Broadband filter of resonance unit of bulk acoustic wave filter

Abstract

The invention relates to the technical field of radio frequency front-end filters, in particular to a broadband filter of a bulk acoustic wave filter resonance unit, which comprises an input port, a resonance unit group and an output port which are sequentially connected, and is characterized in that the resonance unit group comprises a plurality of series resonance units and parallel resonance units; the series resonance unit comprises a series FBAR resonator and a first resonance network connected with the series FBAR resonator in parallel, the first resonance network is formed by connecting a capacitor and an inductor of a first discrete component in series, and the parallel resonance unit comprises a parallel FBAR resonator and a second resonance network connected with the parallel FBAR resonator in series. The second resonant network is formed by connecting a capacitor and an inductor of a second discrete component in parallel. The problem that a conventional filter based on a bulk acoustic wave resonator is narrow in bandwidth is solved, the resonance units serve as a whole, controllability and expansibility are better achieved, and meanwhile the characteristics of high-quality out-of-band rejection and a good rectangular coefficient of the bulk acoustic wave filter are reserved.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency front-end filters, and in particular to a broadband filter of a bulk acoustic wave filter resonant unit. Background Art

[0002] A large number of radio frequency (RF) filters are used in modern mobile phones. Among them, film bulk acoustic wave filters (FBARs) dominate the frequency bands of 1.5 GHz and above. FBARs have excellent properties, with high quality factors, high out-of-band rejection, and low insertion loss, allowing them to accurately filter specific frequencies. However, due to limitations in device processing and material properties, the relative bandwidth of FBARs is very limited. The electromechanical coupling coefficient used to characterize their bandwidth is often only 7%, making it difficult to achieve broadband filtering in today's crowded frequency bands.

[0003] An LC filter refers to a filter that achieves filtering functions in corresponding frequency bands by integrating discrete components such as capacitors and inductors. The currently commonly used LC filter structure is to connect capacitors and inductors in series or to connect capacitors and inductors in parallel. The series LC filter has the lowest impedance at the resonant frequency, which is equivalent to a path; while the parallel LC filter has a larger impedance at the resonant frequency, which is equivalent to an open circuit. LC elements can be integrated with bulk acoustic wave filters to form wide-bandwidth filters. Considering the performance and the trend of miniaturization of RF front-end devices, LC filters can be implemented using IPD (integrated passive device) technology. The present invention is not limited to a single implementation method and can be selected according to needs. The LC filter is flexible in design and can have a very wide bandwidth, but its quality factor and out-of-band suppression are much worse than those of thin film bulk acoustic wave filters (FBAR). Therefore, the present invention proposes a broadband filter with a bulk acoustic wave filter resonant unit. Summary of the Invention

[0004] The purpose of the present invention is to provide a broadband filter with a bulk acoustic wave filter resonant unit to address the technical defects of existing FBARs, such as small bandwidth and low quality factor of the integrated LC network. By integrating LC series or parallel resonant circuits on the basis of traditional thin film bulk acoustic wave filters, a new resonant unit is formed.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A broadband filter of a bulk acoustic wave filter resonant unit includes: an input port, a resonant unit group, and an output port connected in sequence, wherein the resonant unit group includes a plurality of series resonant units and parallel resonant units, wherein the series resonant unit includes a series FBAR resonator and a first resonant network connected in parallel with the series FBAR resonator, wherein the first resonant network is composed of a capacitor and an inductor of a first discrete component connected in series, and the parallel resonant unit includes a parallel FBAR resonator and a second resonant network connected in series with the parallel FBAR resonator, wherein the second resonant network is composed of a capacitor and an inductor of a second discrete component connected in parallel.

[0007] Preferably, the series resonance unit includes a first series resonance unit, a second series resonance unit, and a third series resonance unit with the same structure, and the parallel resonance unit includes a first parallel resonance unit, a second parallel resonance unit, and a third parallel resonance unit with the same structure.

[0008] Preferably, the input port is connected to the first series resonance unit, the other end of the first series resonance unit is connected to the first parallel resonance unit, and the other end of the first parallel resonance unit is grounded;

[0009] A common end of the first series resonant unit and the first parallel resonant unit is connected to the second series resonant unit, the second series resonant unit is connected to the second parallel resonant unit, and the other end of the second parallel resonant unit is grounded;

[0010] A common end of the second series resonant unit and the second parallel resonant unit is connected to the third series resonant unit, the third series resonant unit is connected to the third parallel resonant unit, and the other end of the third parallel resonant unit is grounded;

[0011] A common end of the third series resonant unit and the third parallel resonant unit is connected to a parallel network of a capacitor and an inductor, and the other end of the parallel network is connected to the output port.

[0012] Preferably, the series resonance unit includes a fourth series resonance unit, a fifth series resonance unit, and a sixth series resonance unit with the same structure, and the parallel resonance unit includes a fourth parallel resonance unit, a fifth parallel resonance unit, and a sixth parallel resonance unit with the same structure.

[0013] Preferably, the input port is connected to the fourth series resonant unit, the other end of the fourth series resonant unit is connected to the fourth parallel resonant unit and the fifth series resonant unit, the other end of the fourth parallel resonant unit is connected to the discrete component capacitor, the other end of the fifth series resonant unit is respectively connected to the fifth parallel resonant unit and the sixth series resonant unit, the other end of the sixth series resonant unit is connected to the output port, the other end of the fifth parallel resonant unit is connected to the common end of the fourth parallel resonant unit and the discrete component capacitor, and the other end of the discrete component capacitor is grounded.

[0014] Preferably, the series resonant frequency of the first resonant network is the same as the series resonant frequency of the series FBAR resonator, and the parallel resonant frequency of the second resonant network is the same as the parallel resonant frequency of the parallel FBAR resonator.

[0015] The beneficial effects of the present invention are:

[0016] The present invention not only solves the problem of narrow bandwidth of conventional BAW-based filters, but also treats the resonant unit as a whole, making it more controllable and scalable, while retaining the excellent out-of-band suppression and good rectangular coefficient characteristics of BAW filters.

[0017] The resonant unit in this invention can be inserted into a circuit without changing the existing circuit topology, replacing a single film bulk acoustic wave filter (FBAR) to form a novel topology, thereby expanding the original narrowband filter into a broadband filter. This resonant unit can also serve as a basic module, connected in the novel topology, and by optimizing component values, it can be used to construct broadband filters of different frequency bands as required.

[0018] The bulk acoustic wave filter of the present invention does not require the use of new materials; even conventional BAW can be used as a component of the resonant unit. Compared with the prior art, the present invention interconnects the parallel resonant unit, the series resonant unit, and the discrete components to obtain a broadband filter with a passband starting from 1.75 GHz to 2.48 GHz. While retaining the excellent out-of-band suppression of the FBAR filter, the steepness of the transition band caused by the transmission zero point is also very good. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1Schematic diagram of a parallel resonant unit according to an embodiment of the present invention;

[0021] Figure 2 is the Y parameter of the parallel resonant unit according to the embodiment of the present invention;

[0022] Figure 3 Schematic diagram of a series resonant unit according to an embodiment of the present invention;

[0023] Figure 4 is the Y parameter of the series resonant unit according to the embodiment of the present invention;

[0024] Figure 5 Schematic diagram of a first filter topology structure according to an embodiment of the present invention;

[0025] Figure 6 is the S21 parameter of the first filter topology structure according to an embodiment of the present invention;

[0026] Figure 7 Schematic diagram of a second filter topology structure according to an embodiment of the present invention;

[0027] Figure 8 is the S21 parameter of the second filter topology structure in the embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] This embodiment provides a broadband filter of a bulk acoustic wave filter resonant unit, comprising: an input port, a resonant unit group, and an output port connected in sequence, wherein the resonant unit group comprises a plurality of series resonant units and parallel resonant units, wherein the series resonant unit comprises a series FBAR resonator and a first resonant network connected in parallel with the series FBAR resonator, wherein the first resonant network is composed of a capacitor and an inductor of a first discrete component connected in series, and the parallel resonant unit comprises a parallel FBAR resonator and a second resonant network connected in series with the parallel FBAR resonator, wherein the second resonant network is composed of a capacitor and an inductor of a second discrete component connected in parallel.

[0031] The series resonant frequency of the first resonant network is the same as the series resonant frequency of the series FBAR resonator, and the parallel resonant frequency of the second resonant network is the same as the parallel resonant frequency of the parallel FBAR resonator.

[0032] As one of the connection modes, the series resonant unit includes a first series resonant unit, a second series resonant unit, and a third series resonant unit having the same structure, and the parallel resonant unit includes a first parallel resonant unit, a second parallel resonant unit, and a third parallel resonant unit having the same structure.

[0033] Among them, the input port is connected to the first series resonant unit, the other end of the first series resonant unit is connected to the first parallel resonant unit, and the other end of the first parallel resonant unit is grounded; the common end of the first series resonant unit and the first parallel resonant unit is connected to the second series resonant unit, the second series resonant unit is connected to the second parallel resonant unit, and the other end of the second parallel resonant unit is grounded; the common end of the second series resonant unit and the second parallel resonant unit is connected to the third series resonant unit, the third series resonant unit is connected to the third parallel resonant unit, and the other end of the third parallel resonant unit is grounded; the common end of the third series resonant unit and the third parallel resonant unit is connected to the parallel network of the capacitor and the inductor, and the other end of the parallel network is connected to the output port.

[0034] As another connection method, the series resonance unit includes a fourth series resonance unit, a fifth series resonance unit, and a sixth series resonance unit with the same structure, and the parallel resonance unit includes a fourth parallel resonance unit, a fifth parallel resonance unit, and a sixth parallel resonance unit with the same structure.

[0035] Among them, the input port is connected to the fourth series resonant unit, the other end of the fourth series resonant unit is connected to the fourth parallel resonant unit and the fifth series resonant unit, the other end of the fourth parallel resonant unit is connected to the discrete component capacitor, the other end of the fifth series resonant unit is connected to the fifth parallel resonant unit and the sixth series resonant unit respectively, the other end of the sixth series resonant unit is connected to the output port, the other end of the fifth parallel resonant unit is connected to the common end of the fourth parallel resonant unit and the discrete component capacitor, and the other end of the discrete component capacitor is grounded.

[0036] The following combination Figures 1-8 The two broadband filter structures provided in this embodiment are described in detail, including the following contents:

[0037] like Figure 1As shown, the resonant unit (parallel resonant unit) on the parallel branch in the final filter topology is composed of a lumped capacitor, an inductor and a resonator. The parallel resonant unit is connected in such a way that a parallel resonator is formed by connecting the capacitor C and the inductor L in parallel, and then connecting it in series with the parallel FBAR resonator (film bulk acoustic resonator) to obtain a parallel resonant unit. By design, the resonant frequency of the LC resonator can be made the same as the parallel resonant frequency of the parallel FBAR resonator. In this way, the original parallel resonant frequency of the overall resonant unit obtained after the connection remains unchanged compared with the original single FBAR resonator, so that the series resonant frequency of the overall new resonant unit is shifted to the left, and finally, after being combined with the series resonant unit, the width of the filter passband is increased in the filter design. For the LC resonator, by reasonably designing the parameters, the resonant unit after the combination can obtain better characteristics, such as Figure 2 As shown, the Y parameter of the parallel resonant unit results in a wider frequency interval compared with a single FBAR element.

[0038] like Figure 3 As shown, the resonant unit (series resonant unit) on the series branch in the final filter topology is composed of a lumped capacitor, an inductor and a resonator. The connection method of the series resonant unit is to form a series resonator by connecting the capacitor C and the inductor L in series, and then connecting it in parallel with the series FBAR resonator to obtain a series resonant unit. The resonant frequency of the LC resonator can be made the same as the series resonant frequency of the series FBAR resonator by design. In this way, the original series resonant frequency of the overall resonant unit obtained after the connection is unchanged compared with the original single FBAR resonator, so that the parallel resonant frequency of the overall new resonant unit is shifted to the right, and finally, after combining with the parallel resonant unit, the width of the filter passband is increased in the filter design. For the LC resonator, by reasonably designing the parameters, the resonant unit after the combination can obtain better characteristics, such as Figure 4 As shown, the Y parameter of the series resonant unit results in a wider frequency interval compared with a single FBAR element.

[0039] This embodiment proposes two filter topologies to achieve broadband filtering. This filter is an improvement on the traditional ladder filter. While maintaining high squareness coefficient and out-of-band suppression, it integrates a series and parallel LC resonant circuit with an FBAR filter to form a filter unit, expanding the bandwidth and improving passband ripple.

[0040] In the first filter topology, the first connected element at the input port is the first series resonant unit. This unit is composed of a first resonant network and a series FBAR resonator in parallel. The first resonant network is composed of discrete components, capacitors and inductors, connected in series. The series resonant frequency of the first resonant network is required to be the same as the series resonant frequency of the series FBAR resonator. This is done to shift the parallel resonant frequency of the series resonant unit, formed by the first resonant network and the series FBAR resonator in parallel, to the right compared to the parallel resonant frequency of the original single series FBAR resonator, thus achieving a wider bandwidth. All series resonant units are identical; the ordinal number is used for convenience only.

[0041] The other side of the first series resonant unit is then connected to the first parallel resonant unit, and the other end of the first parallel resonant unit is grounded. The first parallel resonant unit is composed of a second resonant network and a parallel FBAR resonator in series. The second resonant network is composed of discrete components, capacitors and inductors, connected in parallel. Here, the parallel resonant frequency of the second resonant network is required to be the same as the parallel resonant frequency of the parallel FBAR resonator. The purpose of this practice is to shift the series resonant frequency of the parallel resonant unit formed by the second resonant network and the parallel FBAR resonator in series to the left compared to the series resonant frequency of the original single parallel FBAR resonator, that is, to have a larger bandwidth. All parallel resonant units are identical, and the ordinal number is only for convenience of description.

[0042] The common end of the first series resonant unit and the first parallel resonant unit is connected to the second series resonant unit. The second series resonant unit is connected to the second parallel resonant unit, and the other end of the second parallel resonant unit is grounded. The common end of the second series resonant unit and the second parallel resonant unit is connected to the third series resonant unit. The third series resonant unit is connected to the third parallel resonant unit, and the other end of the third parallel resonant unit is grounded. Finally, the common end of the third series resonant unit and the third parallel resonant unit is connected to a parallel network of a capacitor and an inductor, and the other end of the parallel network is connected to the output port.

[0043] The first filter topology proposed in this embodiment is as follows Figure 5The filter consists of six resonant elements, with a parallel LC resonator connected in series at the rightmost end to improve performance within the filter's passband. The two resonant elements are designed to alternate. Starting from the input port, L1 is connected in series with C1 and then in parallel with the series FBAR resonator. L2 is connected in series with C2 and then in parallel with the series FBAR resonator. L3 is connected in series with C3 and then in parallel with the series FBAR resonator, forming the three series resonant elements in the main branch. L5 is connected in parallel with C5 and then in series with the parallel FBAR resonator. L6 is connected in parallel with C6 and then in series with the parallel FBAR resonator. L7 is connected in parallel with C7 and then in series with the parallel FBAR resonator, forming the three parallel resonant elements shown in the figure. One end of each of the three parallel resonant elements is connected to the main branch, and the other end is grounded. Finally, at the rightmost end of the main branch, L4 and C4 are connected in parallel to form an LC parallel resonant circuit, which is connected in series with the main branch. By properly designing the rightmost LC parallel resonant circuit, the performance at the edges of the overall broadband filter can be improved, resulting in a flatter passband and reduced ripple. The center frequency f of the filter is equal to the series resonant frequency fss of the series resonant unit, and the parallel resonant frequency fpp of the parallel resonant unit is equal to the series resonant frequency fss of the series resonant unit. In this way, the current input to the filter at the center frequency of the filter passes through the series resonant unit almost unimpeded, and there is almost no shunt flowing into the ground from the parallel branch. By increasing the number of series and parallel resonant units, the performance of the filter can be further improved. Through reasonable design and debugging, a filter with a wide passband working in the 2GHZ frequency band can be obtained, such as Figure 6 shown.

[0044] The second filter topology still uses the aforementioned series resonant units and parallel resonant units. All series resonant units are identical, and all parallel resonant units are identical.

[0045] At the input port, first connect the first series resonant unit. At the other end of the first series resonant unit, connect the first parallel resonant unit and the second series resonant unit. The other end of the first parallel resonant unit is connected to the discrete component capacitor. The other end of the second series resonant unit is connected to the second parallel resonant unit and the third series resonant unit, respectively. The other end of the third series resonant unit is connected to the output port. The other end of the second parallel resonant unit is connected to the common end of the first parallel resonant unit and the discrete component capacitor. The other end of the discrete component capacitor is grounded. For the discrete component capacitor, the two parallel resonant units mentioned above are in parallel. Overall, this topological structure has good symmetry.

[0046] The second filter topology proposed in this embodiment is as follows Figure 7As shown, the filter consists of five resonant units, and the two parallel branches below are connected together and grounded through a capacitor to enhance out-of-band suppression. The two designed resonant units are connected alternately. The series resonant unit is connected in series on the main branch. L1 is connected in series with C1 and then in parallel with the series FBAR resonator. L2 is connected in series with C2 and then in parallel with the series FBAR resonator. L3 is connected in series with C3 and then in parallel with the series FBAR resonator to form three series resonant units; the parallel resonant circuits of L4 and C4, L5 and C5 are respectively connected in series with a parallel FBAR resonator to form parallel resonant units. One end of the two parallel resonant units is connected to the main branch, and the other end is grounded through capacitor C6. The centralized grounding capacitor on the parallel branch can reduce the reflection loss of the signal at the edge of the passband, improve the passband flatness, and reduce ripples. By increasing the number of series and parallel resonant units, the performance of the filter can be further improved. Through reasonable design and debugging, a filter with a wide passband working in the 2GHZ frequency band can be obtained, such as Figure 8 shown.

[0047] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A broadband filter of a bulk acoustic wave filter resonant unit, characterized in that: include: An input port, a resonant unit group, and an output port are connected in sequence, wherein the resonant unit group includes a plurality of series resonant units and parallel resonant units, wherein the series resonant unit includes a series FBAR resonator and a first resonant network connected in parallel with the series FBAR resonator, wherein the first resonant network is composed of a capacitor and an inductor of a first discrete component connected in series, and the parallel resonant unit includes a parallel FBAR resonator and a second resonant network connected in series with the parallel FBAR resonator, wherein the second resonant network is composed of a capacitor and an inductor of a second discrete component connected in parallel.

2. The broadband filter of the bulk acoustic wave filter resonator unit according to claim 1, characterized in that: The series resonance unit includes a first series resonance unit, a second series resonance unit, and a third series resonance unit with the same structure, and the parallel resonance unit includes a first parallel resonance unit, a second parallel resonance unit, and a third parallel resonance unit with the same structure.

3. The broadband filter of the bulk acoustic wave filter resonator unit according to claim 2, characterized in that: The input port is connected to the first series resonant unit, the other end of the first series resonant unit is connected to the first parallel resonant unit, and the other end of the first parallel resonant unit is grounded; A common end of the first series resonant unit and the first parallel resonant unit is connected to the second series resonant unit, the second series resonant unit is connected to the second parallel resonant unit, and the other end of the second parallel resonant unit is grounded; A common end of the second series resonant unit and the second parallel resonant unit is connected to the third series resonant unit, the third series resonant unit is connected to the third parallel resonant unit, and the other end of the third parallel resonant unit is grounded; A common end of the third series resonant unit and the third parallel resonant unit is connected to a parallel network of a capacitor and an inductor, and the other end of the parallel network is connected to the output port.

4. The broadband filter of the bulk acoustic wave filter resonator unit according to claim 1, characterized in that: The series resonance unit includes a fourth series resonance unit, a fifth series resonance unit, and a sixth series resonance unit with the same structure, and the parallel resonance unit includes a fourth parallel resonance unit, a fifth parallel resonance unit, and a sixth parallel resonance unit with the same structure.

5. The broadband filter of the bulk acoustic wave filter resonator unit according to claim 4, characterized in that: The input port is connected to the fourth series resonant unit, the other end of the fourth series resonant unit is connected to the fourth parallel resonant unit and the fifth series resonant unit, the other end of the fourth parallel resonant unit is connected to the discrete component capacitor, the other end of the fifth series resonant unit is respectively connected to the fifth parallel resonant unit and the sixth series resonant unit, the other end of the sixth series resonant unit is connected to the output port, the other end of the fifth parallel resonant unit is connected to the common end of the fourth parallel resonant unit and the discrete component capacitor, and the other end of the discrete component capacitor is grounded.

6. The broadband filter of the bulk acoustic wave filter resonator unit according to claim 1, characterized in that: The series resonant frequency of the first resonant network is the same as the series resonant frequency of the series FBAR resonator, and the parallel resonant frequency of the second resonant network is the same as the parallel resonant frequency of the parallel FBAR resonator.

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