A filter and filter circuit

Abstract

The application provides a filter and a filter circuit. The filter comprises a chip filter, a first FBAR resonator, a second FBAR resonator, a first matching inductor, a second matching inductor and a third matching inductor; the first matching inductor, the second matching inductor, the third matching inductor and the chip filter are connected in series; one end of the first FBAR resonator is connected between the first matching inductor and the second matching inductor; one end of the second FBAR resonator is connected between the second matching inductor and the third matching inductor; the first matching inductor has a free end as an input end; the first end of the chip filter is connected to the third matching inductor; the series resonance frequency of the first FBAR resonator and the second FBAR resonator is in the frequency range near the stopband of the chip filter. The application can generate a transmission zero point near the stopband of the chip filter and form a wave trap by arranging the FBAR resonator with a high Q value; the series resonance frequency of the FBAR resonator determines the frequency of the transmission zero point, and the stopband near-end rejection of the chip filter is improved.

Description

Technical Field

[0001] This invention relates to the field of filter technology, and more particularly to a filter and a filter circuit. Background Technology

[0002] Filters can effectively remove specific frequency components from a signal, or they can effectively remove other frequency components besides the specific frequency components. Stopband rejection ratio (PSRR) is an important indicator of a filter's performance. A higher PSRR indicates better suppression of out-of-band interference signals.

[0003] Chip filters, manufactured using chip technology, such as MMIC filters, MEMS filters, and silicon-based filters, are widely used in the field of communication technology. The structure of a chip filter determines its good far-end stopband suppression. However, the low Q value of chip filters results in poor near-end stopband suppression and slow roll-off, significantly limiting their applications. Summary of the Invention

[0004] This invention provides a filter to solve the problem of poor near-end suppression in the stopband of chip filters.

[0005] In a first aspect, embodiments of the present invention provide a filter, including a chip filter, a first FBAR resonator, a second FBAR resonator, a first matching inductor, a second matching inductor, and a third matching inductor; the first matching inductor, the second matching inductor, the third matching inductor, and the chip filter are connected in series sequentially; one end of the first FBAR resonator is connected between the first matching inductor and the second matching inductor, and the other end is grounded; one end of the second FBAR resonator is connected between the second matching inductor and the third matching inductor, and the other end is grounded; the floating end of the first matching inductor is the input terminal; the first terminal of the chip filter is connected to the third matching inductor, and the second terminal is the output terminal; the series resonant frequency of the first FBAR resonator and the second FBAR resonator is within the frequency range near the stopband of the chip filter.

[0006] In one possible implementation, the frequency of the first FBAR resonator is the same as the series resonant frequency of the second FBAR resonator; the filter further includes a first frequency-modulated inductor; the first frequency-modulated inductor is connected in series with the second FBAR resonator; or, the first frequency-modulated inductor is connected in series with the first FBAR resonator.

[0007] In one possible implementation, the series resonant frequency of the first FBAR resonator is different from the series resonant frequency of the second FBAR resonator.

[0008] In one possible implementation, the series resonant frequency of the first FBAR resonator and the second FBAR resonator is in the low-end frequency range near the stopband of the chip filter.

[0009] In one possible implementation, the series resonant frequencies of the first FBAR resonator and the second FBAR resonator are in the high-end frequency range near the stopband of the chip filter.

[0010] In one possible implementation, when the first frequency-modulated inductor is connected in series with the first FBAR resonator, the series resonant frequency of the first FBAR resonator is in the low-end frequency range near the stopband of the chip filter; the series resonant frequency of the second FBAR resonator is in the high-end frequency range near the stopband of the chip filter; or,

[0011] When the first frequency-modulated inductor is connected in series with the second FBAR resonator, the series resonant frequency of the second FBAR resonator is in the low-end frequency range of the near-end of the stopband of the chip filter, and the series resonant frequency of the first FBAR resonator is in the high-end frequency range of the near-end of the stopband of the chip filter.

[0012] In one possible implementation, the filter further includes a third FBAR resonator, a fourth FBAR resonator, a fourth matching inductor, a fifth matching inductor, and a sixth matching inductor; the chip filter, the fourth matching inductor, the fifth matching inductor, and the sixth matching inductor are connected in series sequentially; one end of the third FBAR resonator is connected between the fourth and fifth matching inductors, and the other end is grounded; one end of the fourth FBAR resonator is connected between the fifth and sixth matching inductors, and the other end is grounded; a first end of the chip filter is connected to the third matching inductor, and a second end is connected to the fourth matching inductor; the floating end of the sixth matching inductor is the output terminal; the series resonant frequency of the third and fourth FBAR resonators is in the low-end frequency range near the stopband of the chip filter.

[0013] In one possible implementation, the series resonant frequency range of the first FBAR resonator and the second FBAR resonator is 2563 MHz to 2569 MHz; the upper electrode area of ​​the first FBAR resonator and the second FBAR resonator ranges from 5570 square micrometers to 5630 square micrometers; and the inductance of the first frequency-modulated inductor is 0.5 nanohenries.

[0014] In one possible implementation, the chip filter, the first matching inductor, the second matching inductor, and the third matching inductor are fabricated using gallium arsenide monolithic microwave integrated circuit chip technology; the first FBAR resonator and the second FBAR resonator are connected to the chip filter, the first matching inductor, the second matching inductor, and the third matching inductor using a ball-mounted flip-chip process.

[0015] Secondly, embodiments of the present invention provide a filtering circuit, including any of the filters described above.

[0016] This invention provides a filter and a filtering circuit. The filter includes a chip filter, a first FBAR resonator, a second FBAR resonator, a first matching inductor, a second matching inductor, and a third matching inductor. The first matching inductor, the second matching inductor, the third matching inductor, and the chip filter are connected in series. One end of the first FBAR resonator is connected between the first and second matching inductors, and the other end is grounded. One end of the second FBAR resonator is connected between the second and third matching inductors, and the other end is grounded. The floating end of the first matching inductor is the input terminal. The first terminal of the chip filter is connected to the third matching inductor, and the second terminal is the output terminal. The series resonant frequency of the first and second FBAR resonators is within the frequency range of the near-stopband of the chip filter. By setting a high-Q FBAR resonator, a transmission zero is generated near the stopband of the chip filter, forming a notch. The series resonant frequency of the FBAR resonator determines the transmission zero frequency, thereby improving the near-stopband suppression of the chip filter. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a circuit structure diagram of a filter provided in an embodiment of the present invention;

[0019] Figure 2 This is an impedance characteristic curve of an FBAR resonator before and after series inductance provided in an embodiment of the present invention;

[0020] Figure 3 This is a filter circuit structure diagram with an added frequency modulation inductor provided in an embodiment of the present invention;

[0021] Figure 4 A waveform diagram of the amplitude-frequency response of a chip filter provided in an embodiment of the present invention;

[0022] Figure 5 A filter amplitude-frequency response curve is provided for an embodiment of the present invention;

[0023] Figure 6 This is a filter circuit structure diagram that simultaneously generates low-end and high-end transmission zeros, provided as an embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand this solution, the technical solutions in the embodiments of this solution will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this solution, not all of them. Based on the embodiments of this solution, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this solution.

[0025] The term "comprising" and any other variations thereof in the specification, claims, and accompanying drawings of this invention mean "including but not limited to," and are intended to cover a non-exclusive inclusion, not limited to the examples listed herein. Furthermore, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order.

[0026] The implementation of the present invention will be described in detail below with reference to the accompanying drawings:

[0027] Figure 1 This is a circuit diagram of a filter provided in an embodiment of the present invention. (Refer to...) Figure 1 This invention provides a filter comprising a chip filter 100, a first FBAR resonator 201, a second FBAR resonator 202, a first matching inductor L1, a second matching inductor L2, and a third matching inductor L3; the first matching inductor L1, the second matching inductor L2, the third matching inductor L3, and the chip filter 100 are connected in series; one end of the first FBAR resonator 201 is connected between the first matching inductor L1 and the second matching inductor L2, and the other end is grounded; one end of the second FBAR resonator 202 is connected between the second matching inductor L2 and the third matching inductor L3, and the other end is grounded; the floating end of the first matching inductor L1 is the input terminal; the first terminal of the chip filter 100 is connected to the third matching inductor L3, and the second terminal is the output terminal; the series resonant frequency of the first FBAR resonator 201 and the second FBAR resonator 202 is within the frequency range of the near end of the stopband of the chip filter 100.

[0028] FBAR resonators have parallel and series resonant frequencies. The impedance is highest at the parallel resonant frequency and lowest at the series resonant frequency. When an FBAR resonator is placed in a parallel branch, because the impedance is lowest at the series resonant frequency, the signal passes directly to ground through the parallel branch of the FBAR resonator at this frequency, creating a transmission zero and thus forming a notch frequency. The series resonant frequency of the FBAR resonator determines the frequency of the transmission zero, i.e., the notch frequency. FBAR resonators have the advantage of high Q values, typically reaching 1000-2000. The higher the Q value, the faster the current drops at a given frequency offset, resulting in a sharper notch curve and lower insertion loss. The frequency transition between the stopband and passband of the chip filter 100 is called the transition region; the near end of the stopband is the part of the transition region close to the passband at both ends; the lower end of the near end of the stopband is the part of the near end of the passband with a frequency lower than the passband frequency; the higher end of the near end of the stopband is the part of the near end of the passband with a frequency higher than the passband frequency.

[0029] The series resonant frequency of the FBAR resonator is within the frequency range of the near end of the stopband of the chip filter 100. That is, the FBAR resonator generates a transmission zero within the frequency range of the near end of the stopband of the chip filter 100, which improves the near end suppression of the stopband of the chip filter 100.

[0030] Adding an FBAR resonator to the port of chip filter 100 will affect the matching state of the port of chip filter 100; the first matching inductor L1, the second matching inductor L2 and the third matching inductor L3 constitute a matching circuit, which is used to match the impedance of the port of chip filter 100 to 50Ω and eliminate the influence of the FBAR resonator on the matching impedance.

[0031] For example, the floating end of the first matching inductor L1 is the input terminal; the first matching inductor L1, the second matching inductor L2, the third matching inductor L3 and the chip filter 100 are connected in series in sequence; the first terminal of the chip filter 100 is connected to the third matching inductor L3, and the second terminal is the output terminal.

[0032] For example, the floating end of the first matching inductor L1 is the output terminal; the first matching inductor L1, the second matching inductor L2, the third matching inductor L3 and the chip filter 100 are connected in series in sequence; the first terminal of the chip filter 100 is connected to the third matching inductor L3, and the second terminal is the input terminal.

[0033] In an optional embodiment, the frequency of the first FBAR resonator 201 is the same as the series resonant frequency of the second FBAR resonator 202; the filter further includes a first frequency-modulated inductor 301; the first frequency-modulated inductor 301 is connected in series with the second FBAR resonator 202, or the first frequency-modulated inductor 301 is connected in series with the first FBAR resonator 201. For example, the first FBAR resonator 201 and the second FBAR resonator 202 are FBAR resonators of the same type.

[0034] Figure 2 This is an impedance characteristic curve of an FBAR resonator before and after connecting an inductor in series, provided as an embodiment of the present invention. (Refer to...) Figure 2 The horizontal axis of the impedance characteristic curve represents frequency in GHz; the vertical axis represents impedance in dB; m1 is the series resonant frequency, at which the impedance of the FBAR resonator is minimum; m6 is the parallel resonant frequency, at which the impedance of the FBAR resonator is maximum.

[0035] The FBAR resonator provided in this embodiment of the invention has a series resonant frequency of 2566 MHz and a parallel resonant frequency of 2631 MHz. After adding a 0.5 nanohenry inductor to the series connection of the FBAR resonator, the parallel resonant frequency remains unchanged, while the series resonant frequency decreases from 2566 MHz to 2550 MHz.

[0036] When an inductor is connected in series with an FBAR resonator, the parallel resonant frequency of the FBAR resonator remains unchanged, while the series resonant frequency decreases. For example, after the second FBAR resonator 202 is connected in series with the first frequency-modulating inductor 301, the series resonant frequency of the second FBAR resonator 202 decreases, thus reducing the frequency at which the second FBAR resonator 202 generates a transmission zero. The difference in series resonant frequencies between the first FBAR resonator 201 and the second FBAR resonator 202 increases, thereby increasing the width of the notch generated by the two FBAR resonators. Changing the inductance value of the first frequency-modulating inductor 301 can adjust the frequency of the transmission zero and the width of the notch.

[0037] For example, the first frequency modulation inductor 301 is connected in series with the second FBAR resonator 202; one end of the second FBAR resonator 202 is connected between the second matching inductor L2 and the third matching inductor L3, and the other end is connected to the first frequency modulation inductor 301; one end of the first frequency modulation inductor 301 is connected to the second FBAR resonator 202, and the other end is grounded.

[0038] For example, the first frequency modulation inductor 301 is connected in series with the second FBAR resonator 202; one end of the first frequency modulation inductor 301 is connected between the second matching inductor L2 and the third matching inductor L3, and the other end is connected to the second FBAR resonator 202; one end of the second FBAR resonator 202 is connected to the first frequency modulation inductor 301, and the other end is grounded.

[0039] In an optional embodiment, the series resonant frequencies of the first FBAR resonator 201 and the second FBAR resonator 202 are within the high-end frequency range of the near-stopband of the chip filter 100. The high-end of the near-stopband is the end with the higher near-stopband frequency.

[0040] Figure 3 This is a circuit diagram of a filter circuit with an increased frequency modulation inductor provided in an embodiment of the present invention. (Refer to...) Figure 3 :

[0041] In an optional embodiment, a filter includes a chip filter 100, a first FBAR resonator 201, a second FBAR resonator 202, a first matching inductor L1, a second matching inductor L2, a third matching inductor L3, and a first frequency modulation inductor 301; the first matching inductor L1, the second matching inductor L2, the third matching inductor L3, and the chip filter 100 are connected in series; one end of the first FBAR resonator 201 is connected between the first matching inductor L1 and the second matching inductor L2, and the other end is grounded; one end of the second FBAR resonator 202 is connected between the second matching inductor L2 and the third matching inductor L3, and the other end is grounded; the first frequency modulation inductor 301 and the second FBAR resonator 202 are connected in series; one end of the first FBAR resonator 201 is connected between the first matching inductor L1 and the second matching inductor L2, and the other end is grounded; the first frequency modulation inductor 301 and the second FBAR resonator 202 are connected in series; one end of the first FBAR resonator 202 is connected between the second matching inductor L2 and the third matching inductor L3, and the other end is grounded; the first frequency modulation inductor 301 and the second FBAR resonator 202 are connected in series; one end of the first FBAR resonator 202 is connected between the first matching inductor L1 and the second matching inductor L2, and the other end is grounded; the first FBAR resonator 202 and the second FBAR resonator 202 are connected in series ... The resonators 202 are connected in series; one end of the second FBAR resonator 202 is connected between the second matching inductor L2 and the third matching inductor L3, and the other end is connected to the first frequency modulation inductor 301; one end of the first frequency modulation inductor 301 is connected to the second FBAR resonator 202, and the other end is grounded; the floating end of the first matching inductor L1 is the input terminal; the first terminal of the chip filter 100 is connected to the third matching inductor L3, and the second terminal is the output terminal; the frequency of the first FBAR resonator 201 is the same as the series resonant frequency of the second FBAR resonator 202; the series resonant frequency of the first FBAR resonator 201 and the second FBAR resonator 202 is within the frequency range of the high end of the stopband of the chip filter 100. For example, the first frequency modulation inductor 301 is connected in series with the first FBAR resonator 201; one end of the first frequency modulation inductor 301 is connected to the first FBAR resonator 201, and the other end is grounded.

[0042] Figure 4 A frequency response curve of a chip filter 100 provided in an embodiment of the present invention. (Refer to...) Figure 4The horizontal axis represents frequency in GHz, and the vertical axis represents amplitude in dB. The solid curve is the amplitude-frequency response curve of the chip filter 100.

[0043] For example, in a filter provided by an embodiment of the present invention, the series resonant frequency of the first FBAR resonator 201 and the second FBAR resonator 202 is 2566 MHz, and the parallel resonant frequency is 2631 MHz; the inductance value of the first frequency modulation inductor 301 is 0.5 nanohenries; after the second FBAR resonator 202 is connected in series with the first frequency modulation inductor 301, the series resonant frequency is reduced from 2566 MHz to 2500 MHz.

[0044] Figure 5 The image shows the amplitude-frequency response curve of a filter provided in an embodiment of the present invention. (Refer to...) Figure 5 The horizontal axis represents frequency in GHz, and the vertical axis represents amplitude in dB. The solid curve is the amplitude-frequency response curve of the filter. The first FBAR resonator 201 and the second FBAR resonator 202 generate transmission zeros at the high end of the near-end of the stopband of the chip filter 100; at the high-end frequency of the stopband from 2516 MHz to 2599 MHz, the filter amplitude range increases from 7.6 dB to 12.4 dB to 20 dB to 38 dB; the minimum insertion loss increases from 1.97 dB to 2.2 dB, with a relatively small increase in insertion loss.

[0045] In an optional embodiment, the series resonant frequency range of the first FBAR resonator 201 and the second FBAR resonator 202 is 2563 MHz to 2569 MHz; the upper electrode area of ​​the first FBAR resonator 201 and the second FBAR resonator 202 ranges from 5570 square micrometers to 5630 square micrometers; and the inductance value of the first frequency modulation inductor 301 is 0.5 nanohenries.

[0046] In an optional embodiment, the series resonant frequency of the first FBAR resonator 201 and the second FBAR resonator 202 is within the low-end frequency range of the near-stopband of the chip filter 100. The low-end of the near-stopband is the end with the lowest near-stopband frequency.

[0047] In one optional embodiment, the series resonant frequency of the first FBAR resonator 201 is different from the series resonant frequency of the second FBAR resonator 202. For example, the series resonant frequencies of both the first FBAR resonator 201 and the second FBAR resonator 202 are in the low-end frequency range near the stopband; the different series resonant frequencies increase the width of the notch filter. Alternatively, the series resonant frequencies of both the first FBAR resonator 201 and the second FBAR resonator 202 are in the high-end frequency range near the stopband; the different series resonant frequencies increase the width of the notch filter.

[0048] In one optional embodiment, when the first frequency-modulated inductor 301 is connected in series with the first FBAR resonator 201, the series resonant frequency of the first FBAR resonator 201 is in the low-end frequency range of the near-stopband of the chip filter 100; the series resonant frequency of the second FBAR resonator 202 is in the high-end frequency range of the near-stopband of the chip filter 100. In another optional embodiment, when the first frequency-modulated inductor 301 is connected in series with the second FBAR resonator 202, the series resonant frequency of the second FBAR resonator 202 is in the low-end frequency range of the near-stopband of the chip filter, and the series resonant frequency of the first FBAR resonator 201 is in the high-end frequency range of the near-stopband of the chip filter. The two FBAR resonators generate transmission zeros at the low and high ends respectively, improving the near-stopband suppression.

[0049] Figure 6 This is a filter circuit structure diagram that simultaneously generates low-end and high-end transmission zeros, provided as an embodiment of the present invention. (Refer to...) Figure 6 :

[0050] In an optional embodiment, the filter further includes a third FBAR resonator 203, a fourth FBAR resonator 204, a fourth matching inductor L4, a fifth matching inductor L5, and a sixth matching inductor L6.

[0051] The fourth matching inductor L4, the fifth matching inductor L5, the sixth matching inductor L6, and the chip filter 100 are connected in series. One end of the third FBAR resonator 203 is connected between the fourth matching inductor L4 and the fifth matching inductor L5, and the other end is grounded. One end of the fourth FBAR resonator 204 is connected between the fifth matching inductor L5 and the sixth matching inductor L6, and the other end is grounded. The floating end of the first matching inductor L1 is the input terminal. The first terminal of the chip filter 100 is connected to the third matching inductor L3, and the second terminal is connected to the fourth matching inductor L4. The floating end of the sixth matching inductor L6 is the output terminal. The series resonant frequency of the third FBAR resonator 203 and the fourth FBAR resonator 204 is in the low-end frequency range of the stopband near the end of the chip filter 100. The first FBAR resonator 201 and the second FBAR resonator 202 generate transmission zeros in the near-high frequency range of the stopband of the chip filter, thereby improving the suppression of the near-high frequency range of the stopband; the third FBAR resonator 203 and the fourth FBAR resonator 204 generate transmission zeros in the near-low frequency range of the stopband, thereby improving the suppression of the near-low frequency range of the stopband.

[0052] For example, the frequency of the third FBAR resonator 203 is the same as the series resonant frequency of the fourth FBAR resonator 204; the filter also includes a second frequency-modulated inductor; the second frequency-modulated inductor is connected in series with the fourth FBAR resonator 204. For example, the third FBAR resonator 203 and the fourth FBAR resonator 204 are FBAR resonators of the same type.

[0053] In an optional embodiment, the chip filter 100, the first matching inductor L1, the second matching inductor L2, and the third matching inductor L3 are fabricated using gallium arsenide monolithic microwave integrated circuit chip technology. The first FBAR resonator 201 and the second FBAR resonator 202 are connected to the chip filter 100, the first matching inductor L1, the second matching inductor L2, and the third matching inductor L3 using a flip-chip process. The chip filter 100, the first matching inductor L1, the second matching inductor L2, and the third matching inductor L3 are implemented using a monolithic microwave integrated circuit chip technology, with pre-reserved mounting positions for the FBAR resonators, which are then connected to the chip package using a flip-chip process.

[0054] For example, the first frequency modulation inductor 301 and the second frequency modulation inductor are implemented using a monolithic microwave integrated chip process.

[0055] In an optional embodiment, corresponding to any of the filters described above, the present invention also provides a filtering circuit, which includes any of the filters described above and has the advantages of the filters described above, which will not be repeated here.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A filter, characterized in that, It includes a chip filter, a first FBAR resonator, a second FBAR resonator, a first matching inductor, a second matching inductor, and a third matching inductor; The first matching inductor, the second matching inductor, the third matching inductor, and the chip filter are connected in series in sequence; One end of the first FBAR resonator is connected between the first matching inductor and the second matching inductor, and the other end is grounded; One end of the second FBAR resonator is connected between the second matching inductor and the third matching inductor, and the other end is grounded; The floating end of the first matching inductor is the input terminal; the first terminal of the chip filter is connected to the third matching inductor, and the second terminal is the output terminal. The series resonant frequencies of the first FBAR resonator and the second FBAR resonator are within the frequency range of the near end of the stopband of the chip filter. The frequency of the first FBAR resonator is the same as the series resonant frequency of the second FBAR resonator. The filter further includes a first frequency-modulated inductor; the first frequency-modulated inductor is connected in series with a second FBAR resonator; or, the first frequency-modulated inductor is connected in series with a first FBAR resonator.

2. The filter as described in claim 1, characterized in that, The series resonant frequency of the first FBAR resonator is different from that of the second FBAR resonator.

3. The filter as described in claim 1, characterized in that, The series resonant frequencies of the first FBAR resonator and the second FBAR resonator are in the low-end frequency range near the stopband of the chip filter.

4. The filter as described in claim 1, characterized in that, The series resonant frequencies of the first FBAR resonator and the second FBAR resonator are in the high-end frequency range near the stopband of the chip filter.

5. The filter as described in claim 2, characterized in that, When the first frequency-modulated inductor is connected in series with the first FBAR resonator, the series resonant frequency of the first FBAR resonator is in the low-end frequency range near the stopband of the chip filter, and the series resonant frequency of the second FBAR resonator is in the high-end frequency range near the stopband of the chip filter; or, When the first frequency-modulated inductor is connected in series with the second FBAR resonator, the series resonant frequency of the second FBAR resonator is in the low-end frequency range of the near-end of the stopband of the chip filter, and the series resonant frequency of the first FBAR resonator is in the high-end frequency range of the near-end of the stopband of the chip filter.

6. The filter as described in claim 4, characterized in that, The filter also includes a third FBAR resonator, a fourth FBAR resonator, a fourth matching inductor, a fifth matching inductor, and a sixth matching inductor; The chip filter, the fourth matching inductor, the fifth matching inductor and the sixth matching inductor are connected in series in sequence. One end of the third FBAR resonator is connected between the fourth and fifth matching inductors, and the other end is grounded; One end of the fourth FBAR resonator is connected between the fifth and sixth matching inductors, and the other end is grounded; The first end of the chip filter is connected to the third matching inductor, and the second end is connected to the fourth matching inductor; the floating end of the sixth matching inductor is the output end. The series resonant frequencies of the third and fourth FBAR resonators are in the low-end frequency range near the stopband of the chip filter.

7. The filter as described in claim 3, characterized in that, The series resonant frequency range of the first FBAR resonator and the second FBAR resonator is 2563 MHz to 2569 MHz. The upper electrode area of ​​the first FBAR resonator and the second FBAR resonator ranges from 5570 square micrometers to 5630 square micrometers. The inductance of the first frequency modulation inductor is 0.5 nanohenries.

8. The filter according to any one of claims 1 to 7, characterized in that, The chip filter, the first matching inductor, the second matching inductor, and the third matching inductor are fabricated using gallium arsenide monolithic microwave integrated circuit chip technology. The first FBAR resonator and the second FBAR resonator are connected to the chip filter, the first matching inductor, the second matching inductor and the third matching inductor using a ball-mounted flip-chip process.

9. A filter circuit, characterized in that, Includes the filter as described in any one of claims 1 to 8.

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