Disclosure of Invention
In view of the above, it is a primary object of the present invention to provide a filter, a duplexer, a high-frequency front-end circuit, and a communication apparatus, which are useful for improving the roll-off characteristics of the filter, reducing the insertion loss characteristics near the series resonance frequency point of the resonator, and improving the far-band rejection characteristics of the filter.
To achieve the above object, according to one aspect of the present invention, there is provided a filter including a first series branch between an input and an output of the filter, and a plurality of parallel branches; one end of the parallel branch is positioned on the first series branch, the other end of the parallel branch is grounded, the filter also comprises at least one second series branch positioned between the input end and the output end of the filter, and the second series branch comprises an inductor; and for the whole formed by the first series branch and the second series branch, at least 1 acoustic wave resonator exists in the whole, and the acoustic wave resonator is connected in series with the inductor in the series branch.
Optionally, the first series branch comprises two inductors connected in series, and a capacitor is connected between the two inductors in series; the second series branch comprises two inductors which are connected in series, and an acoustic wave resonator is connected between the two inductors in series; the parallel branch comprises two parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, the two parallel resonance units are respectively connected with an input end serial branch node and an output end serial branch node, the other ends of the two parallel resonance units are respectively connected with the inductors, and one ends of the two inductors are jointly connected with the grounding inductor.
Optionally, the first series branch comprises two series resonant units connected in series, each series resonant unit comprising a capacitor and an inductor connected in series; the second series branch comprises two inductors connected in series, and an acoustic wave resonator is connected between the two inductors in series; the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, the three parallel resonance units are respectively connected with an input end series branch node, a series resonance unit connecting node and an output end series branch node, and the other ends of the three parallel resonance units are grounded.
Optionally, the first series branch comprises two series resonant units connected in series, each series resonant unit comprising a capacitor and an inductor connected in series; the second series branch comprises two inductors connected in series, and an acoustic wave resonator is connected between the two inductors in series; the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, the two parallel resonance units are respectively connected with an input end serial branch node and an output end serial branch node, the other ends of the two parallel resonance units are respectively connected with the inductors, and one ends of the two inductors are jointly connected with the grounding inductor; one end of the other parallel resonance unit is connected with the connection node of the series resonance unit, the other end of the parallel resonance unit is connected with an inductor, and the inductor is grounded.
Optionally, the first series branch comprises two series resonant units connected in series, each series resonant unit comprising a capacitor and an inductor connected in series; the second series branch comprises two inductors connected in series, and an acoustic wave resonator is connected between the two inductors in series; the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, the three parallel resonance units are respectively connected with an input end series branch node, a series resonance unit connecting node and an output end series branch node, the other ends of the three parallel resonance units are respectively connected with the inductors, and the three inductors are grounded.
Optionally, the first series branch comprises two series resonant units connected in series, each series resonant unit comprising a capacitor and an inductor connected in series; the second series branch comprises two inductors which are connected in series, two acoustic wave resonators with different frequencies are connected between the two inductors in series, and the two acoustic wave resonators are connected in parallel; the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, the two parallel resonance units are respectively connected with an input end serial branch node and an output end serial branch node, the other ends of the two parallel resonance units are respectively connected with the inductors, and one ends of the two inductors are jointly connected with the grounding inductor; one end of the other parallel resonance unit is connected with the connection node of the series resonance unit, the other end of the parallel resonance unit is connected with an inductor, and the inductor is grounded.
Optionally, the first series branch includes two inductors connected in series, and two acoustic wave resonators with different frequencies are connected in series between the two inductors, and the two acoustic wave resonators are connected in series; the second series branch comprises two inductors which are connected in series, and a capacitor is connected between the two inductors in series; the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, the two parallel resonance units are respectively connected with an input end serial branch node and an output end serial branch node, the other ends of the two parallel resonance units are respectively connected with the inductors, and one ends of the two inductors are jointly connected with the grounding inductor; one end of the other parallel resonance unit is connected with a connection node between the acoustic wave resonators, the other end of the other parallel resonance unit is connected with an inductor, and the inductor is grounded.
Optionally, the first series branch comprises two series resonant units connected in series, each series resonant unit comprising a capacitor and an inductor connected in series; the second series branch comprises two inductors connected in series, and an acoustic wave resonator is connected between the two inductors in series; the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises an acoustic wave resonator and an inductor which are connected in parallel, the two parallel resonance units are respectively connected with an input end series branch node and an output end series branch node, the other ends of the two parallel resonance units are respectively connected with the inductors, and one ends of the two inductors are jointly connected with a grounding inductor; one end of the other parallel resonance unit is connected with the connection node of the series resonance unit, the other end of the parallel resonance unit is connected with an inductor, and the inductor is grounded.
The first series branch comprises two series resonance units which are connected in series, and each series resonance unit comprises a capacitor and an inductor which are connected in series;
the second series branch comprises two inductors which are connected in series, and an acoustic wave resonator is connected between the two inductors in series;
the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, one end of each parallel resonance unit is respectively connected to the input end serial branch node, the serial resonance unit connection node and the output end serial branch node, and the other end of each parallel resonance unit is respectively connected to the inductor; the inductors connected with the parallel resonance units connected with the connection nodes of the series resonance units are grounded, the inductors connected with the other two parallel resonance units are respectively connected with the grounded inductors, and the nodes between the two inductors and the grounded inductors are connected through the first inductor.
Optionally, a coupling structure is formed by mutual inductance between two inductors connected to two parallel resonant units connected to the input end series branch node and the output end series branch node.
According to another aspect of the present invention, there is provided a duplexer including the above filter.
In yet another aspect of the present invention, a high frequency front end circuit is provided, which includes the above filter.
According to still another aspect of the present invention, there is provided a communication apparatus including the above filter.
The invention has the following beneficial effects:
(1) an acoustic wave resonator is arranged on a first series branch or a second series branch between an input end series branch node and an output end series branch node, and the high Q characteristic of the acoustic wave resonator is utilized to ensure that an area between Fs and Fp is used for forming a rapid roll-off edge of the filter, so that the roll-off characteristic of the filter is effectively improved;
(2) by utilizing the low impedance characteristic near the series resonance frequency Fs of the acoustic wave resonator, the insertion loss characteristic of the filter near the resonator Fs is improved to the maximum extent;
(3) the series inductance is introduced into the parallel branch to form series resonance at the far band, and coupling is added between the introduced series inductances, so that the far band rejection characteristic of the filter is effectively improved, and the design flexibility is greatly increased.
Detailed Description
Fig. 1a is an electrical symbol of the piezoelectric acoustic wave resonator, fig. 1b is a diagram of an equivalent electrical model thereof, and the electrical model is simplified to a resonant circuit composed of Lm, Cm and C0 without considering loss terms. According to the resonance condition, the resonance circuit has two resonance frequency points: one is fs when the impedance value of the resonant circuit reaches a minimum value, and fs is defined as a series resonance frequency point of the resonator; and the other is fp when the impedance value of the resonant circuit reaches a maximum value, and fp is defined as a parallel resonance frequency point of the resonator. Wherein the content of the first and second substances,
and fs is smaller than fp; at the same time, the effective electromechanical coupling coefficient Kt of the resonator is defined2eff (hereinafter abbreviated as Kt)2) It can be expressed in fs and fp:
fig. 2 is a relationship between resonator impedance and fs and fp. Under a certain specific frequency, the larger the effective electromechanical coupling coefficient is, the larger the frequency difference between fs and fp is, i.e. the farther the two resonant frequency points are, the larger Kt is2The resonator can meet the design requirements of a wide bandwidth filter. Meanwhile, 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 magnitude of the impedance of the resonator at fp is defined as Rp, which is the maximum value in the impedance curve of the resonator. Rs and Rp are important parameters describing resonance loss characteristics, and 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.
Fig. 3 is a schematic cross-sectional view of a structure of a thin film bulk acoustic resonator, 61 is a semiconductor substrate material, 65 is an air cavity obtained by etching, a bottom electrode 63 of the thin film bulk acoustic resonator is deposited on the semiconductor substrate 61, 62 is a piezoelectric thin film material, and 64 is a top electrode. The area outlined by the dashed line is the overlapping area of the 65 air cavity, the 64 top electrode, the 63 bottom electrode and the 62 piezoelectric layer, which is the effective resonance area. The top electrode and the bottom electrode may be made of gold (Au), tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), iridium (Ir), titanium Tungsten (TiW), aluminum (Al), titanium (Ti), or the like; the material of the piezoelectric layer may be aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO3), Quartz (Quartz), potassium niobate (KNbO3), lithium tantalate (LiTaO3), or the like. The thickness of the piezoelectric film is typically less than 10 microns. The aluminum nitride film is polycrystalline or monocrystalline, and the growth method is sputtering or Metal Organic Chemical Vapor Deposition (MOCVD).
Fig. 4 is a circuit structure diagram (comparative example) of a conventional LC filter 100, as shown in fig. 4, two capacitors connected in series are provided between an input end series branch node P1 and an output end series branch node P2, which are respectively C1 and C2, an inductor L1 is provided between the input end series branch node P1 and an input end T1, an inductor L2 is provided between the output end series branch node P2 and an output end T2, the input end series branch node P1, a line between the capacitors C1 and C2, and the output end series branch node P2 are respectively connected to a parallel branch, the parallel branch includes a capacitor C3 and an inductor L3 connected in parallel, a capacitor C4 and an inductor L4 connected in parallel, a capacitor C5 and an inductor L5 connected in parallel, and the other ends of the three parallel branches are grounded.
The conventional LC filter has general performances such as insertion loss, out-of-band rejection, roll-off and the like due to the limitation of the Q value of the LTCC, and the LTCC has poor far-band rejection characteristics due to the existence of a lead-Inductor (LED).
In view of the defects in the above comparative examples, the present embodiment proposes a new filter, which adds a series branch to the existing filter, and sets an acoustic wave filter on any one series branch to form a combined filter.
Fig. 5 is a schematic diagram of a topology of a filter according to this embodiment, and as shown in fig. 5, the first series branch includes two inductors L0 connected in series, and a capacitor C1 connected in series between the two inductors L0; the second series branch comprises two inductors L0 connected in series, and a series acoustic wave resonator RES1 is connected between the two inductors L0; the parallel branch comprises two parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, C2, C3, L3 and L4 in the figure, the two parallel resonance units are respectively connected with an input end series branch node P1 and an output end series branch node P2, the other ends of the two parallel resonance units are respectively connected with inductors L5 and L6, and one ends of the two inductors L5 and L6 are connected with a grounding inductor LM together (the node P3). In this structure, the parallel branch includes two parallel resonant units, wherein the filter may further include three parallel resonant units, and fig. 6 is a schematic view of a topology structure of a filter having another structure according to this embodiment; in the figure, the first series branch comprises two series resonant units connected in series, each series resonant unit comprises a capacitor and an inductor connected in series, and C2 and C3 are connected with L0; the second series branch comprises two inductors L0 connected in series, and an acoustic wave resonator RES1 is connected between the two inductors L0 in series; the parallel branch comprises three parallel resonant units, each parallel resonant unit comprises a capacitor and an inductor which are connected in parallel, such as C4 and L3, C5 and L4, C6 and L5 which are connected in parallel in the figure; the three parallel resonant cells are connected to the input end series branch node P1, the series resonant cell connection node, and the output end series branch node P2, respectively, and the other ends are grounded.
As shown in fig. 7, the first series branch comprises two series resonant cells connected in series, each series resonant cell comprising a capacitor and an inductor connected in series, two L0, C2 and C3 respectively; the second series branch comprises two inductors L0 connected in series, and an acoustic wave resonator RES1 is connected between the two inductors in series; the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, the capacitors and the inductors are respectively C4 and L3, C5 and L4, and C6 and L5 which are connected in parallel, the two parallel resonance units are respectively connected with an input end series branch node P1 and an output end series branch node P2, the other ends of the two parallel resonance units are respectively connected with an inductor L6 and an inductor L8, and one ends of the two inductors are commonly connected with a grounding inductor LM; one end of the other parallel resonant cell is connected to the series resonant cell connection node, and the other end is connected to an inductor L7, which is grounded.
Fig. 8 is an equivalent circuit diagram 400 of the series branch of the comparative circuit structure 100 without considering the parallel branch, in which the inductor LE is the equivalent inductance of the series branch and the capacitor CE is the equivalent capacitance of the series branch. Taking the topology of the filter disclosed in fig. 6 as a first embodiment (embodiment 1), fig. 9 is an equivalent circuit diagram 401 of the circuit structure 300 of the first embodiment without considering the parallel branches, where the inductor LE is an equivalent inductor of the series branch, the capacitor CE is an equivalent capacitor of the series branch, and 2L0 represents the series inductor of the input and output terminals.
As shown in fig. 10, in which a solid line is an impedance frequency characteristic curve of the resonator RES in fig. 9, and a DOT broken line is an impedance frequency characteristic curve of the equivalent circuit shown in fig. 9, the series resonator frequency Fs of the resonator after the resonator RES is connected in series to the equivalent inductance is shifted to a low frequency side, and since the series equivalent inductance is relatively small, the series resonance frequency Fs of the equivalent circuit 401 is hardly changed, and the parallel resonator frequency Fp of the resonator after the resonator RES is connected in parallel to the equivalent capacitance is shifted to a low frequency side. In summary, the equivalent Kt of the resonator is caused by the introduction of the equivalent inductor and the equivalent capacitor in the equivalent circuit shown in 4012And decreases. The DASH dotted line is an impedance frequency characteristic curve of the equivalent circuit shown in fig. 8, and since the equivalent inductance LE is small, the series resonator point is located at a higher frequency.
As shown in fig. 11 in which a thin solid line is a solid line of the impedance frequency characteristic curve of the equivalent circuit shown in fig. 9, a thick solid line is an insertion loss characteristic curve of the first embodiment, and a broken line is an insertion loss characteristic curve of the comparative example, the pass band edge roll-off characteristics of the embodiment are significantly improved relative to the comparative example because the region between Fs and Fp is ensured for forming the fast roll-off edge of the filter due to the high Q characteristics of the BAW/SAW resonator (acoustic wave resonator); meanwhile, as shown by the dotted rectangular box in fig. 11, since the second series branch is connected across the input terminal node P1 and the output terminal node P2, the low impedance characteristic in the vicinity of the series resonance frequency Fs of the BAW/SAW resonator can minimize the insertion loss in the corresponding passband band.
Fig. 12 shows a parallel branch circuit structure 501 of a comparative example, which is composed of an inductor L and a capacitor C connected in parallel with each other; the topology of the filter disclosed in fig. 7 is taken as a second embodiment, and fig. 13 shows a parallel branch circuit structure 502 of the second embodiment (embodiment 2), which is formed by connecting an inductor L1 and a capacitor C1 in parallel with each other and then connecting an inductor L2 in series.
As shown in fig. 14, in which a thick implementation represents the insertion loss characteristic curve of embodiment 2, and a thin solid line represents the impedance frequency characteristic curve of the parallel branch circuit in the second embodiment shown in fig. 13; the thick broken line is an insertion loss characteristic curve of example 1, and the thin broken line is an impedance frequency characteristic curve of the parallel branch circuit of the first embodiment shown in fig. 12. Since the inductor L2 in the parallel branch circuit of the second embodiment introduces series resonance, a suppression zero is generated at the far band, and the far band suppression characteristic of the filter is effectively improved.
As shown in fig. 15, the change rule of the out-of-band rejection characteristic of the filter is shown along with the change of the inductance of the series inductor L2 in the parallel branch. As the inductance of inductor L2 increases, the damping zero at the far band moves toward the low frequency end.
In addition to the first embodiment and the second embodiment, the topological structure of the filter in this embodiment further includes the following embodiments.
Fig. 16 is a schematic diagram of a topology of a filter provided in a third embodiment, as shown in fig. 16, a first series branch includes two series resonant cells connected in series, each series resonant cell includes two capacitors and inductors connected in series, respectively L0, C2 and C3; the second series branch comprises two inductors L0 connected in series, between which an acoustic wave resonator RES1 is connected in series.
The parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel and are respectively C4, L3, C5, L4, C6 and L5, the three parallel resonance units are respectively connected with an input end series branch node P1, a series resonance unit connecting node and an output end series branch node P2, the other ends of the three parallel resonance units are respectively connected with the inductors L6, L7 and L8, and the three inductors are grounded.
Fig. 17 is a schematic diagram of a topology of a filter provided in a fourth embodiment, as shown in fig. 17, a first series branch includes two series resonant cells connected in series, each series resonant cell includes a capacitor and an inductor connected in series, two L0, C2 and C3; the second series branch comprises two inductors L0 connected in series, two acoustic wave resonators with different frequencies are connected between the two inductors in series, and the two acoustic wave resonators are connected in parallel and are RES1 and RES 2; wherein the frequencies of the resonator RES1 and the resonator RES2 are different from each other.
The parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel and are respectively C4, L3, C5, L4, C6 and L5, the two parallel resonance units are respectively connected with an input end series branch node P1 and an output end series branch node P2, the other ends of the two parallel resonance units are respectively connected with an inductor L6 and an inductor L8, and one ends of the two inductors are commonly connected with a grounding inductor LM; one end of the other parallel resonant cell is connected to the series resonant cell connection node, and the other end is connected to an inductor L7, which is grounded.
Fig. 18 is a schematic diagram of a topology of a filter provided in a fifth embodiment, as shown in fig. 18, a first series branch includes two inductors L0 connected in series, two acoustic wave resonators RES1 and RES2 with different frequencies are connected in series between the two inductors, and the two acoustic wave resonators are connected in series; the second series branch comprises two inductors L0 connected in series, and a capacitor C1 connected in series between the two inductors;
the parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel, C4, L3, C5, L4, C6 and L5, the two parallel resonance units are respectively connected with an input end series branch node P1 and an output end series branch node P2, the other ends of the two parallel resonance units are respectively connected with inductors L6 and L8, and one ends of the two inductors are commonly connected with a grounding inductor LM; one end of the other parallel resonant unit is connected to a connection node between the acoustic wave resonators, and the other end is connected to an inductance L7, which is grounded. In this embodiment, the capacitance in the series unit of the first series arm is replaced by the acoustic wave resonator RES1 and the resonator RES2, and the roll-off characteristic on the right side of the filter pass band is improved.
Fig. 19 is a schematic diagram of a topology of a filter provided in a sixth embodiment, as shown in fig. 19, a first series branch includes two series resonant cells connected in series, each series resonant cell includes a capacitor and an inductor connected in series, two L0, C2 and C3; the second series branch comprises two inductors L0 connected in series, between which an acoustic wave resonator RES1 is connected in series.
The parallel branch comprises three parallel resonance units, each parallel resonance unit comprises an acoustic wave resonator and an inductor which are connected in parallel and respectively include RES2, L3, RES3, L4, RES4 and L5, the two parallel resonance units are respectively connected with an input end series branch node P1 and an output end series branch node P2, the other ends of the two parallel resonance units are respectively connected with inductors L6 and L8, and one ends of the two inductors are commonly connected with a grounding inductor LM; one end of the other parallel resonant cell is connected to the series resonant cell connection node, and the other end is connected to an inductor L7, which is grounded. In this embodiment, the capacitance in the parallel resonance unit is replaced by BAW/SAW resonators, resonator RES2, resonator RES3, and resonator RES4, which are different in resonator frequency from each other, for improving the roll-off characteristic on the left side of the filter passband.
Fig. 20 is a schematic diagram of the topology of a filter provided in the seventh embodiment; as shown in fig. 20, the first series branch includes two series resonant cells connected in series, each series resonant cell including a capacitor and an inductor connected in series, two inductors L0, C2, and C3; the second series branch comprises two inductors L0 connected in series, between which an acoustic wave resonator RES1 is connected in series.
The parallel branch comprises three parallel resonance units, each parallel resonance unit comprises a capacitor and an inductor which are connected in parallel and are respectively C4, L3, C5, L4, C6 and L5, one end of each parallel resonance unit is respectively connected to an input end series branch node P1, a series resonance unit connection node and an output end series branch node P2, and the other end of each parallel resonance unit is respectively connected with an inductor L6, an inductor L7 and an inductor L8; wherein, an inductor L7 connected with the parallel resonant unit connected with the connection node of the series resonant unit is grounded, inductors L6 and L8 connected with the other two parallel resonant units are respectively connected with a grounding inductor LM, and nodes P3 and P6 between the two inductors L6 and L8 and the grounding inductor LM are connected through a first inductor L9.
In this embodiment, a coupling structure is added to the parallel branch between the input end series branch node P1 and the output end series branch node P2, such as an inductive coupling M shown in fig. 16, where the inductive coupling M can improve the far-band rejection characteristic of the filter. Taking the second embodiment as an example, an inductive coupling M is added between the series inductor L6 of the input-end parallel branch and the series inductor L8 of the output-end parallel branch, and the magnitude of the inductive coupling M corresponds to the insertion loss characteristic curve of the second embodiment, as shown in fig. 21, the added coupled combined rejection zeros are separated into two rejection zeros at high and low frequencies, and the larger the inductive coupling amount is, the farther the two rejection zeros are apart. In conclusion, by changing the inductance of the inductor L2 and adding the inductance coupling between the series inductance L6 of the input-end parallel branch and the series inductance L8 of the output-end parallel branch, the out-of-band rejection index requirements of different frequency bands can be met, and the design flexibility is increased to a great extent.
In this embodiment, the filter may be implemented by LTCC, discrete device, IPD, or other forms, and is preferably implemented by LTCC, which has the advantages of low cost, good performance, high reliability, and the like. As shown in fig. 22, a schematic diagram 800 of a three-dimensional structure implemented by the second embodiment based on LTCC is shown, where 86 is a reference plane, 80 is a resonator RES1, 83 of the second series branch is an LTCC dielectric material, 81 is a device input terminal, 82 is an output terminal of the device, P1 corresponds to a node P4 in the circuit diagram of the second embodiment, P2 corresponds to a node P5 in the circuit diagram of the second embodiment, a distance S between a node P1 and the node P2 corresponds to a series inductance in the parallel branch, a higher S generates a lower frequency of a position where a far-band suppression zero is located, a parameter H corresponds to an inductance LM in the second embodiment, and a higher H generates a larger inductive coupling M between the series inductance L6 representing the input-side parallel branch and the series inductance L8 representing the output-side parallel branch, and the two suppression zeros are further apart.
The present embodiment also provides a duplexer, a high frequency front end circuit and a communication device, including one or more of the filters in the above embodiments.
The above-described embodiments should not be construed as limiting the scope of the invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and substitutions may occur depending on design requirements and other factors. 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.