Method for improving filter performance, filter, multiplexer and electronic device
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ROFS MICROSYST TIANJIN CO LTD
- Filing Date
- 2021-09-27
- Publication Date
- 2026-07-21
AI Technical Summary
Existing filters suffer from insufficient power capacity and nonlinear characteristics in terms of improving data transmission rate and spectrum utilization, especially in RF front-end modules where the performance requirements for filters are urgent.
A filter employing a trapezoidal topology reduces nonlinear clutter and increases power capacity by placing at least two series and parallel resonators between the input and output terminals, and by nonlinearly splitting specific resonators in series or parallel, replacing them with sub-resonators with reversed electrode configurations.
It effectively reduces nonlinear clutter in the filter, improves power capacity and nonlinear characteristics, and enhances the flexibility of device design.
Smart Images
Figure CN115882815B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of communication electronics technology, and in particular to a method for improving filter performance, a filter, a multiplexer, and an electronic device. Background Technology
[0002] With the development of wireless communication applications, the demand for data transmission rates is increasing. Corresponding to these higher data transmission rates is the high utilization rate of spectrum resources and the increasing complexity of the spectrum. The increasing complexity of communication protocols places more stringent requirements on various performance aspects of radio frequency (RF) systems. In the RF front-end module, RF filters play a crucial role. Good filter performance can improve the data transmission rate, lifespan, and reliability of the communication system to a certain extent; therefore, there is a very urgent need for continuous improvement of filter performance. The main performance indicators of filters include insertion loss, out-of-band rejection, power capacity, and linearity. Summary of the Invention
[0003] In view of this, the present invention proposes a method, filter, multiplexer, and electronic device for improving filter performance, so as to achieve the inventive objective of improving the power capacity and nonlinear characteristics of the filter.
[0004] The first aspect of the present invention provides a method for improving the power capacity and nonlinear characteristics of a filter, wherein the filter has a trapezoidal topology. The method includes: setting at least two parent series resonators and at least two parent parallel resonators between the input and output terminals of the filter; performing series nonlinear splitting on the first-stage parent series resonator near the input terminal; performing series nonlinear splitting on the lowest parallel resonant frequency among all the parent series resonators; performing parallel nonlinear splitting on the first-stage parent parallel resonator near the output terminal; and performing either series nonlinear splitting or parallel nonlinear splitting on the first-stage parent series resonator near the output terminal. The series nonlinear splitting refers to replacing the parent resonator with two interconnected sub-resonators with reversed electrode configurations, and the parallel nonlinear splitting refers to replacing the parent resonator with two parallel sub-resonators with reversed electrode configurations.
[0005] Optionally, the parent series resonator with the lowest parallel resonant frequency among all the parent series resonators is not the first-stage parent series resonator closest to the input terminal.
[0006] Optionally, if the parent series resonator with the lowest parallel resonant frequency among all the parent series resonators is the first-stage parent series resonator closest to the output terminal, then the first-stage parent series resonator closest to the output terminal is nonlinearly split into series components.
[0007] Optionally, the two sub-resonators after the series nonlinear split have the same area and the same resonant frequency.
[0008] Optionally, the two sub-resonators after the parallel nonlinear split have the same area and the same resonant frequency.
[0009] Optionally, the two sub-resonators after the series nonlinear split have the same shape and size.
[0010] Optionally, the two sub-resonators after the parallel nonlinear split have the same shape and size.
[0011] Optionally, the series nonlinear splitting and the parallel nonlinear splitting are replaced with a series-parallel hybrid nonlinear splitting, wherein the series-parallel hybrid nonlinear splitting refers to a combination structure in which the parent resonator is replaced with four child resonators, whose electrodes are first reversed in pairs and connected in parallel, and then connected in series.
[0012] Optionally, the resonator is a bulk acoustic resonator.
[0013] A second aspect of the present invention provides a filter having a trapezoidal topology, wherein:
[0014] The input and output terminals contain at least two series resonant units and at least two parallel units.
[0015] The first-stage series resonant unit near the input terminal adopts a series nonlinear combination structure. Among all the series resonant units, the one with the lowest parallel resonant frequency adopts a series nonlinear combination structure. The first-stage parallel resonant unit near the output terminal adopts a parallel nonlinear combination structure. The first-stage series resonant unit near the output terminal adopts either a series nonlinear combination structure or a parallel nonlinear combination structure.
[0016] The series nonlinear combination structure includes two sub-resonators connected in series with their electrodes reversed, and the parallel nonlinear combination structure includes two sub-resonators connected in parallel with their electrodes reversed.
[0017] Optionally, the series resonant unit with the lowest parallel resonant frequency among all the series resonant units is not the first-stage series resonant unit closest to the input terminal.
[0018] Optionally, when the first-stage series resonant unit with the lowest parallel resonant frequency among all the series resonant units is the one closest to the output terminal, the first-stage series resonant unit closest to the output terminal adopts a series nonlinear combination structure.
[0019] Optionally, the two sub-resonators in the series nonlinear combination structure have the same area and the same resonant frequency.
[0020] Optionally, the two sub-resonators in the parallel nonlinear combination structure have the same area and the same resonant frequency.
[0021] Optionally, the two sub-resonators in the series nonlinear combination structure have the same shape and size.
[0022] Optionally, the two sub-resonators in the parallel nonlinear combination structure have the same shape and size.
[0023] Optionally, the series nonlinear combination structure and the parallel nonlinear combination structure can be replaced with a series-parallel hybrid nonlinear combination structure, wherein the series-parallel hybrid nonlinear combination structure includes four sub-resonators, the four sub-resonators are first set with their electrodes reversed in pairs and connected in parallel and then connected in series.
[0024] Optionally, the resonator is a bulk acoustic resonator.
[0025] A third aspect of the present invention provides a multiplexer comprising the filter proposed in this invention.
[0026] A fourth aspect of the present invention provides an electronic device comprising the filter or multiplexer of the present invention.
[0027] According to the technical solution of the present invention, by performing series nonlinear splitting on the first-stage series resonator at the signal input end, and / or performing series nonlinear splitting on the resonator with the lowest parallel resonant frequency in the series resonator, and performing parallel nonlinear splitting on the first-stage parallel resonator at the signal output end, and performing series or parallel nonlinear splitting on the first-stage series resonator at the signal output end, it is helpful to improve the power capacity and nonlinear characteristics of the filter, and increase the flexibility of device design. Attached Figure Description
[0028] For illustrative and not limiting purposes, the invention will now be described with reference to preferred embodiments thereof, particularly the accompanying drawings, in which:
[0029] Figure 1A This is the electrical symbol for an acoustic resonator. Figure 1B This is the equivalent electrical model of an acoustic resonator.
[0030] Figure 2 This is a schematic diagram of the impedance-frequency characteristics of a resonator.
[0031] Figure 3 A cross-sectional schematic diagram of a bulk acoustic resonator structure;
[0032] Figure 4 A schematic diagram of a series nonlinear splitting structure with the electrodes of two sub-resonators reversed;
[0033] Figure 5 A schematic diagram of a series nonlinear splitting structure with the electrodes of two sub-resonators reversed;
[0034] Figure 6for Figure 4 The series nonlinear splitting structure shown and Figure 5 A comparison diagram of the nonlinear characteristics of the parallel nonlinear splitting structure shown;
[0035] Figure 7 This is a schematic diagram of the unsplit trapezoidal filter topology;
[0036] Figure 8 This is a schematic diagram showing the relationship between the insertion loss of the first pair of proportional filters and the impedance of the series-parallel resonators.
[0037] Figure 9 This is a schematic diagram showing the relationship between the power density of a resonator and its second-order nonlinearity.
[0038] Figure 10 This is a schematic diagram showing the power density of each resonator in the first proportional trapezoidal filter.
[0039] Figure 11 This is a schematic diagram of the insertion loss of the second parallel series resonator and the insertion loss of the filter.
[0040] Figure 12 This is a schematic diagram of the filter topology according to the first embodiment of the present invention;
[0041] Figure 13 This is a schematic diagram comparing the nonlinear characteristics of the second comparative example with those of the first embodiment;
[0042] Figure 14 This is a schematic diagram of the filter topology according to the second embodiment of the present invention. Detailed Implementation
[0043] This invention proposes a technique for splitting resonators at specific locations in a trapezoidal acoustic wave radio frequency filter, aiming to improve the filter's power capacity and nonlinear characteristics. The first-stage series resonator near the filter's input end typically has the highest power density. Higher power density leads to poorer power capacity and stronger nonlinear clutter. Therefore, the first-stage series resonator near the input end is nonlinearly split. The series resonator with the lowest parallel resonant frequency fp in the filter has higher losses and higher power density at the right edge of the filter's passband. Therefore, to improve the filter's nonlinearity and power capacity characteristics, the resonator with the lowest parallel resonant frequency in the series resonator needs to be nonlinearly split. The first-stage series resonator and the first-stage parallel resonator near the output end have a significant impact on the filter's nonlinearity. Based on the difference in nonlinear response between series and parallel nonlinear splitting, the first-stage parallel resonator at the signal output end is nonlinearly split in parallel, and the first-stage series resonator at the signal output end is nonlinearly split in either series or parallel. Further explanation follows with reference to the accompanying drawings.
[0044] Figure 1A This is the electrical symbol for an acoustic resonator. Figure 1B This is the equivalent electrical model for an acoustic resonator. Acoustic resonators can specifically include thin-film bulk acoustic resonators (FABRs), surface acoustic wave resonators (SAWs), and solid-state assembled resonators (SMRs). Figure 2 This is a schematic diagram of the impedance-frequency characteristics of an acoustic resonator. Ignoring losses, the electrical model simplifies to a resonant circuit composed of Lm, Cm, and C0. According to the resonance condition, this resonant circuit has two resonant frequencies: one is fs, where the impedance of the resonant circuit reaches its minimum value; fs is defined as the series resonant frequency of this resonator, and the Q value of the resonator at fs is defined as Qs. The other is fp, where the impedance of the resonant circuit reaches its maximum value; fp is defined as the parallel resonant frequency of this resonator, and the Q value of the resonator at fp is defined as Qp.
[0045] Figure 3 A cross-sectional schematic diagram of a bulk acoustic resonator structure.
[0046] 101 is the top electrode, and the material can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or a composite of the above metals or their alloys, etc. The top electrode may also include a mass loading layer.
[0047] 102 is the bottom electrode, and the material can be molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite of the above metals or their alloys.
[0048] 103 is a piezoelectric thin film layer, which can be made of materials such as single-crystal aluminum nitride, polycrystalline aluminum nitride, zinc oxide, PZT, etc., and contain rare earth element doping materials with a certain atomic ratio of the above materials.
[0049] N1 is the input node of the high-frequency power signal, N2 is the output node of the high-frequency power signal, and the C-axis direction 100 is from node N1 to node N2 in the resonator thickness direction.
[0050] In a bulk acoustic wave resonator structure, the thickness of the piezoelectric film is equal to half the wavelength of the resonant frequency. When the piezoelectric film of the resonator is perfectly symmetrical in the thickness direction, the top and bottom electrodes have the same potential, and no second-order nonlinear clutter is generated. However, to obtain better performance, the piezoelectric film is generally not symmetrical (such as aluminum nitride and zinc oxide). This asymmetry makes the electric field distribution in the resonator non-uniform, generating a potential difference between the top and bottom electrodes, thus producing nonlinear clutter.
[0051] Figure 4 A schematic diagram of a series nonlinear split structure with the electrodes of two sub-resonators reversed. The parent resonator is split into sub-resonators R-1 and R-2 in an equivalent series configuration with equal area (e.g., the area of the parent resonator before splitting is 5 kum). 2Then, the areas of the sub-resonators R-1 and R-2 after being split in series with equal area are both 10 kum. 2 The C-axis direction 100 of sub-resonator R-1 is set opposite to that of sub-resonator R-2 (the diagram shows the C-axis directions of sub-resonator R-1 and sub-resonator R-2 being opposite, i.e., the bottom electrodes of the two sub-resonators are electrically connected; alternatively, the C-axis directions of sub-resonator R-1 and sub-resonator R-2 can be set opposite, i.e., the top electrodes of the two resonators are electrically connected; as long as the C-axis directions of sub-resonator R-1 and sub-resonator R-2 are opposite when viewed from node N1 or node N2), a1 and b1 are the nonlinear clutter generated by sub-resonator R-1, and a2 and b2 are the nonlinear clutter generated by sub-resonator R-2. Due to the use of... Figure 4 With the electrode reversal setup shown, b1 and a2 are out of phase and have the same amplitude, so they can cancel each other out. b1 has a phase delay through the sub-resonator R-2, so the cancellation effect of b1 and b2 will be worse. However, compared to a single resonator (before splitting), the second-order nonlinear clutter output at node N2 of the series nonlinear splitting structure will be greatly reduced.
[0052] Figure 5 This is a schematic diagram of a parallel nonlinear split structure with the electrodes of two sub-resonators reversed. The parent resonator is split into sub-resonators R-1 and R-2 in an equivalent parallel configuration with equal area (e.g., the area of the parent resonator before splitting is 5 kum). 2 Then, the areas of the equivalent parallel sub-resonators R-1 and R-2, with equal area, are both 2.5 kum. 2 The C-axis direction 100 of sub-resonator R-1 is set opposite to that of sub-resonator R-2 (as long as the C-axis directions of sub-resonator R-1 and sub-resonator R-2 are opposite when viewed from node N1 or node N2), a1 and b1 are the nonlinear clutter generated by sub-resonator R-1, and a2 and b2 are the nonlinear clutter generated by sub-resonator R-2. Due to the use of... Figure 5 With the electrode reversal setup shown, a1 and a2 are out of phase but have the same amplitude, thus canceling each other out. Similarly, b1 and b2 are out of phase but have the same amplitude, also canceling each other out. Therefore, the structure exhibits a smaller second-order nonlinear clutter output at node N2. Figure 5 The parallel nonlinear split structure shown is relative to Figure 4 The series nonlinear split structure shown has better nonlinear characteristics, but the power density of the resonator does not change after the parallel nonlinear split. Figure 4 The power density of the resonator in the series nonlinear split structure shown is reduced to 1 / 4 of the original, and its power capacity characteristics are better.
[0053] Figure 6 for Figure 4 The series nonlinear splitting structure shown and Figure 5 The diagram shows a comparison of the nonlinear characteristics of a parallel nonlinear splitting structure (the nonlinear clutter component output at output N2 when a 20dBm fundamental frequency signal is input to signal input N1). Figure 6 As shown, compared to not using a split resonator, both series nonlinear splitting and parallel nonlinear splitting can reduce the output of nonlinear clutter. However, compared to parallel splitting, series splitting exhibits poorer second-order nonlinear characteristics in the frequency band near the fundamental frequency fp.
[0054] In summary, the series nonlinear split structure exhibits poor second-order nonlinear characteristics in the frequency band near the fundamental frequency fp. However, the power density of the resonator with the series nonlinear split structure is 1 / 4 that of the parallel nonlinear split structure, making the series nonlinear split structure more advantageous for improving the power capacity of the filter.
[0055] Figure 7 This is a schematic diagram of a ladder-shaped filter topology in the prior art that has not been split (this topology corresponds to the first and second pairs of examples below). The filter topology is a ladder-shaped structure composed of series resonators S1-S4 and parallel resonators P1-P4. The filter has a fixed operating frequency and bandwidth (this invention uses a BAND3 transmit filter with a passband of 1710MHz-1785MHz and a bandwidth of 75MHz as an example for illustration).
[0056] T1 is the input terminal of the filter signal;
[0057] T2 is the output terminal of the filter signal;
[0058] L1 and L2 are the series inductances at port T1 and port T2 of the filter, respectively.
[0059] L3 and L4 are series grounding inductors in the parallel branches of the filter.
[0060] To achieve better matching, LC matching circuits may be included at the signal input and / or signal output terminals. Figure 7 The filter topology shown is just an example. This invention does not limit the number of stages, matching method, or grounding method of the parallel branch of the ladder structure filter. The resonator closest to the signal input terminal can also be a parallel resonator.
[0061] The first comparative circuit is based on, for example, Figure 7 In the topology shown, all series resonators in the first proportional circuit have the same resonator frequency, and all parallel resonators have the same resonant frequency. Figure 8 This is a schematic diagram showing the relationship between the insertion loss of the first pair of proportional filters and the impedance of the series-parallel resonators. Figure 8The solid line represents the insertion loss frequency response of the filter, the rectangular curve represents the impedance frequency response of the series resonator, and the circular curve represents the impedance frequency response of the parallel resonator. Figure 8 It is evident that the frequency range from fs to fp of the parallel resonator falls within the filter passband, while the frequency band near fp of the series resonator is outside the filter passband. Therefore, considering only nonlinearity, the effects of series nonlinear splitting and parallel nonlinear splitting are similar for the series resonator, but the parallel resonator requires parallel nonlinear splitting.
[0062] Figure 9 This diagram illustrates the relationship between the power density and second-order nonlinearity of a resonator. With the same power signal input to port N1 of the resonator, the rectangular curve represents the second-order nonlinear clutter component when the resonator area is S1 (with a power density of P1), and the circular curve represents the nonlinear clutter component when the resonator area is 4×S1 (two resonators with areas of 2×S1 connected in series, with the electrodes not reversed, have an equivalent area of S1, but a power density of P1 / 4). Figure 9 It is evident that the lower the power density, the better its nonlinear characteristics.
[0063] Figure 10 The diagram shows the power density of each resonator in the first proportional trapezoidal filter. When a 33dBm power signal is input to port T1 of the filter, the following results are obtained: Figure 10 The diagram shows the power density frequency characteristics of each resonator in the filter. The solid line represents the insertion loss frequency characteristic of the filter; the solid line marked with a diamond represents the power density frequency characteristic of series resonator S1; the solid line marked with a triangle represents the power density frequency characteristic of series resonator S2; the solid line marked with a circle represents the power density frequency characteristic of series resonator S3; the solid line marked with a rectangle represents the power density frequency characteristic of series resonator S4; the dashed line marked with a diamond represents the power density frequency characteristic of parallel resonator P1; the dashed line marked with a triangle represents the power density frequency characteristic of parallel resonator P2; the dashed line marked with a circle represents the power density frequency characteristic of parallel resonator P3; and the dashed line marked with a rectangle represents the power density frequency characteristic of parallel resonator P4. As can be seen from the diagram, the first-stage series resonator S1, which is closest to the power signal input, has the highest power density. Since the first-stage series resonator near the signal input must consider both power capacity and nonlinearity, the first-stage series resonator at the signal input end of the filter needs to undergo series nonlinearity decomposition.
[0064] like Figure 10As shown, since the power density of the first-stage series resonator and the first-stage parallel resonator near the signal output end is relatively low, there is no need to consider power capacity splitting. However, since the resonator is close to the signal output end, it has the greatest impact on the nonlinear characteristics. Therefore, the resonator near the signal output end of the filter needs to be nonlinearly split, and the first-stage parallel resonator near the signal output end of the filter adopts parallel nonlinear splitting.
[0065] The second proportional filter is also based on... Figure 7 The topology shown. Figure 11 This diagram illustrates the insertion loss frequency characteristics of the second parallel-scale filter and the insertion loss frequency characteristics of each series resonator. In the second parallel-scale filter, each series resonator has at least two distinct resonant frequencies, and each parallel resonator has at least two distinct resonant frequencies. The parallel resonant frequency fp of resonators S1 and S4 is 1855MHz, the parallel resonant frequency fp of resonator S2 is 1835MHz, and the parallel resonant frequency fp of resonator S3 is 1840MHz. The lower the parallel resonant frequency fp of the series resonators, the greater the loss of the resonator at the right edge of the filter's passband (located at 1785MHz), and the higher its power density. Therefore, to improve the filter's nonlinearity and power capacity characteristics, the resonator with the lowest parallel resonant frequency in the series resonators needs to undergo series nonlinear decomposition.
[0066] Figure 12 This is a schematic diagram of the ladder filter topology according to the first embodiment of the present invention. The first-stage parallel resonator P4 near the signal output end is split into parallel nonlinear components, the first-stage series resonator S1 near the signal input end is split into series nonlinear components, the resonator S2 with the lowest parallel resonant frequency among the series resonators is split into series nonlinear components, and the first-stage series resonator S4 near the signal output end is split into nonlinear components (either series nonlinear components or parallel nonlinear components).
[0067] The resonator with the lowest parallel resonant frequency in a series resonator can be located in the filter topology near the first-stage series resonator at the signal input end. However, it is preferable to place it in another position in the filter topology other than the first-stage series resonator at the signal input end. This is because the first-stage series resonator at the signal input end is the bottleneck of the filter's power capacity. If the parallel resonant frequency of the resonator at this position is set to the lowest, its power capacity will become relatively poor. When the resonator with the lowest parallel resonant frequency in a series resonator is located at the signal output end, this resonator needs to be split into series nonlinear components.
[0068] Figure 13This diagram illustrates a comparison of the nonlinear characteristics of the second comparative example and the first embodiment. With a 20dBm power signal input to the filter signal input terminal, the curve marked with a rectangle represents the nonlinear frequency characteristic of the circuit shown in the first embodiment of the present invention, and the curve marked with a circle represents the nonlinear frequency characteristic curve of the circuit shown in the second comparative example. As can be seen from the figure, the nonlinearity of the first embodiment is approximately 20dB better than that of the comparative example.
[0069] Figure 14 This is a schematic diagram of the trapezoidal filter topology according to the second embodiment of the present invention. In the first embodiment, the first-stage parallel resonator P4 near the output end is equivalently split into resonators P4-1, P4-2, P4-3, and P4-4 with equal area (for example, the area of resonator P4 before splitting is 5Kum). 2 Then, the areas of the resonators P4-1, P4-2, P4-3, and P4-4 after equivalent parallel splitting with equal area are all 5 kum. 2 The structure is connected in the manner shown in the figure. Compared with the parallel nonlinear splitting in the first embodiment, the above structure can more thoroughly cancel the second-order nonlinear components and achieve better nonlinear characteristics.
[0070] The duplexer of this invention includes any filter disclosed in this invention. The electronic device of this invention includes any filter or duplexer disclosed in this invention.
[0071] According to the technical solution of the present invention, by performing series nonlinear splitting on the first-stage series resonator at the signal input terminal, and / or performing series nonlinear splitting on the resonator with the lowest parallel resonant frequency in the series resonator, and performing parallel nonlinear splitting on the first-stage parallel resonator at the signal output terminal, and performing series or parallel nonlinear splitting on the first-stage series resonator at the signal output terminal, it is helpful to improve the power capacity and nonlinear characteristics of the filter, and increase the flexibility of device design.
[0072] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.
Claims
1. A method for improving the power capacity and nonlinear characteristics of a filter, wherein the filter has a trapezoidal topology, characterized in that, The method includes: At least two parent series resonators and at least two parent parallel resonators are provided between the input and output terminals of the filter; The first-stage parent series resonator closest to the input terminal is nonlinearly split in series. The parent series resonator with the lowest parallel resonant frequency among all parent series resonators is nonlinearly split in series. The first-stage parent parallel resonator closest to the output terminal is nonlinearly split in parallel. Alternatively, the first-stage parent series resonator closest to the output terminal can be nonlinearly split in series or in parallel. The series nonlinear splitting refers to replacing the parent resonator with two sub-resonators connected in series with their electrodes reversed, and the parallel nonlinear splitting refers to replacing the parent resonator with two sub-resonators connected in parallel with their electrodes reversed.
2. The method according to claim 1, characterized in that, The parent series resonator with the lowest parallel resonant frequency among all the parent series resonators is not the first-stage parent series resonator closest to the input terminal.
3. The method according to claim 1, characterized in that, When the lowest parallel resonant frequency among all the parent series resonators is the first-stage parent series resonator closest to the output terminal, the first-stage parent series resonator closest to the output terminal is nonlinearly split into series.
4. The method according to claim 1, characterized in that, The two sub-resonators after the series nonlinear split have the same area and the same resonant frequency.
5. The method according to claim 1, characterized in that, The two sub-resonators after the parallel nonlinear split have the same area and the same resonant frequency.
6. The method according to claim 1, characterized in that, The two sub-resonators after the series nonlinear split have the same shape and size.
7. The method according to claim 1, characterized in that, The two sub-resonators after the parallel nonlinear split have the same shape and size.
8. The method according to claim 1, characterized in that, The series nonlinear splitting and the parallel nonlinear splitting are replaced with a series-parallel hybrid nonlinear splitting, wherein the series-parallel hybrid nonlinear splitting refers to a combination structure in which the parent resonator is replaced with four child resonators, whose electrodes are first reversed in pairs and connected in parallel, and then connected in series.
9. The method according to any one of claims 1 to 8, characterized in that, The resonator is a bulk acoustic resonator.
10. A filter having a trapezoidal topology, characterized in that: The input and output terminals contain at least two series resonant units and at least two parallel units. The first-stage series resonant unit near the input terminal adopts a series nonlinear combination structure. Among all the series resonant units, the one with the lowest parallel resonant frequency adopts a series nonlinear combination structure. The first-stage parallel resonant unit near the output terminal adopts a parallel nonlinear combination structure. The first-stage series resonant unit near the output terminal adopts either a series nonlinear combination structure or a parallel nonlinear combination structure. The series nonlinear combination structure includes two sub-resonators connected in series with their electrodes reversed, and the parallel nonlinear combination structure includes two sub-resonators connected in parallel with their electrodes reversed.
11. The filter according to claim 10, characterized in that, The series resonant unit with the lowest parallel resonant frequency among all the series resonant units is not the first-stage series resonant unit closest to the input terminal.
12. The filter according to claim 10, characterized in that, When the parallel resonant frequency of all the series resonant units is the lowest among the first-stage series resonant units closest to the output terminal, the first-stage series resonant unit closest to the output terminal adopts a series nonlinear combination structure.
13. The filter according to claim 10, characterized in that, The two sub-resonators in the series nonlinear combination structure have the same area and the same resonant frequency.
14. The filter according to claim 10, characterized in that, The two sub-resonators in the parallel nonlinear combination structure have the same area and the same resonant frequency.
15. The filter according to claim 10, characterized in that, The two sub-resonators in the series nonlinear combination structure have the same shape and size.
16. The filter according to claim 10, characterized in that, The two sub-resonators in the parallel nonlinear combination structure have the same shape and size.
17. The filter according to claim 10, characterized in that, The series nonlinear combination structure and the parallel nonlinear combination structure are replaced by a series-parallel hybrid nonlinear combination structure, wherein the series-parallel hybrid nonlinear combination structure includes four sub-resonators, the four sub-resonators are first set with their electrodes reversed in pairs and connected in parallel and then connected in series.
18. The filter according to any one of claims 10 to 17, characterized in that, The resonator is a bulk acoustic resonator.
19. A multiplexer, characterized in that, The filter includes any one of claims 10 to 18.
20. An electronic device, characterized in that, The filter includes any one of claims 10 to 18, or the multiplexer includes the one described in claim 19.