Acoustic filter topology structure

Abstract

Disclosed is an acoustic filter topology structure, relating to the technical field of radio frequency filtering. The filter topology structure comprises two sets of parallel resonators respectively corresponding to a positive branch and a negative branch. Each set of parallel resonators is composed of no less than two resonators connected in parallel in a transverse direction. Input ends of the two sets of parallel resonators are connected together to serve as the input of the filter topology structure, and output ends thereof are each connected in parallel to an electrical balance branch to form positive and negative branch output ports of a BALUN output. The electrical balance branch is composed of an inductor connected to ground. The filter topology structure provided by the present invention can achieve a large-bandwidth filtering response, making the response of the filter independent of the coupling coefficient of the material. Without increasing cost, the design is simpler, the application is more flexible, and the configuration is more convenient. Moreover, on the basis of this topology structure, advanced responses of tunable filtering for multiple bands and multiplexing can be achieved.

Description

An acoustic filter topology TECHNICAL FIELD

[0001] The present application relates to the technical field of radio frequency filtering, in particular to an acoustic filter topology. BACKGROUND

[0002] Radio frequency acoustic filters are indispensable key core components in radio frequency front-ends, which realize frequency selection and filter out interference and noise signals outside the communication frequency band. With the rapid development of communication technology, the operating frequency bands required by wireless communication systems such as mobile phones are showing a trend of continuous growth. The fifth generation mobile communication (5G) and future 6G communication systems need to work on more frequency bands to meet the growing demand for data transmission and achieve seamless coverage of global communication. The number of frequency bands has increased from 4 in the 1990s to nearly 40 now, and each radio frequency band requires 2-3 acoustic filters to support, making the number of filters required by communication terminals surge to 80-100. The significant increase in the number of frequency bands poses unprecedented challenges to the radio frequency front-end system: the complexity of the system, the power handling capability, and the size of the device may approach the system limit.

[0003] The topology of the filter has a significant impact on its filtering effect, and different filter structures can achieve different filtering functions. The traditional acoustic filter based on surface acoustic wave (SAW) and bulk acoustic wave (BAW) resonators usually adopts a ladder configuration. This T-type topology configuration enables the filter to achieve high roll-off and low insertion loss characteristics at the edge of the wave band, while maintaining a relatively compact microwave size. However, the operating frequency and frequency bandwidth of this type of filter are limited by its piezoelectric substrate material, and due to the limitations of its fixed operating frequency, it is difficult to simultaneously meet the application requirements of multi-band signal processing and communication standard diversification. Therefore, how to realize a multi-band adjustable radio frequency acoustic filter has become a hot topic of concern at home and abroad.

[0004] SUMMARY

[0005] In view of the defects of the prior art, the present application provides an acoustic filter topology, which aims to provide a larger filtering response bandwidth and overcome the limitations of the traditional ladder configuration coupling coefficient. And based on this topology, further expansion can be achieved to realize multi-band and multiplexing advanced filtering response.

[0006] In order to achieve the above purpose, the present application provides a new topology of a surface acoustic wave filter, which comprises two groups of parallel resonators corresponding to the positive branch and the negative branch respectively; each group of parallel resonators is composed of not less than two resonators connected in a transverse parallel manner;

[0007] The input ends of the two groups of parallel resonators are connected as the input of the filter topology structure, and the output ends are respectively connected with the electrically balanced branch in parallel to form the positive and negative branch output ports of the BALUN output, and the electrically balanced branch is composed of inductance grounding.

[0008] Further, all the resonators are connected with switches, and different frequency band responses are formed by selecting the on or off.

[0009] Further, the resonators are acoustic resonators, including surface acoustic wave resonators, bulk acoustic wave resonators, plate wave resonators or MEMS resonators.

[0010] Further, the number of resonators in the two groups of parallel resonators is independently set; the impedance and resonant frequency of each resonator are respectively set and distributed along the filter passband.

[0011] The application further provides an acoustic filter module based on the acoustic filter topology structure as described above, and the filter module is formed by cascading a plurality of groups of the acoustic filter topology structure; each group of the acoustic filter topology structure is used as a sub-band response filter.

[0012] The parallel resonators of the positive branch in each group of the acoustic filter topology structure are further connected in parallel, the parallel resonators of the negative branch in each group of the acoustic filter topology structure are further connected in parallel, and the two output ports after the parallel connection are respectively connected with the electrically balanced branch in parallel to form the positive and negative branch output ports of the filter module, and the electrically balanced branch is composed of inductance grounding.

[0013] Further, the input ports in each group of the acoustic filter topology structure independently work, respectively correspond to output sub-band signal responses, and form a multi-band filter.

[0014] Further, the input ends in all the acoustic filter topology structures are connected in parallel and work in parallel to form a multiplexing filter.

[0015] The application has the following beneficial effects:

[0016] The filter topology structure provided by the application can realize large bandwidth filtering response, and the response of the filter is not dependent on the coupling coefficient of the material, the design is more simple, the application is more flexible, and the configuration is more convenient on the basis of not increasing the cost; meanwhile, based on the topology structure, the advanced response of adjustable filtering of multi-band and multiplexing can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0017] Fig. 1 is a schematic diagram of the acoustic filter topology structure of the embodiment of the application.

[0018] Figure 2 is a schematic diagram of a conventional acoustic filter T-type topology.

[0019] Figure 3 is a schematic diagram of a first-order filter response based on the T-type structure.

[0020] Figure 4 is a schematic diagram of a response of a 200MHz bandwidth third-order filter under the filter topology of an embodiment of the present application.

[0021] Figure 5 is a schematic diagram of a multi-band filter structure of an acoustic filter module according to an embodiment of the present application.

[0022] Figure 6 is a schematic diagram of a multi-band multiplexing structure of an acoustic filter module according to an embodiment of the present application.

[0023] Figure 7 is a schematic diagram of a response of a multi-band (4-band) filter of an acoustic filter module according to an embodiment of the present application.

[0024] Figure 8 is a schematic diagram of a response of a multi-band (4-band, in which the response of the second band is disconnected) filter of an acoustic filter module according to an embodiment of the present application.

[0025] Figure 9 is a schematic diagram of a response of a multi-band multiplexing (4-band) filter of an acoustic filter module according to an embodiment of the present application. DETAILED DESCRIPTION

[0026] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are intended to illustrate and explain the present application, and are not intended to limit the present application.

[0027] As shown in Figure 1, an acoustic filter topology according to an embodiment of the present application is provided, which aims to provide a greater filter response bandwidth and overcome the inherent limitations of the conventional ladder configuration. The topology includes two groups of parallel resonators, corresponding to the positive branch and the negative branch, respectively. Each group of parallel resonators is composed of no less than two resonators connected in a horizontal parallel manner. All individual resonators are electrically connected from input to output, and each resonator is connected with a switch, which can be selected to be on or off to form different band responses. The input ends of the two groups of parallel resonators are connected as the input of the filter topology. The output ends are connected in parallel with an electrical balance branch to form the positive and negative branch output ports of the BALUN output. The electrical balance branch is composed of inductors connected to ground, i.e., the output ends of the two groups of parallel resonators form the positive and negative branch output ports of the BALUN output, and are respectively connected to ground through inductors (electrical balance branch).

[0028] The resonators therein are acoustic resonators, including surface acoustic wave resonators, bulk acoustic wave resonators, plate wave resonators, or MEMS resonators, etc.

[0029] The inductance in the electrically balanced branch connected by the positive branch is finely adjusted to be near L=Z0 / (2p f), and the inductance in the electrically balanced branch connected by the negative branch is finely adjusted to be near L=Z0 / (2p f), wherein Z0 is the matching impedance, and f is the working frequency.

[0030] The filter response of this topology is generated from the signal contribution of each individual path, where the impedance and resonance frequency of each acoustic resonator can be set independently and distributed along the filter passband. This topology has two sets of branches from input to output: positive branches (no shift) and negative branches (180-degree shift). This network configuration can provide any advanced filtering response, making the response of the filter independent of the electroacoustic coupling coefficient. A large broadband filter can be formed with limited electro-mechanical coupling coefficients and with any number and any position of transmission zeros.

[0031] The following is an example of the embodiment of the application, in which the positive and negative branches are respectively transversely connected with three resonators. As shown in FIG. 1, the topology includes an input port CH1, positive branches transversely connected in parallel with resonators R1, R3, and R5, and negative branches transversely connected in parallel with resonators R2, R4, and R6. The resonators in the positive and negative branches can be selected to be on or off. Each resonator is alternately distributed from R1 to R6, and the resonance frequencies of the resonators R1 to R6 gradually decrease along the passband. The resonance frequencies can also be flexibly adjusted according to design requirements. The output response is obtained from the contribution of each individual path, and is balanced and tuned by a pair of balanced inductors grounded to form a filter passband.

[0032] A conventional acoustic T-type filter topology is shown in FIG. 2, which includes an input port In, a switch Kn, and an output port Out. Resonator P is a parallel resonator connected to ground through a series node, and S is a series resonator connected in series through the input and output ports. The parallel resonator frequency is lower than the series resonator frequency, and the final filter passband is formed through series-parallel impedance matching.

[0033] Figure 3 shows the response of a first-order filter based on the conventional T- topology, with a coupling coefficient of 6.5% for the resonators forming the filter response, and a passband center at 2.054 GHz. The bandwidth of a filter based on the T-topology depends on the coupling coefficient of the material. Figure 4 shows the filter response based on the topology proposed in the embodiments of the present application, with a coupling coefficient of 6.5% for the resonators, and a number of 6 resonators. In the figure, Admittance is the admittance of the resonators, and S21 is the filter passband based on the structure. As can be seen from Figure 4, the admittance of the resonators R1 to R6 of the topology proposed in the embodiments of the present application decreases gradually along the passband, with a center frequency of 1.94 GHz and a bandwidth of about 200 MHz, and the inductances L1 = 5.15 nH and L2 = 4.15 nH in the two electrically balanced branches. Compared with the conventional T-topology of Figure 3, the filter response based on the topology proposed in the embodiments of the present application has a larger bandwidth and a higher out-of-band rejection under the same coupling coefficient of the resonators. It can be further known that, as long as there are a sufficient number of resonators and their admittances are distributed along the passband, any filter response can be obtained under any coupling coefficient. The number of resonators in the forward branch and the negative branch can be added according to the design requirements, which also indicates that a sufficient number of resonators can be connected in a lateral structure, the admittances of the resonators are distributed in a wide enough frequency band, and then a part of the resonators can be selected as the forward branch and a part of the resonators can be selected as the negative branch according to the lateral switch structure, integrated on a module that can be programmed and adjusted, and the required filter frequency band can be obtained by flexibly configuring the switches K1 to Kn. Compared with the T-topology, the acoustic filter topology proposed in the embodiments of the present application is more convenient to design and more flexible to apply, and can overcome the coupling coefficient limitation, and any response can be formed under any coupling coefficient when the number of resonators is sufficient.

[0034] The embodiments of the present application also provide an acoustic filter module supporting multiplexing and multi-band filtering, which is formed by cascading a plurality of groups of the acoustic filter topology as described above; without any additional matching network to connect each filter or band to each other, or a special synthesis to integrate complex filtering. Each sub-band in the filter module is defined by an independent filter topology, and then simply connected in a lateral manner, and the positions of all the bands are very close, and different bandwidths are used to synthesize each filter. Thus, a multi-band response is achieved. Through the multiplexer of the multi-band response, higher communication capacity and better spectrum utilization can be achieved, so as to improve the performance and efficiency of the communication system, which is of great significance to the increasing demand for multi-band communication and carrier aggregation (CA) technology.

[0035] The filter module is formed by cascading several groups of acoustic filter topology structures; each group of acoustic filter topology structure forms an independent frequency band response filter as a sub-band; the parallel resonator groups of the positive branch in each group of acoustic filter topology structure are further connected in parallel, the parallel resonator groups of the negative branch in each group of acoustic filter topology structure are further connected in parallel, and the two output ports after parallel connection form the positive and negative branch output ports of the filter module in parallel with the electrical balance branch, which is composed of inductance grounding.

[0036] Similarly, the inductance in the electrical balance branch connected to the positive branch of the filter module and the inductance in the electrical balance branch connected to the negative branch are both finely adjusted around L = Z0 / (2πf), where Z0 is the matching impedance and f is the working frequency. All the individual resonators are electrically connected from input to output, and each resonator is connected with a switch, which can be selected to be on or off to form different frequency band responses.

[0037] The input ports in each group of acoustic filter topology structure are independent and correspond to each sub-band signal, and correspond to the output of each sub-band signal response, forming a multi-band filter module.

[0038] As shown in FIG. 5, a multi-band filter module structure of 4 frequency bands and 8 resonators is given. Here, for the sake of simplicity, each group of acoustic filter topology structure is connected with a switch (or each resonator can be connected with a switch), and the filter response is as shown in FIG. 7, with the frequency bands distributed between 1.6 GHz and 2.6 GHz, and the bandwidth of about 200 MHz. The corresponding resonators in the acoustic filter topology structure of the second frequency band are turned off by the corresponding switches, and the filter response is as shown in FIG. 8, and it can be seen that the other three responses are not affected.

[0039] Connecting the input ports of all acoustic filter topology structures can form a multiplexing filter module. As shown in FIG. 6, a filter module structure of 4 passband multiplexing is given, and the filter response is as shown in FIG. 9, with a bandwidth of about 200 MHz, distributed between 1.7 GHz and 2.7 GHz, and the out-of-band suppression is more than 20 dB.

[0040] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application. All other embodiments obtained by those skilled in the art without creative labor shall belong to the scope of protection of the present application.

Claims

1. An acoustic filter topology characterized by: The filter topology comprises two groups of parallel resonators, corresponding to positive and negative branches respectively; each group of the parallel resonators is composed of no less than two resonators connected in transverse parallel; the input ends of the two groups of the parallel resonators are connected as the input of the filter topology, and the output ends are connected with electrically balanced branches in parallel to form positive and negative branch output ports of BALUN output, and the electrically balanced branches are composed of inductors grounded.

2. The acoustic filter topology of claim 1, wherein: All the resonators are connected with switches, which are selected to be on or off to form different frequency band responses.

3. The acoustic filter topology of claim 1, wherein: The resonators are acoustic resonators, including surface acoustic wave resonators, bulk acoustic wave resonators, plate wave resonators or MEMS resonators.

4. The acoustic filter topology of claim 1, wherein: The number of resonators in the two groups of parallel resonators is independently set; the impedance and resonant frequency of each resonator are set respectively and distributed along the filter passband.

5. An acoustic filter module based on the acoustic filter topology according to any one of claims 1 to 4, characterized in that: The filter module is composed of a plurality of groups of the acoustic filter topology cascaded; each group of the acoustic filter topology is a sub-band response filter; The parallel resonators of the positive branch in each group of the acoustic filter topology are further connected in parallel, and the parallel resonators of the negative branch in each group of the acoustic filter topology are further connected in parallel. The two output ports after parallel connection are connected with electrically balanced branches in parallel to form positive and negative branch output ports of the filter module, and the electrically balanced branches are composed of inductors grounded.

6. The acoustic filter module of claim 5, wherein: The input ports in each group of the acoustic filter topology work independently, respectively corresponding to output of each sub-band signal response, forming a multi-band filter.

7. The acoustic filter module of claim 5, wherein: The input ends in all the acoustic filter topologies are connected and work in parallel, forming a multiplexing filter.

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