Filter and multiplexer

Abstract

Provided in the present application are a filter and a multiplexer. The filter comprises a first port (A), a second port (B) and at least one filtering unit (10), wherein the filtering unit (10) comprises a π-type LC network (11) and a resonator (12); the π-type LC network (11) comprises at least one first element (111) and at least two second elements (112); the first element (111) is connected in series between the first port (A) and the second port (B), a first end of at least one second element (112) is connected between the first port (A) and a first end of the first element (111), and a first end of at least one second element (112) is connected between the second port (B) and a second end of the first element (111); and second ends of at least two second elements (112) are connected together, and are then connected to the resonator (12).

Description

Filters and Multiplexers

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 25, 2023, with application number 202311812237.5, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The embodiments of the present application relate to the technical field of signal processing, for example, to a filter and a multiplexer. Background Art

[0003] In communication systems, signal interference can significantly reduce signal transmission efficiency. Filters can effectively suppress out-of-band signal interference to improve signal transmission efficiency. In modern communications, there is an increasing demand for filters with low insertion loss and high roll-off characteristics. Summary of the Invention

[0004] The present application provides a filter and a multiplexer to improve the roll-off characteristics of the filter.

[0005] In a first aspect, an embodiment of the present application provides a filter, comprising a first port, a second port, and at least one filtering unit;

[0006] The filtering unit includes a π-type LC network and a resonator; the π-type LC network includes at least one first element and at least two second elements; the first element is connected in series between the first port and the second port, the first end of at least one second element is connected between the first port and the first end of the first element, and the first end of at least one second element is connected between the second port and the second end of the first element; the second ends of at least two second elements are connected and then connected to the resonator.

[0007] Optionally, the π-type LC network includes one first element and two second elements;

[0008] The first element includes a first inductive element, and the first inductive element is connected in series between the first port and the second port; and / or,

[0009] The two second elements include a first capacitive element and a second capacitive element, the first end of the first capacitive element is connected between the first port and the first end of the first element, the first end of the second capacitive element is connected between the second port and the second end of the first element, and the second end of the first capacitive element and the second end of the second capacitive element are connected to the resonator.

[0010] Optionally, the filter includes at least two filtering units, and the at least two filtering units are connected in series between the first port and the second port.

[0011] Optionally, the filter further includes at least one third port, and at least one of the third ports is arranged between adjacent filtering units.

[0012] Optionally, the frequencies corresponding to the transmission zero points of different filtering units are equal.

[0013] Optionally, the filter further comprises at least one electromagnetic filtering network, wherein the electromagnetic filtering network is connected in series between the first port and the second port.

[0014] Optionally, the filter includes at least two filtering units, and when at least two filtering units are connected in series between the first port and the second port, at least one electromagnetic filtering network is connected between adjacent filtering units.

[0015] Optionally, the electromagnetic filtering network includes a second inductive element, and the second inductive element is connected in series between the first port and the second port.

[0016] Optionally, the electromagnetic filtering network further includes a third capacitive element, and the third capacitive element is connected in series and / or in parallel with the second inductive element.

[0017] In a second aspect, an embodiment of the present application further provides a multiplexer comprising the filter described in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a schematic diagram of the structure of a filter provided in an embodiment of the present application;

[0019] FIG2 is a schematic diagram of the structure of another filter provided in an embodiment of the present application;

[0020] FIG3 is a schematic structural diagram of an LC filter provided by an embodiment;

[0021] FIG4 is a schematic diagram showing a performance comparison of different filters provided in an embodiment of the present application;

[0022] FIG5 is a schematic diagram of the structure of another filter provided in an embodiment of the present application;

[0023] FIG6 is a schematic diagram of the structure of another filter provided in an embodiment of the present application;

[0024] FIG7 is a schematic diagram of the structure of another filter provided in an embodiment of the present application;

[0025] FIG8 is a schematic diagram of the structure of another filter provided in an embodiment of the present application;

[0026] FIG9 is a schematic diagram of the structure of another filter provided in an embodiment of the present application;

[0027] FIG10 is a schematic diagram of the structure of another filter provided in an embodiment of the present application;

[0028] FIG11 is a schematic structural diagram of a multiplexer provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] The present application is described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to illustrate the present application. For ease of description, the accompanying drawings only show portions related to the present application, not all structures.

[0030] Figure 1 is a schematic diagram of the structure of a filter provided in an embodiment of the present application. As shown in Figure 1, the filter includes a first port A, a second port B, and at least one filter unit 10; the filter unit 10 includes a π-type LC network 11 and a resonator 12; the π-type LC network 11 includes at least one first element 111 and at least two second elements 112; the first element 111 is connected in series between the first port A and the second port B, the first end of at least one second element 112 is connected between the first port A and the first end of the first element 111, and the first end of at least one second element 112 is connected between the second port B and the second end of the first element 111; the second ends of the at least two second elements 112 are connected, and then connected to the resonator 12.

[0031] Optionally, the π-type LC network 11 includes a capacitive element and an inductive element, which are used to form a π-type LC filter network to achieve signal filtering. The π-type LC network 11 can be a low-pass filter network. Exemplarily, the first element 111 can include an inductive element, and the second element 112 can include a capacitive element. When there is one first element 111 and two second elements 112, the first element 111 and the second element 112 can form a third-order low-pass filter network. When the passband of the π-type LC network 11 transitions to the stopband, the Z parameter of the π-type LC network 11 has a maximum point, while the Y parameter does not have a minimum point. At this time, there is no transmission zero point in the stopband of the filter. Among them, the Z parameter is the impedance parameter of the π-type LC network 11, and the Y parameter is the admittance parameter of the π-type LC network 11.

[0032] The resonator 12 can be an acoustic wave resonator. Exemplarily, the resonator 12 can be at least one of a bulk acoustic wave (BAW) resonator, a surface acoustic wave (SAW) resonator, and a film bulk acoustic resonator (FBAR) filter. The resonator 12 has a bandpass characteristic and has a transmission zero point in the adjacent band on the high-frequency side of the passband, that is, in the transmission characteristic of the resonator 12, the Z parameter has a maximum point in the adjacent band on the high-frequency side of the passband, so that the resonator 12 has a strong suppression effect at the frequency corresponding to the transmission zero point, thereby making the resonator 12 have a large roll-off slope at the frequency corresponding to the transmission zero point. When the second ends of the at least two second elements 112 are connected, they are connected to the resonator 12, so that the resonator 12 is connected in series with the π-type LC network 11. At this time, the Z parameter of the filter is the sum of the Z parameter of the resonator 12 and the Z parameter of the π-type LC network 11. When the Z parameter of the π-type LC network 11 is added to the Z parameter of the resonator 12, the Z parameter of the filter has a maximum point in the adjacent band on the high-frequency side of the passband, and the Y parameter has a minimum point, thereby increasing the roll-off slope of the adjacent band on the high-frequency side of the passband, improving the adjacent band suppression on the high-frequency side of the passband of the filter, and thus improving the filtering performance of the filter. At the same time, the resonator 12 has a bandpass characteristic and has a minimum point of the Z parameter in the passband, that is, it has a maximum point of the Y parameter in the passband. When the Z parameter of the resonator 12 is added to the Z parameter of the π-type LC network 11, the frequency difference between the zero point and the pole of the filter can be reduced based on the frequency difference between the original zero point and the pole of the resonator 12, thereby increasing the roll-off slope between the passband and the high-frequency side, improving the adjacent band suppression on the high-frequency side of the passband of the filter, and thus improving the filtering performance of the filter. In addition, on the high-frequency side of the passband of resonator 12, the Z parameter of π-type LC network 11 and the Z parameter of resonator 12 have different signs, so that the sum of the Z parameter of π-type LC network 11 and the Z parameter of resonator 12 generates an additional maximum point in the adjacent band range on the high-frequency side of the passband, that is, in the filter unit 10, an additional transmission zero point is generated in the adjacent band on the high-frequency side of the passband of the filter unit 10, thereby increasing the roll-off slope of the adjacent band on the high-frequency side of the passband, improving the adjacent band suppression on the high-frequency side of the passband of the filter, and thus improving the filtering performance of the filter. Among them, the adjacent band can be a frequency band above or below the passband, and the transition band between it and the passband may even be only 0 MHz to tens of MHz, and the bandwidth of the adjacent band is a frequency band range of more than 10% of the center frequency of the passband.

[0033] When one end of the resonator 12 is connected in series with the π-type LC network 11, the other end of the resonator 12 serves as a port of the filter and can be connected to an external circuit, so that the filter can be connected to different types of external circuits, thereby increasing the application range of the filter.

[0034] In this embodiment, by setting the resonator in the filter unit in series with the π-type LC network, the Z parameter of the resonator is added to the Z parameter of the π-type LC network, thereby forming two transmission zeros in the adjacent band range on the high-frequency side of the passband of the filter. At the same time, the frequency difference between the zero and the pole of the filter can be reduced, and the roll-off slope of the adjacent band on the high-frequency side of the passband of the filter is greatly improved, which greatly improves the adjacent band suppression on the high-frequency side of the passband of the filter, thereby improving the filtering performance of the filter.

[0035] FIG2 is a schematic diagram of the structure of another filter provided by an embodiment of the present application. As shown in FIG2 , a π-type LC network 11 includes a first element 111 and two second elements 112. The first element 111 includes a first inductive element L1, which is connected in series between a first port A and a second port B. The second elements 112 include a first capacitive element C1 and a second capacitive element C2, with a first end of the first capacitive element C1 connected between the first port A and the first end of the first element 111, a first end of the second capacitive element C2 connected between the second port B and the second end of the first element 111, and a second end of the first capacitive element C1 and a second end of the second capacitive element C2 connected to each other and then connected to the resonator 12.

[0036] Optionally, Figure 2 exemplarily shows that the first element 111 includes a first inductive element L1, and the two second elements 112 respectively include a first capacitive element C1 and a second capacitive element C2, the first inductive element L1 is connected in series between the first port A and the second port B, and the first end of the first capacitive element C1 is connected between the first port A and the first end of the first element 111, and the first end of the second capacitive element C2 is connected between the second port B and the second end of the first element 111, so that the first inductive element L1, the first capacitive element C1 and the second capacitive element C2 constitute a third-order low-pass filter network. At the same time, the second end of the first capacitive element C1 and the second end of the second capacitive element C2 are connected and then connected to the resonator 12, so that the resonator 12 and the π-type LC network 11 are connected in series, so that the Z parameter of the resonator 12 can be added to the Z parameter of the π-type LC network 11, so that two transmission zeros can be formed in the high-frequency side adjacent band range of the passband of the filter. At the same time, the frequency difference between the zero point and the pole of the filter can be reduced, and the roll-off slope of the high-frequency side adjacent band of the passband of the filter is greatly improved, and the high-frequency side adjacent band suppression of the passband of the filter is greatly improved, thereby improving the filtering performance of the filter.

[0037] For example, FIG3 is a schematic diagram of the structure of an LC filter provided in one embodiment. Its specific structure is the same as the π-type LC network 11 in FIG2 . FIG4 is a schematic diagram of the performance comparison of different filters provided in an embodiment of the present application. Among them, the horizontal axis is the frequency and the vertical axis is the insertion loss. Curve 1 is the frequency-insertion loss curve of the filter provided in FIG2 , and curve 2 is the frequency-insertion loss curve of the filter provided in FIG3 . As shown in FIG4 , curve 1 forms two transmission zero points M in the adjacent band range on the high-frequency side of the passband, the suppression degree of one transmission zero point reaches below -20dB, and the suppression degree of the other transmission zero point reaches about -40dB, and the roll-off slope is very steep. Curve 2 has no transmission zero point in the adjacent band range on the high-frequency side of the passband, the suppression degree is relatively poor, and the roll-off slope is relatively gentle. It can be seen from this that when a resonator 12 is connected in series on the basis of the LC filter provided in Figure 3, two transmission zeros can be formed in the adjacent band range on the high-frequency side of the filter passband, thereby greatly improving the roll-off slope of the adjacent band on the high-frequency side of the passband, greatly improving the adjacent band suppression on the high-frequency side of the filter passband, and thus improving the filtering performance of the filter.

[0038] In other embodiments, the first element 111 may further include multiple inductive elements, which may be connected in series and / or in parallel. The second element 112 may further include at least multiple capacitive elements, which may include an inductive element in addition to the multiple capacitive elements. At least multiple capacitive elements may be connected in series and / or in parallel. Alternatively, the first element 111 and / or the second element 112 may further include a resistive element, which may be connected in series or in parallel with the inductive element and / or the capacitive element to adjust the resonant frequency of the π-type LC network 11. The capacitive element may be a capacitive element or a parasitic capacitance generated between different elements. The resistance value of the capacitive element may be set as needed.

[0039] FIG5 is a schematic diagram of the structure of another filter provided in an embodiment of the present application. As shown in FIG5 , the filter includes at least two filter units 10 , which are connected in series between a first port A and a second port B.

[0040] Optionally, FIG5 exemplarily shows that the filter includes two filter units 10, and the two filter units 10 are connected in series between the first port A and the second port B. When at least two filter units 10 are connected in series between the first port A and the second port B, different filter units 10 can generate two transmission zeros in the adjacent bands on the high-frequency side of the passband of the filter, so that the at least two filter units 10 can significantly improve the roll-off slope of the adjacent bands on the high-frequency side of the passband, thereby improving the adjacent-band suppression on the high-frequency side of the passband of the filter, thereby improving the filtering performance of the filter.

[0041] Exemplarily, the frequencies corresponding to the transmission zero points of different filter units 10 are equal.

[0042] Optionally, the parameters of the π-type LC network 11 and the resonator 12 in different filter units 10 can be the same, so that the frequencies corresponding to the transmission zero points of different filter units 10 are equal. In this case, the passband frequencies of different filter units 12 are the same, and transmission zero points are formed at the same frequency, thereby increasing the roll-off slope of the adjacent band on the high-frequency side of the passband. For example, in different filter units 10, the components of the π-type LC network 11 are the same, and the parameters of the components at the same position are the same. At the same time, the parameters of the resonator 12 in different filter units 10 are the same, so that the resonant frequencies of different filter units 10 can be equal.

[0043] In other embodiments, the transmission zeros of different filter units 10 may be configured to correspond to different frequencies, so that the filter has multiple transmission zeros within the adjacent band on the high-frequency side of the passband. This can also increase the roll-off slope of the adjacent band on the high-frequency side of the passband compared to a filter unit 10 having two transmission zeros. For example, in different filter units 10, the components of the π-type LC network 11 may be different, and / or the parameters of the components at the same position may be different, and / or the parameters of the resonators 12 in different filter units 10 may be different.

[0044] In other embodiments, the filter may include a plurality of filter units 10 , and the plurality of filter units 10 are connected in series between the first port A and the second port B.

[0045] FIG6 is a schematic diagram of the structure of another filter provided in an embodiment of the present application. As shown in FIG6 , the filter further includes at least one third port E, and the at least one third port E is disposed between adjacent filter units 10 .

[0046] Optionally, FIG6 exemplarily illustrates a filter including two filter units 10, with a third port E disposed between the two filter units 10. The third port E can be used to connect to an external circuit, allowing the filter to be connected to different types of external circuits, thereby expanding the filter's application range. Furthermore, the third port E can be connected to an equivalent high-impedance component, rendering the third port E equivalent to an open circuit, thereby satisfying different filter usage scenarios.

[0047] When the filter includes multiple filter units 10, the third port E can be arranged between two adjacent filter units 10, or between the filter unit 10 and the first port A and / or the second port B. In this case, the filter can include multiple third ports E. It can also be arranged between spaced filter units 10. In this case, the filter can include at least one third port E.

[0048] FIG7 is a schematic diagram of the structure of another filter provided by an embodiment of the present application. As shown in FIG7 , the filter further includes at least one electromagnetic filter network 20, which is connected in series between the first port A and the second port B.

[0049] Optionally, the electromagnetic filter network 20 may include inductive and / or capacitive elements. When the electromagnetic filter network 20 includes only inductive or capacitive elements, the electromagnetic filter network 20 can compensate for the π-type LC network 11, thereby reducing the insertion loss of the π-type LC network 11 and improving the filter performance. When the electromagnetic filter network 20 includes both inductive and capacitive elements, the electromagnetic filter network 20 can adjust the filter's passband, resulting in a wider passband.

[0050] For example, Figure 8 is a schematic diagram of the structure of another filter provided by an embodiment of the present application. As shown in Figure 8, the electromagnetic filtering network 20 includes a second inductive element L2, which is connected in series between the first port A and the second port B.

[0051] Optionally, Figure 8 exemplarily shows that the electromagnetic filtering network 20 includes a second inductive element L2, which is connected in series between the second port B and the filtering unit 10. When the first element 111 includes an inductive element and the second element 112 includes a capacitive element, the second inductive element L2 can compensate for the insertion loss of the π-type LC network 11, thereby improving the filtering performance of the filter.

[0052] In other embodiments, the electromagnetic filtering network 20 may also include only capacitive elements. By setting the capacitive elements, the frequency of the filtering unit 10 can be adjusted. It can also be used as a high-pass filtering network in the filter to adjust the passband of the filter.

[0053] In other embodiments, FIG9 is a schematic diagram of another filter structure provided by an embodiment of the present application. As shown in FIG9 , the electromagnetic filter network 20 further includes a third capacitive element C3, which is connected in series and / or in parallel with the second inductive element L2.

[0054] Optionally, FIG9 exemplarily illustrates a third capacitive element C3 connected in series with a second inductive element L2. The second inductive element L2 and the third capacitive element C3 can form a filter network for adjusting the filter's passband, thereby providing the filter with a wider passband. When the filter includes both the electromagnetic filter network 20 and the filter unit 10, the filter can be guaranteed to have a wider passband while also improving the roll-off slope of the adjacent band on the high-frequency side of the filter's passband, significantly improving the adjacent band suppression on the high-frequency side of the filter's passband, thereby enhancing the filter's filtering performance.

[0055] In other embodiments, the second inductive element L2 and the third capacitive element C3 may be connected in parallel to adjust filter performance as required. Alternatively, when at least one of the second inductive element L2 and the third capacitive element C3 includes multiple elements, the second inductive element L2 and the third capacitive element C3 may be connected in series and / or in parallel as required.

[0056] FIG10 is a schematic diagram of the structure of another filter provided in an embodiment of the present application. As shown in FIG10 , the filter includes at least two filter units 10 . When the at least two filter units 10 are connected in series between a first port A and a second port B, at least one electromagnetic filter network 20 is connected between adjacent filter units 10 .

[0057] Optionally, FIG10 exemplarily shows that the filter includes two filter units 10 , and the electromagnetic filter network 20 is connected between the two filter units 10 , so that different filter units 10 can be arranged at intervals.

[0058] In other embodiments, the electromagnetic filtering network 20 may also be disposed between the first port A and the filtering unit 10 , or between the second port B and the filtering unit 10 .

[0059] The present invention also provides a multiplexer. Figure 11 is a schematic diagram of the structure of a multiplexer provided in an embodiment of the present invention. As shown in Figure 11, the multiplexer includes the filter 100 provided in any embodiment of the present invention.

[0060] 11 , the multiplexer includes an input terminal IN and at least two output terminals; each filter 100 is connected in series between the input terminal IN and any output terminal of the multiplexer.

[0061] Optionally, FIG11 exemplarily shows a multiplexer including an input terminal IN and n output terminals, namely OUT1, OUT2, ..., OUTn. Each filter 100 is connected in series between the input terminal IN and an output terminal. For example, the first filter 100 is connected in series between the input terminal IN and the first output terminal OUT1, the second filter 100 is connected in series between the input terminal IN and the first output terminal OUT2 ... and so on. Since the multiplexer has the filter 100 provided in any embodiment of the present application, it has the same beneficial effect as the filter 100, that is, the roll-off slope of the adjacent band on the low-frequency side of the multiplexer passband greatly improves the adjacent band suppression on the low-frequency side of the filter's passband, thereby improving the filtering performance of the filter.

[0062] The multiplexer may further include other filters, which are connected in series between the input terminal IN and any output. The other filters may be low-pass filters, high-pass filters or band-pass filters.

Claims

1. A filter, comprising a first port, a second port, and at least one filtering unit; The filtering unit includes a π-type LC network and a resonator; the π-type LC network includes at least one first element and at least two second elements; the first element is serially connected between the first port and the second port, and the first end of at least one of the second elements is connected between the first port and the first end of the first element, and the first end of at least one of the second elements is connected between the second port and the second end of the first element; after the second ends of at least two of the second elements are connected, they are connected to the resonator.

2. The filter according to claim 1, wherein The π-type LC network includes one of the first elements and two of the second elements; The filter further includes at least one of the following: The first element includes a first inductive element, and the first inductive element is serially connected between the first port and the second port; The two second elements include a first capacitive element and a second capacitive element. The first end of the first capacitive element is connected between the first port and the first end of the first element, and the first end of the second capacitive element is connected between the second port and the second end of the first element. After the second ends of the first capacitive element and the second capacitive element are connected, they are connected to the resonator.

3. The filter according to claim 1 or 2, further comprising at least two of the filtering units, and at least two of the filtering units are serially connected between the first port and the second port.

4. The filter according to claim 3, further comprising at least one third port, and at least one of the third ports is disposed between adjacent ones of the filtering units.

5. The filter according to claim 3, wherein, The frequencies corresponding to the transmission zeros of different ones of the filtering units are equal.

6. The filter according to claim 1, further comprising at least one electromagnetic filtering network, and the electromagnetic filtering network is serially connected between the first port and the second port.

7. The filter according to claim 6, further comprising at least two of the filtering units. When at least two of the filtering units are serially connected between the first port and the second port, at least one of the electromagnetic filtering networks is connected between adjacent ones of the filtering units.

8. The filter according to claim 6 or 7, wherein, The electromagnetic filtering network includes a second inductive element, and the second inductive element is serially connected between the first port and the second port.

9. The filter according to claim 8, wherein, The electromagnetic filtering network further includes a third capacitive element, and the third capacitive element is arranged to be at least one of serially connected and parallel connected with the second inductive element.

10. A multiplexer, comprising: An input end, at least two output ends, and a filter according to any one of claims 1-9, and each of the filters is arranged to be serially connected between the input end and any one of the output ends.

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