WO2022143982A1

WO2022143982A1 - Multiplexer, method for improving isolation of multiplexer, and communication device

Info

Publication number: WO2022143982A1
Application number: PCT/CN2021/143682
Authority: WO
Inventors: 蔡华林; 庞慰
Original assignee: 诺思(天津)微系统有限责任公司
Priority date: 2021-01-04
Filing date: 2021-12-31
Publication date: 2022-07-07
Also published as: CN112865741A

Abstract

Disclosed are a multiplexer, a method for improving the isolation of a multiplexer, and a communication device, wherein there is better isolation between filters in the multiplexer. The multiplexer includes two or more filters connected in parallel, wherein each of the filters includes a plurality of piezoelectric acoustic wave resonators, and the piezoelectric acoustic wave resonators include grounded inductors. The multiplexer has at least one capacitive structure, two poles of the capacitive structure are respectively connected to distal ends of the two grounded inductors, the two grounded inductors belong to different filters, and there is mutual inductance between the two grounded inductors.

Description

Multiplexer, method for improving isolation of multiplexer, and communication device

technical field

The present invention relates to the technical field of filters, in particular to a multiplexer, a method for improving the isolation of the multiplexer, and a communication device.

Background technique

In recent years, the trend of miniaturization and high performance of communication equipment has accelerated, posing higher challenges to the RF front-end. In the RF communication front-end, miniaturization is achieved by reducing the size of the chip and package substrate on the one hand, and better performance is achieved by reducing loss sources and better resonator fit design on the other hand. In the existing filter structure, there are many passive components used for matching, and at the same time, to improve specific performance such as roll-off insertion loss, etc., additional structures such as more inductance, capacitance, and coupling need to be introduced.

A typical structure of a common filter is shown in FIG. 1 , which is a schematic diagram of a structure of an acoustic wave filter according to the prior art. In this filter 10, there are

inductors

121, 122 and a plurality of resonators (usually called series resonators) 101 to 104 between the input terminal 131 and the output terminal 132, and the connection point of each series resonator is connected to the ground terminal. Resonators 111 to 113 (usually referred to as parallel resonators) and inductors 123 to 125 are respectively provided on the multiple branches (usually referred to as parallel branches) of the . Because the parallel resonator is grounded through the inductances 123 to 125, the inductances 123 to 125 are also called ground inductances.

The above-mentioned resonators are piezoelectric acoustic wave resonators, and piezoelectric acoustic wave resonators refer to resonators that utilize piezoelectric effect to generate resonance characteristics. Commonly used ones include but are not limited to: bulk acoustic wave piezoelectric resonators (such as FABR, SMR, etc.), Surface acoustic wave piezoelectric resonators.

A typical structure of a common multiplexer is shown in FIG. 2A , which is a schematic diagram of a structure of a multiplexer according to the prior art. The multiplexer has a common terminal Common and n output terminals F1 to Fn, and contains n filters. Each filter has an inductance to ground. As an illustration, the figure shows two inductances G11 and G12 to ground of filter 1 and two inductances to ground Gn1 and Gn2 of filter n. One end of these inductances to ground is connected to The resonator in the filter (not shown in the figure, please refer to Figure 1), the other end is connected to the ground terminal GND.

FIG. 2B is a schematic diagram of mutual inductance between ground inductances of different filters in a multiplexer according to the prior art. FIG. 2B takes the multiplexer shown in FIG. 2A as an example. For example, the ground inductances G11 and Gn1 in the multiplexer 20 generate mutual inductance M due to their proximity (other parts of the multiplexer are omitted in the figure). The two ground inductors may be traces in the same layer or different layers of the multiplexer package substrate, or may be bonding wires. In practice, similar mutual inductances may occur between any two filters of a multiplexer.

During the process of implementing the present invention, the inventor found that if there is mutual inductance coupling between the ground inductances of different filters in the multiplexer, the isolation between these filters will deteriorate. For example, the mutual inductance M in FIGS. 2A and 2B will deteriorate the isolation between filter 1 and filter n.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a multiplexer, a method for improving the isolation of the multiplexer, and a communication device, and filters in the multiplexer have better isolation. The present invention provides the following technical solutions:

A multiplexer includes two or more parallel filters, each of the filters includes a plurality of piezoelectric acoustic wave resonators, the piezoelectric acoustic wave resonator includes an inductance to ground, and the multiplexer has At least one capacitive structure, two poles of the capacitive structure are respectively connected to the remote ends of two grounding inductors, the two grounding inductors belong to different filters and there is mutual inductance between the two grounding inductors. Capacitive structures are structures capable of producing capacitive properties in certain frequency bands.

Optionally, the capacitive structure includes one of the following: a piezoelectric acoustic wave resonator; a plate capacitor in a filter chip; an interdigital capacitor in the filter chip; a capacitive structure in the filter chip; a filter chip Capacitive devices outside the filter chip; capacitive structure outside the filter chip.

Optionally, the distance between the capacitive structure and the ground inductance without mutual inductance in the filter, as well as the distance from the input end and the output end of the filter, are all more than 50um, or more than 200um.

Optionally, a plurality of the filters are fabricated in the same chip; or, a plurality of the filters are fabricated in a plurality of chips, and the plurality of chips are arranged in a stacked manner or on the same plane.

Optionally, there is mutual inductance between the first inductance to ground and the second inductance to ground, and between the first inductance to ground and the third inductance to ground in the multiple parallel filters, wherein the first, The second and third ground inductances belong to different filters; the remote ends of the first and second ground inductances have a first capacitive structure, and the remote ends of the first and third ground inductances have a first capacitive structure. Has a second capacitive structure.

Optionally, the fourth inductance to ground and the fifth inductance to ground of the first filter in the plurality of parallel filters are respectively the same as the inductance to ground of the sixth and the seventh inductance to ground of the second filter. Mutual inductance exists; a third capacitive structure is provided between the remote ends of the fourth and sixth ground inductances, and a fourth capacitive structure is provided between the remote ends of the fifth and seventh ground inductances.

Optionally, the capacitance value of the capacitive structure is 0.01pF to 10pF.

Optionally, the ground inductance is a trace in the filter substrate, a bonding wire in the filter, or a trace of each pin of the filter chip.

A method for improving isolation of a multiplexer, wherein the multiplexer includes a plurality of parallel filters, each of the filters includes a plurality of piezoelectric acoustic wave resonators, and the piezoelectric acoustic wave resonator includes an inductance to ground , the method includes: setting a capacitive structure between two remote ends of the ground inductance with mutual inductance, the capacitive structure is used to improve the isolation between the two filters in the multiplexer, the The two ground inductances belong to the two filters.

A communication device includes the multiplexer of the present invention.

According to the technical solution of the present invention, for the two filters in the multiplexer, if there is mutual inductance between the ground inductances of the two filters, a capacitive structure is added between the remote ends of the ground inductances. Because the above-mentioned mutual inductance will cause the signal to generate a leakage path between multiple filters and deteriorate the isolation, the addition of the capacitor can reduce the amplitude of the leaked signal by changing the impedance of the leakage path, thereby improving the isolation. According to the technical solution of the present invention, various flexible ways can be used to increase the capacitive structure without increasing the distance between multiple filters, which is also more conducive to the miniaturization of the device.

Description of drawings

For purposes of illustration and not limitation, the present invention will now be described in accordance with preferred embodiments thereof, particularly with reference to the accompanying drawings, wherein:

1 is a schematic diagram of a structure according to an acoustic wave filter in the prior art;

2A is a schematic diagram of a structure of a multiplexer according to the prior art;

2B is a schematic diagram of the mutual inductance between the ground inductances of different filters in a multiplexer according to the prior art;

3 is a schematic diagram of adding a capacitive structure between ground inductances with mutual inductance according to an embodiment of the present invention;

4 is a schematic diagram of another additive capacitive structure according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of yet another additive capacitive structure according to an embodiment of the present invention;

6A-6C are schematic diagrams of capacitive structures arranged in accordance with embodiments of the present invention;

7A to 7C are schematic diagrams of isolation improvement of filters in a duplexer according to an embodiment of the present invention;

8A is a schematic diagram of a distance between a capacitive structure and a pin of a multiplexer according to an embodiment of the present invention;

8B is a schematic diagram illustrating the effect of the distance between the capacitive structure and the pins of the multiplexer on isolation according to an embodiment of the present invention.

Detailed ways

The technical solutions of the embodiments of the present invention will be described below with reference to the accompanying drawings. In a multiplexer, if two ground inductances are close in space, mutual inductance may occur, and the two may be traces on the same layer or different layers in the substrate, or may be any two bonding wires. Mutual inductance between the ground inductances of different filters can lead to signal leakage paths between the filters, thereby deteriorating isolation.

Taking the multiplexer shown in FIG. 2 as an example, for example, there is a mutual inductance M1 between the ground inductance G11 of the filter 1 and the ground inductance Gn1 of the filter n. In the embodiment of the present invention, as shown in FIG. 3 Adding a capacitive structure, FIG. 3 is a schematic diagram of adding a capacitive structure between ground inductances with mutual inductance according to an embodiment of the present invention. Fig. 3 is based on the multiplexer shown in Fig. 2, in which a capacitive structure C1 is set between G11 and Gn1. Both ends of the capacitive structure C1 are respectively connected to the remote ends of the above-mentioned grounding inductance, that is, the ungrounded end of the inductance.

The addition of the capacitive structure can change the impedance of the leakage path, thereby reducing the amplitude of the leakage signal, thereby improving the isolation. In this sense, for any two ground inductances with mutual inductance (which can be any of the parallel branches of the filter), as long as the two belong to different filters, the capacitive structure can be added in the above manner , thereby improving the isolation between filters.

For example, as shown in FIG. 4, FIG. 4 is a schematic diagram of another added capacitive structure according to an embodiment of the present invention, wherein the inductance G11 to ground of filter 1 and the inductance Gn to ground of filter n are between the mutual inductance M1 except for the mutual inductance M1. In addition to the mutual inductance M2 that exists outside, a capacitive structure C2 is also added to the multiplexer shown in FIG. 4 , and the position is shown in the figure.

Also shown in FIG. 5 , FIG. 5 is a schematic diagram of another capacitive structure added according to an embodiment of the present invention, in which the mutual inductance M1 is added between the filter 1 except its ground inductance G11 and the ground inductance Gn1 of the filter n. In addition, the ground inductance G11 and the ground inductance Gk2 of the filter k at the output end Fk also have a mutual inductance M3, and a capacitive structure C3 is also added to the multiplexer shown in FIG. 5, and the location is shown in the figure shown in.

The above capacitive structure is represented by the symbol of capacitance in the figure. In the implementation, it can be a capacitive element, such as a plate capacitor, an interdigital capacitor, etc., which can be realized in the layout of the filter (that is, it is processed and manufactured on the same lining as the filter). Bottom); it can also be a piezoelectric acoustic resonator, using its own capacitive properties in a specific frequency band. It can also be other capacitive structures, that is, structures that can generate capacitive electrical characteristics in certain frequency bands, such as two traces or bonding wires that are close to each other, metal structures with edges close to each other or staggered up and down. That is, the capacitive structure may have multiple implementations, and may coexist in the same multiplexer. For example, the two capacitive structures in FIG. 4 may respectively adopt different structures from the above-mentioned multiple capacitive structures.

For example, as shown in FIGS. 6A to 6C , FIGS. 6A to 6C are schematic diagrams of capacitive structures arranged according to embodiments of the present invention. Taking the multiplexer 60 as an example, on the basis of FIG. 2B , the plate capacitor 61 (as shown in FIG. 6A ) can be integrated in the substrate, and the finger capacitor 62 (as shown in FIG. 6B ) can also be integrated in the substrate. Here It can also be implemented inside the chip; it can also be a discrete device, such as a chip capacitor; in addition, it can be a capacitive structure inside or outside the chip, such as the capacitance generated between the layers in the chip , or capacitance generated between metal parts of different layers of the substrate, etc. The chip mentioned in this article refers to the unit formed by processing the piezoelectric acoustic wave filter on the wafer substrate.

In addition, a resonator can also be integrated between the inductors G11 and G12 with mutual inductance. As shown in FIG. 6C, the 63 resonator 63 plays the role of a capacitive element, which can be connected to one of the inductors G11 and G12 by using a separate chip. It can also be in one filter chip or multiple filter chips of the multiplexer (for example, multiple resonators that function as capacitive elements are required). The resonator frequency of this resonator is different from the resonant frequency of the original resonator in each filter.

After adding the capacitive structure described above, the isolation between the filters is improved. Referring to FIGS. 7A to 7C , FIGS. 7A to 7C are schematic diagrams illustrating the isolation improvement of the filter in the duplexer according to the embodiment of the present invention. As shown in FIG. 7A , the thick line is the isolation curve without mutual inductance, and the thin line is the curve of adding a 5pH mutual inductance and then adding a 0.15pF capacitance to both ends of the mutual inductance. It can be seen that after adding capacitors, the effect of mutual inductance on the deterioration of isolation is almost eliminated.

When the added capacitance is different, the corresponding improvement effect is also different. As shown in FIG. 7B , the thick line in FIG. 7B corresponds to the added capacitance of 0.1 pF, and the thin line corresponds to the added capacitance of 0.15 pF. Also as shown in FIG. 7C , the thick line in FIG. 7C corresponds to the addition of a 0.4pF capacitance, and the thin line corresponds to the addition of a 0.15pF capacitance. It can be seen that the added capacitance value has an optimal value interval, which is related to the frequency. In the frequency range shown in the above figures, the capacitance value can be 0.01pF to 10pF.

There should be some distance between the added capacitive structure and the other pins of the multiplexer to avoid additional coupling paths that would degrade the isolation performance of the multiplexer. As shown in FIG. 8A , FIG. 8A is a schematic diagram of the distance between the capacitive structure and the pins of the multiplexer according to an embodiment of the present invention, wherein D1 to D5 are at least greater than 50um, preferably more than 200um. 8B is a schematic diagram illustrating the influence of the distance between the capacitive structure and the pins of the multiplexer on the isolation according to an embodiment of the present invention, wherein the thick line corresponds to the distance less than 50um, and the thick line corresponds to the distance greater than 200um. As can be seen from the figure, the distance needs to be greater than 50um, and better than 200um.

The above-mentioned specific embodiments do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

A multiplexer, comprising two or more filters in parallel, each of the filters comprising a plurality of piezoelectric acoustic wave resonators, wherein the piezoelectric acoustic wave resonator includes an inductance to ground, characterized in that:

The multiplexer has at least one capacitive structure, and the two poles of the capacitive structure are respectively connected to the remote ends of two grounding inductances, the two grounding inductances belong to different filters and the two grounding There is mutual inductance between inductors.
The multiplexer according to claim 1, wherein the capacitive structure comprises at least one of the following:

Piezoelectric acoustic resonator;

The plate capacitor in the filter chip;

Interpolated capacitors in the filter chip;

Capacitive structure inside the filter chip;

Capacitive devices outside the filter chip;

Capacitive structure outside the filter chip.
The multiplexer according to claim 1, wherein the distance between the capacitive structure and the ground inductance without mutual inductance in the filter, as well as the distance from the input end and the output end of the filter, are all the same. Above 50um, or both above 200um.
The multiplexer of claim 1, wherein:

A plurality of the filters are fabricated in the same chip;

Alternatively, a plurality of the filters are fabricated in a plurality of chips, and the plurality of chips are arranged in a stacked manner or on the same plane.
The multiplexer of claim 1, wherein:

There are mutual inductances between the first inductance to ground and the second inductance to ground, and between the first inductance to ground and the third inductance to ground in the plurality of parallel filters, wherein the first, second, and third inductances exist. The three-to-ground inductances belong to different filters;

A first capacitive structure is provided between the remote ends of the first and second ground inductances, and a second capacitive structure is provided between the remote ends of the first and third ground inductances.
The multiplexer of claim 1, wherein:

The fourth inductance to ground and the fifth inductance to ground of the first filter in the plurality of parallel filters have mutual inductance with the sixth inductance to ground and the seventh inductance to ground in the second filter respectively;

A third capacitive structure is provided between the remote ends of the fourth and sixth ground inductances, and a fourth capacitive structure is provided between the remote ends of the fifth and seventh ground inductances.
The multiplexer of claim 1, wherein:

The capacitance value of the capacitive structure is 0.01 pF to 10 pF.
The multiplexer according to any one of claims 1 to 6, wherein the ground inductance is a trace in a filter substrate, a bonding wire in a filter, or each pin of a filter chip 's line.
A method for improving isolation of a multiplexer, wherein the multiplexer includes a plurality of parallel filters, each of the filters includes a plurality of piezoelectric acoustic wave resonators, and the piezoelectric acoustic wave resonator includes an inductance to ground , characterized in that the method includes:

A capacitive structure is arranged between the remote ends of two ground inductances with mutual inductance, and the capacitive structure is used to improve the isolation between the two filters in the multiplexer. The two ground inductances belong to the two filters.
A communication device, comprising the multiplexer according to any one of claims 1 to 8.