Filter circuit, filter, and communication device

Abstract

A filter circuit, a filter and a communication device relate to the technical field of communication. The filter circuit comprises a series branch which is connected between the first port and the second port and comprises a series resonance circuit and a series impedance element which are connected in series, and the series resonance circuit comprises a series resonator; the parallel branch is connected between the parallel node and the ground potential and comprises a parallel resonance circuit and a parallel impedance element which are connected in series, the parallel resonance circuit comprises a parallel resonator, and the parallel node is located on a connecting path of the first port and the second port; wherein the resonant frequency of the series resonator is smaller than that of the parallel resonator.

Description

Filter circuit, filter, and communication device Technical Field

[0001] The present disclosure relates to the field of communication technology, and in particular to a filtering circuit, a filter, and a communication device. Background Art

[0002] With the development of communication technology, the demand for spectrum utilization is becoming increasingly higher, and the distance between the transmission frequency bands of different information is becoming smaller and smaller during the information transmission process. This requires band-stop filters to pass the transmission signal within a specific frequency range and filter out the noise spectrum or the spectrum without transmission signal to meet the needs of information transmission.

[0003] Overview

[0004] The present disclosure provides a filtering circuit, comprising:

[0005] a series branch connected between the first port and the second port, comprising a series resonant circuit and a series impedance element connected in series with each other, wherein the series resonant circuit comprises a series resonator; and

[0006] a parallel branch connected between a parallel node and a ground potential, comprising a parallel resonant circuit and a parallel impedance element connected in series, wherein the parallel resonant circuit comprises a parallel resonator, and the parallel node is located on a connection path between the first port and the second port;

[0007] The resonant frequency of the series resonator is lower than the resonant frequency of the parallel resonator.

[0008] In some embodiments, the series resonant circuit includes a plurality of series resonators connected in series with each other, and the series resonators are connected between the series impedance element and the first port and / or between the series impedance element and the second port.

[0009] In some embodiments, the resonant frequencies of the plurality of series resonators are the same.

[0010] In some embodiments, the parallel resonant circuit includes a plurality of parallel resonators connected in parallel with each other, and the plurality of parallel resonators are connected between the parallel impedance element and the parallel node, or between the parallel impedance element and the ground potential.

[0011] In some embodiments, the resonant frequencies of the plurality of parallel resonators are the same.

[0012] In some embodiments, the filtering circuit includes a plurality of parallel branches, and the parallel resonators in the plurality of parallel branches all have the same resonant frequency.

[0013] In some embodiments, the plurality of parallel branches include a first parallel branch and a second parallel branch, a parallel node connecting the first parallel branches is a first parallel node, and a parallel node connecting the second parallel branches is a second parallel node;

[0014] The series resonator and / or the series impedance element are connected between the first parallel node and the second parallel node.

[0015] In some embodiments, the parallel impedance element in the first parallel branch and the parallel impedance element in the second parallel branch are capacitors with different capacitance values, or inductors with different inductance values.

[0016] In some embodiments, the filtering circuit further includes:

[0017] A voltage-dividing impedance element is connected in parallel with at least one of the series resonators, or is connected in parallel with at least one of the series resonators and the series impedance element.

[0018] In some embodiments, the voltage-dividing impedance element and the series impedance element are both inductors, and the inductance of the voltage-dividing impedance element is greater than the inductance of the series impedance element; or

[0019] The voltage-dividing impedance element and the series impedance element are both capacitors, and the capacitance value of the voltage-dividing impedance element is greater than the capacitance value of the series impedance element.

[0020] In some embodiments, a difference between a resonant frequency of the parallel resonator and a resonant frequency of the series resonator is greater than or equal to 0.1 GHz and less than or equal to 0.3 GHz.

[0021] In some embodiments, the parallel resonator and the series resonator are elastic wave resonators of the same type, and the types of the elastic wave resonators include surface acoustic wave resonators and bulk acoustic wave resonators.

[0022] In some embodiments, the series impedance element includes at least one of the following: an adjustable capacitor, an adjustable inductor, a non-adjustable capacitor, and a non-adjustable inductor;

[0023] The parallel impedance element includes at least one of the following: an adjustable capacitor, an adjustable inductor, a non-adjustable capacitor, and a non-adjustable inductor.

[0024] In some embodiments, the series impedance element includes an inductor, and the inductance of the inductor is greater than or equal to 0.5 nH and less than or equal to 3.5 nH.

[0025] In some embodiments, the parallel impedance element includes a capacitor, and the capacitance of the capacitor is greater than or equal to 0.5 pF and less than or equal to 7 pF.

[0026] The present disclosure provides a filter comprising one or more filter circuits as described in any one of the embodiments.

[0027] In some embodiments, the plurality of filter circuits include a first filter circuit and a second filter circuit, and the second port of the first filter circuit is connected to the first port of the second filter circuit;

[0028] Among them, the parallel node connecting the parallel branches in the first filter circuit is the third parallel node, the parallel node connecting the parallel branches in the second filter circuit is the fourth parallel node, and the series resonator and / or the series impedance element are connected between the third parallel node and the fourth parallel node.

[0029] In some embodiments, the series resonator in the first filter circuit and the series resonator in the second filter circuit have the same resonant frequency, and the parallel resonator in the first filter circuit and the parallel resonator in the second filter circuit have the same resonant frequency.

[0030] In some embodiments, the resonant frequency of the series resonator in the first filtering circuit is greater than the resonant frequency of the series resonator in the second filtering circuit; or

[0031] The resonant frequency of the series resonator in the first filtering circuit is lower than the resonant frequency of the series resonator in the second filtering circuit.

[0032] The present disclosure provides a communication device, comprising the filter as described in any one of the embodiments.

[0033] The above description is only an overview of the technical solution of the present disclosure. In order to more clearly understand the technical means of the present disclosure, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present disclosure more obvious and easy to understand, the specific implementation methods of the present disclosure are listed below.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or related technologies, the following is a brief introduction to the drawings required for the description of the embodiments or related technologies. Obviously, the drawings described below are some embodiments of the present disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without inventive efforts. It should be noted that the scales in the drawings are for illustration only and do not represent the actual scale.

[0036] FIG1 shows a schematic structural diagram and an S-parameter diagram of a filter circuit in the related art;

[0037] FIG2 exemplarily shows a structural diagram and an S-parameter diagram of a first filter circuit provided by the present disclosure;

[0038] FIG3 exemplarily shows a structural diagram and an S-parameter diagram of a second filter circuit provided by the present disclosure;

[0039] FIG4 exemplarily shows a structural diagram and an S-parameter diagram of a third filtering circuit provided by the present disclosure;

[0040] FIG5 exemplarily shows a structural diagram and an S-parameter diagram of a fourth filtering circuit provided by the present disclosure;

[0041] FIG6 exemplarily shows a structural diagram and an S-parameter diagram of a fifth filtering circuit provided by the present disclosure;

[0042] FIG7 exemplarily shows a structural diagram and an S-parameter diagram of a sixth filtering circuit provided by the present disclosure;

[0043] FIG8 exemplarily shows a schematic diagram of a planar structure of a surface acoustic wave resonator;

[0044] FIG9 exemplarily shows a schematic cross-sectional structure diagram of a thin film bulk acoustic resonator;

[0045] FIG10 exemplarily shows a cross-sectional structural diagram of a solid-state assembly resonator;

[0046] FIG11 exemplarily shows a structural diagram and an S-parameter diagram of a first filter provided by the present disclosure;

[0047] FIG12 exemplarily shows a structural diagram and an S-parameter diagram of the second filter provided by the present disclosure.

[0048] Detailed description

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present disclosure without making any creative efforts shall fall within the scope of protection of the present disclosure.

[0050] A band-stop filter is a filter that can pass most frequency components but attenuate frequency components in a certain range to an extremely low level. It is opposite to the concept of a band-pass filter. A notch filter is a special band-stop filter with an extremely small stopband range and a very high quality factor.

[0051] In the related art, a band-stop filter circuit is shown in FIG1 a, which includes a first port 1, a second port 2, a series resonator S connected between the first port 1 and the second port 2, and a first resonator S connected between the first port 1 and the second port 2. 11 , and one end is grounded and the other end is connected to the series resonator S 11 The parallel resonator P between the second port 2 11 Figure 1(b) shows the S-parameter diagram of the band-stop filter shown in Figure 1(a). It can be seen that there is a narrow stopband near 3.55 GHz, the transmission coefficient S21 is about -5 dB in the passband, the insertion loss is large, the transition band between the passband and the stopband is wide, and the roll-off coefficient is poor.

[0052] To address the above-mentioned issues, the present disclosure provides a filter circuit, as shown in Figure a of any one of Figures 2 to 7 . The filter circuit includes: a series branch 21 connected between a first port 1 and a second port 2, comprising a series resonant circuit 22 and a series impedance element 23 connected in series with each other, wherein the series resonant circuit 22 includes a series resonator S; and a parallel branch 24 connected between a parallel node N and a ground potential GND, comprising a parallel resonant circuit 25 and a parallel impedance element 26 connected in series with each other, wherein the parallel resonant circuit 25 includes a parallel resonator P, wherein the parallel node N is located on the connection path between the first port 1 and the second port 2. The resonant frequency of the series resonator S is lower than the resonant frequency of the parallel resonator P.

[0053] As shown in any of Figures 2 through 7, Figure b shows the S-parameter graph of the filter circuit shown in Figure a. The frequency range corresponding to the notched waveform is the stopband, while the passband lies outside the stopband. It can be seen that the transmission coefficient S21 corresponding to the passband is close to 0dB, the passband insertion loss is low, and the transition band between the passband and stopband is narrow, resulting in an excellent roll-off coefficient, enabling separation of two closely spaced RF signals.

[0054] The filtering circuit provided by the present disclosure is a deep notch filter. By setting a series impedance element 23 in the series branch 21 and a parallel impedance element 26 in the parallel branch 24, and then by reasonably setting the parameters of the series impedance element 23 and the parallel impedance element 26, the passband insertion loss can be reduced and the roll-off coefficient can be optimized.

[0055] In a specific implementation, an optimized S-parameter diagram may be obtained by adjusting the parameters of the series resonator S, the parallel resonator P, the series impedance element 23 , and the parallel impedance element 26 .

[0056] For example, the series resonant circuit 22 can be located between the series impedance element 23 and the first port 1 (as shown in Figures 2 to 7), or between the series impedance element 23 and the second port 2. The series resonant circuit 22 can also be set between the series impedance element 23 and the first port 1 and between the series impedance element 23 and the second port 2. The present disclosure does not limit this.

[0057] Exemplarily, the parallel resonant circuit 25 can be located between the parallel impedance element 26 and the parallel node N (as shown in Figures 2 to 7), or between the parallel impedance element 26 and the ground potential GND. The parallel resonant circuit 25 can also be set between the parallel impedance element 26 and the parallel node N and between the parallel impedance element 26 and the ground potential GND. The present disclosure does not limit this.

[0058] In the present disclosure, the parallel node N may be any node on the connection path between the first port 1 and the second port 2. For example, as shown in FIG. 2 to FIG. 7 a, the parallel node N may be located between the series resonant circuit 22 and the first port 1, between the series resonant circuit 22 and the series impedance element 23, or between the series impedance element 23 and the second port 2.

[0059] In some embodiments, the series impedance element 23 includes at least one of the following: an adjustable capacitor, an adjustable inductor, a non-adjustable capacitor, and a non-adjustable inductor. When the series impedance element 23 is an adjustable capacitor or an adjustable inductor, the stop band position can be fine-tuned.

[0060] In some embodiments, the parallel impedance element 26 includes at least one of the following: an adjustable capacitor, an adjustable inductor, a non-adjustable capacitor, and a non-adjustable inductor. When the parallel impedance element 26 is an adjustable capacitor or an adjustable inductor, the position of the stop band can be fine-tuned.

[0061] Exemplarily, the series impedance element 23 includes an inductor, and the inductance of the inductor may be greater than or equal to 0.5 nH and less than or equal to 3.5 nH.

[0062] Exemplarily, the parallel impedance element 26 includes a capacitor, and the capacitance of the capacitor may be greater than or equal to 0.5 pF and less than or equal to 7 pF.

[0063] In some embodiments, as shown in FIG. 2 or FIG. 4 a , the series resonant circuit 22 includes a series resonator S.

[0064] In some embodiments, as shown in Figure a of Figure 3 or Figure 5, the series resonant circuit 22 includes a plurality of series resonators S connected in series with each other, and the series resonators S are connected between the series impedance element 23 and the first port 1, and / or between the series impedance element 23 and the second port 2.

[0065] In this embodiment, the multiple series resonators S can all be located between the series impedance element 23 and the first port 1 (as shown in Figures 3 and 5), or all be located between the series impedance element 23 and the second port 2, or some of them can be located between the series impedance element 23 and the first port 1, and the other part can be located between the series impedance element 23 and the second port 2. This disclosure does not limit this.

[0066] In which, when a part of the series resonator S is located between the series impedance element 23 and the first port 1 and another part of the series resonator S is located between the series impedance element 23 and the second port 2, the parallel node N can be located between the series resonator S and the first port 1, between two adjacent series resonators S, between the series resonator S and the series impedance element 23, and between the series resonator S and the second port 2.

[0067] In this embodiment, illustratively, the resonant frequencies of the plurality of series resonators S are the same.

[0068] In some embodiments, as shown in FIG. 2 or FIG. 3 a , the parallel resonant circuit 25 includes a parallel resonator P.

[0069] In some embodiments, as shown in FIG. 4 or FIG. 5 a, the parallel resonant circuit 25 includes a plurality of parallel resonators P connected in parallel with each other, and the plurality of parallel resonators P are connected between the parallel impedance element 26 and the parallel node N, or between the parallel impedance element 26 and the ground potential GND.

[0070] In this embodiment, the plurality of parallel resonators P may all be connected between the parallel impedance element 26 and the parallel node N (as shown in FIG. 4 and FIG. 5 ), or all be connected between the parallel impedance element 26 and the ground potential GND, which is not limited in this disclosure.

[0071] In this embodiment, illustratively, the resonance frequencies of the plurality of parallel resonators P are the same.

[0072] In some embodiments, as shown in FIG. 2 to FIG. 5 a, the filtering circuit includes a parallel branch 24 .

[0073] In some embodiments, as shown in FIG. 6 or FIG. 7 a , the filtering circuit includes a plurality of parallel branches 24 , and the parallel resonators P in the plurality of parallel branches 24 all have the same resonant frequency.

[0074] In this embodiment, for example, as shown in FIG. 6 or FIG. 7 a, the plurality of parallel branches 24 include a first parallel branch 241 and a second parallel branch 242. The parallel node N connecting the first parallel branch 241 is a first parallel node N1, and the parallel node N connecting the second parallel branch 242 is a second parallel node N2. A series resonator S and / or a series impedance element 23 are connected between the first parallel node N1 and the second parallel node N2.

[0075] Exemplarily, a series resonator S may be connected between the first parallel node N1 and the second parallel node N2, a series impedance element 23 may be connected, or a series resonator S and a series impedance element 23 may be connected (as shown in FIG. 6 or FIG. 7 a).

[0076] For example, as shown in FIG. 6 or FIG. 7 a, the parallel impedance element 26 in the first parallel branch 241 and the parallel impedance element 26 in the second parallel branch 242 are capacitors having different capacitance values. In FIG. 6 or FIG. 7 a, the parallel impedance element 26 in the first parallel branch 241 is capacitor C1, and the parallel impedance element 26 in the second parallel branch 242 is capacitor C2. The capacitance values ​​of capacitors C1 and C2 are different, for example, the capacitance value of C1 is smaller than the capacitance value of C2.

[0077] Exemplarily, the parallel impedance element 26 in the first parallel branch 241 and the parallel impedance element 26 in the second parallel branch 242 are inductors with different inductance values.

[0078] In a specific implementation, the parallel impedance element 26 in the first parallel branch 241 can be a capacitor, and the parallel impedance element 26 in the second parallel branch 242 can be an inductor; or the parallel impedance element 26 in the first parallel branch 241 can be an inductor, and the parallel impedance element 26 in the second parallel branch 242 can be a capacitor, which is not limited in the present disclosure.

[0079] In some embodiments, as shown in FIG. 7 a , the filter circuit further includes: a voltage divider impedance element 71 connected in parallel with at least one series resonator S, or connected in parallel with at least one series resonator S and a series impedance element 23 .

[0080] Exemplarily, the voltage divider impedance element 71 includes at least one of the following: an adjustable capacitor, an adjustable inductor, a non-adjustable capacitor, and a non-adjustable inductor. When the voltage divider impedance element 71 is an adjustable capacitor or an adjustable inductor, the position of the stop band can be fine-tuned.

[0081] For example, as shown in FIG7 a, both the voltage-dividing impedance element 71 and the series impedance element 23 are inductors, and the inductance of the voltage-dividing impedance element 71 is greater than the inductance of the series impedance element 23. In FIG7 a, the series impedance element 23 includes an inductor L1, and the voltage-dividing impedance element 71 includes an inductor L2, and the inductance of the inductor L2 is greater than the inductance of the inductor L1.

[0082] Exemplarily, both the voltage-dividing impedance element 71 and the series impedance element 23 are capacitors, and the capacitance of the voltage-dividing impedance element 71 is greater than the capacitance of the series impedance element 23 .

[0083] In a specific implementation, the voltage-dividing impedance element 71 may be an inductor and the series impedance element 23 may be a capacitor; or the voltage-dividing impedance element 71 may be a capacitor and the series impedance element 23 may be an inductor, which is not limited in the present disclosure.

[0084] In a specific implementation, since the stopband center is equal to half of the sum of the resonant frequency of the parallel resonator P and the resonant frequency of the series resonator S, the resonant frequency of the parallel resonator P and the resonant frequency of the series resonator S can be adjusted according to actual needs.

[0085] In some embodiments, the difference between the resonant frequency of the parallel resonator P and the resonant frequency of the series resonator S is greater than or equal to 0.1 GHz and less than or equal to 0.3 GHz. Furthermore, the difference between the resonant frequency of the parallel resonator P and the resonant frequency of the series resonator S is greater than or equal to 0.2 GHz and less than or equal to 0.3 GHz. In this way, on the one hand, the stopband can be prevented from being too narrow, and on the other hand, the risk of ripples in the stopband can be reduced.

[0086] In a specific implementation, the difference between the resonant frequency of the parallel resonator P and the resonant frequency of the series resonator S can be adjusted according to actual requirements such as the stopband width and the S parameter.

[0087] In some embodiments, the parallel resonator P and the series resonator S are elastic wave resonators of the same type, and the types of elastic wave resonators include surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators.

[0088] For example, both the parallel resonator P and the series resonator S are SAW resonators, or both the parallel resonator P and the series resonator S are BAW resonators.

[0089] Due to the small size of the elastic wave resonator, both the parallel resonator P and the series resonator S use elastic wave resonators, which can reduce the size of the filter circuit to meet the application requirements of small portable devices. In addition, it can further improve the quality factor, reduce the insertion loss, improve the spectrum suppression effect in the stopband range, narrow the transition band width between the passband and the stopband, and can separate two groups of RF signals with a close distance.

[0090] FIG8 shows a schematic planar structure diagram of a SAW resonator, which includes an interdigital transducer 81, which includes two oppositely arranged comb electrodes 82. The working principle of the SAW resonator is that the interdigital transducer 81 converts an electrical signal into an acoustic wave propagating on the surface of the piezoelectric layer 91. The resonant frequency fp1 of the SAW resonator is determined by the comb spacing p between the comb electrodes 82, that is, fp1 = v1 / p, where v1 is the acoustic wave velocity.

[0091] Exemplarily, BAW resonators include film bulk acoustic resonators (FBARs) and solid-mounted resonators (SMRs). A schematic cross-sectional structure diagram of a film bulk acoustic resonator is shown in FIG9 , and a schematic cross-sectional structure diagram of a solid-mounted resonator is shown in FIG10 . As shown in FIG9 and FIG10 , the working principle of the BAW resonator is to convert an electrical signal into a bulk acoustic wave that propagates along the thickness direction of the piezoelectric layer 91. The resonant frequency fp2 of the BAW resonator is determined by the thickness of the piezoelectric layer 91, that is, fp2 = v / 2t, where t is the thickness of the piezoelectric layer 91 and v is the acoustic wave velocity.

[0092] As shown in FIG9 , because the acoustic impedance of air is approximately zero, total reflection occurs at the interface between the first bottom electrode 92 of the FBAR and the air gap 93. As shown in FIG10 , because the high acoustic impedance layers 101 and the low acoustic impedance layers 102 alternately form a Bragg reflector 103, total reflection occurs at the interface between the second bottom electrode 104 of the solid-state assembled resonator and the Bragg reflector 103.

[0093] The filter circuit provided by the present disclosure is exemplarily described below.

[0094] In the first example, as shown in FIG. 2 a , the filter circuit includes a series branch 21 and a parallel branch 24 .

[0095] In the series branch 21, the series resonant circuit 22 and the series impedance element 23 are connected in series between the first port 1 and the second port 2. The series resonant circuit 22 includes a series resonator S 11 , the series impedance element 23 includes an inductor L1.

[0096] In the parallel branch 24, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the parallel node N and the ground potential GND. The parallel node N is located between the inductor L1 and the second port 2. The parallel resonant circuit 25 includes a parallel resonator P 11 , the parallel impedance element 26 includes a capacitor C1.

[0097] The inductance of the inductor L1 can be, for example, between 0.5nH and 2nH, and the capacitance of the capacitor C1 can be between 5pF and 6pF. The parameter settings corresponding to the S parameters shown in Figure 2b are as follows: 11 The resonant frequency is 3.44GHz, and the parallel resonator P 11 The resonant frequency is 3.55 GHz, the difference between the two is 0.11 GHz, the inductance of inductor L1 is 1.2 nH, and the capacitance of capacitor C1 is 5.7 pF.

[0098] In the second example, as shown in FIG. 3 a , the filter circuit includes a series branch 21 and a parallel branch 24 .

[0099] In the series branch 21, the series resonant circuit 22 and the series impedance element 23 are connected in series between the first port 1 and the second port 2. The series resonant circuit 22 includes n series resonators S connected in series, which are S 11 To S 1n , n is a positive integer. In Figure 3a, n=2, that is, the series resonant circuit 22 includes two series resonators S connected in series, namely S 11 and S 12 , the series impedance element 23 includes an inductor L1.

[0100] In the parallel branch 24, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the parallel node N and the ground potential GND. The parallel node N is located between the inductor L1 and the second port 2. The parallel resonant circuit 25 includes a parallel resonator P 11 , the parallel impedance element 26 includes a capacitor C1.

[0101] The inductance of the inductor L1 can be, for example, between 0.5nH and 3nH, and the capacitance of the capacitor C1 can be between 4pF and 7pF. The parameter settings corresponding to the S parameters shown in Figure 3b are as follows: 11 and S 12 The resonant frequency of the parallel resonator P is 3.44GHz. 11The resonant frequency is 3.55 GHz, the difference between the two is 0.11 GHz, the inductance of the inductor L1 is 1.5 nH, and the capacitance of the capacitor C1 is 5.1 pF.

[0102] In the third example, as shown in FIG. 4 a , the filter circuit includes a series branch 21 and a parallel branch 24 .

[0103] In the series branch 21, the series resonant circuit 22 and the series impedance element 23 are connected in series between the first port 1 and the second port 2. The series resonant circuit 22 includes a series resonator S 11 , the series impedance element 23 includes an inductor L1.

[0104] In the parallel branch 24, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the parallel node N and the ground potential GND. The parallel node N is located between the inductor L1 and the second port 2. The parallel resonant circuit 25 includes m parallel resonators P connected in parallel, which are P 11 To P 1m , m is a positive integer. In Figure 4a, m=2, that is, the parallel resonant circuit 25 includes two parallel resonators P connected in parallel, namely P 11 and P 12 , the parallel impedance element 26 includes a capacitor C1.

[0105] The inductance of the inductor L1 can be, for example, between 0.5nH and 3nH, and the capacitance of the capacitor C1 can be between 3pF and 6pF. The parameter settings corresponding to the S parameters shown in Figure 4b are as follows: 11 The resonant frequency is 3.44GHz, and the parallel resonator P 11 and P 12 The resonant frequencies of both are 3.55 GHz, with a difference of 0.11 GHz. The inductance of inductor L1 is 1.7 nH, and the capacitance of capacitor C1 is 4.2 pF.

[0106] In the fourth example, as shown in FIG. 5 a , the filter circuit includes a series branch 21 and a parallel branch 24 .

[0107] In the series branch 21, the series resonant circuit 22 and the series impedance element 23 are connected in series between the first port 1 and the second port 2. The series resonant circuit 22 includes n series resonators S connected in series, which are S 11 To S 1n , n is a positive integer. In Figure 5a, n=2, that is, the series resonant circuit 22 includes two series resonators S connected in series, namely S 11 and S 12, the series impedance element 23 includes an inductor L1.

[0108] In the parallel branch 24, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the parallel node N and the ground potential GND. The parallel node N is located between the inductor L1 and the second port 2. The parallel resonant circuit 25 includes m parallel resonators P connected in parallel, which are P 11 To P 1m , m is a positive integer. In Figure 5a, m=2, that is, the parallel resonant circuit 25 includes two parallel resonators P connected in parallel, namely P 11 and P 12 , the parallel impedance element 26 includes a capacitor C1.

[0109] The inductance of the inductor L1 can be, for example, between 1nH and 3nH, and the capacitance of the capacitor C1 can be between 3pF and 6pF. The parameter settings corresponding to the S parameters shown in Figure 5b are as follows: 11 and S 12 The resonant frequency of the parallel resonator P is 3.44GHz. 11 and P 12 The resonant frequencies of both are 3.55 GHz, with a difference of 0.11 GHz. The inductance of inductor L1 is 2 nH, and the capacitance of capacitor C1 is 4 pF.

[0110] In the fifth example, as shown in Figure a in Figure 6, the filtering circuit includes a series branch 21 and two parallel branches 24, the two parallel branches 24 are a first parallel branch 241 and a second parallel branch 242, the parallel node N connected to the first parallel branch 241 is a first parallel node N1, and the parallel node N connected to the second parallel branch 242 is a second parallel node N2.

[0111] In the series branch 21, the series resonant circuit 22 and the series impedance element 23 are connected in series between the first port 1 and the second port 2. The series resonant circuit 22 includes a series resonator S 11 , the series impedance element 23 includes an inductor L1.

[0112] In the first parallel branch 241, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the first parallel node N1 and the ground potential GND. The first parallel node N1 is located at the series resonator S 11 Between the first port 1, the parallel resonant circuit 25 includes a parallel resonator P 11 , the parallel impedance element 26 includes a capacitor C1.

[0113] In the second parallel branch 242, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the second parallel node N2 and the ground potential GND. The second parallel node N2 is located between the inductor L1 and the second port 2. The parallel resonant circuit 25 includes a parallel resonator P 12 , the parallel impedance element 26 includes a capacitor C2.

[0114] The inductance of the inductor L1 can be, for example, between 1nH and 3nH, the capacitance of the capacitor C1 can be between 1.5pF and 4pF, and the capacitance of the capacitor C2 can be between 2pF and 5pF. The capacitances of the two capacitors C1 and C2 are different, for example, the capacitance of C1 is smaller than the capacitance of C2. The parameter settings corresponding to the S parameters shown in Figure 6b are as follows: The series resonator S 11 The resonant frequency is 3.44GHz, and the parallel resonator P 11 and P 12 The resonant frequencies of both are 3.55 GHz, with a difference of 0.11 GHz. The inductance of inductor L1 is 2 nH, the capacitance of capacitor C1 is 2.2 pF, and the capacitance of capacitor C2 is 3.2 pF.

[0115] In the sixth example, as shown in Figure a in Figure 7, the filtering circuit includes a series branch 21 and two parallel branches 24, the two parallel branches 24 are a first parallel branch 241 and a second parallel branch 242, the parallel node N connected to the first parallel branch 241 is a first parallel node N1, and the parallel node N connected to the second parallel branch 242 is a second parallel node N2.

[0116] In the series branch 21, the series resonant circuit 22 and the series impedance element 23 are connected in series between the first port 1 and the second port 2. The series resonant circuit 22 includes a series resonator S 11 , the series impedance element 23 includes an inductor L1.

[0117] In the first parallel branch 241, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the first parallel node N1 and the ground potential GND. The first parallel node N1 is located at the series resonator S 11 Between the first port 1, the parallel resonant circuit 25 includes a parallel resonator P 11 , the parallel impedance element 26 includes a capacitor C1.

[0118] In the second parallel branch 242, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the second parallel node N2 and the ground potential GND. The second parallel node N2 is located between the inductor L1 and the second port 2. The parallel resonant circuit 25 includes a parallel resonator P 12, the parallel impedance element 26 includes a capacitor C2.

[0119] The filter circuit further includes a voltage-dividing impedance element 71, which is connected in parallel with the series resonant circuit 22 and the series impedance element 23. That is, the voltage-dividing impedance element 71 is connected between the first port 1 and the second port 2. The voltage-dividing impedance element 71 includes an inductor L2. The inductance of the inductor L2 is greater than the inductance of the inductor L1.

[0120] The inductance of the inductor L1 can be, for example, between 1nH and 3nH, the inductance of the inductor L2 can be between 3nH and 5nH, the capacitance of the capacitor C1 can be between 0.5pF and 2.5pF, and the capacitance of the capacitor C2 can be between 1pF and 3pF. The capacitances of the two capacitors C1 and C2 are different, for example, the capacitance of C1 is smaller than the capacitance of C2. The parameter settings corresponding to the S parameters shown in Figure 7b are as follows: The series resonator S 11 The resonant frequency is 3.44GHz, and the parallel resonator P 11 and P 12 The resonant frequencies are both 3.55 GHz, with a difference of 0.11 GHz. The inductance of inductor L1 is 1.9 nH, the inductance of inductor L2 is 4 nH, the capacitance of capacitor C1 is 1.5 pF, and the capacitance of capacitor C2 is 2 pF.

[0121] The present disclosure provides a filter, comprising one or more filter circuits provided in any one embodiment.

[0122] Those skilled in the art will appreciate that the filter provided by the present disclosure has the advantages of the above-mentioned filtering circuit.

[0123] In some embodiments, as shown in FIG. 11 or FIG. 12 c, the multiple filter circuits include a first filter circuit 111 and a second filter circuit 112, wherein the second port 2 of the first filter circuit 111 is connected to the first port 1 of the second filter circuit 112. The parallel node N connected to the parallel branch 24 in the first filter circuit 111 is a third parallel node N3, and the parallel node N connected to the parallel branch 24 in the second filter circuit 112 is a fourth parallel node N4. A series resonator S and / or a series impedance element 23 are connected between the third parallel node N3 and the fourth parallel node N4.

[0124] In some examples, as shown in FIG11 a, the first filter circuit 111 includes a series branch 21 and a parallel branch 24. In the series branch 21, a series resonant circuit 22 and a series impedance element 23 are sequentially connected in series between the first port 1 and the second port 2. The series resonant circuit 22 includes a series resonator S 11The series impedance element 23 includes an inductor L1. In the parallel branch 24, the parallel resonant circuit 25 and the parallel impedance element 26 are sequentially connected in series between the parallel node N and the ground potential GND. The parallel node N is located between the series resonant circuit 22 and the first port 1. The parallel resonant circuit 25 includes a parallel resonator P 11 , the parallel impedance element 26 includes a capacitor C1.

[0125] As shown in FIG. 11 b, the second filtering circuit 112 includes a series branch 21 and two parallel branches 24. The two parallel branches 24 are respectively a first parallel branch 241 and a second parallel branch 242. The parallel node N connected to the first parallel branch 241 is a first parallel node N1, and the parallel node N connected to the second parallel branch 242 is a second parallel node N2. In the series branch 21, the series resonator S 12 and the inductor L2 are connected in series between the first port 1 and the second port 2. The first parallel node N1 is located at the series resonator S 11 and the first port 1, and the second parallel node N2 is located between the inductor L2 and the second port 2. In the first parallel branch 241, the parallel resonator P 12 and capacitor C2 are connected in series between the first parallel node N1 and the ground potential GND. In the second parallel branch 242, the parallel resonator P 13 The second filter circuit 112 further includes an inductor L3 connected between the first port 1 and the second port 2.

[0126] As shown in FIG11 , the second port 2 of the first filter circuit 111 shown in FIG1 a is connected to the first port 1 of the second filter circuit 112 shown in FIG1 b to obtain the filter shown in FIG1 c.

[0127] As shown in Figure 11, the first filter circuit 111 includes a parallel branch 24, and the parallel node N connected to the parallel branch 24 is the third parallel node N3. The second filter circuit 112 includes two parallel branches 24, and the fourth parallel node N4 can be the first parallel node N1 or the second parallel node N2.

[0128] In the case where the fourth parallel node N4 is the first parallel node N1, a series resonator S is connected between the third parallel node N3 and the fourth parallel node N4. 11 When the fourth parallel node N4 is the second parallel node N2, a series resonator S is connected between the third parallel node N3 and the fourth parallel node N4. 11 , inductor L1 series resonator S 12 and inductor L2.

[0129] In this example, the inductance value of inductor L1 may be between 1nH-3.5nH, the inductance value of inductor L2 may be between 0.5nH-2.5nH, the inductance value of inductor L3 may be between 5nH-7nH, the capacitance value of capacitor C1 may be between 1.5pF-3pF, the capacitance value of capacitor C2 may be between 3.5pF-6pF, and the capacitance value of capacitor C3 may be between 1.5pF-4.5pF.

[0130] In other examples, as shown in FIG. 12 a, the first filter circuit 111 includes a series branch 21 and two parallel branches 24, the two parallel branches 24 being a first parallel branch 241 and a second parallel branch 242, the parallel node N connected to the first parallel branch 241 being a first parallel node N1, and the parallel node N connected to the second parallel branch 242 being a second parallel node N2. In the series branch 21, the series resonator S 11 and the inductor L1 are connected in series between the first port 1 and the second port 2. The first parallel node N1 is located at the series resonator S 11 and the first port 1, and the second parallel node N2 is located between the inductor L1 and the second port 2. In the first parallel branch 241, the parallel resonator P 11 and capacitor C1 are connected in series between the first parallel node N1 and the ground potential GND. In the second parallel branch 242, the parallel resonator P 12 and capacitor C2 are sequentially connected in series between the second parallel node N2 and the ground potential GND.

[0131] As shown in FIG12 b, the second filter circuit 112 includes a series branch 21 and a parallel branch 24. In the series branch 21, two series resonators S 12 and S 13 The inductor L2 is connected in series between the first port 1 and the second port 2. In the parallel branch 24, the parallel resonator P 13 And capacitor C3 are sequentially connected in series between the parallel node N and the ground potential GND.

[0132] As shown in FIG12 , the second port 2 of the first filter circuit 111 shown in FIG12 a is connected to the first port 1 of the second filter circuit 112 shown in FIG12 b to obtain the filter shown in FIG12 c.

[0133] As shown in Figure 12, the first filter circuit 111 includes two parallel branches 24. The third parallel node N3 can be the first parallel node N1 or the second parallel node N2. The second filter circuit 112 includes a parallel branch 24, and the parallel node N of the parallel branch 24 is connected to the fourth parallel node N4.

[0134] In the case where the third parallel node N3 is the first parallel node N1, a series resonator S is connected between the third parallel node N3 and the fourth parallel node N4. 11 , inductor L1, series resonator S 12 , series resonator S 13 When the third parallel node N3 is the second parallel node N2, a series resonator S is connected between the third parallel node N3 and the fourth parallel node N4. 12 , series resonator S 13 and inductor L2.

[0135] In this example, the inductance value of inductor L1 may be between 0.5nH-2.5nH, the inductance value of inductor L2 may be between 1.5nH-3nH, the capacitance value of capacitor C1 may be between 1.5pF-3pF, the capacitance value of capacitor C2 may be between 1pF-3pF, and the capacitance value of capacitor C3 may be between 4pF-6pF.

[0136] To form a single-band stop filter, in some embodiments, the series resonator S in the first filter circuit 111 and the series resonator S in the second filter circuit 112 have the same resonant frequency, and the parallel resonator P in the first filter circuit 111 and the parallel resonator P in the second filter circuit 112 have the same resonant frequency. The single-band stop filter formed by connecting two filter circuits in series can further reduce the passband loss coefficient and optimize the roll-off factor compared to a single filter circuit.

[0137] As shown in FIG11 , FIG1 d shows the S parameter diagram of the filter shown in FIG11 c, and the corresponding parameter settings are as follows: the series resonator S in the first filtering circuit 111 11 The series resonator S in the second filter circuit 112 12 The resonant frequency of the parallel resonator P in the first filter circuit 111 is 3.44 GHz. 11 The parallel resonator P in the second filter circuit 112 12 and P 13 The resonant frequencies are all 3.55 GHz. The inductances of inductors L1, L2, and L3 are 2.2 nH, 1.4 nH, and 6 nH, respectively, and the capacitances of capacitors C1, C2, and C3 are 2.2 pF, 4.5 pF, and 2.9 pF, respectively.

[0138] To form a dual-stopband filter, in some embodiments, the resonant frequency of the series resonator S in the first filter circuit 111 is greater than the resonant frequency of the series resonator S in the second filter circuit 112. The first filter circuit 111 forms a high-stopband, and the second filter circuit 112 forms a low-stopband.

[0139] To form a dual-stopband filter, in some embodiments, the resonant frequency of the series resonator S in the first filter circuit 111 is lower than the resonant frequency of the series resonator S in the second filter circuit 112. The first filter circuit 111 forms a low-stopband, and the second filter circuit 112 forms a high-stopband.

[0140] As shown in FIG12 , FIG. d shows the S parameter diagram of the filter shown in FIG12 , and the corresponding parameter settings are as follows: the series resonator S in the first filtering circuit 111 11 The resonant frequency of the parallel resonator P in the first filter circuit 111 is 3.44 GHz. 11 and P 12 The resonant frequency of the second filter circuit 112 is 3.55 GHz. 12 and S 13 The resonant frequency of the parallel resonator P in the second filter circuit 112 is 4.49 GHz. 13 The resonant frequency is 4.625 GHz. The inductors L1 and L2 have inductances of 1.2 nH and 2.2 nH, respectively, and the capacitors C1, C2, and C3 have capacitances of 2.2 pF, 1.8 pF, and 5.1 pF, respectively. As can be seen, the filter shown in Figure c forms a low-stop band at 3.55 GHz and a high-stop band at 4.62 GHz.

[0141] The present disclosure provides a communication device, comprising the filter provided in any embodiment.

[0142] Those skilled in the art will appreciate that the communication device provided by the present disclosure has the advantages of the above-mentioned filter.

[0143] The communication device provided in the present disclosure may be any product or component with communication function, such as a mobile phone, a phone watch, and an in-vehicle communication device.

[0144] Exemplarily, the above-mentioned filter can be a band-stop filter or a notch filter, which can be used in communication devices such as mobile phones or smartphones, for example, for suppressing dedicated frequency bands to protect low-noise amplifiers, for suppressing harmonics in carrier aggregation systems to allow proper signal reception, or for other functions that require suppression of specific frequencies or narrow frequency ranges.

[0145] In the present disclosure, “a plurality of” means two or more, and “at least one” means one or more, unless otherwise clearly defined.

[0146] In the present disclosure, the orientation or positional relationship indicated by the terms "upper" and "lower" is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present disclosure and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, it should not be understood as a limitation on the present disclosure.

[0147] As used herein, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, product, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, commodity, or apparatus that includes the element.

[0148] References herein to "one embodiment," "some embodiments," "exemplary embodiments," "one or more embodiments," "an example," "an example," "some examples," and the like are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of the present disclosure. Schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be included in any one or more embodiments or examples in any suitable manner.

[0149] In this document, relational terms such as first and second, etc. are used merely to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any actual relationship or order between these entities or operations.

[0150] When describing some embodiments, the expressions "coupled" and "connected" may be used. For example, when describing some embodiments, the term "connected" may be used to indicate that two or more components are in direct physical or electrical contact with each other. For another example, when describing some embodiments, the term "coupled" may be used to indicate that two or more components are in direct physical or electrical contact. However, the term "coupled" or "communicatively coupled" may also mean that two or more components are not in direct contact with each other, but still cooperate or interact with each other. The embodiments disclosed herein are not necessarily limited to the contents of this document.

[0151] “At least one of A, B and C” has the same meaning as “at least one of A, B or C” and both include the following combinations of A, B and C: A only, B only, C only, the combination of A and B, the combination of A and C, the combination of B and C, and the combination of A, B and C.

[0152] “A and / or B” includes the following three combinations: A only, B only, and a combination of A and B.

[0153] As used herein, the term "if" is optionally interpreted to mean "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined that" or "if [stated condition or event] is detected" are optionally interpreted to mean "upon determining" or "in response to determining" or "upon detecting [stated condition or event]" or "in response to detecting [stated condition or event]," depending on the context.

[0154] The use of "for" or "configured to" herein is intended to be open and inclusive language that does not exclude devices adapted or configured to perform additional tasks or steps.

[0155] The use of "based on" or "according to" in this document is intended to be open and inclusive. A process, step, calculation, or other action based on one or more stated conditions or values ​​may, in practice, be based on other conditions or values ​​beyond the stated values. A process, step, calculation, or other action based on one or more stated conditions or values ​​may, in practice, be based on other conditions or values ​​beyond the stated values.

[0156] As used herein, "about," "substantially," or "approximately" includes the stated value and an average value that is within an acceptable range of deviation from the particular value as determined by one of ordinary skill in the art taking into account the measurements in question and the errors associated with the measurement of the particular quantity (i.e., the limitations of the measurement system).

[0157] As used herein, "parallel", "perpendicular", "equal", and "flush" include the situations described and situations similar to the situations described, the range of which is within an acceptable deviation range, wherein the acceptable deviation range is as determined by a person of ordinary skill in the art taking into account the measurement in question and the errors associated with the measurement of the specific quantity (i.e., the limitations of the measurement system). For example, "parallel" includes absolute parallelism and approximate parallelism, wherein the acceptable deviation range of approximate parallelism can be, for example, a deviation within 5°; "perpendicular" includes absolute perpendicularity and approximate perpendicularity, wherein the acceptable deviation range of approximate perpendicularity can also be, for example, a deviation within 5°. "Equal" includes absolute equality and approximate equality, wherein the acceptable deviation range of approximate equality can be, for example, the difference between the two being equal is less than or equal to 5% of either one. "Flush" includes absolute equality and approximate flushness, wherein the acceptable deviation range of approximate flushness can be, for example, the distance between the two being flush is less than or equal to 5% of either one's size.

[0158] It will be understood that when a layer or element is referred to as being on another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may be present therebetween.

[0159] Exemplary embodiments are described herein with reference to cross-sectional and / or plan views that are idealized exemplary drawings. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Therefore, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are contemplated. Therefore, the exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include deviations in shape due to, for example, manufacturing. For example, an etched region shown as a rectangle will typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of the device and are not intended to limit the scope of the exemplary embodiments.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present disclosure.

Claims

1. A filter circuit, comprising: a series branch connected between the first port and the second port, comprising a series resonant circuit and a series impedance element connected in series with each other, wherein the series resonant circuit comprises a series resonator; and A parallel branch, connected between a parallel node and a ground potential, comprising a parallel resonant circuit and a parallel impedance element connected in series, wherein the parallel resonant circuit comprises a parallel resonator, and the parallel node is located on a connection path between the first port and the second port; Wherein, the resonant frequency of the series resonator is lower than the resonant frequency of the parallel resonator.

2. The filter circuit according to claim 1, wherein: The series resonant circuit includes a plurality of series resonators connected in series with each other, and the series resonators are connected between the series impedance element and the first port and / or between the series impedance element and the second port.

3. The filter circuit according to claim 2, wherein: The plurality of series resonators have the same resonant frequency.

4. The filter circuit according to claim 1, wherein: The parallel resonant circuit includes a plurality of parallel resonators connected in parallel with each other, and the plurality of parallel resonators are connected between the parallel impedance element and the parallel node, or between the parallel impedance element and the ground potential.

5. The filter circuit according to claim 4, wherein: The plurality of parallel resonators have the same resonant frequency.

6. The filter circuit according to claim 1, wherein: The filter circuit comprises a plurality of parallel branches, and the parallel resonators in the plurality of parallel branches all have the same resonance frequency.

7. The filter circuit according to claim 6, wherein: The plurality of parallel branches include a first parallel branch and a second parallel branch, a parallel node connecting the first parallel branches is a first parallel node, and a parallel node connecting the second parallel branches is a second parallel node; The series resonator and / or the series impedance element are connected between the first parallel node and the second parallel node.

8. The filter circuit according to claim 7, wherein: The parallel impedance element in the first parallel branch and the parallel impedance element in the second parallel branch are capacitors with different capacitance values, or inductors with different inductance values.

9. The filter circuit according to claim 1, wherein: The filter circuit also includes: A voltage-dividing impedance element is connected in parallel with at least one of the series resonators, or is connected in parallel with at least one of the series resonators and the series impedance element.

10. The filter circuit according to claim 9, wherein: The voltage-dividing impedance element and the series impedance element are both inductors, and the inductance value of the voltage-dividing impedance element is greater than the inductance value of the series impedance element; or The voltage-dividing impedance element and the series impedance element are both capacitors, and the capacitance value of the voltage-dividing impedance element is greater than the capacitance value of the series impedance element.

11. The filter circuit according to any one of claims 1 to 10, wherein: A difference between a resonant frequency of the parallel resonator and a resonant frequency of the series resonator is greater than or equal to 0.1 GHz and less than or equal to 0.3 GHz.

12. The filter circuit according to any one of claims 1 to 10, wherein: The parallel resonator and the series resonator are elastic wave resonators of the same type, and the types of the elastic wave resonators include surface acoustic wave resonators and bulk acoustic wave resonators.

13. The filter circuit according to any one of claims 1 to 10, wherein: The series impedance element includes at least one of the following: an adjustable capacitor, an adjustable inductor, a non-adjustable capacitor, and a non-adjustable inductor; The parallel impedance element includes at least one of the following: an adjustable capacitor, an adjustable inductor, a non-adjustable capacitor, and a non-adjustable inductor.

14. The filter circuit according to any one of claims 1 to 10, wherein: The series impedance element includes an inductor, and the inductance value of the inductor is greater than or equal to 0.5 nH and less than or equal to 3.5 nH.

15. The filter circuit according to any one of claims 1 to 10, wherein: The parallel impedance element includes a capacitor, and the capacitance value of the capacitor is greater than or equal to 0.5 pF and less than or equal to 7 pF.

16. A filter comprising one or more filter circuits according to any one of claims 1 to 15.

17. The filter according to claim 16, wherein: The plurality of filter circuits include a first filter circuit and a second filter circuit, wherein the second port of the first filter circuit is connected to the first port of the second filter circuit; Among them, the parallel node connecting the parallel branches in the first filter circuit is the third parallel node, the parallel node connecting the parallel branches in the second filter circuit is the fourth parallel node, and the series resonator and / or the series impedance element are connected between the third parallel node and the fourth parallel node.

18. The filter according to claim 17, wherein The series resonator in the first filter circuit and the series resonator in the second filter circuit have the same resonant frequency, and the parallel resonator in the first filter circuit and the parallel resonator in the second filter circuit have the same resonant frequency.

19. The filter according to claim 17, wherein: The resonant frequency of the series resonator in the first filtering circuit is greater than the resonant frequency of the series resonator in the second filtering circuit; or The resonant frequency of the series resonator in the first filtering circuit is lower than the resonant frequency of the series resonator in the second filtering circuit.

20. A communication device comprising the filter according to any one of claims 16 to 19.

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