DMS filter and filter circuit

Abstract

The invention relates to a DMS filter and a filter circuit, the DMS filter comprises reflectors and a plurality of IDTs arranged between the reflectors, and each IDT is arranged along the propagation direction of surface acoustic waves; each IDT comprises a plurality of spacing intervals, and each spacing interval is provided with interdigitals which are arranged along the propagation direction of the surface acoustic wave and are sequentially connected end to end; wherein the spacing interval of each IDT comprises a main spacing area and a plurality of spacing adjusting areas, the spacing of the interdigitals in the main spacing area is consistent, the spacing of the adjacent interdigitals in the spacing adjusting areas is different, the same spacing change amplitude is uniformly and monotonically increased or decreased, and the spacing change amplitudes of the adjacent interdigitals in different spacing adjusting areas are different. By adjusting the interdigital spacing in the IDT one by one, the optimization degree of freedom is improved, more resonance points are introduced into the passband, and meanwhile, the positions of the resonance points are more convenient to adjust, so that the purposes of reducing insertion loss in the passband of the filter, improving the standing-wave ratio, expanding the bandwidth and the like are achieved, the filter adapts to different use scenes, and the application range is widened.

Description

Technical Field

[0001] The present application relates to the technical field of filters, and in particular to a DMS filter and a filter circuit. Background Art

[0002] With the emergence of each new generation of communication standards, the public's demand for higher data rates has increased the number of acoustic wave devices required, the communication band has become increasingly crowded, and the demand for different bandwidths has also increased. Therefore, RF surface acoustic wave (SAW) filters must also be continuously improved and innovated according to the development of the times. In DMS (double-mode-SAW) filters, the position of the resonance point is mainly adjusted by the interdigital spacing in the IDT and the gap between different IDTs. In traditional DMS filters, the interdigital spacing in each IDT is the same, and the number of adjustable resonances is quite limited, which cannot meet the high requirements of today's SAW filters and has a limited scope of application. Summary of the invention

[0003] Based on this, it is necessary to provide a DMS filter and a filter circuit that can improve the scope of application in order to solve the above problems.

[0004] In a first aspect, the present application provides a DMS filter, comprising a reflector, and a plurality of IDTs arranged between the reflectors, wherein each of the IDTs is arranged along the propagation direction of a surface acoustic wave; each of the IDTs comprises a plurality of spacing intervals, and each spacing interval is provided with fingers arranged along the propagation direction of the surface acoustic wave and connected end to end in sequence; wherein each spacing interval of the IDT comprises a main spacing zone and a plurality of adjustment spacing zones, wherein the spacing of the fingers in the main spacing zone is consistent, and the spacing of adjacent fingers in the adjustment spacing zone is different, and increases or decreases uniformly and monotonically with the same spacing variation amplitude, and the spacing variation amplitudes of adjacent fingers in different adjustment spacing zones are different.

[0005] In one embodiment, the IDT includes a first IDT, a second IDT, a third IDT, a fourth IDT and a fifth IDT arranged along the propagation direction of the surface acoustic wave, the first IDT, the third IDT and the fifth IDT are all connected to the input end, and the second IDT and the fourth IDT are all connected to the output end.

[0006] In one embodiment, the second IDT, the third IDT and the fourth IDT all include a main spacing area, an adjustment spacing area one and an adjustment spacing area two; in the second IDT, the third IDT and the fourth IDT, the number of the adjustment spacing area one and the adjustment spacing area two are both two, and they are symmetrically arranged relative to the main spacing area, and each adjustment spacing area one is located between the main spacing area and the corresponding adjustment spacing area two.

[0007] In one embodiment, the first IDT and the fifth IDT both include a main spacing region, an adjustment spacing region 1 and an adjustment spacing region 2; in the first IDT and the fifth IDT, the adjustment spacing region 1 is located between the main spacing region and the adjustment spacing region 2, and the main spacing region is located on a side close to the corresponding reflector.

[0008] In one of the embodiments, in the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing between adjacent interdigits in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigits in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing change amplitude in the adjustment spacing zone one is smaller than the spacing change amplitude in the adjustment spacing zone two, which is manifested as the interdigital spacing first slowly decreases and then rapidly decreases from the main spacing zone.

[0009] In one of the embodiments, in the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing between adjacent interdigits in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigits in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing change amplitude in the adjustment spacing zone one is greater than the spacing change amplitude in the adjustment spacing zone two, which is manifested as the interdigital spacing first decreases rapidly and then slowly decreases from the main spacing zone.

[0010] In one of the embodiments, in the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing between adjacent interdigits in the adjustment spacing zone one increases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigits in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, which is manifested as the interdigit spacing first increases and then decreases in the main spacing zone.

[0011] In one of the embodiments, in the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing between adjacent interdigits in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigits in the adjustment spacing zone two increases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, which is manifested as the interdigit spacing first decreases and then increases in the main spacing zone.

[0012] In one embodiment, the changing rules of the first adjustment spacing area and the second adjustment spacing area between different IDTs are the same or different.

[0013] A second aspect of the present application provides a filter circuit, including a ladder filter and the above-mentioned DMS filter.

[0014] In the above-mentioned DMS filter and filter circuit, each IDT includes multiple spacing intervals, and each spacing interval is provided with fingers arranged along the propagation direction of the surface acoustic wave and connected end to end in sequence; wherein, each IDT spacing interval includes a main spacing area and multiple adjustment spacing areas, the spacing of the fingers in the main spacing area is consistent, and the spacing of each adjacent finger in the adjustment spacing area is different, and the spacing changes uniformly and monotonically increase or decrease with the same spacing change amplitude, and the spacing change amplitude of adjacent fingers in different adjustment spacing areas is different. The optimization freedom is improved by adjusting the finger spacing in the IDT root by root through bilinear Delta weighting. Compared with the traditional DMS filter, more resonance points are introduced in the passband. Compared with the single linear Delta weighted DMS filter, the position of the resonance point in the passband is better adjusted to achieve the purpose of reducing the insertion loss in the filter passband, improving the standing wave ratio and expanding the bandwidth, so as to adapt to different usage scenarios and improve the scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the structure of a DMS filter in one embodiment of the present application;

[0016] Figure 2 This is a schematic diagram of the spacing distribution of the third IDT in one embodiment of the present application;

[0017] Figure 3 This is a schematic diagram of the spacing distribution of the fifth IDT in one embodiment of the present application;

[0018] Figure 4 This is a distribution diagram of the interdigital spacing of each IDT in Example 1 of this application;

[0019] Figure 5 This is a distribution diagram of the interdigital spacing of the third IDT in Example 1 of this application;

[0020] Figure 6 This is a distribution diagram of the interdigital spacing of the first IDT in Example 1 of this application;

[0021] Figure 7 This is a distribution diagram of the interdigital spacing of each IDT in Example 2 of this application;

[0022] Figure 8 This is a distribution diagram of the interdigital spacing of the second IDT in Example 2 of this application;

[0023] Figures 9 to 12 This is a performance comparison chart of Example 1 of this application and the single spacing variation amplitude adjustment solution;

[0024] Figures 13 to 17 This is a performance comparison chart of Example 2 of this application and the single spacing variation amplitude adjustment solution;

[0025] Fig.18This is a comparison chart of insertion loss between Example 1 and Example 2 of this application;

[0026] Fig.19 This is a schematic diagram of the structure of a filter circuit in one embodiment of the present application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0029] It can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, “communication connection”, etc. if the connected circuits, modules, units, etc. have electrical signals or data transmission between each other.

[0030] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" etc. specify the presence of stated features, wholes, methods, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, methods, operations, components, parts or combinations thereof.

[0031] In one embodiment, Figure 1 As shown, a DMS filter is provided, including a reflector 110, and a plurality of IDTs 120 arranged between the reflectors 110, each of the IDTs 120 being arranged along the propagation direction of a surface acoustic wave; each of the IDTs 120 including a plurality of spacing intervals, and each of the spacing intervals being provided with fingers arranged along the propagation direction of the surface acoustic wave and connected end to end in sequence; wherein the spacing interval of each of the IDTs 120 includes a main spacing area and a plurality of adjustment spacing areas, the spacing of the fingers in the main spacing area is consistent, the spacing of adjacent fingers in the adjustment spacing area is different, and increases or decreases uniformly and monotonically with the same spacing variation amplitude, and the spacing variation amplitudes of adjacent fingers in different adjustment spacing areas are different.

[0032] The DMS filter is designed to support multiple resonant modes within its passband, wherein the number of IDTs 120 and the number of adjustment spacing zones in each IDT 120 are not unique and can be set according to actual needs. The spacing of the interdigitated fingers in the main spacing zone is consistent, and the spacing of the interdigitated fingers can be the same. Figure 1 As shown, in this embodiment, the number of IDTs 120 is five. Between a pair of reflectors 110, the five IDTs 120 are arranged along the propagation direction of the surface acoustic wave, and are named as the first IDT, the second IDT, the third IDT, the fourth IDT and the fifth IDT from one reflector 110 to another. The first IDT, the third IDT and the fifth IDT are all connected to the input terminal 1, and the second IDT and the fourth IDT are all connected to the output terminal 2. In each IDT 120, the interdigital fingers are arranged along the propagation direction of the surface acoustic wave and are connected end to end in sequence, and the spacing of some interdigital fingers is kept constant, which is defined as the main spacing area. Adjustment spacing areas are set on both sides or one side of the main spacing area. The number of adjustment spacing areas can be two or more, and three to five interdigital fingers are set in each adjustment spacing area. The spacing between adjacent interdigital fingers in the same adjustment spacing area is not equal, but increases or decreases uniformly and monotonically with the same spacing change amplitude delta, and the spacing change amplitude delta of the two adjustment spacing areas is different.

[0033] In one embodiment, Figure 1 and Figure 2 As shown, the second IDT, the third IDT and the fourth IDT all include a main spacing area, an adjustment spacing area 1 and an adjustment spacing area 2; in the second IDT, the third IDT and the fourth IDT, the number of the adjustment spacing area 1 and the adjustment spacing area 2 are both two, and they are symmetrically arranged relative to the main spacing area, and each adjustment spacing area 1 is located between the main spacing area and the corresponding adjustment spacing area 2. Further, as Figure 1 and Figure 3 As shown, the first IDT and the fifth IDT each include a main spacing region, an adjustment spacing region 1 and an adjustment spacing region 2; in the first IDT and the fifth IDT, the adjustment spacing region 1 is located between the main spacing region and the adjustment spacing region 2, and the main spacing region is located on a side close to the corresponding reflector 110. Figure 1, each IDT 120 is divided into multiple spacing intervals, represented by different colors, where red is the main spacing area, purple is the adjustment spacing area one, and green is the adjustment spacing area two. The two outer IDTs 120 (the first IDT and the fifth IDT) have three spacing intervals, and the three middle IDTs 120 (the second IDT, the third IDT, and the fourth IDT) have five spacing intervals. The second IDT, the third IDT, and the fourth IDT are designed to be centrally symmetrical in the overall structure. The spacing change amplitude delta of different adjustment spacing areas in each IDT 120 is different, realizing the bilinear cross-finger weighted configuration of the DMS filter. By introducing an additional spacing change amplitude delta variable, the IDT of the filter is divided into multiple spacing sizes. The change of the period introduces more resonance points and better adjusts the position of the resonance points, so that the result optimization has more degrees of freedom. At the same time, the uniform and regular change also avoids the problem of too many optimization parameters leading to too long optimization time.

[0034] The DMS structure uses acoustic coupling to propagate the sound wave laterally through the IDT, and achieves filtering through continuous reflection and frequency selection at the boundary. In the DMS filter, the gap connection between different IDTs causes energy to leak into the substrate material in the form of bulk acoustic waves due to period discontinuity. If the operating frequency is controlled below the bulk wave frequency, the energy leakage caused by the bulk acoustic wave can be effectively suppressed. Therefore, by changing the spacing of several fingers at the edges of different IDTs to control the period and operating frequency, the energy leakage of this bulk acoustic wave can be suppressed and the insertion loss can be reduced. At the same time, bilinear weighting has more optimization variables and more optimization freedom than single linear weighting. The number of adjusted fingers and the size of the spacing change amplitude delta will affect the final filter performance.

[0035] The bilinear weighted setting method of the interdigital fingers in the first IDT, the second IDT, the third IDT, the fourth IDT, and the fifth IDT is not unique. It can be that in the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing of adjacent interdigital fingers in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude along the direction away from the main spacing zone, and the spacing of adjacent interdigital fingers in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude along the direction away from the main spacing zone, and the spacing change amplitude of the adjustment spacing zone one is smaller than the spacing change amplitude of the adjustment spacing zone two, which is manifested as the interdigital spacing slowly decreases and then decreases rapidly from the main spacing zone; it can be that in the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing of adjacent interdigital fingers in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude along the direction away from the main spacing zone, and the spacing of adjacent interdigital fingers in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude along the direction away from the main spacing zone. The spacing of adjacent interdigits in the adjustment spacing zone 1 decreases uniformly, and the spacing variation amplitude of the adjustment spacing zone 1 is greater than the spacing variation amplitude of the adjustment spacing zone 2, which is manifested as the interdigital spacing first decreases rapidly and then decreases slowly from the main spacing zone; it can also be that in the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing of adjacent interdigits in the adjustment spacing zone 1 increases monotonically and uniformly with the same spacing variation amplitude in the direction away from the main spacing zone, and the spacing of adjacent interdigits in the adjustment spacing zone 2 decreases monotonically and uniformly with the same spacing variation amplitude in the direction away from the main spacing zone, which is manifested as the interdigital spacing first increases and then decreases from the main spacing zone; it can also be that in the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing of adjacent interdigits in the adjustment spacing zone 1 decreases monotonically and uniformly with the same spacing variation amplitude in the direction away from the main spacing zone, and the spacing of adjacent interdigits in the adjustment spacing zone 2 increases monotonically and uniformly with the same spacing variation amplitude in the direction away from the main spacing zone, which is manifested as the interdigital spacing first decreases and then increases from the main spacing zone.

[0036] Among them, the change rules of the adjustment spacing zone 1 and the adjustment spacing zone 2 between different IDTs are the same or different, that is, the change rules of the adjustment spacing zone 1 of each IDT can be completely the same, partially the same, or completely different, and the change rules of the adjustment spacing zone 2 of each IDT can also be completely the same, partially the same, or completely different. The following is an example of the interdigital bilinear weighting setting of five IDTs combined with a specific example.

[0037] like Figures 4 to 6 In the example 1 shown, the number of adjusted fingers in each IDT 120 is 7, 4 in adjustment spacing zone 1, and 3 in adjustment spacing zone 2. The second, third and fourth IDTs are all centrosymmetric structures, and the spacing between adjacent fingers in the main spacing zone of each IDT 120 remains consistent.

[0038] Among them, in the third IDT, the pitch between adjacent interdigital fingers in the first adjustment pitch area monotonically and uniformly decreases in the direction away from the main pitch area with the same pitch change amplitude, and the pitch between adjacent interdigital fingers in the second adjustment pitch area monotonically and uniformly decreases in the direction away from the main pitch area with the same pitch change amplitude, and the pitch change amplitude of the first adjustment pitch area is less than that of the second adjustment pitch area. As Figure 4 and Figure 5 shown, the entire structure of the third IDT is centrosymmetric. The area within the middle red frame is the main pitch area, where the pitch between interdigital fingers remains constant. The 4 interdigital fingers within the blue frame are the first adjustment pitch area, and each interdigital finger monotonically and uniformly decreases with the same pitch change amplitude Delta3_1. The 3 interdigital fingers within the green frame are the second adjustment pitch area, and each interdigital finger monotonically and uniformly decreases with the same pitch change amplitude Delta3_2. Among them, Delta3_1 < Delta3_2, which shows that the pitch between interdigital fingers first decreases slowly and then rapidly starting from the main pitch area.

[0039] Furthermore, continuing to refer to Figure 4 , in the second IDT / fourth IDT, the pitch between adjacent interdigital fingers in the first adjustment pitch area monotonically and uniformly decreases in the direction away from the main pitch area with the same pitch change amplitude, and the pitch change amplitude of the first adjustment pitch area in the second IDT / fourth IDT; in the second IDT / fourth IDT, the pitch between adjacent interdigital fingers in the second adjustment pitch area monotonically and uniformly decreases in the direction away from the main pitch area with the same pitch change amplitude, and the pitch change amplitude of the second adjustment pitch area in the second IDT / fourth IDT. In the second IDT and the fourth IDT, it shows that the pitch between interdigital fingers first decreases slowly and then rapidly starting from the main pitch area. It can be understood that the pitch change amplitude of the first adjustment pitch area in the second IDT may be the same as or different from that of the first adjustment pitch area in the fourth IDT. The pitch change amplitude of the second adjustment pitch area in the second IDT may be the same as or different from that of the second adjustment pitch area in the fourth IDT.

[0040] In addition, in the first IDT / fifth IDT, the pitch between adjacent interdigital fingers in the first adjustment pitch area monotonically and uniformly decreases in the direction away from the main pitch area with the same pitch change amplitude, and the pitch between adjacent interdigital fingers in the second adjustment pitch area monotonically and uniformly decreases in the direction away from the main pitch area with the same pitch change amplitude, and the pitch change amplitude of the first adjustment pitch area is greater than that of the second adjustment pitch area. As Figure 6As shown, taking the first IDT as an example, the red frame is the main spacing area, the interdigital spacing remains constant, the 4 interdigital fingers in the blue frame are the adjustment spacing area 1, each interdigital finger decreases monotonically and uniformly with the same spacing change amplitude Delta1_1, and the 3 interdigital fingers in the green frame are the adjustment spacing area 2, each interdigital finger decreases monotonically and uniformly with the same spacing change amplitude Delta1_2. Among them, Delta1_1 is greater than Delta1_2, which is manifested as the interdigital spacing first decreases rapidly and then slowly decreases from the main spacing area. It can be understood that the spacing change amplitude of the adjustment spacing area 1 in the first IDT can be the same as or different from the spacing change amplitude of the adjustment spacing area 1 in the fifth IDT. The spacing change amplitude of the adjustment spacing area 2 in the first IDT can be the same as or different from the spacing change amplitude of the adjustment spacing area 2 in the fifth IDT. In order to further improve the degree of freedom of optimization, the spacing change amplitudes of each adjustment spacing area in the five IDTs can be different from each other.

[0041] like Figures 7 and 8 In the second example shown, the number of adjusted fingers in each IDT 120 is 9, 4 in adjustment spacing zone 1, and 5 in adjustment spacing zone 2. The second, third and fourth IDTs are all centrosymmetric structures, and the spacing between adjacent fingers in the main spacing zone of each IDT 120 remains consistent.

[0042] Among them, in the third IDT, the spacing between adjacent interdigits in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude along the direction away from the main spacing zone, and the spacing between adjacent interdigits in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude along the direction away from the main spacing zone, and the spacing change amplitude of the adjustment spacing zone one is smaller than the spacing change amplitude of the adjustment spacing zone two, which is manifested as the interdigital spacing first slowly decreases and then quickly decreases starting from the main spacing zone.

[0043] Furthermore, in the second IDT / fourth IDT, the spacing between adjacent interdigits in the first adjustment spacing zone increases monotonically and uniformly with the same spacing variation amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigits in the second adjustment spacing zone decreases monotonically and uniformly with the same spacing variation amplitude in the direction away from the main spacing zone. Figure 8As shown, taking the second IDT as an example, the red frame is the main spacing area, the interdigital spacing remains constant, the 4 interdigits in the blue frame are the adjustment spacing area 1, each interdigit increases monotonically and uniformly with the same spacing change amplitude Delta2_1, and the 5 interdigits in the green frame are the adjustment spacing area 2, each interdigit decreases monotonically and uniformly with the same spacing change amplitude Delta2_2, which is manifested as the interdigital spacing first increases and then decreases from the main spacing area. It can be understood that the spacing change amplitude of the adjustment spacing area 1 in the second IDT can be the same as or different from the spacing change amplitude of the adjustment spacing area 1 in the fourth IDT. The spacing change amplitude of the adjustment spacing area 2 in the second IDT can be the same as or different from the spacing change amplitude of the adjustment spacing area 2 in the fourth IDT. In other examples, the second IDT / fourth IDT can also be that the adjustment spacing area 1 decreases monotonically and uniformly with the same spacing change amplitude Delta2_1, and the adjustment spacing area 2 increases monotonically and uniformly with the same spacing change amplitude Delta2_2, which is manifested as the interdigital spacing first decreases and then increases from the main spacing area.

[0044] In addition, in the first IDT / fifth IDT, the spacing between adjacent interdigits in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigits in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing change amplitude in the adjustment spacing zone one is smaller than the spacing change amplitude in the adjustment spacing zone two, which is manifested as the interdigital spacing slowly decreasing first and then rapidly decreasing from the main spacing zone. It can be understood that the spacing change amplitude of the adjustment spacing zone one in the first IDT may be the same as or different from the spacing change amplitude of the adjustment spacing zone one in the fifth IDT. The spacing change amplitude of the adjustment spacing zone two in the first IDT may be the same as or different from the spacing change amplitude of the adjustment spacing zone two in the fifth IDT. In order to further increase the degree of freedom in optimization, the spacing change amplitudes of each adjustment spacing zone in the five IDTs may be different from each other.

[0045] Specifically, the design indicators of surface acoustic wave filters are mainly:

[0046] 1. Insertion Loss: refers to the attenuation of the circuit signal after the filter is introduced, compared to when the filter is not introduced. Usually the insertion loss within the filter's operating bandwidth is considered.

[0047] 2. VSWR (Voltage Standing Wave Ratio): refers to the voltage standing wave ratio of the filter within the passband. The larger the VSWR, the higher the reflected power and the more mismatched the system impedance. In the design of surface acoustic wave filters, the VSWR in the passband is usually required to be below 1.5.

[0048] 3. Out-of-band rejection: refers to the ability of the filter to suppress signals outside the passband, which reflects the frequency selectivity of the filter. Usually, out-of-band rejection and insertion loss are two contradictory design indicators. If one is excellent, the other will perform poorly, so comprehensive consideration is needed.

[0049] The DMS filter provided in the present application improves the degree of optimization freedom by adjusting the interdigital spacing within the IDT root by root through bilinear Delta weighting. Compared with the traditional DMS filter, more resonance points are introduced into the passband. Compared with the single linear Delta weighted DMS filter, the position of the resonance point in the passband is better adjusted to achieve the purpose of reducing the insertion loss in the filter passband, improving the standing wave ratio and expanding the bandwidth.

[0050] Specifically, a filter for the B40 (2300-2400MHz) frequency band can be designed based on the PDK (Process Design Kit) model library. The circuit structure is a combination of a ladder type filter structure and a 5-IDT DMS filter. The SAW filter is obtained by adjusting the physical parameters of the SAW filter through simulation design. During the design process, the ladder type structure remains unchanged, and only the interdigital spacing in the IDT of the DMS filter is adjusted, while the other physical parameters remain unchanged, so as to compare the differences in simulation results of different interdigital spacing adjustment methods.

[0051] The performance comparison of the DMS filter in Example 1 is as follows: Figures 9 to 12 , which are comparison diagrams of insertion loss, standing wave ratio, left out-of-band suppression and right out-of-band suppression. The red line is the result of Example 1, and the blue line is the result of single Delta adjustment. It can be seen from the figure that the overall insertion loss in the passband has been significantly improved, and the VSWR in the passband has been reduced to below 1.5, expanding the bandwidth. The left out-of-band suppression meets the relevant performance indicators, and the two methods of right out-of-band suppression have little change.

[0052] The performance comparison of the DMS filter in Example 2 is as follows: Figures 13 to 17 , which are comparison diagrams of insertion loss, standing wave ratio, left out-of-band suppression, right out-of-band suppression and local insertion loss in the passband. The red line is the result of Example 2, and the blue line is the result of single Delta adjustment. It can be seen from the figure that the insertion loss in the passband has been significantly improved as a whole, especially in the 2320MHz~2355MHz part, with an increase of about 0.14dB. The VSWR in the passband is reduced to below 1.5. The out-of-band suppression on the left side meets the relevant performance indicators, and the out-of-band suppression on the right side does not change much, achieving the purpose of reducing insertion loss without reducing out-of-band suppression.

[0053] The comparison of the simulation results of DMS filter in Example 1 and Example 2 is shown in the figure below. Fig.18As shown, the red line is Example 1, and the blue line is Example 2. From the simulation results of the coupling model (COM, Coupling-of-Modes), for reducing insertion loss, the more the number of interdigit adjustments, the smaller the minimum insertion loss in the passband. Example 2 is more improved than Example 1, but at the same time, the insertion loss on the right side of the passband is larger, and it is necessary to make a choice based on specific design requirements. At the same time, the number of interdigit adjustments increases, and the range of interdigit spacing changes is also larger. There can be a change pattern of first increasing and then decreasing, and the change amplitude between adjacent interdigits can be smaller.

[0054] Among them, the coupling model is a simulation design algorithm model commonly used by various SAW filter manufacturers. Each manufacturer extracts the corresponding COM parameters from the test data of the actual processed resonator according to its own process conditions, and improves the accuracy of the COM model through continuous optimization and iteration. B40 (2300-2400MHz) is an indoor supplementary frequency band in operator applications and an important frequency band used in time division duplex (TDD) technology in mobile communications. For commercial filters, in the B40 frequency band, the insertion loss in the passband is improved by nearly 0.1dB, which significantly helps to improve the competitiveness of commercial filters, and also has more design margins for the subsequent design when comprehensively considering out-of-band suppression and insertion loss.

[0055] In one embodiment, a filter circuit is also provided, including a ladder filter and the above-mentioned DMS filter. The DMS filter is generally designed in conjunction with the ladder filter, such as Fig.19 As shown, the ladder filter includes a series resonator S1, a series resonator S2, a parallel resonator P1 and a parallel resonator P2. The series resonator S1 and the parallel resonator P1 are connected to one side of the DMS filter, and the parallel resonator P1 is grounded; the series resonator S2 and the parallel resonator P2 are connected to the other side of the DMS filter, and the parallel resonator P2 is grounded. The anti-resonance points of the series resonators S1 and S2 form a zero point on the right side of the passband, and the resonance points of the parallel resonators P1 and P2 form a zero point on the left side of the passband. A filter composed of a pair of series-parallel resonators is called a first-order ladder filter. Among them, the DMS filter is mainly responsible for supporting the passband bandwidth, and the four resonators are responsible for improving the overall rectangularity and out-of-band suppression of the filter.

[0056] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A DMS filter, characterized in that: It comprises a reflector and a plurality of IDTs arranged between the reflectors, wherein each of the IDTs is arranged along the propagation direction of a surface acoustic wave; each of the IDTs comprises a plurality of spacing intervals, and each spacing interval is provided with fingers arranged along the propagation direction of the surface acoustic wave and connected end to end in sequence; wherein each spacing interval of the IDT comprises a main spacing area and a plurality of adjustment spacing areas, wherein the spacing of the fingers in the main spacing area is consistent, and the spacing of adjacent fingers in the adjustment spacing area is different, and increases or decreases uniformly and monotonically with the same spacing variation amplitude, and the spacing variation amplitudes of adjacent fingers in different adjustment spacing areas are different.

2. The DMS filter according to claim 1, characterized in that: The IDT includes a first IDT, a second IDT, a third IDT, a fourth IDT and a fifth IDT arranged along a propagation direction of the surface acoustic wave, the first IDT, the third IDT and the fifth IDT are connected to an input end, and the second IDT and the fourth IDT are connected to an output end.

3. The DMS filter according to claim 2, characterized in that: The second IDT, the third IDT and the fourth IDT all include a main spacing area, an adjustment spacing area one and an adjustment spacing area two; in the second IDT, the third IDT and the fourth IDT, the number of the adjustment spacing area one and the adjustment spacing area two are both two, and they are symmetrically arranged relative to the main spacing area, and each adjustment spacing area one is located between the main spacing area and the corresponding adjustment spacing area two.

4. The DMS filter according to claim 3, characterized in that: The first IDT and the fifth IDT both include a main spacing region, an adjustment spacing region 1 and an adjustment spacing region 2; in the first IDT and the fifth IDT, the adjustment spacing region 1 is located between the main spacing region and the adjustment spacing region 2, and the main spacing region is located on a side close to the corresponding reflector.

5. The DMS filter according to claim 4, characterized in that: In the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing between adjacent interdigitated fingers in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigitated fingers in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing change amplitude in the adjustment spacing zone one is smaller than the spacing change amplitude in the adjustment spacing zone two, which is manifested as the interdigitated finger spacing first slowly decreases and then rapidly decreases from the main spacing zone.

6. The DMS filter according to claim 4, characterized in that: In the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing between adjacent interdigitated fingers in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigitated fingers in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing change amplitude in the adjustment spacing zone one is greater than the spacing change amplitude in the adjustment spacing zone two, which is manifested as the interdigitated finger spacing first decreasing rapidly and then slowly decreasing from the main spacing zone.

7. The DMS filter according to claim 4, characterized in that: In the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing between adjacent interdigitated fingers in the adjustment spacing zone one increases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigitated fingers in the adjustment spacing zone two decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, which is manifested as the interdigitated finger spacing first increasing and then decreasing from the main spacing zone.

8. The DMS filter according to claim 4, characterized in that: In the first IDT, the second IDT, the third IDT, the fourth IDT, or the fifth IDT, the spacing between adjacent interdigitated fingers in the adjustment spacing zone one decreases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, and the spacing between adjacent interdigitated fingers in the adjustment spacing zone two increases monotonically and uniformly with the same spacing change amplitude in the direction away from the main spacing zone, which is manifested as the interdigitated finger spacing first decreasing and then increasing in the main spacing zone.

9. The DMS filter according to claim 4, characterized in that: The changing rules of the adjustment spacing zone 1 and the adjustment spacing zone 2 between different IDTs are the same or different.

10. A filter circuit, characterized in that: It comprises a ladder filter and the DMS filter described in any one of claims 1 to 9.

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