Bulk acoustic wave filter and out-of-band rejection improvement method thereof
阅读说明：本技术 一种体声波滤波器及其带外抑制改善方法 (Bulk acoustic wave filter and out-of-band rejection improvement method thereof ) 是由 庞慰 徐利军 于 2019-08-30 设计创作，主要内容包括：本发明公开了一种体声波滤波器及其带外抑制改善方法,包括：一条串联支路、多条并联支路及并联谐振电路,串联支路由串联谐振器依次串联组成；并联支路由并联谐振器和电感组成,每个并联支路一端接于两个相邻串联谐振器之间或者串联支路的首末端,另一端通过电感接地；所述并联谐振电路一端接于两个相邻串联谐振器之间或者串联支路的首末端,另一端接地；当该并联谐振电路的谐振频率处于滤波器通带时,相当于开路状态,不影响信号传输,在滤波器通带外高频段,该并联谐振电路相当于电容,该电容对信号传输起到抑制作用,在滤波器通带外低频段,该并联谐振电路相当于电感,该电感会对信号传输起到抑制作用,进而实现体声波滤波器的带外抑制改善。(The invention discloses a bulk acoustic wave filter and an out-of-band rejection improving method thereof, which comprises the following steps: the parallel resonance circuit comprises a series branch, a plurality of parallel branches and a parallel resonance circuit, wherein the series branch is formed by sequentially connecting series resonators in series; the parallel branch consists of parallel resonators and an inductor, one end of each parallel branch is connected between two adjacent series resonators or the head end and the tail end of each series branch, and the other end of each parallel branch is grounded through the inductor; one end of the parallel resonant circuit is connected between two adjacent series resonators or the head end and the tail end of the series branch, and the other end of the parallel resonant circuit is grounded; when the resonance frequency of the parallel resonance circuit is in the passband of the filter, the parallel resonance circuit is equivalent to an open circuit state, signal transmission is not influenced, the parallel resonance circuit is equivalent to a capacitor at a high frequency band outside the passband of the filter, the capacitor plays a role in inhibiting signal transmission, the parallel resonance circuit is equivalent to an inductor at a low frequency band outside the passband of the filter, the inductor can play a role in inhibiting signal transmission, and then the out-of-band inhibition of the bulk acoustic wave filter is improved.)
1. A bulk acoustic wave filter, comprising:
a series branch, a plurality of parallel branches and a parallel resonance circuit,
the series branch is formed by connecting series resonators in series in sequence;
the parallel branch consists of parallel resonators and an inductor, one end of each parallel branch is connected between two adjacent series resonators or the head end and the tail end of each series branch, and the other end of each parallel branch is grounded through the inductor;
one end of the parallel resonant circuit is connected between two adjacent series resonators or the head end and the tail end of the series branch, and the other end of the parallel resonant circuit is grounded.
2. The bulk acoustic wave filter according to claim 1, wherein the number of the parallel resonant circuits is two, and one end of each of the two parallel resonant circuits is connected in parallel between two adjacent series resonators or between the ends of the series arms through a single-pole double-throw switch, and the other end of each of the two parallel resonant circuits is grounded.
3. The bulk acoustic wave filter according to claim 1, wherein the parallel resonant circuit is coupled in parallel to the first ends of the series arms or between the series resonators of the bulk acoustic wave filter.
4. The bulk acoustic wave filter according to claim 1, wherein the parallel resonance circuit is composed of a resonator and an inductor in parallel.
5. The bulk acoustic wave filter according to claim 1, wherein the series branch is formed by four series resonators connected in series in sequence, the parallel branch is formed by five parallel resonators and four inductors, the five parallel resonators are respectively connected in parallel between the first end and the second end of the series branch and each series resonator, wherein the first and second parallel resonators are connected to the same inductor ground, and the remaining parallel resonators are connected to the inductor ground individually.
6. A wireless communication device comprising the bulk acoustic wave filter of any of claims 1-5.
7. A method for improving out-of-band rejection of a bulk acoustic wave filter is characterized by comprising the following steps:
(1) loading the parallel resonators of the bulk acoustic wave resonators with the same mass load, not loading the mass load on the series resonators, and adjusting the parallel resonant frequency of the parallel resonators to be the same as the series resonant frequency of the series resonators;
(2) the mass load is loaded on the resonators in the parallel resonant circuit of the bulk acoustic wave resonator, the mass load is far larger than the mass loads loaded on other parallel resonators, and the resonant frequency of the parallel resonant circuit is adjusted to be just positioned in the passband of the filter.
8. The method according to claim 7, wherein when there are two parallel resonant circuits, the step (2) loads different mass loads to the resonators in the two parallel resonant circuits of the bulk acoustic wave resonator, and the mass loads applied are much larger than the mass loads applied to the other parallel resonators, adjusts the resonant frequency of the parallel resonant circuit to just within the pass band of the filter, and adjusts the out-of-band rejection through the selection of the single-pole double-throw switch.
Technical Field
The invention relates to the field of semiconductors and micro-electro-mechanical systems, in particular to a bulk acoustic wave filter and an out-of-band rejection improving method thereof.
Background
With the rapid development of wireless communication technology, many rf devices are widely used in the communication field, for example, a large number of filters are used in personal mobile terminals such as mobile phones. The filter is mainly used for filtering out unwanted radio frequency signals and improving the performance of a transmitting path or a receiving path. Along with the expansion of communication system services, in addition to higher requirements on the performance of the filter, higher requirements are also put forward on the volume size of the filter.
The bulk acoustic wave filter generates resonance using the piezoelectric effect of the piezoelectric crystal, and since the resonance is generated by a mechanical wave, rather than an electromagnetic wave, as a resonance source, the wavelength of the mechanical wave is much shorter than that of the electromagnetic wave. Therefore, the bulk acoustic wave resonator and the filter formed by the bulk acoustic wave resonator are greatly reduced in size compared with the conventional electromagnetic filter. On the other hand, since the crystal 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 the complicated design requirements such as a steep transition zone, low insertion loss and the like can be met. Due to the characteristics of small size, high roll-off, low insertion loss and the like of the bulk acoustic wave filter, the filter taking the bulk acoustic wave filter as the core is widely applied to communication systems.
At present, a communication system develops towards a multi-band, multi-system and multi-mode direction, the used frequency bands are more and more dense, in order to improve the communication quality and reduce the interference between the frequency bands, a higher requirement is bound to be put forward on the out-of-band rejection of a filter, the prior art generally adopts the increase of the number of stages of the filter to improve the out-of-band rejection, but the defect brought by the increase of the number of stages of the filter is that more loss is introduced and the in-band insertion loss is deteriorated.
Therefore, how to improve the out-of-band rejection of the bulk acoustic wave filter is a technical problem that needs to be solved by those skilled in the art.
Disclosure of Invention
In view of this, the present invention provides a bulk acoustic wave filter, which improves the out-of-band rejection of the bulk acoustic wave filter by connecting a parallel resonant circuit in parallel with the parallel branch of the bulk acoustic wave filter.
To achieve the above object, according to one aspect of the present invention, there is provided a bulk acoustic wave filter including:
a series branch, a plurality of parallel branches and a parallel resonance circuit,
the series branch is formed by connecting series resonators in series in sequence;
the parallel branch consists of parallel resonators and an inductor, one end of each parallel branch is connected between two adjacent series resonators or the head end and the tail end of each series branch, and the other end of each parallel branch is grounded through the inductor;
one end of the parallel resonant circuit is connected between two adjacent series resonators or the head end and the tail end of the series branch, and the other end of the parallel resonant circuit is grounded.
With reference to the first aspect and the foregoing implementation manner, in a first possible implementation manner of the first aspect, there are two parallel resonant circuits, one end of each of the two parallel resonant circuits is connected in parallel between two adjacent series resonators or between the head and the tail of a series branch through a single-pole double-throw switch, and the other end of each of the two parallel resonant circuits is grounded.
With reference to the first aspect and the foregoing implementation manner of the first aspect, in a second possible implementation manner of the first aspect, the parallel resonant circuit is coupled in parallel between the first end and the second end of the series branch of the bulk acoustic wave filter or the series resonator.
With reference to the first aspect and the foregoing implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the parallel resonant circuit is formed by connecting a resonator and an inductor in parallel.
With reference to the first aspect and the foregoing implementation manner, in a fourth possible implementation manner of the first aspect, the series branch is formed by sequentially connecting four series resonators in series, the parallel branch is formed by five parallel resonators and four inductors, the five parallel resonators are respectively connected in parallel between the head end and the tail end of the series branch and each series resonator, the first and second parallel resonators are connected to the same inductor and grounded, and the remaining parallel resonators are connected to the inductor and grounded separately.
In a second aspect, a method for improving out-of-band rejection of a bulk acoustic wave filter is provided, which includes the following steps:
(1) loading the parallel resonators of the bulk acoustic wave resonators with the same mass load, not loading the mass load on the series resonators, and adjusting the parallel resonant frequency of the parallel resonators to be the same as the series resonant frequency of the series resonators;
(2) the mass load is loaded on the resonators in the parallel resonant circuit of the bulk acoustic wave resonator, the mass load is far larger than the mass loads loaded on other parallel resonators, and the resonant frequency of the parallel resonant circuit is adjusted to be just positioned in the passband of the filter.
When the resonance frequency of the parallel resonance circuit is in the passband of the filter, the parallel resonance circuit is equivalent to an open circuit state and does not influence the transmission of signals, and the parallel resonance circuit is equivalent to a capacitor at a high frequency band outside the passband of the filter, and the capacitor can inhibit the transmission of high frequency signals.
With reference to the second aspect and the foregoing implementation manner, in a first possible implementation manner of the first aspect, when there are two parallel resonant circuits, the step (2) loads different mass loads to resonators in the two parallel resonant circuits of the bulk acoustic wave resonator, where the mass loads are much larger than mass loads applied to other parallel resonators, adjusts a resonant frequency of the parallel resonant circuit to be just within a pass band of the filter, and adjusts out-of-band rejection through selection of the single-pole double-throw switch.
In a third aspect, a wireless communication device is provided that includes the bulk acoustic wave filter.
Therefore, the bulk acoustic wave filter provided by the application can be designed by connecting a parallel resonance circuit in parallel with a parallel branch of the bulk acoustic wave filter, when the resonance frequency of the parallel resonance circuit is in the pass band of the filter, the parallel resonance circuit is equivalent to an open circuit state and does not influence the transmission of signals, the high frequency band outside the pass band of the filter is equivalent to a capacitor, the capacitor can inhibit the signal transmission, and similarly, the low frequency band outside the pass band of the filter is equivalent to an inductor, the inductor can inhibit the signal transmission, and the out-of-band inhibition of the bulk acoustic wave filter is improved.
Drawings
For purposes of illustration and not limitation, the present invention will now be described in accordance with its preferred embodiments, particularly with reference to the accompanying drawings, in which:
fig. 1 is a schematic structural diagram of a conventional bulk acoustic wave filter provided in a comparative example of the present application.
Fig. 2 is a schematic structural diagram of a bulk acoustic wave filter provided in
Fig. 3 is a comparison graph of the characteristic curves on the left side of the pass band of the bulk acoustic wave filter of the present application in comparison with that of example 1.
Fig. 4 is a comparison of the passband middle characteristic curves of the bulk acoustic wave filter of the present application in comparison to example 1.
Fig. 5 is a comparison of the right-hand characteristic curves of the passbands of the bulk acoustic wave filters of the present application in comparison with example 1.
Fig. 6 is a schematic structural diagram of a bulk acoustic wave filter provided in
Fig. 7 is a schematic structural diagram of a bulk acoustic wave filter provided in
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be understood that the description of first and second is merely for the purpose of referring to and distinguishing between different signals, instructions, etc., and the first and second are not limited by the order of priority.
Comparative example
Fig. 1 shows a schematic structural diagram of a conventional bulk acoustic wave filter, as shown in fig. 1, the bulk acoustic wave filter includes a series branch and a plurality of parallel branches, the series branch is formed by sequentially connecting a plurality of series bulk acoustic wave resonators in series, each parallel branch is formed by a parallel resonator and an inductor, one end of each parallel branch is connected between two adjacent series resonators or between the head and the tail of the series branch, and the other end of each parallel branch is grounded through the inductor.
Specifically, in fig. 1, the existing bulk acoustic wave filter topology is a 4-5 ladder structure, and mainly includes 4 series resonators, 5 parallel resonators, and 4 inductors. The series resonator comprises S11, S12, S13 and S14, the parallel resonator comprises P11, P12, P13, P14 and P15, and the inductor comprises L11, L12, L13 and L14. The series resonators S11, S12, S13 and S14 are connected in series in sequence to form a series branch, and the first end and the last end of the series branch are connected to the
The parallel resonators P11, P12, P13, P14 and P15 of the filter need to be loaded with mass loads, so that the parallel resonance frequency of the parallel resonators is close to the series resonance frequency of the series resonators S11, S12, S13 and S14, thereby forming a band-pass filter, and the inductors L11, L12, L13 and L14 play a role in controlling the transmission zero of the filter, thereby influencing out-of-band rejection. Because the inductance added in the prior art is limited, the influence range on the out-of-band rejection is limited, if the out-of-band rejection needs to be further improved, the number of stages is generally increased, and the insertion loss is further deteriorated. There is therefore a need for a new bulk acoustic wave filter that further improves out-of-band rejection with little impact on insertion loss.
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