Bulk acoustic wave filter, harmonic suppression method thereof, and multiplexer and communication device

Abstract

The application relates to the technical field of filters, in particular to a bulk acoustic wave filter, a harmonic suppression method of the bulk acoustic wave filter, a multiplexer and a communication device. The filter comprises a first ladder topology structure composed of a plurality of low-frequency resonators, wherein the filter has a first transmission peak and a second transmission peak in a high-order harmonic region. The harmonic suppression method of the bulk acoustic wave filter comprises the following steps: a high-frequency resonator group is arranged between a first topology structure output end and an output end of the filter, the high-frequency resonator group comprises at least one first high-frequency resonator and / or at least one second high-frequency resonator; and the resonant frequencies of the first high-frequency resonator and the second high-frequency resonator are adjusted to be located in the harmonic region of the filter, so that the first transmission peak and the second transmission peak are suppressed. The technical scheme provided by the application improves the influence of high-order harmonics on the out-of-band suppression of the filter by adding the high-frequency resonator group.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of filter, in particular to a bulk acoustic wave filter, a harmonic suppression method thereof, a multiplexer and a communication device. BACKGROUND

[0002] Mobile communication is developing rapidly towards multi-band and multi-standard, and filters and multiplexers as key devices of radio frequency front end are widely concerned, especially in the field of personal mobile communication which has developed most rapidly in recent years. At present, filters and duplexers widely used in the field of personal mobile communication such as mobile phone terminals are mostly composed of surface acoustic wave resonators or bulk acoustic wave resonators. Compared with surface acoustic wave resonators, bulk acoustic wave resonators have more advantages in performance, and have characteristics such as high Q value, wide frequency coverage range and good heat dissipation performance, and are more suitable for the development needs of future 5G or even 6G communication. On the one hand, the resonance of bulk acoustic wave resonators is generated by mechanical waves rather than electromagnetic waves as the source of resonance, and the wavelength of mechanical waves is much shorter than that of electromagnetic waves, so the size of bulk acoustic wave resonators and filters composed of bulk acoustic wave resonators is greatly reduced compared with that of traditional electromagnetic filters. On the other hand, the crystal direction growth of piezoelectric crystals can be well controlled at present, and the loss of resonators is very small and the quality factor is high, which can meet the complex design requirements of steep transition band and low insertion loss.

[0003] Generally, bulk acoustic wave resonators are suitable for frequency bands above 1.2 GHz, and the reason why they are not suitable for frequency bands below 1.2 GHz is that when the frequency is low, the piezoelectric layer is thick, which leads to a large resonator area, which is not conducive to product miniaturization. However, with the emergence of scandium-doped aluminum nitride technology and process, this problem has been solved. In addition, when the resonance frequency is low, the amplitude of high-order resonance of the resonator is very strong, and the ladder topology structure composed of resonators will form a poor insertion filter pseudo passband near the high frequency band, i.e. the high-order resonance frequency of the resonator, which will cause the out-of-band rejection of the filter, especially the deterioration of the high frequency band rejection, which will affect the normal use of the filter.

[0004] Figure 1 is an impedance curve diagram of an existing low-frequency bulk acoustic wave resonator. The low-frequency bulk acoustic wave resonator uses a typical stacked structure, as shown in Figure 1 , the impedance curve includes two resonance regions, i.e. a base frequency resonance region and a harmonic resonance region. The base frequency resonance region has a lower frequency, resonates at about 900 MHz, includes a series resonance frequency point and a parallel resonance frequency point, and the impedance Rp of the parallel resonance frequency point is about 6500 ohms. The harmonic resonance region has a higher frequency, resonates at about 3000 MHz, includes a series resonance frequency point and a parallel resonance frequency point, and the Rp of the parallel resonance frequency point is 800 ohms, which has a higher impedance value.

[0005] Figure 2 is an impedance curve of a series resonator and a shunt resonator in the existing filter; Figure 3 is a transmission curve of the existing filter. As shown in Figure 2 , the solid line in the figure is the impedance curve of the series resonator, and the impedance curve of the series resonator is exactly the same as the impedance curve shown in Figure 1 , which also includes two resonance regions, i.e. a fundamental frequency resonance region and a harmonic resonance region; Figure 2 the dashed line in the figure is the impedance curve of the shunt resonator, which realizes frequency shift by using the method of loading mass load commonly, and the impedance curve is similar to the impedance curve of the series resonator, including two resonance regions, i.e. a fundamental frequency resonance region and a harmonic resonance region, the fundamental frequency resonance region has a lower frequency, resonates at about 865MHz, and includes a series resonance frequency point and a shunt resonance frequency point, wherein the shunt resonance frequency point has an impedance Rp of about 6500 ohms, and the harmonic resonance region has a higher frequency, resonates at about 2900MHz, and includes a series resonance frequency point and a shunt resonance frequency point, wherein the shunt resonance frequency point has an Rp of 800 ohms, which has a higher impedance value. By comparing the two curves, it can be seen that the shunt resonance frequency point of the fundamental frequency of the shunt resonator is located near the series resonance frequency point of the fundamental frequency of the series resonator, and a ladder topology structure filter composed of multiple series and shunt resonators will form a passband at the fundamental frequency, i.e. Figure 3 a passband near 900MHz in Figure 3 , in addition, as shown in , a pseudo passband is also formed near 2900MHz, the existence of the pseudo passband deteriorates the out-of-band rejection near the frequency, which seriously affects the use and promotion of the bulk acoustic wave filter in the low frequency band, and therefore needs to be overcome.

[0006] Figure 4 At present, in view of the deterioration of the out-of-band rejection caused by the high-order harmonic of the resonator, a general technical means is to add an LC resonant circuit composed of an inductor and a capacitor at the input or output end of the filter, and to make the resonant frequency of the LC resonant circuit exactly located in the harmonic resonance region of the filter. Generally, the LC resonant circuit can bring an additional suppression of about 30dB, so through this technical means, the high-order harmonic suppression of the low-frequency bulk acoustic wave filter can be effectively improved, and generally can be improved by more than 30dB. Figure 4 is an improved topology structure of the existing filter. As shown in , the improved filter is composed of two parts, the first part is a ladder structure filter 11, and the second part is an LC resonant circuit 12, the LC resonant circuit 12 is composed of a capacitor and an inductor in series, the ladder structure filter 11 is connected in series between the input port 1 and the output port 2, and the LC resonant circuit 12 is connected to the output port 2 at one end and to the ground at the other end. It should be noted that the LC resonant circuit 12 can also be connected to the input port 1 at one end and to the ground at the other end.

[0007] Figure 5 This is a graph showing the improvement in the transmission curve of an existing filter. For example... Figure 5 As shown in the figure, the solid line represents the transmission curve of the trapezoidal filter 11. The line segment indicated by label 1 in the figure represents the harmonic region, which has poor suppression. The dashed line 2 in the figure represents the transmission curve of the LC resonant circuit, whose resonant position is located at the point of worst harmonic suppression, which can bring about 30dB of suppression. This can improve the high-order harmonic suppression of the low-frequency bulk acoustic wave filter. However, while the LC resonant circuit can suppress harmonics, it is also required that it does not have a significant impact on the fundamental frequency passband. Otherwise, the insertion loss of the fundamental frequency passband will deteriorate. Therefore, the LC resonant circuit is generally composed of a small capacitor and a large inductor. The inductance value is generally greater than 4nH. However, inductors greater than 4nH are difficult to implement in the substrate and cannot be integrated, which is not conducive to the miniaturization of low-frequency filters.

[0008] Therefore, in order to enable the application of bulk acoustic resonators in low-frequency filters, how to reduce the impact of higher harmonics on the out-of-band suppression of the filter using bulk acoustic resonator technology remains a technical problem to be solved. Summary of the Invention

[0009] This invention provides a bulk acoustic wave filter, its harmonic suppression method, a multiplexer, and a communication device, which helps to improve the impact of high-order harmonics on the out-of-band suppression of the filter.

[0010] One aspect of the present invention provides a harmonic suppression method for a bulk acoustic wave filter, the filter comprising a first trapezoidal topology composed of a plurality of low-frequency resonators, wherein the filter has a first transmission peak and a second transmission peak in the higher harmonic region, the method comprising: setting a high-frequency resonator group between the output end of the first topology and the output end of the filter, the high-frequency resonator group comprising at least one first high-frequency resonator and / or at least one second high-frequency resonator, wherein the first high-frequency resonator is a first high-frequency series resonator or a first high-frequency parallel resonator, and the second high-frequency resonator is a second high-frequency parallel resonator; adjusting the position of the resonant frequency of the first high-frequency resonator and / or the second high-frequency resonator in the harmonic region of the filter, thereby suppressing the first transmission peak and the second transmission peak.

[0011] Optionally, the method further includes: increasing a mass load on the first high-frequency resonator so that the parallel resonant frequency of the first high-frequency series resonator or the series resonant frequency of the first high-frequency parallel resonator is lower than the series resonant frequency of the second parallel resonator.

[0012] Optionally, the method further includes setting the area of ​​the first high-frequency resonator to 4 to 6 times the area of ​​the second high-frequency resonator, thereby reducing the impact of the high-frequency resonator group on the filter passband insertion loss.

[0013] In another aspect of the present application, a bulk acoustic wave filter is provided, comprising a low-frequency resonator group and a high-frequency resonator group; the low-frequency resonator group comprises a first ladder topology structure composed of a plurality of low-frequency series resonators and a plurality of low-frequency parallel resonators; the high-frequency resonator group comprises a second topology structure composed of at least one first high-frequency resonator and / or at least one second high-frequency resonator, wherein the first high-frequency resonator is a first high-frequency series resonator or a first high-frequency parallel resonator, and the second high-frequency resonator is a second high-frequency parallel resonator; an input end of the first ladder topology structure is connected to a filter input end, an output end of the first ladder topology structure is connected to an input end of the second topology structure, and an output end of the second topology structure is connected to a filter output end.

[0014] Optionally, the second topology structure comprises one first high-frequency series resonator and one second high-frequency parallel resonator; a first end of the first high-frequency series resonator is connected to the output end of the first topology structure, and a second end thereof is connected to the filter output end; a first end of the second high-frequency parallel resonator is connected to the first end or the second end of the first high-frequency series resonator, and a second end thereof is grounded.

[0015] Optionally, the second topology structure comprises two first high-frequency series resonators and one second high-frequency parallel resonator; the two first high-frequency series resonators are connected in series with each other, and are connected in series between the output end of the first topology structure and the filter output end; a first end of the second high-frequency parallel resonator is connected between the two first high-frequency series resonators, and a second end thereof is grounded.

[0016] Optionally, the second topology structure comprises one first high-frequency series resonator and two second high-frequency parallel resonators; the first high-frequency series resonator is connected in series between the output end of the first topology structure and the filter output end; first ends of the two second high-frequency parallel resonators are respectively connected to two ends of the first high-frequency series resonator, and second ends of the two second high-frequency parallel resonators are grounded.

[0017] Optionally, the second topology structure comprises two second high-frequency parallel resonators; first ends of the two second high-frequency parallel resonators are connected to the filter output end, and second ends thereof are grounded.

[0018] Optionally, a mass loading layer is arranged on a top electrode of the first high-frequency resonator, and a parallel resonant frequency of the first high-frequency series resonator or a series resonant frequency of the first high-frequency parallel resonator is lower than a series resonant frequency of the second parallel resonator.

[0019] Optionally, an area of the first high-frequency resonator is set to be 4 to 6 times of an area of the second high-frequency resonator.

[0020] In yet another aspect of the present application, a multiplexer is provided, comprising the bulk acoustic wave filter described above.

[0021] Still another aspect of the present application provides a communication device comprising the above-mentioned bulk acoustic wave filter.

[0022] According to the technical scheme of the present application, the filter is composed of a low-frequency resonator group and a high-frequency resonator group, and is connected in series, wherein the low-frequency resonator group covers the fundamental frequency band through a ladder topology structure, and the high-frequency resonator group is composed of 2-3 resonators and can form an L-shaped, T-shaped or π-shaped topology structure, in the high-frequency resonator group, the parallel resonance frequency of the high-frequency series resonator is located at the center position of the first transmission peak of the harmonic region of the low-frequency filter, and the series resonance frequency of the high-frequency parallel resonator is located at the center position of the second transmission peak of the harmonic region of the low-frequency filter, thereby the pseudo passband can be suppressed and the harmonic suppression can be improved; in addition, compared with the traditional series LC resonant circuit scheme, the technical scheme of the present application can further reduce the size of the filter, which is beneficial to the miniaturization of the product. BRIEF DESCRIPTION OF DRAWINGS

[0023] For the purpose of illustration and not limitation, the present application will now be described according to the preferred embodiments of the present application, in particular with reference to the accompanying drawings, in which:

[0024] Figure 1 is the impedance curve of the existing low-frequency bulk acoustic wave resonator;

[0025] Figure 2 is the impedance curve of the series resonator and the parallel resonator in the existing filter;

[0026] Figure 3 is the transmission curve of the existing filter;

[0027] Figure 4 is the improved topology structure of the existing filter;

[0028] Figure 5 is the transmission curve improvement effect diagram of the existing filter;

[0029] Figure 6 is one of the topology structures of the filter provided by the embodiments of the present application;

[0030] Figure 7 is Figure 6 is the transmission curve of the low-frequency resonator group of the filter in

[0031] Figure 8 is the transmission curve of the low-frequency resonator group of the filter provided by the embodiments of the present application and the transmission curve of the high-frequency resonator group;

[0032] Figure 9 is the transmission curve comparison diagram of the filter provided by the embodiments of the present application;

[0033] Figure 10 is a topology of a filter provided by an embodiment of the present application;

[0034] Figure 11 is a topology of a filter provided by an embodiment of the present application;

[0035] Figure 12 is a topology of a filter provided by an embodiment of the present application;

[0036] Figure 13 is a topology of a filter provided by an embodiment of the present application;

[0037] Figure 14 is a structure diagram of a filter provided by an embodiment of the present application. DETAILED DESCRIPTION

[0038] In an embodiment of the present application, the influence of high-order harmonics on the out-of-band rejection of the filter is improved by adding a high-frequency resonator group, which is described in detail below.

[0039] An embodiment of the present application provides a solution for improving the high-order harmonic rejection by using a hybrid resonator, which requires fewer high-frequency resonators to be added and occupies less area, and has greater advantages in filter miniaturization compared with the LC resonant circuit solution described above. Figure 6 is a topology of a filter provided by an embodiment of the present application;

[0040] As Figure 6As shown, the filter is composed of two parts, i.e. a low-frequency resonator group and a high-frequency resonator group. The sub-filter formed by the low-frequency resonator group covers a frequency range of 880-915 MHz, and has a ladder topology structure of 5-4 structure (the present embodiment takes the 5-4 structure as an example, but is not limited to the 5-4 structure, and can be any M-N structure, where M and N are natural numbers). The 5-4 structure contains one series branch and four parallel branches. The series branch is composed of low-frequency series resonators S11, S12, S13, S14 and S15 connected in sequence and connected in series between port 1 and port 2. The four parallel branches are connected at one end between adjacent low-frequency series resonators and connected at the other end to ground. Each parallel branch includes a low-frequency parallel resonator. For example, the first parallel branch includes a low-frequency parallel resonator P11, the second parallel branch includes a low-frequency parallel resonator P12, the third parallel branch includes a low-frequency parallel resonator P13, and the fourth parallel branch includes a low-frequency parallel resonator P14. The thickness of the low-frequency resonator is adjusted so that the series resonance frequency of the low-frequency series resonator is located at the center frequency of the base frequency of the filter. The low-frequency parallel resonators P11, P12, P13 and P14 need to be loaded with mass loads so that their series resonance frequencies are all lower than the series resonance frequency of the low-frequency series resonator, and at the same time, the parallel resonance frequencies of the low-frequency parallel resonators P11, P12, P13 and P14 are located near the center frequency of the base frequency of the filter. By optimizing the area of the low-frequency series resonator and the mass load of the low-frequency parallel resonator, the base frequency insertion loss and the adjacent band suppression of the low-frequency resonator group meet the index requirements.

[0041] Figure 7 is Figure 6 The transmission curve of the low-frequency resonator group of the filter and the high-frequency resonator impedance curve are compared. As shown in Figure 7 the solid line in the figure is the transmission curve formed by the low-frequency resonator group. Due to the large amplitude of the high-order harmonic of the low-frequency resonator, two larger peaks will appear in the high-order harmonic region of the filter. In order to suppress these two peaks, two high-frequency resonators need to be arranged between port 2 and port 3 to form an L-type topology structure, in which Figure 6 as shown, the high-frequency series resonator S21 in the topology structure is connected in series between port 2 and port 3, and the high-frequency parallel resonator P21 is connected at one end to port 3 and at the other end to ground. As Figure 7As shown, it should be noted that the parallel resonant frequency of the high-frequency series resonator S21 is located at the center of the first transmission peak in the harmonic region of the filter, while the series resonant frequency of the parallel resonator is located at the center of the second transmission peak in the harmonic region of the filter. That is, in this high-frequency resonator group, the parallel resonant frequency of the high-frequency series resonator S21 is lower than the series resonant frequency of the high-frequency parallel resonator P21. Therefore, relative to the high-frequency parallel resonator P21, the high-frequency series resonator S21 needs to be loaded with a mass load. Furthermore, to reduce the impact on the filter's passband insertion loss, the area of ​​the high-frequency series resonator S21 should be much larger than that of the high-frequency parallel resonator P21. Generally, the area of ​​the high-frequency series resonator S21 can be set to be 4-6 times the area of ​​the high-frequency parallel resonator P21. Figure 7 The dashed line 1 in the figure represents the impedance curve of the high-frequency series resonator S21, whose parallel resonant frequency is 3.17 GHz. This position is exactly the center of the first transmission peak in the harmonic region of the filter. The dashed line 2 represents the impedance curve of the high-frequency parallel resonator P21, whose series resonant frequency is 3.36 GHz. This position is exactly the center of the second transmission peak in the harmonic region of the filter.

[0042] Figure 8 This is a comparison diagram of the transmission curves of the low-frequency resonator group and the high-frequency resonator group of the filter provided in the embodiments of the present invention. Figure 9 A comparison diagram of filter transmission curves provided for embodiments of the present invention. For example... Figure 8 As shown, the L-shaped topology composed of a high-frequency series resonator S21 and a high-frequency parallel resonator P21 has the following transmission curve: Figure 8 The thick dashed line 1 in the image shows a suppression dip in the 3-3.6 GHz range, with a suppression level between 14-25 dB, while the transmission loss introduced into the filter's fundamental passband is close to 0 dB. For example... Figure 9 As shown in the figure, the thick solid line represents the transmission curve of the filter with only a low-frequency resonator. It can be seen from the figure that there are two transmission peaks in the harmonic region. The dashed line represents the transmission curve of the filter after adding a high-frequency resonator group. Figure 9 As shown, the suppression of both peaks in the harmonic region was improved by about 17dB, resulting in an overall suppression level of more than 30dB in the region.

[0043] Figure 10 This is the second filter topology provided in the embodiments of the present invention. For example... Figure 10 As shown, this topology is similar to Figure 6 Compared to one of the topologies shown, the main difference lies in the position of the high-frequency parallel resonator P21 in the high-frequency resonator group. Figure 10In the above, the high-frequency series resonator S21 and the high-frequency parallel resonator P21 still form an L-shaped topology. The high-frequency series resonator S21 is still connected in series between port 2 and port 3, but one end of the high-frequency parallel resonator P21 is connected to port 2 and the other end is grounded. Figure 10 In the filter shown, the characteristics of the high-frequency series resonator S21 remain unchanged, and the characteristics of the high-frequency parallel resonator P21 also remain unchanged. The characteristics of this filter are similar to those of the previous filter. Figure 6 The characteristics of the filters shown are the same, so they will not be described in detail here.

[0044] Figure 11 This is the third filter topology provided in the embodiments of the present invention. For example... Figure 11 As shown, the filter consists of two parts: a low-frequency resonator group and a high-frequency resonator group. The trapezoidal topology of the sub-filter formed by the low-frequency resonator group is similar to... Figure 6 The trapezoidal topology shown is the same and will not be described again here. The stack thickness of the low-frequency resonators is adjusted so that the series resonant frequency of the low-frequency series resonator is located at the center frequency of the filter's fundamental frequency. The low-frequency parallel resonators P11, P12, P13, and P14 require a mass load so that their series resonant frequencies are lower than the series resonant frequencies of the low-frequency series resonators, while simultaneously ensuring that the parallel resonant frequencies of the low-frequency parallel resonators P11, P12, P13, and P14 are near the center frequency of the filter's fundamental frequency. By optimizing the area of ​​the low-frequency series resonators and the mass load of the low-frequency parallel resonators, the fundamental frequency insertion loss and adjacent band rejection of this low-frequency resonator group meet the required specifications.

[0045] like Figure 11 As shown, the high-frequency resonator group comprises three high-frequency resonators forming a T-shaped topology, connected in series between ports 2 and 3. High-frequency series resonators S21 and S22 are connected in series together and then in series between ports 2 and 3. One end of the high-frequency parallel resonator P21 is connected to the node between the series resonators S21 and S22, and the other end is grounded. The parallel resonant frequency of the series resonators S21 and S22 is located at the center of the first transmission peak in the harmonic region of the filter, while the series resonant frequency of the parallel resonator P21 is located at the center of the second transmission peak in the harmonic region of the filter. In this high-frequency resonator group, the parallel resonant frequency of the high-frequency series resonator is lower than the series resonant frequency of the high-frequency parallel resonator. Therefore, the high-frequency series resonators S21 and S22 need to be loaded with mass load relative to the high-frequency parallel resonator P21. In addition, in order to reduce the impact on the filter passband insertion loss, the areas of the high-frequency series resonators S21 and S22 are comparable and much larger than those of the high-frequency parallel resonator P21. Generally, the area of ​​the high-frequency series resonators S21 and S22 can be set to be 4-6 times the area of ​​the high-frequency parallel resonator P21.

[0046] Figure 12 is the fourth topology of the filter provided by the embodiments of the present application. As shown in the figure, the topology of the filter is different from the first topology shown in the figure Figure 12 , the main difference between the two is that the topology of the high-frequency resonator group is different Figure 11 , in the first topology, the topology of the high-frequency resonator group includes one high-frequency series resonator and two high-frequency parallel resonators, which form a π-type topology, the high-frequency series resonator S21 is connected in series between port 2 and port 3, the high-frequency parallel resonator P21 is connected to port 2 at one end and to ground at the other end, and the high-frequency parallel resonator P22 is connected to port 3 at one end and to ground at the other end. The characteristics of the high-frequency series resonator remain unchanged, and the characteristics of the high-frequency parallel resonator remain unchanged. The characteristics of the filter are the same as those of the filter shown in the figure Figure 12 , which will not be described here one by one Figure 11

[0047] Figure 13 is the fifth topology of the filter provided by the embodiments of the present application. As shown in the figure, in the topology of the filter, the topology of the low-frequency resonator group remains unchanged, and in the topology of the high-frequency resonator group, there is no high-frequency series resonator, but two high-frequency parallel resonators, the high-frequency parallel resonator P21 is connected to port 2 at one end and to ground at the other end, and the high-frequency parallel resonator P22 is connected to port 2 at one end and to ground at the other end. Among them, the series resonance frequency of the high-frequency parallel resonator P21 is located at the center position of the first transmission peak in the harmonic region of the filter, and the series resonance frequency of the high-frequency parallel resonator P22 is located at the center position of the second transmission peak in the harmonic region of the filter, that is, in this high-frequency resonator group, the series resonance frequency of the high-frequency parallel resonator P21 is lower than that of the high-frequency parallel resonator P22, so the high-frequency parallel resonator P21 needs to load a mass load relative to the high-frequency parallel resonator P22. Figure 13

[0048] Figure 14 is a structural diagram of the filter provided by the embodiments of the present application. As shown in the figure, in the figure, the packaging substrate is an organic material, the low-frequency resonator is made on a wafer 502, the wafer is inverted and welded on a substrate 501, the high-frequency resonator is made on a wafer 503, the wafer is also inverted and welded on the substrate 501, and the wafer 502 and the wafer 503 are electrically connected on the substrate 501 through vias, thereby forming a complete filter. Figure 14

[0049] ​​​According to the technical scheme of the embodiment of the present application, the filter is composed of a low-frequency resonator group and a high-frequency resonator group, and is connected in series, wherein the low-frequency resonator group covers the fundamental frequency band through a ladder topology structure, and the high-frequency resonator group is composed of 2-3 resonators and can form an L-shaped, T-shaped or π-shaped topology structure; in the high-frequency resonator group, the parallel resonant frequency of the high-frequency series resonator is located at the center position of the first transmission peak of the harmonic region of the low-frequency filter, and the series resonant frequency of the high-frequency parallel resonator is located at the center position of the second transmission peak of the harmonic region of the low-frequency filter, so that the pseudo passband can be suppressed and the harmonic suppression can be improved; in addition, compared with the traditional series LC resonant circuit scheme, the technical scheme of the embodiment of the present application can further reduce the size of the filter, which is beneficial to the miniaturization of the product.

[0050] The above detailed description does not constitute a limitation on the protection scope of the present application. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can occur depending on design requirements and other factors. Any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A bulk acoustic wave filter harmonic rejection method, the filter comprising a first ladder topology consisting of a plurality of low frequency resonators, wherein, The filter has first and second transmission peaks in a high harmonic region, and the method comprises: A high-frequency resonator group is arranged between the output end of the first topology structure and the output end of the filter, and the high-frequency resonator group comprises at least one first high-frequency resonator and / or at least one second high-frequency resonator, wherein the first high-frequency resonator is a first high-frequency series resonator or a first high-frequency parallel resonator, and the second high-frequency resonator is a second high-frequency parallel resonator; The resonant frequency of the first high-frequency resonator and / or the second high-frequency resonator is adjusted to be located in the harmonic region of the filter, so as to suppress the first and second transmission peaks; The first high-frequency resonator is a first high-frequency series resonator, the parallel resonant frequency of which is adjusted to be located at the center of the first transmission peak, the second high-frequency resonator is a second high-frequency parallel resonator, the series resonant frequency of which is adjusted to be located at the center of the second transmission peak, and the parallel resonant frequency of the first high-frequency series resonator is lower than the series resonant frequency of the second high-frequency parallel resonator by increasing the mass load on the first high-frequency series resonator.

2. The method of claim 1, wherein, The method further comprises: setting the area of the first high-frequency resonator to be 4 to 6 times the area of the second high-frequency resonator, so as to reduce the influence of the high-frequency resonator group on the passband insertion loss of the filter.

3. A bulk acoustic wave filter configured to perform the method of any one of claims 1-2, wherein, The filter comprises a low-frequency resonator group and a high-frequency resonator group; The low-frequency resonator group comprises a first ladder topology structure composed of a plurality of low-frequency series resonators and a plurality of low-frequency parallel resonators, and the high-frequency resonator group comprises a second topology structure composed of at least one first high-frequency resonator and / or at least one second high-frequency resonator, wherein the first high-frequency resonator is a first high-frequency series resonator or a first high-frequency parallel resonator, and the second high-frequency resonator is a second high-frequency parallel resonator; The input end of the first ladder topology structure is connected to the input end of the filter, the output end of the first ladder topology structure is connected to the input end of the second topology structure, and the output end of the second topology structure is connected to the output end of the filter.

4. The bulk acoustic wave filter of claim 3, wherein: The second topology structure comprises one first high-frequency series resonator and one second high-frequency parallel resonator; The first end of the first high-frequency series resonator is connected to the output end of the first topology structure, and the second end is connected to the output end of the filter; The first end of the second high-frequency parallel resonator is connected to the first end or the second end of the first high-frequency series resonator, and the second end of the second high-frequency parallel resonator is grounded.

5. The bulk acoustic wave filter of claim 3, wherein, The second topology structure comprises two first high-frequency series resonators and one second high-frequency parallel resonator; The two first high-frequency series resonators are connected in series with each other and are connected in series between the output end of the first topology structure and the output end of the filter; The first end of the second high-frequency parallel resonator is connected between the two first high-frequency series resonators, and the second end is grounded.

6. The bulk acoustic wave filter of claim 3, wherein, The second topology structure comprises one first high-frequency series resonator and two second high-frequency parallel resonators; The first high-frequency series resonator is connected in series between the output end of the first topology structure and the output end of the filter; First ends of the two second high-frequency parallel resonators are respectively connected with two ends of the first high-frequency series resonator, and second ends of the two second high-frequency parallel resonators are grounded.

7. The bulk acoustic wave filter of claim 3, wherein, The second topology comprises two second high-frequency parallel resonators; First ends of the two second high-frequency parallel resonators are connected with filter output ends, and second ends are grounded.

8. The bulk acoustic wave filter of any one of claims 3 to 7, wherein, A mass loading layer is provided on a top electrode of the first high-frequency resonator, and a parallel resonant frequency of the first high-frequency series resonator or a series resonant frequency of the first high-frequency parallel resonator is lower than a series resonant frequency of the second parallel resonator.

9. The bulk acoustic wave filter of any one of claims 3-7, wherein, An area of the first high-frequency resonator is set to be 4 to 6 times of an area of the second high-frequency resonator.

10. A multiplexer, characterized by A bulk acoustic wave filter comprising a plurality of bulk acoustic wave filters according to any one of claims 3 to 9.

11. A communication device, characterized by A bulk acoustic wave filter according to any one of claims 3 to 9.

Images