WO2021203761A1

WO2021203761A1 - Filter, multiplexer, and communication device

Info

Publication number: WO2021203761A1
Application number: PCT/CN2021/000058
Authority: WO
Inventors: 边子鹏; 庞慰
Original assignee: 诺思(天津)微系统有限责任公司
Priority date: 2020-04-07
Filing date: 2021-04-07
Publication date: 2021-10-14
Also published as: CN111431505A; CN111431505B

Abstract

The present invention relates to the technical field of filters, and in particular to a filter, a multiplexer, and a communication device. In the filter, inductive coupling or capacitive coupling is added between different parallel branches, and an inductive coupling or capacitive coupling mode is used for the filter, such that the insertion loss performance of the filter does not deteriorate, and the out-of-band rejection characteristic of the filter can also be improved.

Description

Filters and multiplexers and communication equipment

Technical field

The present invention relates to the field of filter technology, in particular to a filter, multiplexer and communication equipment.

Background technique

With the development of wireless communication applications, people have higher and higher requirements for data transmission rates. Corresponding to the data transmission rate is the high utilization of spectrum resources and the complexity of the spectrum. The complexity of the communication protocol puts forward strict requirements on the various performances of the radio frequency system. In the radio frequency front-end module, the radio frequency filter plays a vital role. It can filter out-of-band interference and noise to meet the requirements of the radio frequency system and communication. The agreement requires the signal-to-noise ratio.

Radio frequency filters are mainly used in wireless communication systems, such as radio frequency front-ends of base stations, mobile phones, computers, satellite communications, radars, and electronic countermeasures systems. The main performance indicators of radio frequency filters are insertion loss, out-of-band suppression, power capacity, linearity, device size and temperature drift characteristics. Good filter performance can improve the data transmission rate, life and reliability of the communication system to a certain extent. Therefore, the design of high-performance and simplified filters for wireless communication systems is very important. At present, the small-size filter devices that can meet the needs of communication terminals are mainly piezoelectric acoustic wave filters. The resonators that constitute this type of acoustic wave filter mainly include: FBAR (Film Bulk Acoustic Resonator), SMR (Solidly Mounted Resonator, solid-state assembly resonator) and SAW (Surface Acoustic Wave, surface acoustic wave resonator). Among them, the filters manufactured based on the principle of bulk acoustic wave FBAR and SMR (collectively referred to as BAW, bulk acoustic wave resonator) have the advantages of lower insertion loss and faster roll-off characteristics compared to filters manufactured based on the principle of surface acoustic wave SAW. .

A typical structure of an ordinary filter is shown in FIG. 1A, and FIG. 1A is a schematic diagram of a structure of an acoustic wave filter in the prior art. In this filter 100, there are

inductors

121, 122 and a plurality of resonators (usually called series resonators) 101 to 104 between the input terminal 131 and the output terminal 132, and the connection point of each series resonator is between the ground terminal Resonators 111 to 113 (usually referred to as parallel resonators) and inductors 123 to 125 are respectively provided on the multiple branches (usually referred to as parallel branches). A mass load layer is added to each parallel resonator, so that the frequency of the parallel resonator and the frequency of the series resonator are different to form the passband of the filter.

In the current wireless communication system, in order to meet the requirements of high cell capacity and big data transmission rate, some communication frequency bands need to be allocated a wider communication frequency band. The band range is from 2496MHz to 2690MHz, with a bandwidth of 194MHz, and the relative bandwidth is up to 7.5%. At the same time, it requires communication signals on the low-frequency side, such as WLAN (2402.5MHz to 2481.5MHz), Band40 (2300MHz to 2400MHz), etc. A certain degree of inhibition. At this time, it is no longer effective to use the traditional method of improving the electromechanical coupling coefficient to expand the application bandwidth of the filter, which requires a special method to achieve this high bandwidth.

In order to achieve the above-mentioned high bandwidth, patent application CN109643984A discloses a ladder-shaped broadband piezoelectric filter, which is provided with a bandwidth adjustment unit between the connection point and the ground point of any two series resonators of a common filter The bandwidth adjusting unit includes a series-connected inductor and a resonator, the frequency of the resonator is close to the frequency of the above-mentioned series resonator, and the inductance value of the inductor is significantly greater than the inductance value of the inductors on each parallel branch of the filter. By introducing the bandwidth adjustment unit, the relative bandwidth of the filter is enlarged.

In order to improve the out-of-band suppression characteristics of acoustic wave resonator filters, common solutions are to increase the number of stages of the filter, change the impedance ratio between the series resonator and the parallel resonator, and change the filter cascade. However, the above methods will deteriorate the insertion loss of the filter, that is, the improvement of the filter's out-of-band suppression characteristic is at the cost of the deterioration of the filter insertion loss, and the increase of the resonator or the peripheral device will also increase the size of the device. For the broadband piezoelectric filter disclosed in the aforementioned patent application CN109643984A, there is also a need to further improve the out-of-band suppression performance.

Summary of the invention

In view of this, the present invention proposes a filter, a multiplexer, and a communication device, which improves the out-of-band suppression characteristics of the filter without deteriorating the insertion loss of the filter.

To achieve the above objective, according to one aspect of the present invention, a filter is provided.

The filter of the present invention includes a series branch provided with a plurality of acoustic wave resonators and a plurality of parallel branches, and includes a bandwidth adjustment unit. The parallel branch near the input end of the filter has a first inductance and is close to the There is a second inductance in the parallel branch of the output end of the filter, and a third inductance in the bandwidth adjustment unit, and there is a coupling between the third inductance and the first inductance; there is a coupling between the third inductance and the second inductance .

Optionally, there is a coupling between the first inductor and the second inductor.

Optionally, the input terminal and the output terminal have a matching circuit, and the structure of the matching circuit is one of the following: a capacitor or an inductance is connected in series between the first terminal and the second terminal; One end of a capacitor or inductor, and the other end of the capacitor or inductor is grounded.

Optionally, in the filter: the chip on which the multiple acoustic resonators are located is located on the multilayer packaging substrate; the third inductor is realized by a lumped parameter element and is arranged on the upper surface of the multilayer packaging substrate; The second inductor and the second inductor are arranged inside the multilayer package substrate and close to the third inductor to generate coupling.

Optionally, in the filter: the chip on which the multiple acoustic resonators are located is located on the multilayer packaging substrate; the first inductor, the second inductor and the third inductor are arranged inside the multilayer packaging substrate.

Optionally, the second ends of the first and second inductors are directly grounded and there is a mutual inductance between the two, and the first and second inductors are located on the same side of the third inductor and are coupled to the third inductor respectively.

Optionally, the second end of the first inductor and the second inductor are connected at any middle layer of the multilayer substrate, and then grounded through the coupling inductor. The first and second inductors are located on the same side of the third inductor, and are located on the same side of the third inductor. There is a coupling between the three inductors.

Optionally, the first inductance, the second inductance and the third inductance are connected in any middle layer of the multilayer substrate, and then grounded through the coupling inductance.

According to another aspect of the present invention, there is provided a multiplexer including the filter of the present invention. The multiplexer here also includes a duplexer.

According to another aspect of the present invention, there is provided a communication device including the filter according to the present invention.

According to the technical solution of the present invention, in the filter including the bandwidth adjustment unit, the inductance in the bandwidth adjustment unit is coupled with the inductance in the parallel branch close to the input and output ends, so as to improve the out-of-band of the filter. Suppress characteristics.

Description of the drawings

For purposes of illustration and not limitation, the present invention will now be described according to preferred embodiments of the present invention, particularly with reference to the accompanying drawings, in which:

Fig. 1A is a schematic diagram of a structure of an acoustic wave filter according to the prior art;

Fig. 1B is a circuit diagram of a filter according to an embodiment of the present invention;

Fig. 2 is a schematic cross-sectional view of the structure of the film bulk acoustic wave resonator;

Figure 3A is the electrical symbol of the piezoelectric acoustic wave resonator;

Figure 3B is an equivalent electrical model diagram of the piezoelectric acoustic resonator;

Figure 4 is a schematic diagram of the relationship between resonator impedance and fs and fp;

5A is a circuit diagram of an input end matching circuit MC1 and an output end matching circuit MC2;

Fig. 5B is another circuit diagram of the input end matching circuit MC1 and the output end matching circuit MC2;

FIG. 5C is a circuit diagram of yet another input end matching circuit MC1 and output end matching circuit MC2;

FIG. 5D is a circuit diagram of another input end matching circuit MC1 and output end matching circuit MC2;

6 is a comparison curve of the insertion loss frequency characteristics of the filter provided by the embodiment of the present invention and the comparative example;

FIG. 7 is a circuit diagram of another structure of a filter provided by an embodiment of the present invention;

Fig. 8 is a three-dimensional circuit model of a filter provided by an embodiment of the present invention;

FIG. 9A is a first implementation manner of a three-dimensional circuit model of a filter provided by an implementation manner of the present invention;

FIG. 9B is a schematic diagram of the package substrate of the filter of FIG. 9A on the AA′ cross-section;

FIG. 10A is a second implementation manner of a three-dimensional circuit model of a filter provided by an implementation manner of the present invention;

10B is a schematic diagram of the package substrate of the filter of FIG. 10A on the BB′ cross-section;

Detailed ways

In the embodiment of the present invention, inductive coupling or capacitive coupling is added between different parallel branches of the filter, and the out-of-band suppression characteristics of the filter are improved without deteriorating the insertion loss of the filter, which will be described in detail below.

FIG. 1B is a circuit diagram of a filter according to an embodiment of the present invention. The structure of the filter is also based on the idea in the patent application CN109643984A. The filter 100 in Figure 1B contains a bandwidth adjustment unit, which is a special parallel grounding path used to expand the relative bandwidth of the filter. change. This will be described in detail below.

As shown in FIG. 1B, T1 is the input terminal of the filter 100, T2 is the output terminal of the filter, and the input terminal T1 and the output terminal T2 are ports connected to the external signal of the filter. The series resonators connected in series between the input terminal T1 and the output terminal T2 are respectively a first resonator S11, a second resonator S12 and a third resonator S13. The input terminal matching circuit MC1 is connected in series between the input terminal T1 and the first resonator S11, and the output terminal matching circuit MC2 is connected in series between the input terminal T2 and the third resonator S13. One end of the first first resonator P11 is connected to the node between the first resonator S11 and the input end matching circuit MC1, and one end of the first second resonator P12 is connected to the node between the first resonator S11 and the second resonator S12 Connected, the other ends of the first one resonator P11 and the first two resonators P12 are connected to each other and connected to one end of the first inductor LP1, and the other end of the first inductor LP1 is grounded; one end of the first three resonator P13 is connected to the second The resonator S12 is connected to the node between the third resonator S13, one end of the first four resonator P14 is connected to the node between the third resonator S13 and the output terminal matching circuit MC2, the first three resonator P13 and the first The other ends of the four resonators P14 are connected to each other and to one end of the second inductor LP2, and the other end of the second inductor LP2 is grounded. There is an inductive coupling or a capacitive coupling between the first inductor LP1 and the second inductor LP2.

One end of the second first resonator P21 is connected to the node between the first resonator S11 and the second resonator S12, and one end of the second second resonator P22 is connected to the node between the second resonator S12 and the third resonator S13 Connected, the other ends of the second first resonator P21 and the second second resonator P22 are connected to each other and connected to one end of the third inductor LS, and the other end of the third inductor LS is grounded. The above P21, P22 and LS constitute the bandwidth adjustment unit .

In the embodiment of the present invention, when the bandwidth adjustment unit is introduced, the positions of the bandwidth adjustment unit and the original inductance device are adjusted so that the third inductor LS in the bandwidth adjustment unit is connected to the first inductor LP1 and the second inductor respectively. There is coupling between LP2, which can specifically produce inductive coupling and capacitive coupling. As will be seen in the following description, this coupling helps to improve the out-of-band suppression characteristics of the filter.

FIG. 7 is a circuit diagram of another structure of the filter provided by the embodiment of the present invention; as shown in FIG. 7, the structure of the filter 300 is basically the same as the structure of the filter 100, and the difference between the two is that the first inductor LP1 and the second inductor LP1 The other ends of the two inductors LP2 are connected to each other and connected to one end of the fourth inductor LM, and the other end of the fourth inductor LM is grounded. In the filter 300, the coupling between the first inductor LP1 and the second inductor LP2 is realized by the fourth inductor LM. Therefore, the fourth inductor LM serves as a coupling inductor, so that there is no need to directly couple between the first inductor LP1 and the second inductor LP2.

The series resonant frequencies of the first resonator S11, the second resonator S12, and the third resonator S13 are fss1, fss2, and fss3, respectively, and the parallel resonant frequencies are fsp1, fsp2, and fsp3; the first resonator P11, the first second resonator The series resonance frequencies of the first three-resonator P12, the first three-resonator P13, and the first four-resonator P14 are fps11, fps12, fps13, and fps14, respectively, and the parallel resonance frequencies are fpp11, fpp12, fpp13, and fpp14; the second-first resonator P21 and the first The series resonant frequencies of the two-two resonator P22 are fps21 and fps22, respectively, and the parallel resonant frequencies are fpp21 and fpp22. In the embodiment of the present invention, the first resonator S11, the second resonator S12, and the third resonator S13 realize that the series resonance frequencies are different from each other through different designs of the mass load, such as adjusting the area and thickness of the mass load to make the mass load The difference in the series resonance frequency between the first resonator S11, the second resonator S12, and the third resonator S13 is smaller than a specified value; similarly, the first resonator P11 in the embodiment of the present invention The series resonant frequencies of the first two resonators P12, the first three resonators P13, and the first four resonators P14 are different from each other; the resonant frequencies of the second first resonator P21 and the second second resonator P22 are the same as those of the first resonator S11 , The resonant frequencies of the second resonator S12 and the third resonator S13 are equal or similar.

2 is a schematic cross-sectional view of the structure of the thin film bulk acoustic wave resonator, including the semiconductor substrate material 21, the piezoelectric layer 22, the bottom electrode 23, the top electrode 24 and the air cavity 25, wherein the semiconductor substrate material 21 is etched to obtain air The cavity 25 and the bottom electrode 23 are deposited on the semiconductor substrate 21. In the figure, the area selected by the dashed line is the overlapping area of the air cavity 25, the top electrode 24, the bottom electrode 23 and the piezoelectric layer 22, and the overlapping area is the effective resonance area of the film bulk acoustic wave resonator. Among them, the material of the top electrode 24 and the bottom electrode 23 can be made of gold (Au), tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), iridium (Ir), titanium tungsten (TiW), aluminum (Al), titanium (Ti) and other similar metals; the material of the piezoelectric layer 22 can be aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNb03), quartz (Quartz), potassium niobate (KNb03) or lithium tantalate (LiTa03), etc. The thickness of the piezoelectric layer 22 is generally less than 10 microns. When the material of the piezoelectric layer 22 is aluminum nitride (AlN), the aluminum nitride film has a polycrystalline form or a single crystal form, and the growth method is thin film sputtering or metal organic chemical vapor deposition (MOCVD).

Figure 3a is the electrical symbol of the piezoelectric acoustic wave resonator, and Figure 3b is the equivalent electrical model diagram of the piezoelectric acoustic wave resonator. As shown in Figures 3a and 3b, the electrical model can be simplified to Lm without considering the loss term. , Cm and C0 composed of a resonant circuit. According to the resonance conditions, the resonant circuit has two resonant frequencies: one is the fs when the impedance of the resonant circuit reaches a minimum value, and fs is defined as the series resonant frequency of the resonator; the other is when the impedance of the resonant circuit When fp reaches the maximum value, fp is defined as the parallel resonance frequency of the resonator. in,

And, fs is less than fp; the effective electromechanical coupling coefficient Kt2eff of the resonator (hereinafter abbreviated as Kt2), it can be expressed by fs and fp:

Figure 4 is a schematic diagram of the relationship between the resonator impedance and fs and fp. As shown in Figure 4, at a specific frequency, the greater the effective electromechanical coupling coefficient, the greater the frequency difference between fs and fp, that is, the farther the two resonance frequency points are, the larger the Kt2 resonator can meet Design requirements for wide bandwidth filters. At the same time, the impedance amplitude of the resonator at fs is defined as Rs, which is the minimum value in the impedance curve of the resonator; the impedance amplitude of the resonator at fp is defined as Rp, which is the value in the impedance curve of the resonator maximum. Rs and Rp are important parameters to describe resonance loss characteristics. When Rs is smaller and Rp is larger, the loss of the resonator is smaller, the Q value is higher, and the insertion loss characteristics of the filter are better at this time.

Fig. 5A is a circuit diagram of an input end matching circuit MC1 and an output end matching circuit MC2. In Fig. 5A, an inductor 31L is used as a matching circuit in series with the input end of the filter or in series with the output end of the filter; Fig. 5B is another The circuit diagram of the input end matching circuit MC1 and the output end matching circuit MC2. In Fig. 5B, the capacitor 31C is used as a matching circuit in series with the input end of the filter or in series with the output end of the filter; Fig. 5C is another input end matching circuit MC1 and The circuit diagram of the output end matching circuit MC2. In Figure 5C, the inductor 32L is used as a matching circuit in parallel to the input end of the filter or in parallel to the output end of the filter; Figure 5D is another input end matching circuit MC1 and output end matching circuit MC2 In the circuit diagram of FIG. 5D, the capacitor 32C is used as a matching circuit in parallel with the input end of the filter or in parallel with the output end of the filter.

6 is a comparison curve of the insertion loss frequency characteristics of the filter provided by the embodiment of the present invention and the comparative example; wherein, the embodiment of the present invention adopts the circuit structure of the filter 100 shown in FIG. 1B, and the filter structure used in the comparative example The circuit structure is the same as that of the filter 100, except that there is no coupling between the different parallel branches of the comparative filter. As shown in Figure 6, the solid line is the corresponding insertion loss frequency characteristic curve of the filter 100 (with coupling), and the dashed line is the corresponding insertion loss frequency characteristic curve of the comparative example (without coupling). Inductance coupling or capacitive coupling is added between the second inductor LP2 and the third inductor LS, and the first inductor LP1 and the second inductor LP2 to realize the change of the filter's far-band impedance, so as to realize the filter's passband insertion loss without deterioration. Improve out-of-band suppression under conditions.

Fig. 8 is a three-dimensional circuit model of a filter provided by an embodiment of the present invention. The three-dimensional circuit model 401 includes a chip 41, a solder ball 42 and a package substrate, wherein the chip 41 is electrically connected to the package substrate by a solid line of the solder ball 42. The packaging substrate includes a dielectric material 43, and a first wiring layer 44, a second wiring layer 46, a third wiring layer 48, and a fourth wiring layer 50 provided in the dielectric material 43, wherein the first wiring layer 44 and the second wiring layer The layers 46 are electrically connected through the first-second via hole 45, the second wiring layer 46 and the third wiring layer 48 are electrically connected through the second-third via hole 47, and the third wiring layer 48 and the fourth wiring layer 50 are electrically connected. They are electrically connected through the third to fourth via holes 49.

FIG. 9A is the first implementation of the three-dimensional circuit model of the filter according to the embodiment of the present invention. As shown in FIG. 9A, the dashed frame 53 in the three-dimensional circuit model 501 of the filter is the third inductor LS, and 51 is the first inductor LP1 52 is the second inductor LP2, where MSP1 is the coupling between the third inductor LS and the first inductor LP1, MSP2 is the coupling between the third inductor LS and the first parallel LP2, and MPP is the first inductor LP1 and the first inductor LP2. The coupling between the two inductors LP2, the size of MSP1, MSP2 and MPP can be adjusted by the spatial distance between the inductors. FIG. 9B is a schematic diagram of the package substrate of the filter of FIG. 9A on the AA′ cross-section. As shown in FIG. 9B, 51 is a first inductor LP1 and 52 is a second inductor LP2, both of which are arranged inside the packaging substrate 502 and are grounded respectively (that is, in the case of FIG. 1B), and there is a coupling MPP between them.

10A is the second implementation of the three-dimensional circuit model of the filter provided by the embodiment of the present invention. The names of the components in the figure are the same as those in FIG. Schematic diagram of the package substrate of the filter on the BB' section. As shown in FIG. 10B, 51 is the first inductor LP1 and 52 is the second inductor LP2, and 54 is the LM as the coupled inductor in FIG.

In the filter provided by the embodiment of the present invention, inductive coupling or capacitive coupling is added between different parallel branches, and the out-of-band suppression characteristics of the filter can be further improved without increasing the insertion loss of the filter.

The foregoing specific implementations do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that, depending on design requirements and other factors, various modifications, combinations, sub-combinations, and substitutions can occur. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

A filter includes a series branch provided with a plurality of acoustic wave resonators and a plurality of parallel branches, and includes a bandwidth adjustment unit. The parallel branch close to the input end of the filter has a first inductance and is close to the The parallel branch at the output end of the filter has a second inductance, the bandwidth adjustment unit is a parallel grounding path, and there is a third inductance in it, which is characterized by:

There is a coupling between the third inductor and the first inductor;

There is a coupling between the third inductor and the second inductor.
The filter according to claim 1, wherein there is a coupling between the first inductor and the second inductor.
The filter according to claim 1, wherein the input terminal and the output terminal have a matching circuit, and the structure of the matching circuit is one of the following:

Series capacitance or inductance between the first terminal and the second terminal;

Between the first end and the second end is one end of the capacitor or the inductor, and the other end of the capacitor or the inductor is grounded.
The filter according to claim 1, wherein in the filter:

The chip on which the plurality of acoustic wave resonators are located is located on the multilayer packaging substrate;

The third inductor is realized by a lumped parameter element, and is arranged on the upper surface of the multilayer package substrate;

The first and second inductors are disposed inside the multilayer package substrate and close to the third inductor to generate coupling.
The filter according to claim 1, wherein in the filter:

The chip on which the plurality of acoustic wave resonators are located is located on the multilayer packaging substrate;

The first inductance, the second inductance and the third inductance are arranged inside the multilayer packaging substrate.
The filter according to claim 5, wherein the second ends of the first and second inductors are directly grounded and there is a coupling between the two, and the first and second inductors are located on the same side of the third inductor and are connected to the There is coupling between the third inductors.
The filter according to claim 5, wherein the second end of the first inductor and the second inductor are connected in any middle layer of the multilayer substrate, and then grounded through a coupled inductor, and the first and second inductors are located in the first and second inductors. The three inductors are on the same side, and there is coupling between the third inductors.
The filter according to claim 5, wherein:

The first inductance, the second inductance and the third inductance are connected in any middle layer of the multilayer substrate, and then grounded through the coupling inductance.
A multiplexer, characterized by comprising the filter according to any one of claims 1 to 8.
A communication device, characterized by comprising the filter according to any one of claims 1 to 8.