Filtering device
By connecting interdigitated capacitors in parallel in the surface acoustic wave filter and adjusting the arrangement direction and method of the electrode fingers, the problem of increased far-end clutter caused by the capacitors was solved, achieving higher out-of-band suppression performance and rectangularity.
Patent Information
- Application Number
- CN202410617980.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-17
- Publication Date
- 2025-11-18
AI Technical Summary
Existing surface acoustic wave filters suffer from far-end clutter issues when increasing capacitance to improve rectangularity.
The parallel-connected interdigitated capacitors have electrodes that extend roughly parallel to the direction of surface acoustic wave propagation. The capacitors' resonant characteristics are reduced by using a non-periodic or flip-symmetrical arrangement.
Without increasing device size or manufacturing complexity, it significantly suppresses far-end clutter and improves the out-of-band rejection performance of the filter.
Smart Images
Figure CN120979377A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of resonators, and relates to a filter device. BACKGROUND
[0002] With the development of 5G mobile communication technology, the number of communication frequency bands also increases sharply, and the frequency interval between adjacent channels is getting smaller and smaller. In mobile communication terminals, in order to realize higher rate signal transmission, more and more filters are applied to the radio frequency front end. In order to avoid interference between adjacent frequency bands, the filter needs to have a more steep transition band, a lower temperature drift coefficient and a higher quality factor (Q value).
[0003] As a main device for filtering radio frequency signals, the surface acoustic wave filter must have low loss, high out-of-band suppression and high quality factor. Among them, the rectangularity is an important index for measuring the filtering performance of the surface acoustic wave filter. At present, in order to improve the rectangularity of the filter structure, the form of increasing capacitance is usually adopted, and the added capacitance occupies a very small area and does not increase the area of the chip. However, in general, the extension direction of the electrode finger of the capacitance is the same as the extension direction of the finger strip of the resonator, and the wavelength of the capacitance is usually very small, which will cause spurious waves in the far end of the filter.
[0004] Therefore, it is urgent to find a layout structure of the surface acoustic wave resonator to eliminate the far-end spurious waves caused by the capacitance under the premise of improving the rectangularity of the filter.
[0005] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely describing the technical scheme of the present application, and for the convenience of understanding by those skilled in the art. The above technical scheme cannot be considered as known to those skilled in the art only because it is described in the background section of the present application. SUMMARY
[0006] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a filter device for solving the problem of far-end spurious waves caused by increasing capacitance when improving the rectangularity of the filter structure in the prior art.
[0007] To achieve the above-mentioned purpose and other related purposes, the present application provides a filter device, comprising:
[0008] A piezoelectric layer, a surface acoustic wave resonator and a capacitor are arranged on the piezoelectric layer, the capacitor is arranged as a pair of interdigital electrodes and includes oppositely arranged first and second electrode arms, first electrode fingers connected to the first electrode arm and second electrode fingers connected to the second electrode arm, the first and second electrode fingers are alternately arranged in a non-periodic manner between the first and second electrode arms, the surface acoustic wave resonator is connected in parallel with the capacitor, and the electrode fingers of the capacitor extend in a direction substantially parallel to the propagation direction of the surface acoustic wave in the piezoelectric layer.
[0009] Optionally, at least one pair of first or second electrode fingers are arranged adjacent along the extension direction of the gap between the first and second electrode arms.
[0010] Optionally, a first dummy electrode finger is further connected to the first electrode arm, and a second dummy electrode finger is further connected to the second electrode arm, the first electrode finger and the second dummy electrode finger have a coincident extension direction, and the second electrode finger and the first dummy electrode finger have a coincident extension direction.
[0011] Optionally, the capacitor is arranged as interdigital electrodes in which, along the extension direction of the gap between the first and second electrode arms, the alternately arranged first electrode fingers and first dummy electrode fingers and the alternately arranged second electrode fingers and second dummy electrode fingers are respectively flipped and arranged with the center line of the first and second electrode arms as the rotation axis.
[0012] Optionally, the capacitor is arranged as interdigital electrodes in which, along the extension direction of the gap between the first and second electrode arms, the alternately arranged first electrode fingers and first dummy electrode fingers and the alternately arranged second electrode fingers and second dummy electrode fingers are respectively flipped and arranged at least twice with the perpendicular line of the first and second electrode arms as the rotation axis.
[0013] Optionally, further comprising an input port and an output port, the surface acoustic wave resonator is connected between the input port and the output port, and the surface acoustic wave resonator is connected in parallel with the capacitor.
[0014] Optionally, at least two first surface acoustic wave resonators and a second surface acoustic wave resonator are arranged on the piezoelectric layer, the filter device further comprises an input port and an output port, the first surface acoustic wave resonators and the second surface acoustic wave resonator are connected in cascade, the first surface acoustic wave resonators are connected in series between the input port and the output port, and the second surface acoustic wave resonator is connected in parallel with the capacitor.
[0015] Optionally, the second surface acoustic wave resonator comprises a ground electrode, and the node between the adjacent first surface acoustic wave resonators is grounded through the ground electrode of the second surface acoustic wave resonator.
[0016] Optionally, the surface acoustic wave resonator comprises a first bus bar and a second bus bar arranged in parallel, a plurality of third electrode fingers connected to the first bus bar, and a plurality of fourth electrode fingers connected to the second bus bar, and the first electrode finger and the second electrode finger of the capacitor extend in a direction perpendicular to the third electrode finger and the fourth electrode finger of the surface acoustic wave resonator.
[0017] Optionally, the material of the piezoelectric layer comprises one of lithium tantalate and lithium niobate.
[0018] As described above, in the filter device of the present application, by connecting the interdigital electrode pair of the capacitor in parallel to both ends of the surface acoustic wave resonator, arranging the electrode fingers of the capacitor to have an extension direction consistent with the propagation direction of the surface acoustic wave, and arranging the electrode fingers of the capacitor in a non-periodic manner along the extension direction of the electrode arm, the requirement of high rectangularity of the filter device is met without increasing the size of the device, the resonance characteristics of the capacitor are greatly weakened, the influence of the far-end clutter is suppressed, the out-of-band rejection performance is improved, and the process cost and difficulty are not increased, which has high industrial utilization value. BRIEF DESCRIPTION OF DRAWINGS
[0019] Figure 1 A schematic diagram showing the orientation relationship between the resonator and the electrode fingers of the capacitor in the filter device of the present application.
[0020] Figure 2 A schematic diagram showing the topology structure of a typical ladder filter.
[0021] Figure 3 A schematic diagram showing the topology structure of the filter device of the present application, in which the two ends of a series resonator are connected in parallel with a capacitor.
[0022] Figure 4 An equivalent model diagram of the resonator shown in the figure, Figure 3
[0023] An equivalent model diagram of the resonator shown in the figure, Figure 5 Figure 4 A comparison diagram of the admittance curves before and after the capacitor connected in parallel to the two ends of the resonator shown in the figure.
[0024] Figure 6 A schematic diagram showing the orientation relationship between the surface acoustic wave resonator and the electrode fingers of the capacitor in the filter device of the present application.
[0025] Figure 7 A schematic diagram showing the arrangement mode of the interdigital electrodes of the capacitor in the filter device of the present application.
[0026] Figure 8 A schematic diagram showing the interdigital electrodes of the capacitor in the filter device of the present application having a flipped symmetric arrangement.
[0027] Figure 9 A schematic diagram showing another arrangement of the interdigital electrodes of the capacitor in the filter device of the present application having a flipped symmetric arrangement.
[0028] Figure 10 A comparative diagram showing the frequency response curves of the interdigital electrodes of the capacitor in the filter device according to the present application before and after being rotated by 90°, and after having a flipped symmetric arrangement.
[0029] Figure 11 A comparative diagram showing the frequency response curves of the interdigital electrodes of the capacitor in the filter device according to the present application before and after being rotated by 90°, and after having a flipped symmetric arrangement. Figure 10 A partial enlarged view of the frequency response curves shown.
[0030] BRIEF DESCRIPTION OF DRAWINGS
[0031] 01, 02 Electrode arms
[0032] 11 First electrode arm
[0033] 12 Second electrode arm
[0034] 13 Interdigital transducer
[0035] 1, 3, 5, 7, 9 Series resonators
[0036] 2, 4, 6, 8 Shunt resonators
[0037] C Capacitor
[0038] 131 First bus bar
[0039] 231 Second bus bar
[0040] 112 First electrode finger
[0041] 212 Second electrode finger
[0042] 132 First electrode finger
[0043] 232 Second electrode finger
[0044] 112d First dummy electrode finger
[0045] 212d Second dummy electrode finger
[0046] 132d First dummy electrode finger
[0047] 232d Second dummy electrode finger
[0048] IN Input port
[0049] OUT output port
[0050] 10 piezoelectric layer
[0051] S center line
[0052] S1, S2, S3 perpendicular line DETAILED DESCRIPTION
[0053] The present application is herein described, by way of example only, with the
[0054] Throughout the specification, where an element such as a layer, region or substrate is described as being "on" or "connected to" another element, it can be directly on or connected to the other element or intervening elements can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element, there are no intervening elements present. It will be understood that, although the terms "first," "second," "third," etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. Rather, these terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the examples.
[0055] Throughout the specification, where an element such as a layer, region or substrate is described as being "on" or "connected to" another element, it can be directly on or connected to the other element or intervening elements can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element, there are no intervening elements present. It will be understood that, although the terms "first," "second," "third," etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. Rather, these terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the examples.
[0056] For ease of description, spatially relative terms, such as "above", "below", "upper", "lower", and the like, can be used herein for describing an element's relationship to another element as illustrated in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as above other elements would then be oriented below the other elements. Accordingly, the term "above" encompasses both a "above" and "below" orientation. The device can be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative terms used herein interpreted accordingly.
[0057] Referring to Figures 1 to 11 It is to be understood that the figures provided in the embodiments are only schematic and that the drawings are only intended to aid in the understanding of the application. The drawings are not to be considered as limiting the application in any way. The figures show only those components of the application that are necessary in order to demonstrate the principles of the application, and therefore do not show all components of a device in which the application can be used. The figures are to be considered in conjunction with the detailed description of specific embodiments of the application.
[0058] In most cases, the node of the surface acoustic wave filter is connected to a capacitor to improve the filter's rectangularity. Figure 1 A schematic diagram of the orientation relationship between the electrode fingers of a resonator and a capacitor in a filter device is provided. The capacitor includes oppositely arranged electrode arms 01 and 02, and electrode fingers connected to the electrode arms 01 and 02. The electrode fingers are arranged alternately in the extension direction of the gap between the electrode arms 01 and 02.
[0059] In order to improve the out-of-band rejection performance of the filter and suppress the far-end spur introduced by the interdigital capacitor in the filter, the inventors of the present application have improved the arrangement of the interdigital electrodes of the capacitor and rotated the electrode fingers of the capacitor so that the electrode fingers of the capacitor have an extension direction that is substantially parallel to the propagation direction of the surface acoustic wave in the piezoelectric layer, as shown in Figure 1 The X direction, without significantly increasing the size of the device and the difficulty of the process.
[0060] Hereinafter, the surface acoustic wave filter of the present application will be described in detail with reference to the accompanying drawings.
[0061] The embodiment provides a filter device, comprising a piezoelectric layer, wherein a surface acoustic wave resonator and a capacitor are arranged on the piezoelectric layer, the surface acoustic wave resonator is connected in parallel with the capacitor, and the capacitor is arranged as a pair of interdigital electrodes, the interdigital electrodes comprise a plurality of electrode fingers arranged in a non-periodic manner, and the electrode fingers of the capacitor extend in a direction substantially parallel to a surface acoustic wave propagation direction of the piezoelectric layer. By rotating the interdigital electrodes of the capacitor by 90°, the capacitor is substantially free of the resonant characteristics of the interdigital transducer structure, thereby greatly suppressing far-end clutter of the filter.
[0062] Specifically, the piezoelectric layer 10 can be a material layer bonded or formed on a substrate (not shown), and the material of the piezoelectric layer 10 includes but is not limited to lithium tantalate (LiTaO3), lithium niobate (LiNbO3), or similar piezoelectric materials with a specific acoustic wave propagation direction. The piezoelectric layer 10 can be a single-layer structure formed of one material, or a composite layer formed of two or more materials. The thickness, size and shape of the piezoelectric layer 10 can be selected according to actual conditions without special limitation as long as the performance of the device is ensured.
[0063] The filter device comprises an input port and an output port, and the surface acoustic wave resonator is connected between the input port and the output port. According to the frequency of a radio frequency (RF) signal, the RF signal can pass through the input port and the output port, or the RF signal can be blocked between the input port and the output port.
[0064] In an implementation, the filter device comprises at least one first surface acoustic wave resonator and a second surface acoustic wave resonator, the first surface acoustic wave resonator and the second surface acoustic wave resonator are connected in cascade, a plurality of first surface acoustic wave resonators are connected in series between the input port and the output port, and a node between adjacent first surface acoustic wave resonators is connected to the second surface acoustic wave resonator. The first surface acoustic wave resonator and the second surface acoustic wave resonator respectively comprise an input signal electrode and an output signal electrode, the first surface acoustic wave resonator is connected to the input port via the input signal electrode, and the first surface acoustic wave resonator is connected to the output port via the output signal electrode. Figure 2 A typical topology diagram of a ladder filter, Figure 3 A topology diagram of the filter device of the present application, in which the filter device adopts the topology of a ladder filter, and a node between adjacent two of the series resonators 1, 3, 5, 7 and 9 is grounded through the shunt resonator 2, 4, 6 or 8. Figure 3 As shown, the capacitor is connected in parallel to both ends of the series resonator 5, i.e., the first surface acoustic wave resonator.
[0065] It should be noted that the specific details of the present application are described herein with the filter device adopting the topology of a ladder filter, but the present application is not intended to limit the topology of the filter device to this, which includes a lattice filter or other topologies.
[0066] In a specific embodiment, the second surface acoustic wave resonator further comprises a ground electrode, and the node between the adjacent first surface acoustic wave resonators is grounded through the ground electrode of the second surface acoustic wave resonator.
[0067] In another implementation, the filter device comprises a first surface acoustic wave resonator and a second surface acoustic wave resonator connected in cascade, and the second surface acoustic wave resonator is connected in parallel with the capacitor.
[0068] The first surface acoustic wave resonator and the second surface acoustic wave resonator are respectively arranged as an interdigital transducer, which comprises parallelly arranged bus bars, and the bus bars are connected with alternately arranged electrode fingers and dummy electrode fingers. Referring to Figure 6 Fig. 1 is a schematic diagram of the directional relationship of the electrode fingers of the surface acoustic wave resonator and the capacitor in the filter device of the present application. As shown in Figure 6 The interdigital transducer 13 comprises parallelly arranged first bus bar 131 and second bus bar 231, the first bus bar 131 is connected with alternately arranged first electrode finger 132 and first dummy electrode finger 132d, and the second bus bar 231 is connected with alternately arranged second electrode finger 232 and second dummy electrode finger 232d, wherein the first electrode finger 132 and the second dummy electrode finger 232d have coinciding or approximately coinciding extension directions, the second electrode finger 232 and the first dummy electrode finger 132d have coinciding or approximately coinciding extension directions, and the adjacent first electrode finger and second electrode finger are staggered arranged in the middle region of the gap between the first bus bar and the second bus bar to define an interdigital region.
[0069] The first surface acoustic wave resonator and the second surface acoustic wave resonator can adopt interdigital transducers with the same or different structural parameters, and the finger width, the finger spacing, the acoustic aperture or similar parameters of the interdigital transducer can be flexibly designed according to the required performance of the filter. In some embodiments, the gap between the first bus bar 131 and the second bus bar 231 further comprises a unipole region, in which the first electrode finger 132 and the first dummy electrode finger 132d are alternately arranged, and in which the second electrode finger 232 and the second dummy electrode finger 232d are alternately arranged, and the unipole region is configured to adjust the size of the acoustic aperture of the interdigital transducer.
[0070] The at least one first surface acoustic wave resonator is connected in parallel with the capacitor, and the capacitor can be connected in parallel to any series resonator in the n-stage filter. As the filter has a higher order, it can better suppress high-frequency noise and interference. For example, as Figure 3As shown, the capacitor C is connected in parallel to both ends of the third series resonator. Figure 4 As shown, the capacitor C is connected in parallel to both ends of the third series resonator. Figure 3 As shown, the capacitor C is connected in parallel to both ends of the third series resonator. Figure 5 As shown, the capacitor C is connected in parallel to both ends of the third series resonator. Figure 4 As shown, the capacitor C is connected in parallel to both ends of the third series resonator, wherein the light color curve represents the admittance curve of the resonator before the parallel capacitor, and the dark color curve represents the admittance curve of the resonator after the parallel capacitor. It can be seen that Figure 5 As shown, the capacitor C is connected in parallel to both ends of the third series resonator, wherein the light color curve represents the admittance curve of the resonator before the parallel capacitor, and the dark color curve represents the admittance curve of the resonator after the parallel capacitor. It can be seen that
[0071] The capacitor C includes a first electrode arm and a second electrode arm arranged oppositely. As shown, Figure 6 As shown, the first electrode arm 11 and the second electrode arm 12 are oppositely arranged, and the electrode fingers on the first electrode arm 11 and the second electrode arm 12 respectively extend towards each other, and the electrode fingers 112, 122 on the first electrode arm and the second electrode arm are staggered along the extension direction of the gap between the first electrode arm and the second electrode arm.
[0072] Continuing to refer to Figure 6 As shown, the first electrode finger 132 and the second electrode finger 232 of the interdigital transducer extend in a direction perpendicular or substantially perpendicular to the propagation direction of the surface acoustic wave of the piezoelectric layer, and generally the propagation direction of the surface acoustic wave is perpendicular to the positioning edge; that is, the first electrode finger 132 and the second electrode finger 232 of the interdigital transducer extend in a direction substantially parallel to the positioning edge. In the embodiment, unlike the resonator and the electrode fingers of the capacitor shown in Figure 1 As shown, the first electrode finger 132 and the second electrode finger 232 of the interdigital transducer extend in a direction perpendicular or substantially perpendicular to the propagation direction of the surface acoustic wave of the piezoelectric layer, and generally the propagation direction of the surface acoustic wave is perpendicular to the positioning edge; that is, the first electrode finger 132 and the second electrode finger 232 of the interdigital transducer extend in a direction substantially parallel to the positioning edge. In the embodiment, unlike the resonator and the electrode fingers of the capacitor shown in
[0073] Generally, when a capacitor is arranged in a filter, the capacitor and the surface acoustic wave resonator have similar interdigital structures and are arranged along the propagation direction of the surface acoustic wave, so that the capacitor also has the characteristics of the interdigital transducer and generates a resonance peak at a corresponding frequency point, but the wavelength generated by the interdigital structure of the capacitor is generally smaller.
[0074] As shown, the first electrode arm 11 and the second electrode arm 12 are oppositely arranged, and the electrode fingers on the first electrode arm 11 and the second electrode arm 12 respectively extend towards each other, and the electrode fingers 112, 122 on the first electrode arm and the second electrode arm are staggered along the extension direction of the gap between the first electrode arm and the second electrode arm. Figure 6As shown, the first electrode arm 11 and the second electrode arm 12 of the capacitor are arranged opposite to each other. The first electrode arm 11 includes a first electrode finger 112 extending toward the second electrode arm, and the second electrode arm 12 includes a second electrode finger 122 extending toward the first electrode arm. Dummy electrode fingers are also connected to the first electrode arm and the second electrode arm. The stability of the capacitor operation is increased by changing the sensing area between the periodically patterned electrode fingers of the interdigitated electrode pair.
[0075] While ensuring the adjustability and stability of the capacitor, the first electrode fingers and the second electrode fingers are arranged alternately in a non-periodic manner along the expansion direction of the gap between the first electrode arm and the second electrode arm, which further weakens the resonant characteristics of the capacitor.
[0076] The first electrode arm 11 and the second electrode arm 12 of the capacitor are also connected to dummy electrode fingers. The first electrode finger and the dummy electrode finger connected to the second electrode arm have the same or approximately the same extension direction. The second electrode finger and the dummy electrode finger connected to the first electrode arm have the same or approximately the same extension direction.
[0077] See Figure 7 This is a schematic diagram of the interdigitated electrode arrangement of the capacitor in the filtering device of the present invention. Figure 7 In the implementation shown, the capacitor includes a first electrode arm 11 and a second electrode arm 12 disposed opposite to each other, a first electrode finger 112 connected to the first electrode arm and a second electrode finger 122 connected to the second electrode arm, the first electrode finger 112 and the second electrode finger 122 extending toward each other and arranged alternately, and at least one pair of first electrode fingers or second electrode fingers are disposed adjacent to each other along the expansion direction of the gap between the first electrode arm 11 and the second electrode arm 12.
[0078] In another implementation, dummy electrode fingers are connected to the first and second electrode arms of the capacitor, and at least one pair of the first electrode fingers or the second electrode fingers are arranged adjacent to each other along the expansion direction of the gap between the first electrode arm 11 and the second electrode arm 12; correspondingly, at least one pair of dummy electrode fingers connected to the first electrode arm or the second electrode arm are arranged adjacent to each other. See also Figure 7 This is a schematic diagram showing the interdigitated electrodes of the capacitor in the filtering device of the present invention arranged in a symmetrical, flipped configuration. Figure 8 As shown, the capacitor is arranged with interdigitated electrodes as follows: along the expansion direction of the gap between the first electrode arm 11 and the second electrode arm 12, the alternating first electrode fingers 112 and the first dummy electrode fingers 112d are flipped about the center line S passing through the first electrode arm and the second electrode arm as the rotation axis, and the alternating second electrode fingers 122 and the second dummy electrode fingers 122d are flipped about the same. The "center line" mentioned here refers to the extension line connecting the midpoints of the oppositely arranged first electrode arm and second electrode arm.
[0079] See Figure 9 This is a schematic diagram illustrating another arrangement of the interdigitated electrodes of the capacitor in the filtering device of the present invention, characterized by flipped symmetry. (See diagram below.) Figure 9 As shown, the capacitor is arranged with interdigitated electrodes as follows: along the expansion direction of the gap between the first electrode arm 11 and the second electrode arm 12, the alternating first electrode fingers 112 and the first dummy electrode fingers 112d, and the alternating second electrode fingers 122 and the second dummy electrode fingers 122d are successively rotated around the perpendicular lines S1, S2, and S3 passing through the first electrode arm and the second electrode arm as axes of rotation. That is, between the first electrode arm 11 and the second electrode arm 12, and between the first electrode arm 11 and the second electrode arm 12, the first electrode fingers and the second electrode fingers are symmetrically arranged around the axes of symmetry S1, S2, and S3. It should be noted that the figure illustrates a symmetrically mirrored interdigitated structure with four electrode array units to describe the specific structure of the present invention, but the capacitor is also configured as an interdigitated structure with m electrode array units, as long as m is an even number. The "perpendicular line" mentioned here refers to a parallel line connecting the midpoints of the first electrode arm and the second electrode arm.
[0080] To verify the effect of the extension direction of the capacitor's electrode fingers on the performance improvement of the RF filter, the preferred implementation of the present invention and the figures were tested, and the results are shown in [figure missing]. Figure 10 and Figure 11 The fine dotted line, dashed line, and solid line represent the frequency response curves of the parallel capacitors with interdigitated arrays in the trapezoidal filter before and after rotating them by 90°, and after rotating the capacitors by 90° and arranging the interdigitated electrodes of the capacitors in a symmetrical flipped configuration, respectively. Figure 11 for Figure 10 The image shows a magnified view of the frequency response curves of the trapezoidal filter.
[0081] Depend on Figure 10 As can be seen from the comparison of the frequency response curves of the trapezoidal filter before and after the capacitor is rotated by 90°, the resonant peak near 1.9 GHz is significantly weakened after the capacitor's electrodes are rotated by 90°. This is consistent with... Figure 5 The admittance curves of the resonator shown before and after the parallel capacitor is connected across its terminals exhibit the same trend, but a very small resonance peak still exists at the resonance point. Furthermore, by comparing... Figure 11 The enlarged view of the frequency response curve comparison diagram of the trapezoidal filter shows that after rotating the capacitor by 90° and arranging the electrodes with a flipped symmetrical finger pattern, the admittance amplitude at the resonant point further decreases. Figure 6 The capacitor structure shown further weakens the capacitor's resonant characteristics by disrupting its periodicity, thereby improving the resonant peak at that frequency point.
[0082] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A filtering device, characterized in that, The piezoelectric layer is provided with a surface acoustic wave resonator and a capacitor, the capacitor is arranged as a pair of interdigital electrodes and includes oppositely arranged first and second electrode arms, first electrode fingers connected to the first electrode arm and second electrode fingers connected to the second electrode arm, the first and second electrode fingers are alternately arranged in a non-periodic manner between the first and second electrode arms, the surface acoustic wave resonator is connected in parallel with the capacitor, and the electrode fingers of the capacitor extend in a direction substantially parallel to the propagation direction of the surface acoustic wave in the piezoelectric layer. At least one pair of first or second electrode fingers are arranged adjacent along the extension direction of the gap between the first and second electrode arms.
2. The filtering device of claim 1, wherein: The first electrode arm is further connected with a first dummy electrode finger, and the second electrode arm is further connected with a second dummy electrode finger, the first electrode finger and the second dummy electrode finger have a coincident extension direction, and the second electrode finger and the first dummy electrode finger have a coincident extension direction.
3. The filtering device of claim 1, wherein: The capacitor is arranged as interdigital electrodes in which, along the extension direction of the gap between the first and second electrode arms, the alternately arranged first electrode fingers and first dummy electrode fingers and the alternately arranged second electrode fingers and second dummy electrode fingers are respectively arranged in a flipped manner with the center line of the first and second electrode arms as the rotation axis.
4. The filtering device of claim 3, wherein: The capacitor is arranged as interdigital electrodes in which, along the extension direction of the gap between the first and second electrode arms, the alternately arranged first electrode fingers and first dummy electrode fingers and the alternately arranged second electrode fingers and second dummy electrode fingers are respectively arranged in a flipped manner at least twice with the perpendicular line of the first and second electrode arms as the rotation axis.
5. The filtering device of claim 3, wherein: Further comprising:
6. The filtering device of claim 1, wherein, An input port and an output port, the surface acoustic wave resonator is connected between the input port and the output port, and the surface acoustic wave resonator is connected in parallel with the capacitor. The piezoelectric layer is provided with at least two first surface acoustic wave resonators and a second surface acoustic wave resonator, the filter device further comprises an input port and an output port, the first surface acoustic wave resonators and the second surface acoustic wave resonator are connected in cascade, the first surface acoustic wave resonators are connected in series between the input port and the output port, and the second surface acoustic wave resonator is connected in parallel with the capacitor.
7. The filtering device of claim 1, wherein: The second surface acoustic wave resonator includes a ground electrode, and the nodes between adjacent first surface acoustic wave resonators are grounded through the ground electrode of the second surface acoustic wave resonator.
8. The filtering device of claim 7, wherein: The surface acoustic wave resonator includes first and second parallel bus bars, a plurality of third electrode fingers connected to the first bus bar, and a plurality of fourth electrode fingers connected to the second bus bar, and the first and second electrode fingers of the capacitor extend in a direction perpendicular to the third and fourth electrode fingers of the surface acoustic wave resonator.
9. The filtering device of claim 6, wherein: The material of the piezoelectric layer includes one of lithium tantalate and lithium niobate.
10. The filtering device of claim 1, wherein: