodiment. The first one is that since the resonant frequency of the series resonator is located on the mid-high frequency side of the passband, the second surface acoustic wave resonator in this embodiment includes the series resonator connected in series in the surface acoustic wave resonator, that is, the series resonator will be identified as the second surface acoustic wave resonator in this embodiment, and it will be set to deflect at a second preset angle relative to the vertical direction of the flat edge of the wafer used by the substrate 1, so that its insertion loss on the mid-high frequency side of the passband is less than that of the first surface acoustic wave resonator, thereby reducing the overall insertion loss of the filter and further improving the insertion loss characteristics of the filter. If the transposition angle of the parallel resonator is set to 6° and the transposition angle of the series resonator is set to 4°, the insertion loss characteristics of the filter can be further improved.

[0062] The second type is that the first surface acoustic wave resonator also includes a first preset number of series resonators connected in series among the surface acoustic wave resonators; the second surface acoustic wave resonator includes a second preset number of series resonators connected in series among the surface acoustic wave resonators; the first preset number is less than the second preset number.

[0063] It should be noted that, similar to the above-mentioned first preset angle, in this embodiment, the second preset angle is not only a fixed value, but is usually a range of values, that is, the above-mentioned second preset angle can have multiple different values. In this embodiment, the multiple series resonators in the second surface acoustic wave resonator can have at least two different second preset angles. That is, for the series resonator belonging to the second surface acoustic wave resonator, the above-mentioned angle formed by itself and the substrate can specifically be multiple angles. As long as the angle is within the value range of the second preset angle, the insertion loss of the second surface acoustic wave resonator on the high-frequency side of the passband can be made smaller than that of the first surface acoustic wave resonator. In this embodiment, it is not required that the angle between the second surface acoustic wave resonator and the substrate be the same. Obviously, different second preset angles will optimize different frequencies. In this embodiment, multiple second preset angles can be determined according to the specific characteristic curve of the surface wave resonator to optimize the performance of the filter at different frequencies.

[0064] Because in the process of deflecting the SAW resonator, the performance of some frequency points on the low- and medium-frequency side of the passband when the SAW resonator is at the first preset angle is better than the performance when the SAW resonator is at the second preset angle, and the overall performance of the high- and medium-frequency side of the passband when the SAW resonator is at the second preset angle is better than the performance when the SAW resonator is at the first preset angle. In order to balance the insertion loss on both sides of the passband, in this embodiment, a small number of series resonators will be identified as first SAW resonators, which are deflected by the first preset angle; most of the series resonators will be identified as second SAW resonators, which are deflected by the second preset angle, so as to obtain better insertion loss. If the transposition angle of the parallel resonator and a small number of series resonators is set to 6°, and the transposition angle of other series resonators is set to 4°, better insertion loss will be obtained.

[0065] Specifically, in the present embodiment, the substrate may be a POI (piezo on insulator) substrate. A POI substrate is a substrate having a piezoelectric layer on the upper layer, an oxide layer in the middle layer, and a base on the lower layer. The POI substrate is generally a single crystal piezoelectric layer, a buried oxide layer, and a high-resistance base from top to bottom. In the present embodiment, the interdigitated electrodes are specifically arranged on the surface of the piezoelectric layer. Preferably, the thickness of the piezoelectric layer of the POI substrate may be less than 1 λ, where λ is the period length of the interdigitated electrodes. When the thickness of the piezoelectric layer is less than the above λ, the Q value of the device will be further improved. At the same time, because the piezoelectric layer with poor heat dissipation is thinner, the heat dissipation characteristics of the device will be improved.

[0066] Please refer to Figures 7 to 11, SAW (surface acoustic wave) devices can generally be divided into conventional SAW, TC-SAW (Temperature compensated-SAW, temperature compensated surface acoustic wave device) and POI-SAW (piezo on insulator-SAW). Surface acoustic wave devices (POI-SAW) based on piezoelectric materials on insulating substrates have the highest quality factor and better heat dissipation capabilities. However, using the conventional IDT (interdigital transducer) structure, the device has a strong lateral parasitic mode.

[0067] like Figure 7 , which is the Q value curve of a conventional SAW device. The substrate uses lithium tantalate with a cutting angle of 42Y-X. The solid line is the direction of the arrangement of the forked electrodes (i.e., the direction of sound wave propagation) perpendicular to the flat edge direction of the wafer, and the dotted line is the image obtained by rotating the arrangement of the forked electrodes 8° compared to the perpendicular flat edge direction. The vertical marked line on the left corresponds to the resonant frequency fs, and the two vertical lines on the right correspond to the anti-resonance frequencies of the solid curve and dotted curve structures, respectively. It can be seen from the dotted line results that after the resonator is rotated, the ripple below fs becomes weaker, but the overall Q curve becomes worse. At the same time, because the fp of the structure corresponding to the dotted line is lower, the corresponding device equivalent coupling coefficient (equivalent coupling coefficient, k2eff) is smaller, making it difficult to make a large bandwidth filter.

[0068] like Figure 8 This is the result of the corresponding comparison of the POI-SAW device. Because POI-SAW has a strong lateral parasitic mode, it is reflected in the solid line result, and there are many spikes in the Q curve between fs and fp. After rotating the arrangement direction of the device's interdigital electrodes, as shown by the dotted line, the curve becomes smooth, the device's noise mode is weakened or suppressed, and the passband ripple performance of the corresponding filter is improved; at the same time, the overall Q dotted line of the device has not deteriorated significantly, and even has improved in local positions. Therefore, the comparison shows that in POI-SAW devices, the method of rotating the interdigital electrodes is more effective in improving the device's lateral mode and improving the device's overall Q value.

[0069] Figures 9 to 11 The working mechanism is further explained. Figures 9 to 11 This is the lateral dispersion curve of the POI-SAW device. The horizontal axis is the wave number and the vertical axis is the frequency. Figures 9 to 11 The three curves in the middle circle are the cases where the interdigitated electrodes are short-circuited, and the star-shaped curves correspond to the open-circuit cases. Fig. 9 , Figure 10 to Figure 11, corresponding to the arrangement direction of the interdigital electrodes perpendicular to the flat edge of the wafer, and then rotated 4° and 8°. Analysis of the three short-circuit curves shows that when the horizontal coordinate is 0, the corresponding curve slope gradually changes from positive to negative. The positive curve slope corresponds to a type I device, which will produce a lateral parasitic mode above fs. The negative curve slope corresponds to a type II device, which will produce a lateral parasitic mode below fs. After rotating the device, the slope of the curve changes from positive to negative, and the lateral mode of the device above fs gradually weakens. Because the position below fs is the forbidden band working position of the device, the lateral parasitic mode has a weak effect. Therefore, for POI devices with type I, changing the device angle can effectively suppress the lateral mode, while POI-SAW devices generally exhibit type I characteristics.

[0070] A filter provided by an embodiment of the present invention optimizes the insertion loss of the surface acoustic wave resonators with resonance frequencies on different sides of the passband by making the first surface acoustic wave resonator with resonance frequency on the low-frequency side of the passband and the second surface acoustic wave resonator with resonance frequency on the high-frequency side of the passband deflect at different angles, thereby effectively reducing the overall insertion loss of the filter, so that the filter has a lower insertion loss. The design of resonators with a fully uniform transposition angle may cause the problem of large insertion loss due to inherent defects of the resonator in certain positions. Setting the transposition angles of different resonators to different angles can effectively solve this problem.

[0071] The present application also provides a filtering device, which includes a filter provided by any of the above invention embodiments, and the filtering device may include one or more of the above filters. Other structures of the filtering device can refer to the prior art and will not be described in detail here.

[0072] Since the above filter can have a lower insertion loss, the corresponding filter device provided by this embodiment can generally achieve a lower insertion loss. The specific contents of the filter have been described in detail in the above invention embodiments, and will not be repeated here.

[0073] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0074] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0075] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0076] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0077] The above is a detailed introduction to a filter and a filtering device provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A filter, characterized in that: The invention comprises a substrate and a plurality of surface acoustic wave resonators formed based on interdigital electrodes arranged on the surface of the substrate; The surface acoustic wave resonator comprises a first surface acoustic wave resonator having a resonance frequency located at the low frequency side of the passband, and a second surface acoustic wave resonator having a resonance frequency located at the high frequency side of the passband; The first surface acoustic wave resonator comprises a first interdigital electrode disposed on the surface of the substrate, and the second surface acoustic wave resonator comprises a second interdigital electrode disposed on the surface of the substrate; The arrangement direction of the first interdigitated electrodes has a first preset angle with a direction perpendicular to the flat edge direction of the wafer used for the substrate, so that the insertion loss of the first surface acoustic wave resonator on the low-frequency side of the passband is smaller than that of the second surface acoustic wave resonator; the arrangement direction of the second interdigitated electrodes has a second preset angle with a direction perpendicular to the flat edge direction of the wafer used for the substrate, so that the insertion loss of the second surface acoustic wave resonator on the high-frequency side of the passband is smaller than that of the first surface acoustic wave resonator.

2. The filter according to claim 1, characterized in that The first surface acoustic wave resonator includes parallel resonators connected in parallel in the surface acoustic wave resonator.

3. The filter according to claim 2, characterized in that The plurality of parallel resonators in the first surface acoustic wave resonator have at least two different first preset angles.

4. The filter according to claim 2, characterized in that The second surface acoustic wave resonator includes series resonators connected in series in the surface acoustic wave resonator.

5. The filter according to claim 4, characterized in that The plurality of series resonators in the second surface acoustic wave resonator have at least two different second preset angles.

6. The filter according to claim 2, characterized in that The first surface acoustic wave resonator further includes a first preset number of series resonators connected in series among the surface acoustic wave resonators; the second surface acoustic wave resonator includes a second preset number of series resonators connected in series among the surface acoustic wave resonators; the first preset number is less than the second preset number.

7. The filter according to claim 1, characterized in that The interdigitated electrodes in the surface acoustic wave resonator are rotated clockwise relative to the direction perpendicular to the flat edge of the wafer used for the substrate to form the first surface acoustic wave resonator and the second surface acoustic wave resonator; or the interdigitated electrodes in the surface acoustic wave resonator are rotated counterclockwise relative to the direction perpendicular to the flat edge of the wafer used for the substrate to form the first surface acoustic wave resonator and the second surface acoustic wave resonator.

8. The filter according to claim 1, characterized in that Along the arrangement direction of the interdigital electrodes, reflection grids are arranged at both ends of the interdigital electrodes.

9. The filter according to claim 1, characterized in that The angle value range of the first preset angle and the angle value range of the second preset angle do not exceed 20°.

10. The filter according to claim 9, characterized in that The first preset angle has an angle range of 0° to 6°, including the right endpoint value.

11. The filter according to claim 9, characterized in that The second preset angle has an angle range of 2° to 8°, including endpoint values.

12. The filter according to claim 1, characterized in that The substrate is a POI substrate.

13. The filter according to claim 12, characterized in that The thickness of the piezoelectric layer of the POI substrate is less than 1λ, where λ is the period length of the interdigital electrodes.

14. A filtering device, characterized in that: Comprising a filter as claimed in any one of claims 1 to 13.

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