Method and device for improving bandwidth of a SAW filter and SAW filter

Abstract

The application discloses a method and device for improving bandwidth of a SAW filter and the SAW filter, and relates to the technical field of filters, to solve the problem that the resonant bandwidth of an existing SWA filter is limited by the coupling coefficient of piezoelectric material and cannot meet the demand of a high-bandwidth acoustic filter. The method comprises the following steps: obtaining measured data of a measured resonator in a target frequency range; based on the measured data, a measured curve fitting method is used to construct a coupling mode theory model of the resonator; a plurality of filter branches with adjacent center frequencies are constructed; a global optimization algorithm is used to reversely optimize physical parameters of a filter topology structure, so that the bandwidth of the optimized filter topology structure reaches a target bandwidth, and target physical parameters of the SAW filter are obtained. The method for improving bandwidth of a SAW filter provided by the application is used to improve the bandwidth of the SAW filter without changing the coupling coefficient of piezoelectric material.

Description

Technical Field

[0001] This invention relates to the field of filter technology, and in particular to a method, apparatus, and SAW filter for increasing the bandwidth of a SAW filter. Background Technology

[0002] Surface acoustic wave (SAW) resonators are passive bandpass filters made using the piezoelectric effect and the physical properties of surface acoustic wave propagation. Due to their small size, strong radiation resistance, high speed, low power consumption, and high reliability, SAW resonators are gaining increasing importance in communication circuit design. The resonant frequency of SAW resonators can be precisely tuned over a wide range using photolithography, and their small form factor, low connection loss, and low cost make them ideal for monolithic integration of filters at different frequencies.

[0003] However, the piezoelectric materials of existing SAW filters have a large inherent electromechanical coupling coefficient and soften as the temperature rises, which can easily lead to a large frequency shift in the filter. In industry, SiO2 temperature compensation is generally used to solve the above-mentioned temperature drift problem, but this method will significantly reduce the resonant bandwidth and can only be applied to low-frequency narrowband scenarios, which cannot meet the needs of mobile communication for high-frequency, broadband acoustic filters. Summary of the Invention

[0004] The purpose of this invention is to provide a method, apparatus, and SAW filter for improving the bandwidth of a SAW filter, in order to solve the problem that the resonant bandwidth of existing SAW filters is limited by the coupling coefficient of piezoelectric materials, which cannot meet the requirements of high-bandwidth acoustic filters.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for improving the bandwidth of a SAW filter, comprising: Obtain measured data of the measured resonator within the target frequency band range; Based on the measured data, the coupled-mode theoretical model of the resonator is constructed using the measured curve fitting method; Construct multiple filter branches with adjacent center frequencies; each filter branch is obtained by combining multiple coupled-mode theoretical models according to a trapezoidal filter structure; the sum of the frequency ranges of the multiple filter branches is the target frequency range; A global optimization algorithm is used to perform reverse optimization on the physical parameters of the filter topology, so that the bandwidth of the optimized filter topology reaches the target bandwidth, and the target physical parameters of the SAW filter are obtained. The filter topology consists of multiple filter branches connected in parallel and matching inductors set at the output port and the input port.

[0006] Optionally, the step of constructing the coupled-mode theoretical model of the resonator based on the measured physical parameters using the measured curve fitting method includes: The initial model of the coupled-mode theoretical model is determined based on the measured resonator. Generate a measured admittance curve based on the measured data; The key parameters of the initial model are adjusted using the nonlinear least squares method so that the error between the predicted admittance curve and the measured admittance curve of the adjusted initial model is within a preset error, thus obtaining the coupled-mode theoretical model.

[0007] Optionally, the step of using a global optimization algorithm to perform reverse optimization on the physical parameters of the filter topology, so that the bandwidth of the optimized filter topology reaches the target bandwidth, results in the following optimized filter topology: The optimization objectives and constraints are determined as follows: the optimization objectives are that the insertion loss in the passband is less than a preset loss, the passband amplitude fluctuation is less than a preset amplitude, the flatness at the junction of adjacent passbands is less than a preset flatness, the peak value of the group delay peak is less than a preset peak value, and the target bandwidth requirement is met; the constraints are that the overall performance of the filter topology reaches the preset requirements. Based on the simulated annealing optimization algorithm, the physical parameters of the filter topology are iteratively optimized in the circuit simulation platform until the optimization target is reached, and the optimized filter topology is obtained.

[0008] Optionally, the initial model for determining the coupled-mode theoretical model based on the measured resonator includes: Based on the piezoelectric substrate material and geometry of the measured resonator, material property analysis and propagation characteristic analysis are performed to determine the material parameters in the coupled-mode theoretical model. The material parameters include propagation loss coefficient, electromechanical coupling coefficient, capacitance per unit length, acoustic wave propagation constant, and surface acoustic wave propagation velocity. The physical parameters in the coupled-mode theoretical model are determined based on the measured geometry of the resonator. An initial model of the coupled-mode theory model is constructed based on the material parameters and the physical parameters.

[0009] Optionally, the initial model for constructing the coupled-mode theoretical model based on the material parameters and the physical parameters includes: Based on coupled-mode theory, a differential equation describing the sound field propagation and electromechanical conversion within the measured resonator is established. Based on the differential equation, the material parameters and physical parameters are mapped to the parameters of equivalent circuit elements to obtain the initial model of the coupled-mode theoretical model.

[0010] Optionally, the physical parameters include the number of interdigitated pairs, the number of reflective grating roots, the finger width, and the acoustic aperture; the step of iteratively optimizing the physical parameters of the filter topology in a circuit simulation platform based on the simulated annealing optimization algorithm until the optimization objective is achieved includes: The objective function value is calculated based on the current physical parameters, and then compared with the optimization objective to obtain the comparison result. Based on the comparison results, the number of interdigitated fingers, the number of reflective grating roots, the finger width, and the acoustic aperture of the filter topology are adjusted until the objective function value reaches the optimization target.

[0011] Optionally, the number of constructed filter branches is two, and the target frequency band range is the sum of the first target frequency band range and the second target frequency band range; the first target frequency band range and the second target frequency band range partially overlap; the construction of multiple filter branches with adjacent center frequencies includes: Multiple coupled-mode theoretical models are connected according to a trapezoidal filter structure to obtain the first filter branch and the second filter branch; Adjust the physical parameters of the resonator in the first filter branch so that the frequency range of the first filter branch is the first target frequency range; Adjust the physical parameters of the resonator in the second filter branch so that the frequency range of the first filter branch is the second target frequency range, thus completing the construction of the two filter branches.

[0012] Compared with existing technologies, this invention provides a method for improving the bandwidth of a SAW filter, comprising: acquiring measured data of a resonator within a target frequency band; constructing a coupled-mode theoretical model of the resonator based on the measured data using a measured curve fitting method; constructing multiple filter branches with adjacent center frequencies; the filter branches are obtained by combining multiple coupled-mode theoretical models according to a trapezoidal filter structure; and using a global optimization algorithm to perform reverse optimization of the physical parameters of the filter topology, so that the bandwidth of the optimized filter topology reaches the target bandwidth, thereby obtaining the target physical parameters of the SAW filter. This application, by connecting multiple trapezoidal filter branches with adjacent center frequencies in parallel and introducing matching inductors at the input and output ports, can achieve continuous synthesis of the passband in the frequency domain, thereby improving the bandwidth of the SAW filter. Specifically, by using parallel filter branches, a phase synergy synthesis effect can be achieved within the target frequency band. A global optimization algorithm can be used to rationally design the resonator parameters of the SAW filter, ensuring that within the target power frequency band: in the central region of the passband, the admittance phases of each parallel branch tend to be in phase, and the total admittance phasor exhibits a superposition enhancement state, thereby reducing insertion loss; in the left and right edge regions of the passband, different filter branches become dominant paths, their phase changes remain continuous, and the overall passband is smoothly spliced ​​from multiple branches; the matching inductor provides consistent phase compensation and impedance adjustment for the parallel branches at the system level, further improving the phase continuity at adjacent passband edges and suppressing passband dips, thus achieving an improvement in the electromechanical coupling coefficient independent of a single resonator and significantly extending the bandwidth of the SAW filter. This method only requires constructing a filter topology based on the coupled-mode theory model and optimizing its parameters; no manual modification of the resonator parameters is required. The method is simple, efficient, and accurate.

[0013] Secondly, the present invention provides a SAW filter, which is prepared using the method for increasing the bandwidth of a SAW filter, characterized in that the SAW filter includes at least: multiple trapezoidal SAW filter branches with adjacent center frequencies, matching inductors disposed at the input port and output port of the SAW filter; multiple trapezoidal SAW filter branches are connected in parallel; each trapezoidal SAW filter branch is composed of multiple resonators.

[0014] Optionally, the resonator is a two-port resonator, which includes a piezoelectric substrate, an input interdigital transducer, an output interdigital transducer, and two sets of reflective gratings; the input interdigital transducer, the output interdigital transducer, and the two sets of reflective gratings are disposed on the surface of the piezoelectric substrate; the two sets of reflective gratings are disposed on the outside of the input interdigital transducer and the output interdigital transducer.

[0015] Compared with the prior art, the beneficial effects of the SAW filter provided by the present invention are the same as the beneficial effects of the method for improving the bandwidth of a SAW filter described in the above technical solution, and will not be repeated here.

[0016] Thirdly, the present invention provides an apparatus for improving the bandwidth of a SAW filter, characterized in that it comprises: The measured data acquisition module is used to acquire measured data of the measured resonator within the target frequency band range; The coupled-mode theoretical model construction module is used to construct the coupled-mode theoretical model of the resonator based on the measured data and using the measured curve fitting method. A filter branch construction module is used to construct multiple filter branches with adjacent center frequencies; the filter branches are obtained by combining multiple coupled-mode theoretical models according to a trapezoidal filter structure; the sum of the frequency ranges of the multiple filter branches is the target frequency range; The physical parameter optimization module is used to perform reverse optimization of the physical parameters of the filter topology using a global optimization algorithm, so that the bandwidth of the optimized filter topology reaches the target bandwidth, and the target physical parameters of the SAW filter are obtained; the filter topology consists of multiple filter branches connected in parallel and matching inductors set at the output port and the input port.

[0017] Compared with the prior art, the beneficial effects of the device for improving the bandwidth of a SAW filter provided by the present invention are the same as the beneficial effects of the method for improving the bandwidth of a SAW filter described in the above technical solution, and will not be repeated here. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 A flowchart of a method for increasing the bandwidth of a SAW filter provided by the present invention; Figure 2 A schematic diagram of the transmission loss curves of the branch and total paths of the filter topology before optimization provided by the present invention; Figure 3 A phase diagram illustrating the admittance of the branch and total paths of the filter topology before optimization provided by this invention; Figure 4 A schematic diagram of the transmission loss curves of the branch and the total path of the optimized filter topology provided by the present invention; Figure 5 A phase diagram illustrating the admittance of the branches and the total path of the optimized filter topology provided by this invention; Figure 6A schematic diagram of the structure of a SAW filter with two branches provided by the present invention; Figure 7 This is a schematic diagram of a device structure for improving the bandwidth of a SAW filter, as provided by the present invention.

[0019] Figure label: 1-First trapezoidal SAW filter branch, 11-Resonator, 2-Second trapezoidal SAW filter branch, 3-Matching inductor. Detailed Implementation

[0020] To facilitate a clear description of the technical solutions in the embodiments of the present invention, the terms "first" and "second" are used to distinguish identical or similar items with essentially the same function and effect. For example, the first threshold and the second threshold are merely used to distinguish different thresholds and do not limit their order. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and that the terms "first" and "second" are not necessarily different.

[0021] It should be noted that in this invention, the terms "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in this invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0022] In this invention, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, a combination of a and b, a combination of a and c, a combination of b and c, or a, b, and c, where a, b, and c can be single or multiple.

[0023] Before introducing the embodiments of the present invention, the relevant terms involved in the embodiments of the present invention are first defined as follows: Global optimization algorithms are a class of algorithms that can traverse and search the entire parameter search space to find the global optimal solution of the objective function without relying on the rationality of the initial values.

[0024] 5G radio represents a significant leap forward in mobile communications, enabling unprecedented data rates, low latency, and high-reliability network capacity. With the accelerated deployment of new radio interfaces, filters required for rapidly developing and technologically innovative 5G UHF applications remain one of the major unresolved issues in the RF front-end. Filters above 3GHz generally use BAW (Bipolar Wave) filters; however, the manufacturing process is complex and difficult to achieve domestically. SAW filters, on the other hand, utilize piezoelectric materials with inherently high electromechanical coupling coefficients, such as LiNbO3 or LiTaO3 crystals. LiNbO3 or LiTaO3 crystals have low sound velocity and soften with increasing temperature, easily leading to significant frequency shifts in the filter. Using SiO2 temperature compensation to address this temperature drift problem would drastically reduce the resonant bandwidth. Consequently, SAW filters cannot achieve a large bandwidth of around 200MHz at 3.5GHz.

[0025] To address the aforementioned problems, this invention provides a method, apparatus, and SAW filter for increasing the bandwidth of a SAW filter. By connecting multiple trapezoidal SAW filter branches with adjacent center frequencies in parallel and introducing matching inductors at the input and output ports, continuous synthesis of the passband in the frequency domain is achieved. The bandwidth expansion mechanism of this method does not rely on increasing the electromechanical coupling coefficient of a single resonator, but rather on the phase synergistic synthesis effect of the parallel branches within the target frequency band. By optimizing the physical parameters of each branch resonator, the admittance phase change trend is kept consistent within the passband overlap region, thereby forming a smooth, dip-free, large-bandwidth synthesized passband. A detailed description follows with reference to the accompanying drawings.

[0026] See Figure 1 This invention provides a method for improving the bandwidth of a SAW filter, comprising the following steps: Step 101: Obtain the measured data of the measured resonator in the target frequency band range.

[0027] The target frequency band is the frequency band required for the designed SAW filter. The measured data were obtained by performing RF electrical performance tests and environmental reliability tests on the measured resonator.

[0028] In practical applications, the test resonator can be directly selected from pre-produced resonators, or a piezoelectric substrate material can be chosen, and then the test resonator can be fabricated using a custom-designed wafer fabrication process. The physical parameters of the selected test resonators are not entirely the same.

[0029] For example, the physical parameters of different measured resonators are shown in Table 1: Table 1. Physical parameters of the measured resonator Step 102: Based on the measured data, construct the coupled-mode theoretical model of the resonator using the measured curve fitting method.

[0030] The measured curve fitting method is a method that uses impedance curves, admittance curves, and S-parameter curves acquired by a vector network analyzer to match the equivalent circuit model of the resonator, and then uses an algorithm to fit and solve the component parameters in the model.

[0031] Step 103: Construct multiple filter branches with adjacent center frequencies.

[0032] The filter branch is a virtual structure obtained by combining multiple coupled-mode theoretical models according to a trapezoidal filter structure. The coupled-mode theoretical models are used to simulate the resonators in the filter branch. The sum of the frequency ranges of the multiple filter branches is the target frequency range. The physical parameters of different filter branches differ to form a staggered distribution of passband frequencies.

[0033] Step 104: Use a global optimization algorithm to perform reverse optimization on the physical parameters of the filter topology, so that the bandwidth of the optimized filter topology reaches the target bandwidth, and obtain the target physical parameters of the SAW filter.

[0034] In practical applications, within circuit simulation platforms, the filter topology, including the coupled-mode theoretical model and matching inductor, is used as the optimization object. With the overall frequency response of the filter topology as the objective, inverse iterative optimization is performed on physical parameters such as the number of interdigital pairs of the resonator, the number of reflector roots, the finger width, and the acoustic aperture. This ensures that the phase change trend of the parallel filter branches remains consistent within the target frequency band, thereby obtaining a smooth and continuous large bandwidth passband. The global optimization algorithm can be one or more of the following: simulated annealing, genetic algorithm, or particle swarm optimization.

[0035] The above filter topology consists of multiple filter branches connected in parallel and matching inductors located at the output and input ports. The matching inductors act on all filter branches for system-level phase and impedance co-adjustment; specifically, they coordinately adjust the equivalent impedance of the ports and the phase characteristics of adjacent passband edges. By using matching inductors, the originally independent trapezoidal filters can form a continuous overall response in the frequency domain. In practical applications, resonators are manufactured according to the target physical parameters, and then assembled according to the filter topology to obtain a SAW filter with the target bandwidth.

[0036] In step 104 above, the bandwidth of the filter topology before optimization is dominated by the branches, and its bandwidth cannot meet the design requirements. Specifically, this can be addressed by... Figures 2-3 To explain, among other things, Figure 2 The red and blue curves represent the transmission loss curves of the two filter branches, respectively, while the black curve represents the transmission loss curve of the entire filter topology. The parameters marking frequency point m1 are: Figure 3The red and blue curves represent the phase of the admittance of the two filter branches, while the black curve represents the phase of the admittance of the entire filter topology. m3, m7, m8, m9, and m15 are marked frequencies. At frequency m15, the phases of the red and blue parallel branches are approximately -91.9° and +96.2°, respectively, with a phase difference of nearly 180°, indicating a clear antiphase relationship between the two branches at this frequency, suggesting a tendency to cancel each other out. However, the total admittance phase is approximately -93.4°, highly consistent with the red branch, indicating that although the branches are approximately opposite, the total phase does not reflect this or average characteristic, but is dominated by the dominant branch. Combined with the amplitude response, it can be seen that the amplitudes of both branches are high but unequal near 1.100 GHz, with the total amplitude being approximately -3 dB, indicating incomplete cancellation, thus maintaining a clear directionality in the synthesized phasor. Further frequency sweep results show that when a branch enters a phase abrupt change or strong resonance region, the phase and amplitude responses of the total path will converge accordingly, demonstrating the obvious branch dominance and frequency band dependence characteristics in the parallel network.

[0037] Therefore, physical parameter tuning is required through the optimization step in step 104 to obtain a filter with a wider bandwidth. This can be combined with... Figures 4-5 Please provide an explanation. For example... Figure 4 and Figure 5 As shown, at the marked frequency m15, the phases of the two parallel branches are approximately 29.1° and 18.7°, respectively, with a small phase difference, exhibiting near-in-phase characteristics. The corresponding total admittance phase is approximately 25.5°, located between the two and slightly biased towards the red branch, indicating that there is no obvious anti-phase cancellation at this frequency point, but rather that they participate in synthesis in a near-in-phase manner, with the total phase formed by the weighted superposition of the phasors of the two branches. The amplitude response shows that both branches are in the passband near 1.100 GHz, with losses of approximately -6.6 dB and -5.4 dB, respectively, which are close in magnitude, while the total amplitude is approximately -3 dB, demonstrating the beneficial gain brought by parallel synthesis. The frequency sweep results further show that when one branch enters a strong resonance or deep trough region, its amplitude decays and is accompanied by a rapid phase change, and the total response subsequently approaches that of the other branch. Overall, the parallel branches in this frequency band are nearly in phase and have similar amplitudes at their operating points, enabling the total circuit to achieve smooth and stable phase synthesis and superior amplitude performance, demonstrating the cooperative working characteristics of the parallel structure within the passband.

[0038] Figure 1The above method, by paralleling multiple trapezoidal filter branches with adjacent center frequencies and introducing matching inductors at the input and output ports, can achieve continuous synthesis of the passband in the frequency domain, thereby improving the bandwidth of the SAW filter. Specifically, through parallel filter branches, a phase synergistic synthesis effect can be achieved within the target frequency band; a global optimization algorithm can be used to rationally design the resonator parameters of the SAW filter, so that within the target power frequency band: in the central region of the passband, the admittance phases of each parallel branch tend to be in phase, and the total admittance phasor exhibits a superposition enhancement state, thereby reducing insertion loss; in the left and right edge regions of the passband, different filter branches become the dominant paths, and their phase changes remain continuous, making the overall passband smoothly spliced ​​from multiple branches; the matching inductors provide consistent phase compensation and impedance adjustment for the parallel branches at the system level, further improving the phase continuity at adjacent passband edges, suppressing passband dips, thereby achieving an improvement in the electromechanical coupling coefficient independent of a single resonator, and also significantly expanding the bandwidth of the SAW filter.

[0039] based on Figure 1 In addition to the method described herein, this specification also provides some specific implementation methods of the method, which will be described below.

[0040] As an alternative approach, step 102 can be implemented based on S21-S23: S21: Determine the initial model of the coupled-mode theoretical model based on the measured resonator.

[0041] Specifically, S21 can be implemented based on S211-S213: S211: Based on the piezoelectric substrate material and geometry of the measured resonator, perform material property analysis and propagation characteristic analysis to determine the material parameters in the coupled-mode theoretical model. This step determines the types of material parameters.

[0042] The material parameters of a resonator include propagation loss coefficient, electromechanical coupling coefficient, capacitance per unit length, acoustic wave propagation constant, and surface acoustic wave velocity. Coupled-mode theory describes the three core processes of acoustic mode resonance, mode coupling, and energy loss in a resonator, simplifying the complex piezoelectric acoustic propagation problem into a model in the form of ordinary differential equations.

[0043] S212: Determine the physical parameters in the coupled-mode theoretical model based on the measured geometry of the resonator.

[0044] This section defines the types of physical parameters, including the number of interdigital pairs, the number of reflector roots, the finger width, and the acoustic aperture.

[0045] S213: Construct an initial model of the coupled mode theory model based on the material parameters and the physical parameters.

[0046] Specifically, S213 is implemented based on S2131-S2132: S2131: Based on coupled-mode theory, establish differential equations and boundary conditions describing the sound field propagation and electromechanical conversion within the measured resonator.

[0047] The sound field propagation equation describes the amplitude change, loss, and excitation coupling relationship during propagation; the electromechanical conversion equation establishes the relationship between port current, sound wave amplitude, and excitation voltage. Boundary conditions are set based on the sound wave reflection boundary defined by the reflector grating structure, resulting in a closed set of equations.

[0048] S2132: Based on the differential equation, the material parameters and physical parameters are mapped to the parameters of equivalent circuit elements to obtain the initial model of the coupled-mode theoretical model.

[0049] For example, the propagation loss coefficient can be mapped to a mutual inductance element, a resistive element, a unit-length capacitance to a capacitive element, and the sound wave propagation constant to the distributed parameters of the transmission line. The initial model is a model that substitutes the measured physical parameters of the resonator.

[0050] The initial model of the coupled-mode theoretical model of the resonator can be directly obtained based on the actual physical structure and real-world physical conditions. This is existing technology and will not be described in detail here.

[0051] S22: Generate a measured admittance curve based on the measured data.

[0052] In practical applications, measured data can be converted into admittance curves using plotting software.

[0053] S23: The key parameters of the initial model are adjusted using the nonlinear least squares method to ensure that the error between the predicted admittance curve and the measured admittance curve of the adjusted initial model is within a preset error range. The material parameters corresponding to each measured resonator are extracted, and the average value of the material parameters corresponding to each measured resonator is used as the final material parameters and input into the initial model to obtain the coupled-mode theoretical model. The coupled-mode theoretical model can be verified by simulation before use.

[0054] In practical applications, the key parameters that can be adjusted include coupling coefficient, loss rate, etc.

[0055] As an optional approach, assume that the number of filter branches constructed is two, and the target frequency band range is the sum of the first target frequency band range and the second target frequency band range; the first target frequency band range partially overlaps with the second target frequency band range. For example, the target frequency band range is 3400MHz~3600MHz, the first target frequency band range can be 3400 MHz~3500 MHz, and the second target frequency band range can be 3500 MHz~3600 MHz. Step 103 is specifically implemented by S31-S33: S31: Connect multiple coupled-mode theoretical models according to the trapezoidal filter structure to obtain the first filter branch and the second filter branch.

[0056] SAW filters are trapezoidal filters, composed of alternating cascaded series and parallel resonators, with a trapezoidal topology.

[0057] S32: Adjust the physical parameters of the resonator of the first filter branch so that the frequency range of the first filter branch is the first target frequency range.

[0058] S33: Adjust the physical parameters of the resonator of the second filter branch so that the frequency range of the first filter branch is the second target frequency range, thus completing the construction of the two filter branches.

[0059] The above is just an example. In practical applications, the number of filter branches can be set according to requirements. The construction method is the same as that for filters with two branches, and will not be repeated here.

[0060] As an alternative approach, step 104 can be implemented based on S41-S42: S41: Determine the optimization objective and constraints.

[0061] The optimization objectives are to minimize insertion loss within the passband; achieve a flat passband amplitude response; eliminate dips at the junctions of adjacent passbands; ensure continuous group delay without significant abrupt changes; and meet the target bandwidth requirements.

[0062] In practical applications, the above objectives need to be quantified. The quantified optimization objectives are: the insertion loss in the passband is less than the preset loss, the passband amplitude fluctuation is less than the preset amplitude, the flatness at the junction of adjacent passbands is less than the preset flatness, the peak value of the group delay peak is less than the preset peak value, and the target bandwidth requirement is met. The constraint condition is that the overall performance of the filter topology meets the preset requirements. The preset loss, preset amplitude, preset flatness, and preset peak value can all be set according to the requirements.

[0063] S42: Determine the objective function based on the optimization objective.

[0064] In practical applications, the parameters of the optimization target can be directly input into the circuit simulation platform. The circuit simulation platform will convert the optimization target into an objective function and generate an optimization target plugin. When there are multiple optimization targets, multiple optimization target plugins will be generated.

[0065] S43: Based on the simulated annealing optimization algorithm, the physical parameters of the filter topology are iteratively optimized in the circuit simulation platform until the optimization target is reached, and the optimized filter topology is obtained.

[0066] Specifically, initialization is performed first by randomly generating an initial solution and setting parameters such as initial temperature, cooling rate, maximum number of iterations, and temperature threshold. A cooling plan is also set up, and new solutions are accepted based on the probability function of the initial solution. Through cooling, new solutions are obtained iteratively until convergence.

[0067] Each iteration of the loop proceeds as follows: Calculate the objective function value based on the current physical parameters, compare the objective function value with the optimization target, and obtain the comparison result; adjust the number of interdigitated fingers, the number of reflector roots, the finger width, and the acoustic aperture of the filter topology based on the comparison result. The loop terminates when the objective function value reaches the optimization target.

[0068] Based on the same design concept, this invention also provides a SAW filter, which is fabricated using the aforementioned method for improving the bandwidth of a SAW filter. The SAW filter includes: multiple trapezoidal SAW filter branches with adjacent center frequencies; matching inductors disposed at the input and output ports of the SAW filter; multiple trapezoidal SAW filter branches connected in parallel; and each trapezoidal SAW filter branch consisting of multiple resonators. The physical parameters of the resonators are determined based on coupled-mode theory modeling.

[0069] The number of branches in a SAW filter can be set according to requirements, for example, such as Figure 6 As shown, the SAW filter includes a first trapezoidal SAW filter branch 1 and a second trapezoidal SAW filter branch 2, with two matching inductors 3 disposed at the input and output ports of the SAW filter. The first trapezoidal SAW filter branch 1 includes multiple resonators 11.

[0070] As an alternative, the resonator is a two-port resonator, which includes a piezoelectric substrate, an input interdigital transducer, an output interdigital transducer, and two sets of reflective gratings; the input interdigital transducer, the output interdigital transducer, and the two sets of reflective gratings are disposed on the surface of the piezoelectric substrate; the two sets of reflective gratings are disposed outside the input interdigital transducer and the output interdigital transducer.

[0071] For example, the piezoelectric substrate material of the resonator is selected as standard 42°YX lithium tantalate ( The resulting SAW filter can achieve a continuous bandwidth of approximately 200 MHz in the 3.5 GHz band, and has the advantages of simple structure, small size, and ease of implementation.

[0072] The SAW filter obtained by this invention has a simple structure, small device size, and is easy to manufacture and integrate; it is suitable for the design of high-frequency broadband SAW filters and has good engineering application value.

[0073] The embodiments of the present invention can divide functional modules according to the above method examples. For example, each function can be divided into its own functional module, or two or more functions can be integrated into one processing module. The integrated module can be implemented in hardware or as a software functional module. It should be noted that the module division in the embodiments of the present invention is illustrative and only represents one logical functional division; other division methods may be used in actual implementation.

[0074] When dividing each function into modules according to its corresponding function. Figure 7 A schematic diagram of a device structure for improving the bandwidth of a SAW filter provided by the present invention is shown. Figure 7 As shown, the device includes: The measured data acquisition module 701 is used to acquire the measured data of the measured resonator in the target frequency band range; The coupled-mode theoretical model construction module 702 is used to construct the coupled-mode theoretical model of the resonator based on the measured data and using the measured curve fitting method. The filter branch construction module 703 is used to construct multiple filter branches with adjacent center frequencies; the filter branches are obtained by combining multiple coupled-mode theoretical models according to a trapezoidal filter structure; the sum of the frequency ranges of the multiple filter branches is the target frequency range; The physical parameter optimization module 704 is used to perform reverse optimization of the physical parameters of the filter topology using a global optimization algorithm, so that the bandwidth of the optimized filter topology reaches the target bandwidth, and the target physical parameters of the SAW filter are obtained; the filter topology consists of multiple filter branches connected in parallel and matching inductors set at the output port and the input port.

[0075] Optionally, the coupled-mode theoretical model construction module 702 may specifically include: The initial model building unit is used to determine the initial model of the coupled-mode theoretical model based on the measured resonator; A measured admittance curve generation unit is used to generate a measured admittance curve based on the measured data; The fitting unit is used to adjust the key parameters of the initial model using the nonlinear least squares method, so that the error between the predicted admittance curve and the measured admittance curve of the adjusted initial model is within a preset error, thereby obtaining the coupled-mode theoretical model.

[0076] Optionally, the initial model building unit may specifically include: The material parameter determination subunit is used to perform material property analysis and propagation characteristic analysis based on the piezoelectric substrate material and geometry of the measured resonator, and to determine the material parameters in the coupled-mode theoretical model; the material parameters include propagation loss coefficient, electromechanical coupling coefficient, capacitance per unit length, acoustic wave propagation constant, and surface acoustic wave propagation velocity; The physical parameter type determination subunit is used to determine the physical parameters in the coupled-mode theoretical model based on the geometric structure of the measured resonator. Construct sub-units to form the initial model for building the coupled-mode theoretical model based on the material parameters and the physical parameters.

[0077] Optionally, the building subunit can be specifically used for: Based on coupled-mode theory, a differential equation describing the sound field propagation and electromechanical conversion within the measured resonator is established. Based on the differential equation, the material parameters and physical parameters are mapped to the parameters of equivalent circuit elements to obtain the initial model of the coupled-mode theoretical model.

[0078] Optionally, the physical parameter optimization module 704 may specifically include: The optimization objective and constraint determination unit is used to determine the optimization objective and constraint; the optimization objective is that the insertion loss in the passband is less than a preset loss, the passband amplitude fluctuation is less than a preset amplitude, the flatness at the junction of adjacent passbands is less than a preset flatness, the peak value of the group delay peak is less than a preset peak value, and the target bandwidth requirement is met; the constraint is that the overall performance of the filter topology reaches a preset requirement. The simulated annealing optimization unit is used to iteratively optimize the physical parameters of the filter topology in a circuit simulation platform based on the simulated annealing optimization algorithm until the optimization target is reached, thus obtaining the optimized filter topology.

[0079] Optionally, the physical parameters include the number of interdigitated pairs, the number of reflective grating roots, the finger width, and the acoustic aperture; the simulated annealing optimization unit can specifically be used to: calculate the objective function value based on the current physical parameters, and compare the objective function value with the optimization objective to obtain the comparison result; Based on the comparison results, the number of interdigitated fingers, the number of reflective grating roots, the finger width, and the acoustic aperture of the filter topology are adjusted until the objective function value reaches the optimization target.

[0080] Optionally, the number of filter branches constructed is two, and the target frequency band range is the sum of the first target frequency band range and the second target frequency band range; the first target frequency band range and the second target frequency band range partially overlap. Optionally, the filter branch construction module 703 may specifically include: Branch construction unit is used to connect multiple coupled-mode theoretical models according to the trapezoidal filter structure to obtain the first filter branch and the second filter branch; The first filter branch parameter adjustment unit is used to adjust the physical parameters of the resonator of the first filter branch so that the frequency range of the first filter branch is the first target frequency range. The second filter branch parameter adjustment unit is used to adjust the physical parameters of the resonator of the second filter branch so that the frequency range of the first filter branch is the second target frequency range, thus completing the construction of the two filter branches.

[0081] The above mainly describes the solutions provided by the embodiments of the present invention from the perspective of the interaction between various modules. It is understood that, in order to achieve the above functions, it includes corresponding hardware structures and / or software modules for executing each function. Those skilled in the art should readily recognize that, in conjunction with the units and algorithm steps of the various examples described in the embodiments disclosed herein, the present invention can be implemented in hardware or a combination of hardware and computer software. Whether a function is executed in hardware or by computer software driving hardware depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0082] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer programs or instructions. When the computer program or instructions are loaded and executed on a computer, the processes or functions described in the embodiments of the present invention are performed entirely or partially. The computer can be a general-purpose computer, a special-purpose computer, a computer network, a terminal, a user equipment, or other programmable device. The computer program or instructions can be stored in a computer-readable storage medium or transferred from one computer-readable storage medium to another. For example, the computer program or instructions can be transferred from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, such as a floppy disk, hard disk, or magnetic tape; it can also be an optical medium, such as a digital video disc (DVD); or it can be a semiconductor medium, such as a solid-state drive (SSD).

[0083] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0084] Although the invention has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein without departing from the spirit and scope of the invention. Accordingly, this specification and drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if such modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include such modifications and modifications.

Claims

1. A method of increasing the bandwidth of a SAW filter, characterized by, include: Obtain measured data of the measured resonator within the target frequency band range; Based on the measured data, the coupled-mode theoretical model of the resonator is constructed using the measured curve fitting method; Construct multiple filter branches with adjacent center frequencies; The filter branch is obtained by combining multiple coupled-mode theoretical models according to a trapezoidal filter structure; the sum of the frequency ranges of the multiple filter branches is the target frequency range; A global optimization algorithm is used to perform reverse optimization on the physical parameters of the filter topology, so that the bandwidth of the optimized filter topology reaches the target bandwidth, and the target physical parameters of the SAW filter are obtained. The filter topology consists of multiple filter branches connected in parallel and matching inductors set at the output port and the input port.

2. The method of claim 1, wherein, The construction of the coupled-mode theoretical model of the resonator based on the measured physical parameters and using the measured curve fitting method includes: The initial model of the coupled-mode theoretical model is determined based on the measured resonator. Generate a measured admittance curve based on the measured data; The key parameters of the initial model are adjusted using the nonlinear least squares method so that the error between the predicted admittance curve and the measured admittance curve of the adjusted initial model is within a preset error, thus obtaining the coupled-mode theoretical model.

3. The method of claim 1, wherein the SAW filter is a ladder-type SAW filter. The process involves using a global optimization algorithm to perform reverse optimization of the physical parameters of the filter topology, ensuring that the bandwidth of the optimized filter topology reaches the target bandwidth. The resulting optimized filter topology includes: The optimization objectives and constraints are determined as follows: the optimization objectives are that the insertion loss in the passband is less than a preset loss, the passband amplitude fluctuation is less than a preset amplitude, the flatness at the junction of adjacent passbands is less than a preset flatness, the peak value of the group delay peak is less than a preset peak value, and the target bandwidth requirement is met; the constraints are that the overall performance of the filter topology reaches the preset requirements. Based on the simulated annealing optimization algorithm, the physical parameters of the filter topology are iteratively optimized in the circuit simulation platform until the optimization target is reached, and the optimized filter topology is obtained.

4. The method of claim 2, wherein the SAW filter is a ladder-type SAW filter. The initial model for determining the coupled-mode theoretical model based on the measured resonator includes: Based on the piezoelectric substrate material and geometry of the measured resonator, material property analysis and propagation characteristic analysis are performed to determine the material parameters in the coupled-mode theoretical model. The material parameters include propagation loss coefficient, electromechanical coupling coefficient, capacitance per unit length, acoustic wave propagation constant, and surface acoustic wave propagation velocity. The physical parameters in the coupled-mode theoretical model are determined based on the measured geometry of the resonator. An initial model of the coupled-mode theory model is constructed based on the material parameters and the physical parameters.

5. The method of claim 4, wherein the SAW filter is a ladder-type SAW filter. The initial model for constructing the coupled-mode theory model based on the material parameters and the physical parameters includes: Based on coupled-mode theory, a differential equation describing the sound field propagation and electromechanical conversion within the measured resonator is established. Based on the differential equation, the material parameters and physical parameters are mapped to the parameters of equivalent circuit elements to obtain the initial model of the coupled-mode theoretical model.

6. The method for improving the bandwidth of a SAW filter according to claim 3, characterized in that, The physical parameters include the number of interdigitated pairs, the number of reflector roots, the finger width, and the acoustic aperture; the simulated annealing optimization algorithm iteratively optimizes the physical parameters of the filter topology in a circuit simulation platform until the optimization objective is achieved, including: The objective function value is calculated based on the current physical parameters, and then compared with the optimization objective to obtain the comparison result. Based on the comparison results, the number of interdigitated fingers, the number of reflective grating roots, the finger width, and the acoustic aperture of the filter topology are adjusted until the objective function value reaches the optimization target.

7. The method for improving the bandwidth of a SAW filter according to claim 1, characterized in that, The number of filter branches constructed is two, and the target frequency band range is the sum of the first target frequency band range and the second target frequency band range; the first target frequency band range and the second target frequency band range partially overlap. The construction of multiple filter branches adjacent to the center frequency includes: Multiple coupled-mode theoretical models are connected according to a trapezoidal filter structure to obtain the first filter branch and the second filter branch; Adjust the physical parameters of the resonator in the first filter branch so that the frequency range of the first filter branch is the first target frequency range; Adjust the physical parameters of the resonator in the second filter branch so that the frequency range of the first filter branch is the second target frequency range, thus completing the construction of the two filter branches.

8. A SAW filter, prepared using the method for increasing the bandwidth of a SAW filter according to any one of claims 1-7, characterized in that, The SAW filter includes at least: multiple trapezoidal SAW filter branches with adjacent center frequencies, matching inductors disposed at the input and output ports of the SAW filter; multiple trapezoidal SAW filter branches connected in parallel; and each trapezoidal SAW filter branch consisting of multiple resonators.

9. A SAW filter according to claim 8, characterized in that, The resonator is a two-port resonator, which includes a piezoelectric substrate, an input interdigital transducer, an output interdigital transducer, and two sets of reflective gratings. The input interdigital transducer, the output interdigital transducer, and the two sets of reflective gratings are disposed on the surface of the piezoelectric substrate. The two sets of reflective gratings are disposed on the outside of the input interdigital transducer and the output interdigital transducer.

10. A device for increasing the bandwidth of a SAW filter, characterized in that, include: The measured data acquisition module is used to acquire measured data of the measured resonator within the target frequency band range; The coupled-mode theoretical model construction module is used to construct the coupled-mode theoretical model of the resonator based on the measured data and using the measured curve fitting method. A filter branch construction module is used to construct multiple filter branches with adjacent center frequencies; the filter branches are obtained by combining multiple coupled-mode theoretical models according to a trapezoidal filter structure; the sum of the frequency ranges of the multiple filter branches is the target frequency range; The physical parameter optimization module is used to perform reverse optimization of the physical parameters of the filter topology using a global optimization algorithm, so that the bandwidth of the optimized filter topology reaches the target bandwidth, and the target physical parameters of the SAW filter are obtained; the filter topology consists of multiple filter branches connected in parallel and matching inductors set at the output port and the input port.

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