WO2021088476A1 - Method for improving power capacity of bulk acoustic wave filter, and filtering element - Google Patents

Abstract

The present invention relates to the technical field of filters, in particular to a method for improving the power capacity of a bulk acoustic wave filter and a filtering element. The method comprises the following steps: step S1: increasing the area of resonators in a current filter, making the power density of the resonators reach a preset value, and recording the current value of a port impedance value of the filter; and step S2: in the cases where the current value is less than a specified value, determining an impedance transformation network according to the current value and the specified value, the impedance transformation network being used for being connected in series to an input end and an output end of the filter so as to form a series body, and making the port impedance of the series body reach the specified value. The present invention does not deteriorate the insertion loss of the filter, and improves the power capacity on the premise of ensuring the performance of the bulk acoustic wave filter.

Description

Method for improving power capacity of bulk acoustic wave filter and filter element Technical field

The present invention relates to the field of filter technology, in particular to a method and filter element for increasing the power capacity of a bulk acoustic wave filter.

Background technique

Bulk acoustic wave filters use the piezoelectric effect of piezoelectric crystals to generate resonance. Because resonance is generated by mechanical waves instead of electromagnetic waves as the source of resonance, the wavelength of mechanical waves is much shorter than that of electromagnetic waves. Therefore, the volume of the bulk acoustic wave filter and its resonator is greatly reduced compared with the traditional electromagnetic filter. On the other hand, since the crystal orientation growth of the piezoelectric crystal can be well controlled at present, the loss of the resonator is extremely small, the quality factor is high, and it can cope with complex design requirements such as steep transition band and low insertion loss. Due to the small size, high roll-off, and low insertion loss of the bulk acoustic wave filter, the filter with this as the core has been widely used in communication systems.

The bulk acoustic wave filter has the above advantages, but it has the disadvantage of small power capacity, and the average power it can withstand is generally about 1W. At present, the main method for increasing the power capacity of the bulk acoustic wave filter is to split the resonator and reduce the density of the resonator. As shown in Figure 1, the resonators S11, S12, and P11 are all split into two series-connected resonators. The area of each resonator is twice as large as the original. This split theoretically makes the original power The power density of the high-density resonator is further reduced, thereby increasing the power capacity of the filter; however, as shown in Figure 2, a single resonator A1 is split into the connection relationship of two resonators B1 and B2, and C1 is the resonance in the figure. The connection part between the B1 and B2, this connection path will introduce additional loss, thereby deteriorating the filter insertion loss, and it is also unfavorable for increasing the power capacity.

Therefore, how to increase the power capacity of the BAW filter without deteriorating the insertion loss of the BAW filter is still a technical problem to be solved.

Summary of the invention

In view of this, the main purpose of the present invention is to provide a method and filter element for increasing the power capacity of a bulk acoustic wave filter, so as to increase the power capacity of the bulk acoustic wave filter without deteriorating the performance of the bulk acoustic wave filter.

In order to achieve the above objective, according to one aspect of the present invention, a method for increasing the power capacity of a bulk acoustic wave filter is provided, which includes the following steps: Step S1: Increase the area of each resonator in the current filter; The power density of the filter reaches the preset value, and the current value of the impedance value of the filter port is recorded; Step S2: In the case that the current value is less than the specified value, determine the impedance transformation network according to the current value and the specified value, The impedance transformation network is used to connect the input end and the output end of the filter in series to form a series body, and make the port impedance of the series body reach the specified value.

Optionally, the method further includes: when the current value is equal to a specified value, using the filter obtained in step S1 as a result of increasing the power capacity of the bulk acoustic wave filter.

Optionally, the step of increasing the area of each resonator in the current filter includes: adjusting the area of each resonator in the current filter according to the current setting value of the filter port impedance value, and the current setting The fixed value is less than the specified value.

Optionally, the impedance transformation network includes a transformer, or includes an impedance circuit composed of an inductor and a capacitor.

The present invention also provides a method for increasing the power capacity of a bulk acoustic wave filter, which includes the following steps: Step S1: Among a plurality of filters connected in parallel, the area of each resonator in each current filter is increased to make these resonators The power density of the filter reaches the preset value, and the current value of the impedance value of the filter port is recorded; Step S2: In the case that the current value is less than the specified value, determine the impedance transformation network according to the current value and the specified value, The impedance transformation network is used to connect the input end and the output end of the filter in series to form a series body, and make the port impedance of the series body reach the specified value.

Optionally, the method further includes: when the current value is equal to a specified value, using the filter obtained in step S1 as a result of increasing the power capacity of the bulk acoustic wave filter.

Optionally, the step of increasing the area of each resonator in the current filter includes: adjusting the area of each resonator in the current filter according to the current setting value of the filter port impedance value, and the current setting The fixed value is less than the specified value.

Optionally, the impedance transformation network includes a transformer, or includes an impedance circuit composed of an inductor and a capacitor.

Optionally, in the step S1, among the multiple filters connected in parallel, adjacent filters have an interval of a limited width.

According to another aspect of the present invention, a filter element is provided, which includes a substrate on which an individual acoustic wave filter is provided, and the input end and output end of the bulk acoustic wave filter are respectively connected in series with impedance transformation networks.

Optionally, the impedance transformation network includes a transformer, or includes an impedance circuit composed of an inductor and a capacitor.

The present invention also provides a filter element, including a substrate on which a plurality of parallel BAW filters are arranged, and the input and output ends of the plurality of parallel BAW filters are respectively connected in series with impedance transformation networks.

Optionally, the impedance transformation network includes a transformer, or includes an impedance circuit composed of an inductor and a capacitor.

Optionally, there is a space with a defined width on the substrate between the adjacent BAW filters.

According to the technical solution of the present invention, the power density of the filter is increased by increasing the area of the resonator and reducing its power density; wherein, the above operation will reduce the port impedance of the filter, in order to make the port of the bulk acoustic wave filter The impedance can reach the specified value, and the impedance transformation network is connected in series with the input/output terminals to form a series body, so that the port impedance of the series body can reach the specified value.

The method and filter element for increasing the power capacity of the bulk acoustic wave filter do not need to split the resonator, thereby not deteriorating the insertion loss of the filter, and improving the power capacity under the premise of ensuring the performance of the bulk acoustic wave filter.

Description of the drawings

For the purpose of illustration and not limitation, the present invention will now be described according to preferred embodiments of the present invention, particularly with reference to the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a filter that splits a resonator to increase power capacity in the prior art;

Figure 2 is a schematic diagram of a split resonator in the prior art;

FIG. 3 is a flowchart of a method provided in Embodiment 1 of the present invention;

Fig. 4 is a circuit diagram of a filter element provided in the third embodiment of the present invention;

5A-5F are circuit diagrams of the impedance change network provided by the third embodiment of the present invention;

Fig. 6 is a circuit diagram of a filter element provided in the fourth embodiment of the present invention;

Fig. 7 is a circuit diagram of a filter element provided in the fourth embodiment of the present invention;

FIG. 8 is a schematic diagram of the assembled structure when two bulk acoustic wave filters are connected in parallel;

Fig. 9 is a schematic diagram of the assembled structure when four bulk acoustic wave filters are connected in parallel.

Detailed ways

Example one

Fig. 3 is a flowchart of a method for increasing the power capacity of a bulk acoustic wave filter provided by an embodiment of the present invention. This method can be realized by using computer software, that is, using a computer for aided design. As shown in Figure 3, the method includes the following steps:

Step S1: Increase the area of each resonator in the current filter; make the power density of these resonators reach a preset value, and record the current value of the filter port impedance value;

Step S2: In the case that the current value is less than the specified value, determine an impedance transformation network according to the current value and the specified value, and the impedance transformation network is used to connect the input end and the output end of the filter in series to form a series body, and Make the port impedance of the series body reach the specified value.

The above method will be further explained below.

According to the method provided in this embodiment, the power capacity of the filter is improved by reducing the power density of the resonator. During specific operation, the area of each resonator in the filter is increased, and the power density of the filter is reduced when the input power remains unchanged. But at this time, the filter port impedance will also be correspondingly reduced and may not reach certain specified values, such as 50 ohms commonly used in the industry. In this case, in the embodiment of the present invention, the input end and the output end of the filter are respectively connected to the impedance transformation network, so that the port impedance of the entire device, that is, the filter and the impedance transformation network at both ends, can be increased to the specified value. value. The impedance transformation network here can be implemented based on a transformer, or an impedance circuit can be formed by using inductors and capacitors. For example, a quarter transmission line or a transformer with a voltage ratio of N:1 or a π-type impedance transformation network, a T-type impedance transformation network, and an L-type impedance transformation network implemented by LC are used.

In computer-aided design, using existing computer design tools, you can first specify a filter port impedance, and get the area of each resonator in the filter based on the port impedance. According to this method, if the area of each resonator in the filter needs to be increased, a smaller filter port impedance can be specified. Based on the above specified value, the specified filter port impedance is for example 60% of the specified value, then The calculated area of each resonator in the filter will be larger than the area of each resonator in the filter whose port impedance is the specified value, which means that the area of each resonator in the filter is increased. When the power density of the filter is reduced, the power capacity is improved. If the power capacity still does not meet the requirements at this time, you can continue to increase the area of each resonator in the filter, that is, continue to specify a smaller filter port impedance value, so as to calculate a larger resonator area until the power capacity meets So far. After the power capacity meets the requirements, the filter port impedance has not met the requirements. At this time, as described above, design a suitable impedance transformation network to correct it.

Example two

The embodiment of the present invention provides a method for increasing the power capacity of a bulk acoustic wave filter, which includes the following steps:

Step S1: Among multiple filters connected in parallel, increase the area of each resonator in each filter so that the power density of these resonators reaches a preset value, and record the current value of the filter port impedance value ；

Step S2: When the current value is less than the specified value, determine an impedance transformation network according to the current value and the specified value. The impedance transformation network is used to connect the input end and the output end of the filter in series to form a series body, and Make the port impedance of the series body reach the specified value.

In this embodiment, multiple parallel filters are included. When adjusting the area of the resonator, the area of each resonator in each filter needs to be adjusted, and the current setting value of each filter is the same. In this way, the input energy can be divided into N, where N is the number of filters connected in parallel. In terms of structure, adjacent filters have an interval of a limited width, and the larger the interval, the smaller the impact on the performance of the filter; Multiple filters are connected in parallel. When each filter reaches the limit power, the power capacity of the overall network can be increased by N times. This method is more conducive to increasing the power capacity of the filter and can meet the construction requirements of 5G base stations.

Example three

As shown in FIG. 4, this embodiment provides a filter element, including a substrate, on which an individual acoustic wave filter 41, a first impedance transformation network 42 and a second impedance transformation network 43, and the bulk acoustic wave filter 41 are provided The input terminal is connected in series with the first impedance transformation network 42, and the output terminal is connected in series with the second impedance transformation network 43.

The bulk acoustic wave filter 41 has the same structure as the existing filter. It is a non-split structure, including one series branch and three parallel branches. The series branch is composed of resonators S21, S22, S23, and S24 connected in sequence. One end of the parallel branch is connected between adjacent series resonators, and the other end is grounded. Among them, the first parallel branch is composed of resonator P21 and inductor L21, the second parallel branch is composed of resonator P22 and inductor L22, and the third parallel branch is composed of resonator P22 and inductor L22. The branch is composed of a resonator P31 and an inductor L31. The parallel resonators P21, P22, and P23 need to be loaded with a mass load so that their resonant frequencies are all lower than the resonant frequencies of the series resonators.

The input and output ends of the BAW filter 41 are respectively connected to the impedance transformation network. As the area of the resonator in the BAW filter 41 increases, the deletion power density of the resonator is reduced, and its power capacity is increased. However, it is possible There is a situation in which the port impedances of the input and output ends of the bulk acoustic wave filter 41 are reduced. Therefore, it is necessary to connect a port impedance network in series to transform the port impedance, wherein the impedance value of the impedance transformation network is calculated according to the method of the first embodiment. Out. There may also be a situation where the port impedance values of the input end and the output end of the bulk acoustic wave filter 41 do not change. At this time, there is no impedance transformation network at the input and output ends.

Taking the specified value of the port impedance value of the bulk acoustic wave filter 41 as 50 ohms as an example, when the current value of the port impedance value of the bulk acoustic wave filter 41 is less than 50 ohms, the port impedance value decreases, increasing the area of the resonator. The power density is reduced, thereby increasing the power capacity. The bulk acoustic wave filter 41 also needs to meet the requirement of a port impedance of 50 ohms when in use. Therefore, the first impedance transformation network 42 and the second impedance transformation network 43 provided at the input and output ends of the bulk acoustic wave filter 41 are used. Increase the port impedance and transform it from less than 50 ohms to 50 ohms. Among them, the impedance transformation network includes a transformer, or an impedance circuit composed of inductors and capacitors. For example, it is possible to use a quarter transmission line as shown in FIG. 5A, or a transformer with a voltage ratio of N:1 as shown in FIG. 5B; or a π-type impedance transformation network implemented by LC as shown in FIGS. 5C and 5D; Or the T-type impedance transformation network implemented by LC as shown in FIGS. 5E and 5F; or the L-type impedance transformation network implemented by LC (not shown in the figure), etc.

Example four

As shown in FIG. 6, this embodiment provides another filter element, including a substrate, and a filter group 61 is provided on the substrate. The filter group 61 is two parallel-connected bulk acoustic wave filters, namely the bulk acoustic wave filter 611 and A bulk acoustic wave filter 612, and a third impedance transformation network 62 and a fourth impedance transformation network 63 connected in series to the input end and the output end of the filter bank 61, respectively. Compared with the third embodiment in terms of structure, the bulk acoustic wave filter becomes two, and they are arranged in parallel; and the impedance value of the impedance transformation network is calculated according to the method of the second embodiment. In this way, the input energy can be divided into 2. When each filter reaches the limit power, the power capacity of the overall network can be doubled. The parallel connection of two BAW filters in Figure 6 can increase the power capacity. 2 times.

As shown in Fig. 7, a filter bank 71 is provided on the substrate and includes N parallel BAW filters, namely BAW filter 711, BAW filter 712... BAW filter 71N, the input of filter bank 71 The fifth impedance transformation network 72 and the sixth impedance transformation network 73 are respectively connected in series with the output terminal and the output terminal; wherein, compared with the structure in the third embodiment, N individual acoustic wave filters are connected in parallel, which can increase the power capacity by N times.

Among them, when multiple parallel BAW filters are provided, in terms of structure, it is necessary to increase the distance between the BAW filters as much as possible to reduce the electromagnetic and thermal coupling between each other.

As shown in FIG. 8, it includes a bulk acoustic wave filter 611 and a bulk acoustic wave filter 612. Two filters 611 and 612 are soldered in parallel on a substrate 610. The substrate 610 is a multilayer substrate, and the dielectric material can be ceramic or epoxy resin. In order to improve the heat dissipation capacity, ceramic substrates are preferred; in addition, each layer of the substrate 610 should be covered with a larger metal area to improve the horizontal heat dissipation capacity of the substrate 610, and each layer of metal is connected vertically with vias 628 to improve the vertical direction. Heat dissipation capacity. 621 and 631 directly below the two BAW filters 611 and 612 are metal layers, which are connected to the ground through a via 628, and the two BAW filters are fixed on the metal layers 621 and 631 of the substrate by welding. The input end of the bulk acoustic wave filter 611 is connected through the bonding wire 625 and the metal pad 622, and is connected to the substrate input end 627 through the transmission lines 641 and 626, and the output end of the bulk acoustic wave filter 611 is connected through the bonding wire 624 and the metal pad. 623 is connected and connected to the substrate output terminal 637 through transmission lines 642 and 636. Similarly, the input end of the bulk acoustic wave filter 612 is connected through a bonding wire 634 and the metal pad 632, and is connected to the substrate input end 627 through the transmission lines 643 and 626, and the output end of the bulk acoustic wave filter 612 is connected through a bonding wire 635 and the metal pad. The pad 633 is connected, and is connected to the substrate output terminal 637 through the transmission lines 644 and 636. It should be noted that the transmission lines 641, 642, 643, 644, 626, and 636 can be implemented by microstrip lines or strip lines, and the transmission lines 641 and 643 are the same length, and the transmission lines 642 and 644 are the same length.

As shown in Figure 9, when N individual acoustic wave filters are connected in parallel (take 4 BAW filters as an example), 4 BAW filters 711, 712, 713, and 714 are welded on the four corners of the base plate 710. The base plate 710 It is a multi-layer substrate, and its dielectric material can be ceramic or epoxy resin. In order to improve the heat dissipation capacity, the ceramic substrate is preferred. In addition, each layer of the substrate 710 should be covered with a relatively large metal area to improve the horizontal heat dissipation capacity of the substrate, and Each layer of metal is connected vertically with vias 720 to improve the heat dissipation capacity in the vertical direction. 721, 731, 741 and 751 directly below the 4 BAW filters 711, 712, 713 and 714 are metal layers, which are connected to the bottom ground through vias 720. The 4 BAW filters are fixed on the surface of the substrate by welding. On metal 721, 731, 741 and 751. The input ends of the bulk acoustic wave filters 711 and 713 are respectively connected through bonding wires 722 and 742 and one end of the transmission lines 724 and 744 through pads, and the other end of the transmission lines 724 and 744 is connected to one end of the transmission line 761. The input ends of the bulk acoustic wave filters 712 and 714 are connected through bonding wires 732 and 752 and one end of the transmission lines 734 and 754, respectively. The other ends of the transmission lines 734 and 754 are connected to the other end of the transmission line 761, and one is drawn from the middle of the transmission line 761. The transmission line 762 to the substrate input terminal 765. Similarly, the output ends of the BAW filters 711 and 713 are connected through bonding wires 723 and 743 and one end of the transmission lines 725 and 745, respectively. The other ends of the transmission lines 725 and 745 are connected to one end of the transmission line 763. The output terminals of 712 and 714 are respectively connected by bonding wires 733, 753 and one end of the transmission lines 735, 755 with pads. The other end of the transmission lines 735 and 755 is connected to the other end of the transmission line 763. A transmission line 764 is drawn from the middle of the transmission line 763 to the substrate. The output terminal 766. It should be noted that the transmission line used in this embodiment can be realized by a microstrip line or a strip line, and the lengths of the transmission lines 724, 734, 744, and 754 are equal, and the lengths of the transmission lines 725, 735, 745, and 755 are equal. In addition, as shown in the figure As shown in 9, transmission lines 761 and 745 will have some overlapping lines. In order to reduce the electromagnetic coupling between them, part of the transmission line 745 is transferred to another layer of wiring through the via 720. In addition, the wiring of the two layers is Add a shielding layer 767 between them to achieve electromagnetic isolation. Similarly, transmission lines 763 and 734 will have some overlapping lines. In order to reduce the electromagnetic coupling between them, part of the transmission line 734 is transferred to another layer through the via 720. In addition, a shielding layer 768 is added between the two layers of wiring, which plays a role of electromagnetic isolation.

The filter element in this embodiment is more conducive to increasing the power capacity of the bulk acoustic wave filter by arranging the bulk acoustic wave filter in parallel, which can meet the construction requirements of 5G base stations.

The foregoing specific implementations do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that, depending on design requirements and other factors, various modifications, combinations, sub-combinations, and substitutions can occur. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (14)

1. A method for increasing the power capacity of a bulk acoustic wave filter is characterized in that it includes the following steps:

   Step S1: Increase the area of each resonator in the current filter; make the power density of these resonators reach a preset value, and record the current value of the filter port impedance value;

   Step S2: In the case that the current value is less than the specified value, determine an impedance transformation network according to the current value and the specified value, and the impedance transformation network is used to connect the input end and the output end of the filter in series to form a series body, and Make the port impedance of the series body reach the specified value.
2. The method according to claim 1, characterized in that the method further comprises: when the current value is equal to the specified value, using the filter obtained in step S1 as a result of increasing the power capacity of the bulk acoustic wave filter .
3. The method according to claim 1, wherein the step of increasing the area of each resonator in the current filter comprises: adjusting the current filter in the filter according to the current set value of the filter port impedance value The area of each resonator, the current set value is less than the specified value.
4. The method according to claim 1, wherein the impedance transformation network includes a transformer, or an impedance circuit composed of an inductor and a capacitor.
5. A method for increasing the power capacity of a bulk acoustic wave filter is characterized in that it includes the following steps:

   Step S1: Among multiple filters connected in parallel, increase the area of each resonator in each filter so that the power density of these resonators reaches a preset value, and record the current value of the filter port impedance value ；

   Step S2: When the current value is less than the specified value, determine an impedance transformation network according to the current value and the specified value. The impedance transformation network is used to connect the input end and the output end of the filter in series to form a series body, and Make the port impedance of the series body reach the specified value.
6. The method according to claim 5, wherein the method further comprises: when the current value is equal to the specified value, using the filter obtained in step S1 as a result of increasing the power capacity of the bulk acoustic wave filter.
7. The method according to claim 5, wherein the step of increasing the area of each resonator in the current filter comprises: adjusting the current filter in the filter according to the current set value of the filter port impedance value The area of each resonator, the current set value is less than the specified value.
8. The method according to claim 5, wherein the impedance transformation network includes a transformer, or an impedance circuit composed of an inductor and a capacitor.
9. The method according to claim 5, wherein, in the step S1, among the multiple filters connected in parallel, adjacent filters have an interval of a limited width.
10. A filter element is characterized by comprising a substrate, an individual acoustic wave filter is arranged on the substrate, and the input end and the output end of the bulk acoustic wave filter are respectively connected in series with an impedance transformation network.
11. The filter element according to claim 10, wherein the impedance transformation network includes a transformer, or an impedance circuit composed of an inductor and a capacitor.
12. A filter element is characterized by comprising a substrate on which a plurality of bulk acoustic wave filters are arranged in parallel, and the input and output ends of the plurality of parallel bulk acoustic wave filters are respectively connected in series with impedance transformation networks.
13. The filter element according to claim 12, wherein the impedance transformation network includes a transformer, or an impedance circuit composed of an inductor and a capacitor.
14. The filter element according to claim 12, wherein the adjacent BAW filters have a space with a defined width on the substrate.

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