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WO2021028273A1 - Cascade de résonateurs à ondes acoustiques de volume - Google Patents

Cascade de résonateurs à ondes acoustiques de volume Download PDF

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Publication number
WO2021028273A1
WO2021028273A1 PCT/EP2020/071933 EP2020071933W WO2021028273A1 WO 2021028273 A1 WO2021028273 A1 WO 2021028273A1 EP 2020071933 W EP2020071933 W EP 2020071933W WO 2021028273 A1 WO2021028273 A1 WO 2021028273A1
Authority
WO
WIPO (PCT)
Prior art keywords
resonator
resonators
filter circuit
saw
cascade
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/EP2020/071933
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English (en)
Inventor
Matthias PERNPEINTNER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
RF360 Europe GmbH
Original Assignee
RF360 Europe GmbH
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Filing date
Publication date
Application filed by RF360 Europe GmbH filed Critical RF360 Europe GmbH
Publication of WO2021028273A1 publication Critical patent/WO2021028273A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H03H9/6423—Means for obtaining a particular transfer characteristic
    • H03H9/6433—Coupled resonator filters
    • H03H9/644—Coupled resonator filters having two acoustic tracks
    • H03H9/6456—Coupled resonator filters having two acoustic tracks being electrically coupled
    • H03H9/6469—Coupled resonator filters having two acoustic tracks being electrically coupled via two connecting electrodes
    • H03H9/6473—Coupled resonator filters having two acoustic tracks being electrically coupled via two connecting electrodes the electrodes being electrically interconnected
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14544—Transducers of particular shape or position
    • H03H9/14591—Vertically-split transducers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H03H9/6423—Means for obtaining a particular transfer characteristic
    • H03H9/6433—Coupled resonator filters
    • H03H9/644—Coupled resonator filters having two acoustic tracks
    • H03H9/6456—Coupled resonator filters having two acoustic tracks being electrically coupled
    • H03H9/6459—Coupled resonator filters having two acoustic tracks being electrically coupled via one connecting electrode
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H03H9/6423—Means for obtaining a particular transfer characteristic
    • H03H9/6433—Coupled resonator filters
    • H03H9/644—Coupled resonator filters having two acoustic tracks
    • H03H9/6456—Coupled resonator filters having two acoustic tracks being electrically coupled
    • H03H9/6459—Coupled resonator filters having two acoustic tracks being electrically coupled via one connecting electrode
    • H03H9/6463—Coupled resonator filters having two acoustic tracks being electrically coupled via one connecting electrode the tracks being electrically cascaded
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H03H9/6423—Means for obtaining a particular transfer characteristic
    • H03H9/6433—Coupled resonator filters
    • H03H9/644—Coupled resonator filters having two acoustic tracks
    • H03H9/6456—Coupled resonator filters having two acoustic tracks being electrically coupled
    • H03H9/6469—Coupled resonator filters having two acoustic tracks being electrically coupled via two connecting electrodes
    • H03H9/6476—Coupled resonator filters having two acoustic tracks being electrically coupled via two connecting electrodes the tracks being electrically parallel

Definitions

  • the invention relates to filter circuits comprising cascaded SAW resonators that are modified to improve spurious modes and other parameters of the filter performance.
  • SAW resonators are used to form filter circuits, e.g. by circuiting same in a ladder type or lattice type arrangement. Further, SAW resonators may be part of a filter circuits realized in a technology other than ladder type or even other than SAW to function as a single element improving selectivity or forming additional poles in the transfer characteristic of the filter circuit.
  • main SAW mode typically a Rayleigh or SH-like mode
  • spurious resonances are present in SAW resonators. These spurious resonances can be due to e.g. transversal modes, differently polarized modes, volume modes or other unwanted modes.
  • a filter circuit comprises a first SAW resonator having a first aperture and a second SAW resonator having a second aperture. Both SAW resonators are connected in series or in parallel. First and second aperture are set at different values. It is preferred that the aperture differ by at least 5% in value. With such a modification it is possible to reduce the effects of unwanted transversal modes that are produced by a single SAW resonator.
  • cascaded resonators In this context and in the following two resonators circuited in series or in parallel are called cascaded resonators and form a circuit element that is called a resonator cascade.
  • a cascade can replace one or more SAW resonators in any filter circuit.
  • some design modification e.g. increasing the resonator area may be necessary in order to adapt the static capacitance that is reduced in a series circuit of resonators when compared with a single resonator.
  • cascades can reduce the effects of spurious modes on the filter performance.
  • cascades can improve insertion attenuation, skirt steepness, group delay ripple, compression and power durability of SAW filters as well as their sensitivity to fabrication tolerances.
  • resonator cascades are widely employed for improving power durability, compression and linearity as well as reducing the static capacitance and balancing impedance levels.
  • Cascades can comprise series and parallel connected resonators. Usually, within a cascade the individual resonators are equal to allow a perfect superposition of their admittances.
  • the proposed cascade of two or more resonators maybe particular advantageous in cases where a full suppression of transversal or other spurious modes in a filter circuit cannot be achieved by simple design measures due to fabrication tolerances, design restrictions or other competing design targets.
  • the resonance frequency of some spurious modes depends on the aperture of the resonator.
  • a cascade of two or more resonators with different apertures allows to spread unwanted features in the resonators' admittances over different frequencies and in this way reduce the effect of these unwanted resonances on the admittance of the full cascade.
  • the aperture of a SAW resonator By changing the aperture of a SAW resonator the frequency of each higher mode is shifted by a specific amount. A shift by a larger amount is achieved for spurious modes having a respective increased frequency.
  • Each of first and second SAW resonator as well as any other higher numbered SAW resonator in the cascade comprises just one IDT arranged in an acoustic track between two reflectors.
  • a filter circuit may comprise a ladder type or lattice type structure of reactance elements.
  • One or more of these reactance elements may be replaced by a SAW resonator cascade of two or more SAW resonators having two, three or more different apertures.
  • first, second and optionally any higher numbered SAW resonators can be directly connected in series to each other to represent together a single cascaded resonator.
  • Some of the series connected resonators itself may represent a parallel circuit of two or more single resonators.
  • a cascade results having two or more “stages” where every stage comprises one single resonator or a circuit of two or more single resonators circuited in parallel.
  • a first and a second resonator or optionally more resonators having different apertures and being circuited in parallel can form a cascade having a single stage only and can provide the already mentioned advantage of spreading the resonance frequencies of spurious modes.
  • a difference of at least 5% between the highest and lowest aperture of the SAW resonators is preferred.
  • greater differences of 10%, 20% or more are possible too and may provide further advantage.
  • the aperture of two resonators that are directly subsequent in the cascade may differ by a smaller amount if the difference between highest and lowest aperture is high enough to achieve the desired suppression of spurious modes.
  • the values of apertures are evenly distributed over the total range of aperture values. This includes the optional provision that each aperture value is present in a cascade only once.
  • the aperture values are symmetrically distributed around a mean aperture.
  • the filter circuit maybe designed as a band pass.
  • the filter circuit maybe a low pass or a high pass.
  • a notch filter is another possible embodiment as in all these filter circuits suppression of spurious modes is possible with a cascade of at least two SAW resonators having different aperture each.
  • a preferred use of the filter circuit is use as a Tx filter.
  • a preferred application of the proposed cascade is a filter circuit working at high frequencies e.g. in a band with a frequency of about 2.3GHz and more.
  • the proposed cascaded SAW resonators may replace a reactance element of a known filter circuit e.g. a ladder type filter. However it is possible to add such a resonator cascade to any other filter circuit as a parallel of series element. If a known filter circuit comprises already cascaded SAW resonators the implementation of the new cascade can be done without any design adaption necessary. If a known filter circuit comprises single SAW resonators only that are prone to produce spurious modes the filter topography need to be adapted in case of series cascaded resonators only because replacing single SAW resonators by a series resonator cascade requires a multiple of chip area when compared to a single non-cascaded resonator. However, if the performance of the filter circuit can be sufficiently improved by introducing the new cascade the enhanced area requirement will be overcompensated and need not be a real disadvantage anymore.
  • a known filter circuit already comprising cascaded or non-cascaded resonators it is preferable to replace those resonators or resonator cascade by the new cascade which are producing spurious modes at critical frequencies e.g. at or near a band edge.
  • those resonators or resonator cascade are producing spurious modes at critical frequencies e.g. at or near a band edge.
  • the series resonator having the lowest frequency is prone to produce a spurious mode close to the upper band edge.
  • the new resonator cascade can be designed like a known cascade.
  • the direct series connection of two adjacent SAW resonators or of their IDTs respectively is realized by combining the two adjacent bus bars of the resonators to form a common busbar shared by the two resonators.
  • Figure 2 shows a ladder type structure of resonators including a first and a second SAW resonator according to an embodiment
  • Figure 3 shows a lattice type structure of resonators including a first and a second SAW resonator according to an embodiment
  • Figure 4 shows a structure of a filter circuit including a first and a second SAW resonator according to an embodiment
  • Figure 5 shows a hybrid filter circuit including a first and a second SAW resonator and an LC filter according to an embodiment
  • Figure 6 shows a series circuit of a first, a second and a third SAW resonator having different apertures
  • Figure 7 shows calculated admittance of a series circuit of a first, a second and a third SAW resonator having different apertures
  • Figure 8 shows a first and a second SAW resonator having different apertures circuited in parallel according to a second general embodiment.
  • Figure 1 shows a cascade of a first and a second SAW resonator Ri, R2 having different apertures APi, AP2 circuited in series according to a first general embodiment of the invention.
  • a block diagram of the two resonators is shown.
  • the second resonator R2 is depicted enlarged in view of the first resonator Ri.
  • a schematic finger structure of the series cascades resonators is shown.
  • Each of the two resonators comprises an IDT (interdigital transducer) arranged between two reflectors REF in an acoustic path.
  • IDT interdigital transducer
  • Figure 2 shows a filter circuit comprising a ladder type structure of reactance elements that are depicted as resonators RS, RP for simplicity reasons. Some of the reactance elements may be realized as coils or capacitors. At least one of the reactance elements includes a cascade of a first and a second SAW resonator having different apertures AP according to the embodiment of Figure 1. These two SAW resonators form a cascaded resonator.
  • Such a cascaded resonator - if it comprises series connected resonators - needs to be adapted in size according to the design rules of a ladder type filter circuit to set correct static capacities of the resonators including the cascaded resonator. If the cascaded resonators Ri, R2 are circuited in parallel according to Figure 8 no adaption in design of the filter is necessary.
  • the ladder type structure is formed as usual and comprises a number of at least one basic sections each comprising a series resonator RS in a series arm formed between a first and a second terminal Ti, T2 and a parallel branch connected to ground with a parallel resonator RP arranged therein.
  • the number of basic sections BSLT can be increased in the filter circuit if higher selection of the filter circuit is required.
  • the number of resonators that are cascaded can be set arbitrarily. But each of the cascaded resonators is formed according to the first embodiment. Hence it is sufficient to replace each cascaded resonator of a known ladder type structure of resonators according to the art by a cascade of resonators according to the invention.
  • the number of resonators in the cascade is at least two but may be set to a higher number.
  • each of the resonators in the cascade has a different aperture.
  • FIG. 3 shows a filter circuit comprising a lattice type structure of reactance elements usually formed by series and parallel resonators RS, RP.
  • a lattice type structure comprises basic sections BSLC each comprising series and parallel resonators.
  • the parallel resonators arranged in parallel branches connect two series lines circuited in parallel.
  • the parallel branches are crossing to form a kind of a twisted ladder.
  • Figure 4 shows a filter circuit comprising a first filter element Ft and connected in series thereto a series resonator RS.
  • a parallel resonator RP is circuited in a parallel arm connected to ground.
  • the first filter Ft is a filter circuit realized in an arbitrary technique.
  • the first filter may be a DMS filter for example, an LC filter formed from passive L and C elements (inductances and capacitances) or any other filter circuit.
  • At least one of the parallel resonator RP or series resonator RS comprises a cascade of resonators according to the invention. If the first filter comprises further resonators, these too may be formed form such cascades.
  • Figure 5 shows as an example a schematic hybrid filter with a series impedance element IES formed as a capacitor for example and a parallel impedance element IEP formed as an inductor for example.
  • a basic section BS of a ladder type structure is circuited in series thereto and comprise a series resonator RS and a parallel resonator RP.
  • At least one of the parallel resonator RP or series resonator RS comprises a cascade of resonators according to the invention.
  • the filter circuit of Figure 5 may comprise a higher number of LC units or basic sections of a ladder type structure.
  • Figure 6 shows a cascade of three series-connected SAW resonators Ri, R2 and R3 according to an embodiment where each aperture AP of a resonator RS, RP is different from the two others.
  • the aperture increases from the first aperture APi assigned to the first resonator in the cascade to the second and the third aperture AP3 such that APi ⁇ AP2 ⁇ AP3.
  • these three resonators comprise bus bars that are commonly owned and hence shared by the two adjacent IDTs of two adjacent resonators.
  • a cascade according to the second general embodiment may comprise three resonators circuited in parallel and having a different aperture each (not shown in the figures).
  • Figure 7 shows calculated admittance for a cascade of three resonators having the same design and pitch but different apertures compared with admittances of respective single resonators with three different apertures.
  • the upper diagram shows the real part of admittance and the lower diagram depicts the respective magnitude.
  • the three thin lines 1, 2 and 3 are assigned to admittances of resonators having different apertures.
  • Line 2 accords to a resonator having a target aperture.
  • Line 1 accords to a resonator having an aperture that is 10% higher than target aperture according to line 2.
  • Line 3 accords to a resonator having an aperture that is 10% lower than target aperture according to line 2.
  • Bold line C accords to the aperture of the cascade of the three single resonators. All resonators are normalized to the same static capacitance as the resonator with target aperture according to line 2. For better visibility the lines 1 and 3 are depicted offset to lines 2 and C. The same is true for the lower diagram.
  • Figure 8 shows a first and a second SAW resonator Ri, R2 having different apertures APi, AP2 circuited in parallel according to a second general embodiment of the invention.
  • a block diagram of the two resonators is shown with the second resonator depicted enlarged in view of the first resonator along a transversal direction that is the direction normal to the propagation direction.
  • a schematic finger structure is shown at the bottom part of Figure 8 .
  • Each of the two resonators comprises an IDT (interdigital transducer) arranged between two reflectors REF in an acoustic path.
  • the two resonators Ri, R2 use a common middle reflector that is common to the two resonators.
  • each resonator may have two reflectors that are not shared by two adjacent resonators.
  • two parallel cascaded resonators need not be arranged directly adjacent to each other. Cascading uses only advantages that result from electrically circuiting two resonators with different apertures. Not shown are embodiment comprising series and parallel cascaded resonators forming a single cascade that can replace a single resonator in an arbitrary filter circuit.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Abstract

La présente invention concerne des cascades de résonateurs SAW avec différentes ouvertures qui peuvent réduire les effets de modes transverses indésirables et d'autres modes parasites du résonateur SAW. En tant que partie de circuits de filtre, des cascades de résonateurs SAW ont le potentiel d'améliorer l'atténuation d'insertion, la raideur de jupe, l'ondulation de retard de groupe, la compression et la durabilité de puissance de filtres SAW ainsi que leur sensibilité à des tolérances de fabrication.
PCT/EP2020/071933 2019-08-14 2020-08-04 Cascade de résonateurs à ondes acoustiques de volume Ceased WO2021028273A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102019121866.7 2019-08-14
DE102019121866.7A DE102019121866A1 (de) 2019-08-14 2019-08-14 SAW-Resonator-Kaskade

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WO2021028273A1 true WO2021028273A1 (fr) 2021-02-18

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020021194A1 (en) * 2000-06-30 2002-02-21 Hiroaki Maehara Surface acoustic wave filter
US20080258983A1 (en) * 2005-10-28 2008-10-23 Thomas Bauer Saw Filter Comprising a Broadband Band-Stop Filter
WO2009060594A1 (fr) * 2007-11-06 2009-05-14 Panasonic Corporation Résonateur à ondes élastiques, filtre à ondes élastiques et dispositif de partage d'antenne utilisant ces éléments
US20100060103A1 (en) * 2006-11-08 2010-03-11 Yosuke Hamaoka Surface acoustic wave resonator

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010046794B4 (de) * 2010-09-28 2015-07-16 Epcos Ag Mit akustischen Wellen arbeitendes Filter mit verringerten Nichtlinearitäten
US10097158B2 (en) * 2014-10-16 2018-10-09 Taiyo Yuden Co., Ltd. Acoustic wave device, filter, and duplexer
JP6656135B2 (ja) * 2016-10-21 2020-03-04 太陽誘電株式会社 フィルタおよびマルチプレクサ

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020021194A1 (en) * 2000-06-30 2002-02-21 Hiroaki Maehara Surface acoustic wave filter
US20080258983A1 (en) * 2005-10-28 2008-10-23 Thomas Bauer Saw Filter Comprising a Broadband Band-Stop Filter
US20100060103A1 (en) * 2006-11-08 2010-03-11 Yosuke Hamaoka Surface acoustic wave resonator
WO2009060594A1 (fr) * 2007-11-06 2009-05-14 Panasonic Corporation Résonateur à ondes élastiques, filtre à ondes élastiques et dispositif de partage d'antenne utilisant ces éléments

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DE102019121866A1 (de) 2021-02-18

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