HK1172161B

HK1172161B - A device and method for cascading filters of different materials

Info

Publication number: HK1172161B
Application number: HK12112718.2A
Authority: HK
Inventors: Chun-Yun Jian
Original assignee: 苹果公司
Priority date: 2009-04-15
Filing date: 2010-04-13
Publication date: 2015-10-02

Description

Apparatus and method for cascading filters of different materials

Technical Field

The invention relates to cascading multiple filters.

Background

There is a strong need for compact filters with improved performance over the current level in the telecommunications market, particularly in the field of 4G wireless communication systems and in existing wireless systems. Since 4G systems are targeted for very high speed data transfer, they require much wider bandwidth than existing systems such as GSM, CDMA and UMTS. On the other hand, the limited frequency resources in 4G systems require wireless operator companies to set as narrow a guard band as possible to achieve maximum user capacity. Combining these two problems means that 4G wireless systems require the use of small RF filters with not only wide bandpass or stopband but also steep transition bands for their wireless terminal devices.

RF filters based on acoustic materials, such as Surface Acoustic Wave (SAW), thin Film Bulk Acoustic Resonator (FBAR), and/or Bulk Acoustic Wave (BAW) filters, are widely used in compact and portable terminal devices for various wireless systems due to their small size and low cost. However the current filter performance levels of these filters are still far from the 4G wireless system filter requirements.

Some non-acoustic microwave technology type filters (such as metal type cavity filters or dielectric filters) can be designed to meet the filter performance requirements for these applications, but these types of designs are very costly and result in physically large filters. Metallic cavity filters and dielectric filters are thus undesirable, particularly for applications in wireless terminals where size and weight are important.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a filter comprising: at least one first filter, each first filter being a band-stop type filter having a first set of filter parameters that are a function of a first material used to fabricate the respective first filter; at least one second filter, each second filter having a second set of filter parameters that are a function of a second material used to fabricate the respective second filter, each second filter being one of: a band-stop filter; and a bandpass filter; wherein at least one of the at least one first filter and at least one of the at least one second filter are cascaded together; wherein the first material and the second material are different materials; and wherein the filter has a third set of filter parameters that is a function of the first material and the second material.

In some embodiments, each first filter is a narrow band stop type filter having at least one stop band in the filter response, each stop band having a steep transition band relative to the transition band of each second filter.

In some embodiments, the first material has a smaller magnitude (magnitude) temperature coefficient than the second material, such that each first filter has less temperature-dependent frequency drift than each second filter.

In some embodiments, each second filter is one of the following filters: a wide band pass filter; and a wideband band-stop type filter.

In some embodiments, the second material has a higher electro-mechanical (electro-mechanical) coupling coefficient than the first material.

In some embodiments, each first filter has one of: a first stop band disposed at a low side edge of the pass band of one of the at least one second filter; a first stop band arranged at a low side edge of the stop band of one of the at least one second filter; a first stop band arranged at a high side edge of the pass band of one of the at least one second filter; a first stop band arranged at a high side edge of the stop band of one of the at least one second filter; two stop bands, a first stop band of the two stop bands being arranged at a low-side edge of the pass band of one of the at least one second filter, and a second stop band of the two stop bands being arranged at a high-side edge of the pass band of one of the at least one second filter; and two stop bands, a first stop band of the two stop bands being arranged at a low side edge of the stop band of one of the at least one second filter, and a second stop band of the two stop bands being arranged at a high side edge of the stop band of one of the at least one second filter.

In some embodiments, each first filter is made using any one of the following: surface Acoustic Wave (SAW) technology; film Bulk Acoustic Resonator (FBAR) technology; and Bulk Acoustic Wave (BAW) filter technology; and each second filter is made using any one of the following: SAW technology; FBAR technology; and BAW filter technology.

In some embodiments, the first material comprises at least one of: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a AlN; and combinations thereof.

In some embodiments, the second material comprises at least one of: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a ZnO; AlN; and combinations thereof.

In some embodiments, a first filter of the at least one first filter and a second filter of the at least one second filter are cascaded together in the package using at least one of: a link electrically connecting the first filter and the second filter directly; and a shared connection point within the package to which the first filter and the second filter are electrically connected.

In some embodiments, the filter further comprises at least one of: a circuit matching element for matching at least one of an input to the filter and an output from the filter; a circuit matching element for matching a first filter of the at least one first filter; a circuit matching element for matching a second filter of the at least one second filter; and a circuit matching element for matching a point in the filters at which a first filter of the at least one first filter and a second filter of the at least one second filter are cascaded together.

According to a second aspect of the present invention, there is provided a method for making a filter, the method comprising: cascading at least one first filter with at least one second filter, each first filter being a band stop type filter having a first set of filter parameters that are a function of a first material used to fabricate the respective first filter, each second filter having a second set of filter parameters that are a function of a second material used to fabricate the respective second filter, each second filter being one of: a band-stop filter; and a bandpass filter; wherein the first material and the second material are different materials; and wherein the filter has a third set of filter parameters that are a function of both the first material and the second material.

In some embodiments, cascading the at least one first filter and the at least one second filter comprises: cascading a first filter of the at least one first filter and a second filter of the at least one second filter, the first filter being a narrow band stop-band type filter having at least one stop band in filter response, each stop band having a sharp transition band relative to a transition band of each of the at least one second filter.

In some embodiments, the first material has a smaller magnitude temperature coefficient than the second material such that each of the at least one first filter has less temperature dependent frequency drift than each of the at least one second filter.

In some embodiments, cascading the at least one first filter and the at least one second filter comprises: cascading a first filter of the at least one first filter with a second filter of the at least one second filter, the second filter being: a wide band pass filter; and a wideband band-stop type filter.

In some embodiments, the second material has a higher electromechanical coupling coefficient than the first material.

In some embodiments, cascading the at least one first filter and the at least one second filter comprises: cascading a first filter of the at least one first filter and a second filter of the at least one second filter, wherein the first filter is made using any one of: surface Acoustic Wave (SAW) technology; film Bulk Acoustic Resonator (FBAR) technology; and Bulk Acoustic Wave (BAW) filter technology; and wherein the second filter is made using any one of: SAW technology; FBAR technology; and BAW filter technology.

In some embodiments, each first filter has one of: a first stop band disposed at a low side edge of the pass band of one of the at least one second filter; a first stop band arranged at a low side edge of the stop band of one of the at least one second filter; a first stop band arranged at a high side edge of the pass band of one of the at least one second filter; a first stop band arranged at a high side edge of the stop band of one of the at least one second filter; two stop bands, a first stop band of the two stop bands being arranged at a low-side edge of the pass band of one of the at least one second filter, and a second stop band of the two stop bands being arranged at a high-side edge of the pass band of one of the at least one second filter; and two stop bands, a first stop band of the two stop bands being arranged at a low-side edge of the stop band of one of the at least one second filter, and a second stop band of the two stop bands being arranged at a high-side edge of one of the stop bands of the at least one second filter.

In some embodiments, cascading the at least one first filter and the at least one second filter comprises: cascading a first filter of the at least one first filter and a second filter of the at least one second filter, wherein the first material is used to makeA first filter, the first material comprising at least one of: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a AlN; and combinations thereof.

In some embodiments, cascading the at least one first filter and the at least one second filter comprises: cascading a first filter of the at least one first filter and a second filter of the at least one second filter, wherein the second filter is fabricated using a second material comprising at least one of: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a ZnO; AlN; and combinations thereof.

In some embodiments, cascading the at least one first filter and the at least one second filter comprises: cascading together a first filter of the at least one first filter and a second filter of the at least one second filter in the package using at least one of: a link electrically connecting the first filter and the second filter directly; and a shared connection point to which the first filter and the second filter are electrically connected.

In some embodiments, cascading the at least one first filter and the at least one second filter comprises: circuit matching at least one of an input to the device and an output from the filter; the circuit matches a first filter of the at least one first filter; the circuit matches a second filter of the at least one second filter; and the circuit matches a point in the filters at which a first filter of the at least one first filter and a second filter of the at least one second filter are cascaded together.

According to a third aspect of the invention, there is provided a method for filtering a signal, the method comprising: providing a signal to an input of a first filter, the first filter being a band stop type filter having a first set of filter parameters, the first set of filter parameters being a function of a first material used to fabricate the first filter; filtering the signal using a first filter, thereby producing an output of the first filter; providing the output of the first filter to a second filter, the second filter having a second set of filter parameters, the second set of filter parameters being a function of a second material used to fabricate the second filter, the second filter being one of a band stop filter and a band pass filter; filtering the output of the first filter using a second filter, thereby producing an output of the second filter; wherein the first material and the second material are different materials; and wherein the combination of the first filter and the second filter has a third set of filter parameters that are a function of both the first material and the second material.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Drawings

Embodiments of the invention will now be described with reference to the following drawings:

FIG. 1A is a graphical depiction of a pair of broadband bandpass filter responses for a high temperature response and a low temperature response;

FIG. 1B is a graphical depiction of a broadband group filter response pair for a high temperature response and a low temperature response;

FIG. 2A is a graphical depiction of a narrow band bandpass filter response pair for a high temperature response and a low temperature response;

FIG. 2B is a graphical depiction of a narrow band rejection filter response pair for a high temperature response and a low temperature response;

FIG. 3 is a block diagram of two filters cascaded in series according to some embodiments of the invention;

FIGS. 4A through 4E are graphical depictions of the filter responses of individual filters and the passband filter responses of filters cascading the individual filters according to some embodiments of the invention;

FIGS. 5A through 5C are graphical depictions of the filter responses of individual filters and the passband filter responses of filters cascading the individual filters according to some embodiments of the invention;

FIGS. 6A through 6C are graphical depictions of the filter response of individual filters and the band-stop filter response of filters cascading the individual filters according to some embodiments of the invention;

FIGS. 7A through 7C are graphical depictions of the filter response of individual filters and the band-stop filter response of filters cascading the individual filters according to some embodiments of the invention;

FIG. 8 is a block diagram of a cascaded filter and matching network according to some embodiments of the invention;

figure 9A is a schematic diagram of a direct wire bond connection between two cascaded filters in a package according to one embodiment of the present invention;

figure 9B is a schematic diagram of a shared circuit pad electrical connection between two cascaded filters in a package according to one embodiment of the present invention;

FIG. 9C is a schematic diagram of a flip-flop implementation for two cascaded filters according to one embodiment of the present invention;

FIG. 10 is a flow chart of a method for implementing some embodiments of the invention; and is

FIG. 11 is a flow chart of another method for implementing some embodiments of the present invention.

Detailed Description

Due to the desire for miniaturized size and low cost, Surface Acoustic Wave (SAW), thin Film Bulk Acoustic Resonator (FBAR), and/or Bulk Acoustic Wave (BAW) technology filters have become a highly utilized component in compact and portable type terminal devices for various modern wireless communication systems. Band-pass and band-stop filters can be designed using SAW, FBAR and BAW technologies. However, current SAW, BAW and FBAR filter design techniques do not provide filter solutions with further improvements in filter performance, such as steeper transition bands and higher power handling capability. After more than 30 years of SAW filter technology development, 15 years of FBAR filter technology development and 10 years of BAW filter technology development, it can be considered that substantially near maximum filter performance has been achieved for these types of devices. Therefore, unless new materials are implemented, large-scale performance improvements are not possible for single-substrate filters based on existing SAW, FBAR and BAW filter design technologies.

The materials used to make filters with high electromechanical coupling coefficients are suitable for implementing band-stop or band-pass filters with correspondingly wide transition bands and wide stop bands or wide pass bands. However, these materials often have poor temperature stability due to large magnitude temperature coefficients, which causes the frequency response in devices made from these materials to have large temperature-dependent frequency response shifts. Current wideband filters designed using SAW, FBAR and BAW technologies have two particularly troublesome disadvantages: not sufficiently steep transition band bandwidth and large temperature-dependent frequency response drift. Figure 1A illustrates an example of a computer simulation of the response of a bandpass filter for a single substrate material filter that can be fabricated by any one of SAW, FBAR or BAW technologies. The frequency range indicated along the x-axis is from 1.30GHz to 1.55 GHz. The attenuation on the y-axis ranges from 10dB to-100 dB. The first filter response 10 in fig. 1A is the frequency response of a filter operating at a temperature of approximately 85 ℃. The 3dB bandwidth of the first filter response 10 is in the range of approximately 0.080GHz, from 1.370GHz to 1.450 GHz. The second filter response 12 in fig. 1A is the frequency response of the same filter operating at a temperature of approximately-40 c. The 3dB bandwidth of the second filter response 12 is in the range of approximately 0.080GHz, also from 1.380GHz to 1.460 GHz. For each frequency response 10, 12, it can be seen that the transition band on either side of the passband is quite large, e.g., for the filter response 10 in fig. 1A, the 20dB down transition bandwidth is approximately 0.010GHz from 1.360GHz to 1.370GH on the lower side of the passband and approximately 0.010GHz from 1.460GHz to 1.470GHz on the upper side of the passband. The temperature dependent frequency response drift (frequency change when the attenuation values are similar) between the high and low temperature filter responses 10 and 12 is approximately equal to 0.010 GHz.

FIG. 1B illustrates a high temperature band-stop filter response 14 and a low temperature band-stop filter response 16 showing similar frequency response drift with temperature and a similar wide transition band for the filter response illustration of FIG. 1A.

There is little room in the existing SAW, FBAR and BAW design technologies for further improvements in narrowing the transition band bandwidth. Currently, the steepness of the maximum achievable transition band in such filters is limited by the inherent Q-factor of the materials used in the filters. A high Q factor achieves a steep transition band filter characteristic. However, materials with high electromechanical coupling coefficients (which is a material property that enables high bandwidth filter characteristics) generally have lower Q factors than materials with lower electromechanical coupling coefficients. Materials with high electromechanical coupling coefficients also generally have poorer temperature stability. The transition band bandwidth of a wideband filter, such as the filter shown in fig. 1A and 1B, is relatively wide and the filter response varies more significantly over the operating temperature range.

The materials used to make the low temperature coefficient filter are suitable for implementing band stop or band pass filters with low temperature dependent frequency drift. Materials with low temperature coefficients also typically have low coupling coefficients. A low coupling coefficient results in a narrow band filter.

Quartz is one of the most temperature stable substrates in crystal device technology and has a very high Q, but its coupling coefficient is very small, e.g., 0.11% in some SAW implementations. Thus, quartz is suitable for designing a narrow band type filter having a very steep transition band.

Figure 2A illustrates an example of a computer simulation of the response of a bandpass filter for a single substrate material filter that may have been fabricated by any one of SAW, FBAR or BAW technologies. The frequency and attenuation range are similar to fig. 1A discussed above. The first frequency response 20 of the filter in fig. 2A is the frequency response operating at a temperature of approximately 85 ℃. The 3dB bandwidth of the first filter response 20 is in the range of approximately 0.008GHz from 1.442GHz to 1.450 GHz. The second filter response 22 in fig. 2A is the frequency response of the same filter operating at a temperature of approximately-40 c. The 3dB bandwidth of the second filter response 22 is in the range of approximately 0.008GHz from 1.443GHz to 1.451 GHz. The 3dB bandwidth is an approximation 1/10 of the 3dB bandwidth shown in fig. 1 for a device made of a material with a high coupling coefficient. For each of the frequency responses 20, 22, the transition bands on either side of the pass band can be considered to be quite small, particularly with respect to the transition bands of the wideband filter response of fig. 1A. For example, the 20dB down transition bandwidth of the filter response of FIG. 2A is approximately 0.001GHz from 1.442GHz to 1.443GHz on the lower side of the passband and from 1.450GHz to 1.451GHz on the upper side of the passband. The transition band bandwidth is an approximation 1/10 of the transition band bandwidth shown in fig. 1A for a device made of a material with a high coupling coefficient. The temperature dependent frequency response drift (frequency change when the attenuation values are similar) between the filter responses 20 and 22 is approximately equal to 0.002 GHz. This is an approximation 1/5 of the temperature dependent frequency response shift shown in fig. 1A for devices made with higher coupling coefficient materials. Fig. 2B illustrates a band-stop filter response showing a similar frequency response drift with temperature and a similar narrow transition band.

The filter response parameters associated with the examples of fig. 1A, 1B, 2A, and 2B are merely exemplary in nature. The parameters involved in designing a filter for any given application vary from implementation to implementation.

One way to improve the disadvantage of a large temperature-dependent frequency response in SAW filters made of materials with high coupling coefficients is to deposit SiO on top of the material with high coupling coefficient₂A film. SiO 2₂With a temperature coefficient opposite to that of the high coupling coefficient materials used for SAW designs. Thus, SiO₂The thin film compensates for the high temperature coefficient of the material with the high coupling coefficient. However, this process adversely affects the achievable filter performance because of the SiO₂Film reduction of combined SiO-coated₂Thereby reducing the achievable maximum bandwidth of the SAW filter. In addition, since SiO is present₂The film induced mass loading effect reduces the phase velocity of the SAW on the combined substrate, which in the physical implementation of the SAW device corresponds to a reduction in the width of the electrode fingers. For high frequencies (>2 GHz) SAW filter design is undesirable.

In some embodiments of the invention, a filter solution is provided that is suitable for particular types of 1900MHz CDMA and/or 1.5GHz to 2.5GHz WiMAX wireless systems with reduced guard bands. These wireless systems would benefit from high performance filters with low insertion loss, high power handling capability, and narrow transition bands. It is further desirable that filters for such applications be low cost and compact so that they can be used in wireless terminals such as cellular phones, PDA computers with wireless functionality, and the like. Although some particular types of 1900MHz CDMA and/or 1.5GHz to 2.5GHz WiMAX wireless systems with reduced guard bands may benefit from embodiments of the filter solution as described herein, it will be appreciated that embodiments of the invention may be applicable to other communication standards operating in other frequency bands.

In general, for filters made of SAW, FBAR and BAW, a material (K) having a high coupling coefficient is used²>2%) low insertion loss requirement<3 dB) or a wideband band-pass type filter (3% or more). The higher the coupling coefficient of the material usedThe wider the maximum bandwidth of the filter. However, materials with high coupling coefficients typically have a larger magnitude temperature coefficient than materials with lower coupling coefficients. For example 42Y-X LiTaO₃(considered as a material with a high coupling coefficient) has a coupling coefficient K²=4.7% and temperature coefficient-45 ppm/° c. On the other hand, ST-quartz (considered as a material with a low coupling coefficient) has a coupling coefficient K²=0.12% and temperature coefficient at room temperature 0ppm/° c. In general, the frequency drift due to temperature change is larger in a filter made of a material having a high coupling coefficient than in a filter made of a material having a low coupling coefficient. Furthermore, materials with high coupling coefficients typically have a poor Q factor compared to materials with lower coupling coefficients. From 42Y-X LiTaO₃SAW resonators made have a Q ranging from 1000 to 2000, while SAW resonators made of ST quartz may have a Q of 10,000 or more. The difference in Q-factors of resonators made of different materials appears as a difference in the steepness of the transition band of the filter.

Material with low coupling coefficient (K) in contrast to material with high coupling coefficient²<2%) for narrowband type bandpass or bandstop filter designs. These low coupling coefficient material type narrow band pass or band stop filters always have steeper transition bands and less temperature dependent frequency drift than wide band pass or band stop filters of high coupling coefficient material types due to the characteristics of high Q and small temperature coefficient mentioned above. Materials with low coupling coefficients are often used for narrower band type filter designs.

Table 1 below includes a list of different materials (material names) that can be used to fabricate SAW, BAW and FBAR devices, and also specifically defines the type of device (filter type) that the corresponding material can be used to fabricate. Table 1 also includes the acoustic wave velocity (velocity), electromechanical coupling coefficient (K) for each material in the table²) And a temperature coefficient at room temperature (temperature coefficient at room temperature).

Table 1-materials used in SAW, FBAR and BAW devices.

Name of Material	Filter type	Rate (m/s)	Coefficient of coupling (K)²）（%）	Temperature coefficient at room temperature (ppm/. degree. C.)
					ST-quartz	SAW	3150	0.12	0
LST-quartz	SAW	3948	0.11	0
					STW-quartz	SAW	3700 to 5040	0.17 to 0.34	0
48.5Y-26.7X Langasite	SAW	2735	0.31	1.1
					SiO₂ZnO/Diamond	SAW	10,000	1.2	0
SiO₂AlN/Diamond	SAW	11,000	0.65	0
					45X-Z Li₂B₄O₇	SAW	3440	1	0
(-15)Y-75X Li₂B₄O₇	SAW	4120	1.6	1.5
					(-42.7)Y-90X Li₂B₄O₇	SAW	6700	2	6.5
X-112Y LiTaO₃	SAW	3288	0.64	-18
					Y-Z LiTaO₃	SAW	3230	0.66	-35
36 to 42Y-X LiTaO₃	SAW	4200	4.7	-45
					128Y-X LiNbO₃	SAW	3992	5.5	-74
Y-Z LiNbO₃	SAW	3488	4.9	-84
					41Y-X LiNbO₃	SAW	4792	17.2	-78
64Y-X LiNbO₃	SAW	4742	11.3	-79
					ZnO	FBAR	6080	8.5	-60
AlN	FBAR	11300	6.5	-25
					ZnO	BAW	6080	7.5	-48
AlN	BAW	11300	6	-22

In some embodiments, a first type of filter having a lower coupling coefficient and a lower temperature coefficient is fabricated from a first material comprising at least one of the following materials: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a AlN; and combinations thereof.

In some embodiments, the second type of higher coupling coefficient is made of a second material comprising at least one of the following materialsThe filter of (2): quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a ZnO; AlN; and combinations thereof.

There is an overlap in the types of materials that can be used to fabricate filters with different material properties (i.e., high/low coupling coefficient and high/low temperature coefficient). However, as long as the materials used have high and low properties with respect to each other, a cascaded filter with the desired properties can be designed and fabricated. Cascaded filter parameters that may be implemented by selecting materials may include, but are not limited to, the width of the wideband portion of the filter response (for bandpass or bandstop), the amount of temperature-dependent frequency drift of the response, and the steepness of the transition band.

By using SAW, FBAR and/or BAW design techniques, some embodiments of the invention result in cost-effective devices having compact physical size. One aspect of the invention is to cascade at least two filters of SAW, FBAR or BAW design, at least one filter made from a material with a low temperature coefficient (enabling a low temperature dependent frequency drift) and at least one filter made from a material with a large electromechanical coupling coefficient (enabling a broadband (> 3%) pass band or a broadband stop band). The combination of at least two filters whose materials have these different characteristics achieves overall filter performance with filter parameters including a wide band pass band or band stop band, a sharp transition band and a low temperature dependent frequency drift of the overall cascaded frequency filter response.

In some embodiments of the invention, a band-stop filter made of a material having a low temperature coefficient is cascaded with one of a band-stop filter or a bandpass filter made of a material having a high coupling coefficient to implement a wideband filter having an ultra-narrow transition band of the cascaded filter response and a very stable temperature-dependent frequency drift.

In the specific example of a cascaded filter implemented according to one embodiment described herein, the cascaded filter has a very wide pass/stop band (> 3% or >60MHz at 1.93 GHz) and a very sharp transition band (< 0.5% or <10MHz at 1.93 GHz) and a very stable temperature dependent frequency drift (< 360ppm in-40 ℃ to 80 ℃).

Fig. 3 illustrates a block diagram of two filters, filter a and filter B, cascaded together. In some embodiments, filter a is a narrow band filter fabricated using a substrate material having a lower coupling coefficient than the coupling coefficient of the material used to fabricate filter B. The material used to make filter a has a magnitude temperature coefficient that is less than the temperature coefficient of the material used to make filter B, and thus filter a has a temperature-dependent frequency drift that is less than the temperature-dependent frequency drift of filter B. Filter a provides a narrower transition band than that of filter B based on the material properties of the material used to make filter a.

Filter B is a wide band filter made using a substrate material having a coupling coefficient higher than that of the material used to make filter a. Filter B provides a wide pass band or stop band based on the material properties of filter B.

The frequency response of the two cascaded filters, filter a and filter B, provides a wide pass band or wide stop band with a narrow transition band on at least one edge of the wide pass band or wide stop band. In some embodiments, when filter a has a filter response with only a single narrow band stop band, the filter response of cascaded filters a and B has a narrow transition band on only one side of the wide band pass band or stop band (either the high frequency end or the low frequency end depending on the design parameters of filter a). In some embodiments, when filter a has a filter response with at least two narrow stopbands, the filter response of cascaded filters a and B has narrow transition bands on either side of the wideband passband or stopband.

Some embodiments of the present invention provide a novel cascaded FBAR-type band pass or band stop filter having a narrower transition band, improved temperature stability, and also a wide pass band or stop band, as compared to a single-core FBAR-type band stop filter or a single-core FBAR-type band pass filter.

Aluminum nitride (AlN) and zinc oxide (ZnO) films are popular and widely used piezoelectric materials for FBAR type devices. AlN has a temperature coefficient of approximately-25 ppm/deg.C and a coupling coefficient of approximately 6.5%. ZnO has a temperature coefficient of approximately 60 ppm/deg.C and a coupling coefficient of approximately 8.5%. AlN has a better Q factor than ZnO. Using AlN with a larger Q factor than ZnO and better temperature stability than ZnO as the material for making the filter provides a filter with a steep transition band and low temperature-dependent frequency drift. Using ZnO having a higher coupling coefficient than AlN as a material for making a filter provides a filter having a passband of a wider frequency band or a wide band stop band filter. A new FBAR filter with filter parameters including a narrower transition band, a wider pass band or a wider stop band and a lower temperature dependent frequency drift than either of the single-core AlN or ZnO FBAR filters can provide alone is obtained by cascading two FBAR type filters, one of which is a band-stop type filter made using AlN and the other of which is a band-pass type filter or a band-stop type filter made using ZnO. In an alternative implementation, the above mentioned band stop type FBAR filter made of AlN may be replaced with a SAW band stop filter or a BAW band stop filter having filter characteristics such as a steep transition band and a small frequency drift in a temperature range to obtain a new performance band pass or band stop type filter.

In a given filter design, the steepness of the filter transition band, the maximum frequency drift over the operating temperature range, and manufacturing tolerances for specific materials must all be taken into account in order to meet the guard band specifications. In general, single material substrate filters made with high coupling coefficient materials require much wider guard band specifications than narrow band filters of low coupling coefficient materials, where high coupling coefficient materials have wider band response and a greater amount of temperature dependent frequency drift.

In some embodiments, the cascaded filters include at least one first filter, each first filter being a band-stop type filter having a first set of filter parameters that are a function of a first material used to fabricate the at least one first filter. The cascaded filters also include at least one second filter, each second filter having a second set of filter parameters that are a function of a second material used to fabricate the at least one second filter. Each of the second filters is one of a band-stop type filter and a band-pass type filter. At least one first filter and at least one second filter are cascaded together to form a cascaded filter. In some embodiments, the first material and the second material are different materials. The cascaded filter has a third set of filter parameters that are a function of both the first material and the second material.

In some embodiments, the cascaded filter comprises two separate dies made of different materials. In some embodiments, the same filter design technique is used for both filters, but different materials are used for the respective filters. Both filters can be designed and fabricated using, for example, SAW, FBAR or BAW. In some embodiments, different filter designs and fabrication techniques may be used to fabricate different filters, and different materials used for the respective filters. In a first example, a first filter is made using SAW and a second filter is made using FBAR. In a second example, a first filter is fabricated using FBAR and a second filter is fabricated using BAW. In a third example, the first filter is made using SAW and the second filter is made using BAW. In a fourth example, a first filter is made using BAW and a second filter is made using FBAR. Other filter combinations are contemplated based on permutations of different filter designs and fabrication techniques. Since the two cascaded filters can be a hybrid combination of SAW, FBAR and BAW filters, this cascaded filter design has a wide variety of design flexibility.

Regardless of the filter design and fabrication technique used to fabricate each filter, at least one filter of the first filter type is fabricated using a low coupling coefficient material having a low temperature coefficient relative to the material used to fabricate at least one filter of the second filter type to produce a narrow band filter with a sharp transition band and low temperature dependent frequency drift. At least one filter of the second filter type is fabricated using a high coupling coefficient material relative to the material used to fabricate the at least one filter of the first filter type to produce a wide band type filter.

Due to the different properties of the materials of the two filters, a narrow band stop type filter can be used to improve a wide band type filter with the disadvantages of a non-steep transition band and a large temperature dependent frequency drift over the operating temperature range. As long as the narrow band-stop type filter has a sufficiently wide stop band and a sufficiently deep stop level to compensate for the drift of the frequency response of the wide band filter with temperature variations, the frequency responses of the two filters cascaded together will provide a performance that has all the beneficial characteristics of each of the two types of filters, namely: 1) a wide passband or stopband; 2a steep transition band on at least one edge of the wide pass band or stop band; and 3) low temperature dependent frequency drift of the filter response.

In some embodiments, two filters share one package. In some embodiments, the cascaded filter package is smaller than when two filters are packaged separately.

Two individual dies are electrically cascaded through wires and pads inside the package. In some implementations, the two cascaded filters are electrically coupled together via shorting wires and/or circuit pads within the package. In such an implementation, there are almost no additional losses, which enables the overall cascaded filter design to achieve the desired low insertion loss.

In some embodiments, the link directly electrically connects the first filter and the second filter. For example, a stub bond may be used to directly connect one filter to another filter. An example of a stub bond 910 that directly connects filter a and filter B in a package 900 is illustrated in fig. 9A.

In some embodiments, each of the at least one first filter and the at least one second filter is electrically connected to a shared connection point within the package, respectively. In some embodiments, a stub wire bond may connect each filter to a circuit pad located within the package, and create an electrical connection between the filters via the shared circuit pads. An example of a first stub bond 915 connecting filter a to pad 930 and a second stub bond 925 connecting filter B to pad 930 in package 920 is illustrated in fig. 9B.

In some embodiments, flip chip bonding techniques may be used to bond each filter to the package using metal bumps. An example of a die of filter a and a die of filter B connected to package 940 via metal block 950 is illustrated in fig. 9C. Circuit paths within the package between the contact points of the metal block connections may provide electrical connections between the filters.

The above examples are only some of the possible implementations for cascading and packaging multiple die filters. Other packaging approaches are contemplated. In addition, although only two filters are illustrated in the examples of fig. 9A, 9B and 9C, it will be understood that the principles illustrated in these figures may be applied to a multi-filter implementation.

In some embodiments, a multiple filter cascade approach is used to implement filter designs for irregular filter specifications with different guard bandwidths.

In some embodiments, only two filters are cascaded together, but each of the two filters may provide multiple pass bands or stop bands. For example, a first filter fabricated using a first material may provide two narrow-band stop bands with narrow transition bands that are substantially spaced apart by a single wide-band pass-band or equivalent distance of a wide-band stop-band of a second filter fabricated using a second material.

In some embodiments, multiple filters, each with a particular filter response, that collectively provide the desired overall filter response may be cascaded together. For example, a first filter of a first filter type made of a first material may provide a narrow band stop band with a sharp transition band at the lower frequency end of the wide pass band or wide stop band of a second filter type made of a second material. A third filter of the first filter type, made of the first material, may provide a narrow band stop band with a sharp transition band at the upper frequency end of the wide band pass band or the wide band stop band. In some embodiments, the third filter may be fabricated using a third material having properties more similar to the first material than the second material. In such a manner, it may be possible to have transition bands of different steepnesses at the high and low frequency ends of the wideband passband or wideband stopband portion of the filter.

Four different embodiments of the cascaded filter will now be described for different types of filter response characteristics.

Example embodiment #1

A first exemplary embodiment of a wideband pass-band filter cascaded with a narrowband stop-band filter having a stop-band at the higher frequency side of the wideband filter will now be described with respect to fig. 4A to 4E.

Figure 4A illustrates a graphical plot of two filter responses, one filter response 40 showing the high temperature (approximately 85 c) response and one filter response 41 showing the low temperature (approximately-40 c) response of a wideband passband filter. The wide band filter is made of a material having a higher coupling coefficient than the material used to make the narrow band filter. Fig. 4A is substantially the same as fig. 1A.

Figure 4B illustrates a graphical plot of two filter responses, one filter response 42 showing a high temperature response and one filter response 43 showing a low temperature response, of the narrow band stop band filter. The narrow band filter is made of a material having a lower coupling coefficient than the material used to make the wide band filter and a lower temperature coefficient than the material used to make the wide band filter. Fig. 4B is similar to fig. 2B except that the band-stop filter response of fig. 4B lies in the frequency range of 1.450GHz to 1.480 GHz.

Fig. 4C illustrates a graphical plot of the filter response 44 of the resulting cascaded filter at higher temperatures. The frequency range and attenuation range of the plot are the same as fig. 4A and 4B. The 3dB bandwidth of the filter response is in the range of approximately 0.080GHz from 1.370GHz to 1.450 GHz. The transition band on the lower frequency side of the filter response is quite large, e.g., the transition bandwidth is approximately 0.01GHz from 1.36GHz to 1.37GHz at 20 dB. The transition band on the higher frequency side of the filter response is smaller than the lower frequency side, e.g., the transition bandwidth is approximately 0.001GHz from 1.450GHz to 1.451GHz at 20 dB.

Fig. 4D illustrates a graphical plot of the filter response 45 of the resulting cascaded filter at a lower temperature. The frequency range and attenuation range of the plot are the same as fig. 4C. The 3dB bandwidth of the filter response is in the approximate 0.075GHz range from 1.378GHz to 1.453 GHz. The transition band on the lower frequency side of the filter response is quite large, e.g., the 20dB transition bandwidth is approximately 0.010GHz from 1.368GHz to 1.378 GHz. The transition band on the higher frequency side of the filter response is smaller than the lower frequency side, e.g., the 20dB lower transition band is approximately 0.001GHz from 1.453GHz to 1.454 GHz.

Fig. 4E illustrates a graphical plot of two filter responses, one filter response 46 showing a high temperature response and one filter response 47 showing a low temperature response, of the resulting cascaded filter. This is essentially FIGS. 4C and 4D, which overlap each other. In the passband filter response 46. On the lower frequency side of 47, the transition bands are substantially parallel and have a frequency spacing of approximately 0.010GHz for a given attenuation. On the upper frequency side of the passband filter response 46, 47, the transition band is narrower than the lower frequency end and substantially parallel. The high and low temperature responses 46, 47 have a frequency separation of approximately 0.003GHz for a given attenuation. Thus, the higher frequency side transition band of the pass band has approximately 2/3 less temperature dependent frequency drift than the lower frequency side transition band of the pass band.

In some embodiments, when designing an appropriate transition band for a filter based on cascading two filters in the manner described above, a particular consideration as part of the design process is the stop band bandwidth of the narrow band filter. As shown in fig. 4A and 4B, the stop band width of the narrow band filter must be wide enough to cover the lack of rejection caused by the frequency response drift of the wide band filter over the operating temperature range.

Careful design must be made in designing the filter to ensure that the overall cascaded filter performance is satisfactory at any temperature within the desired operating temperature range by properly designing the stopband bandwidth of the narrow band stop filter.

Example embodiment #2

A second exemplary embodiment of a wideband pass-band filter cascaded with filters having two narrow stop-bands, one on the lower frequency side of the wideband filter and one on the higher frequency side of the wideband filter, will now be described with respect to fig. 5A to 5C.

Fig. 5A includes a high temperature (approximately 85 deg.c) filter response 50 and a low temperature (approximately-40 deg.c) filter response 51 that are substantially the same as the two filter responses shown in fig. 4A.

Figure 5B illustrates a graphical depiction of two filter responses, one filter response 52 showing a high temperature response and one filter response 53 showing a low temperature response, of a narrow band stop band filter. The narrow-band filter is made of a material with a low stable coupling coefficient when the temperature changes. Figure 5B has a first stop band (approximately 0.030GHz from 1.35GHz to 1.38 GHz) and a second stop band (approximately 0.030GHz from 1.45GHz to 1.48 GHz).

Fig. 5C illustrates a graphical plot of two filter responses, one filter response 54 showing a high temperature response and one filter response 55 showing a low temperature response, of the resulting cascaded filter. On the lower frequency side of the filter responses 54, 55, the transition bands are substantially parallel and have a frequency spacing of approximately 0.002GHz for a given attenuation. On the higher frequency side of the filter responses 54, 55, the transition bands are substantially parallel and have a frequency spacing of approximately 0.002GHz for a given attenuation. Since two filters are cascaded, the overall filter response has a wide-band passband with sharp transition bands on each side of the passband and low frequency drift over temperature variations.

Example embodiment #3

A third example embodiment of a wideband band-stop filter cascaded with a narrowband band-stop filter having a stop band on the lower frequency side of the wideband filter will now be described with respect to fig. 6A to 6C.

Fig. 6A illustrates a graphical plot of two filter responses, one filter response 60 showing a high temperature (approximately 85 ℃) response and one filter response 61 showing a low temperature (approximately-40 ℃) response, for a wideband band-stop filter. The broadband filter is made of a material with a high coupling coefficient. Fig. 6A is substantially the same as fig. 1B.

Fig. 6B illustrates a graphical depiction of two filter responses, one filter response 62 showing a high temperature response and one filter response 63 showing a low temperature response, of a narrow band stop filter. The narrow-band filter is made of a material with a lower coupling coefficient and stability in temperature change. Fig. 6B is similar to fig. 2B except that the band-stop filter response of fig. 6B is in the frequency range of 1.37GHz to 1.40 GHz.

Fig. 6C illustrates a graphical depiction of two filter responses, one filter response 64 showing a high temperature response and one filter response 65 showing a low temperature response, for two cascaded filters. On the lower frequency side of the filter responses 64, 65, the transition bands are substantially parallel and have a frequency spacing of approximately 0.002GHz for a given attenuation. On the higher frequency side of the filter responses 64, 65, the transition bands are substantially parallel and have a frequency spacing of approximately 0.010GHz for a given attenuation. The lower frequency side transition band of the stop band has approximately 4/5 less temperature dependent frequency drift than the higher frequency side transition band of the stop band.

Example embodiment #4

A fourth example embodiment of a wideband band-stop filter cascaded with a filter having two narrow band stop bands, one stop band on the lower frequency side of the wideband filter and one stop band on the higher frequency side of the wideband filter, will now be described with respect to fig. 7A to 7C.

Fig. 7A includes a high temperature (approximately 85 deg.c) filter response 70 and a low temperature (approximately-40 deg.c) filter response 71 that are substantially the same as the two filter responses shown in fig. 6A.

Fig. 7B illustrates a graphical depiction of two filter responses, one filter response 72 showing a high temperature response and one filter response 73 showing a low temperature response, of a narrow band stop filter. The narrow-band filter is made of a material with a lower coupling coefficient and stability in temperature change. The two filter responses shown in fig. 7B and 6B are substantially the same.

Fig. 7C illustrates a graphical plot of two filter responses, one filter response 74 showing a high temperature response and one filter response 75 showing a low temperature response, of the resulting cascaded filter. On the lower frequency side of the filter responses 74, 75, the transition bands are substantially parallel and have a frequency spacing of approximately 0.002GHz for a given attenuation. On the higher frequency side of the filter responses 74, 75, the transition bands are substantially parallel and have a frequency spacing of approximately 0.002GHz for a given attenuation. Due to the two cascaded filters, the overall filter response has a wide band stop band, steep transition bands on each side of the stop band and low frequency drift upon temperature changes.

The filter response parameters associated with the examples of fig. 4A-4E, 5A-5C, 6A-6C, and 7A-7C are merely exemplary in nature. The parameters involved in designing a filter for any given application, such as, but not limited to, transition band steepness, passband or bandstop bandwidth, and temperature-dependent frequency drift, are implementation specific.

In some embodiments, a matching network may be used in conjunction with a cascaded filter design. In some embodiments, the use of a matching network may improve the performance of the overall filter. Fig. 8 is a block diagram illustrating how matching circuits may be used together with respect to a cascaded filter design. In fig. 8, filter a and filter B are cascaded together in a package 860 and provide an overall filter response. The first matching circuit 810 is coupled to the input of filter a. The first matching circuit 810 has a pair of inputs 812, 814. The inputs to the cascaded filters may be applied at inputs 812, 814. A second matching circuit 820 is coupled to the output of filter B. The second matching circuit 820 has a pair of outputs 822, 824. The outputs of the cascaded filters are provided at outputs 822, 824. A third matching circuit 830 is coupled to filter a for matching filter a itself. The third matching circuit 830 is grounded. A fourth matching circuit 840 is coupled to filter B for matching the filter B itself. The fourth matching circuit 840 is grounded. A fifth matching circuit 850 is coupled to the connection between filter a and filter B for matching the connection between filter a and filter B. The fifth matching circuit 850 is grounded.

Fig. 8 illustrates a set of matching networks for a filter comprising two cascaded filters of the type generally described above. In some embodiments, not all of the matching networks described in fig. 8 are used in conjunction with cascaded filters. The number of matching networks and their location relative to the cascaded filters is implementation specific.

The matching network may be implemented by using discrete components or transmission lines or some combination thereof. In some implementations, the matching network may include a discrete inductor.

A method of making the filter will now be described with reference to figure 10.

The first step 10-1 of the method involves cascading at least one first filter and at least one second filter. Each first filter is a band-stop type filter having a first set of filter parameters that are a function of a first material used to fabricate at least one first filter. Each second filter has a second set of filter parameters that are a function of a second material used to fabricate the at least one second filter. Further, each of the second filters is one of a band-stop type filter and a band-pass type filter. The first material and the second material are different materials. The filter has a third set of filter parameters that are a function of both the first material and the second material.

Although the above method describes making the filter using two filters, it will be understood that: according to the embodiments of the present invention described above, more than a single filter per first and second filter may be used in cascading filters, such that there may be more than one first filter and more than one second filter. Also if more than one first filter is used, the materials for more than one first filter may not necessarily be identical, but rather more similar to each other than to the materials for more than one second filter. The same applies to more than one second filter.

A filtering method of the filter will now be described with reference to fig. 11.

The first step 11-1 of the method involves providing a signal to the input of the first filter. The first filter is a band-stop type filter having a first set of filter parameters that are a function of a first material used to fabricate the at least one first filter.

The second step 11-2 of the method involves filtering the signal using a first filter, thereby producing an output of the first filter.

The third step 1-3 of the method involves providing the output of the first filter to a second filter having a second set of filter parameters that are a function of a second material used to fabricate at least one second filter, each second filter being one of a band stop type filter and a band pass type filter.

A fourth step 11-4 of the method involves filtering the output of the first filter using a second filter, thereby producing an output of the second filter.

The first material and the second material are different materials. The combination of the at least one first filter and the at least one second filter used to filter the signal has a third set of filter parameters that are a function of both the first material and the second material.

Although the above method description describes filtering a signal using two filters, it will be understood that: according to the embodiments of the invention described above, more than a single filter per first and second filter may be used to filter the signal, so that there may be more than one first filter and more than one second filter. Also if more than one first filter is used, the materials for more than one first filter may not necessarily be identical, but rather more similar to each other than to the materials for more than one second filter. The same applies to the plurality of second filters.

Some embodiments of the present invention may also provide low insertion loss, high power handling capability, broadband passband or broadband stopband, narrow transition band, and low temperature dependent frequency drift performance to low cost and compact size duplexers or multiplexers by applying aspects of the cascaded filters of the present invention.

Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A filter, comprising:

at least one first filter, each first filter being a band-stop type filter having a first set of filter parameters that are a function of a first material used to fabricate the respective first filter;

at least one second filter, each second filter having a second set of filter parameters that are a function of a second material used to fabricate the respective second filter, each second filter being one of:

a band-stop filter; and

a band-pass filter;

wherein at least one of the at least one first filter and at least one of the at least one second filter are cascaded together;

wherein the first material and the second material are different materials;

wherein the filter has a third set of filter parameters that are a function of both the first material and the second material; and wherein the first material has a smaller magnitude temperature coefficient than the second material such that each first filter has less temperature-dependent frequency drift than each second filter.

2. The filter of claim 1, wherein each first filter is a narrow band stop type filter having at least one stop band in the filter response, each stop band having a sharp transition band relative to a transition band of each second filter.

3. The filter of claim 1 or 2, wherein each second filter is one of:

a wide band pass filter; and

a wideband band stop filter.

4. The filter of claim 1 or 2, wherein the second material has a higher electromechanical coupling coefficient than the first material.

5. The filter of claim 1 or 2, wherein:

each first filter has one of:

a first stop band arranged at a low side edge of the pass band of one of the at least one second filter;

a first stop band arranged at a low side edge of the stop band of one of the at least one second filter;

a first stop band arranged at a high-side edge of the pass band of one of the at least one second filter;

a first stop band arranged at a high side edge of the stop band of one of the at least one second filter;

two stop bands, a first of the two stop bands being disposed at a low-side edge of a pass band of one of the at least one second filter, and a second of the two stop bands being disposed at a high-side edge of the pass band of one of the at least one second filter; and

two stop bands, a first of the two stop bands being arranged at a low side edge of a stop band of one of the at least one second filter, and a second of the two stop bands being arranged at a high side edge of the stop band of one of the at least one second filter.

6. The filter of claim 1 or 2, wherein:

each first filter is made using any one of: surface Acoustic Wave (SAW) technology; film Bulk Acoustic Resonator (FBAR) technology; and Bulk Acoustic Wave (BAW) filter technology; and is

Each second filter is made using any one of: SAW technology; FBAR technology; and BAW filter technology.

7. The filter of claim 1 or 2, wherein the first material comprises at least one of: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a AlN; and combinations thereof.

8. A filter according to claim 1 or 2, wherein the second materialComprising at least one of: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a ZnO; AlN; and combinations thereof.

9. The filter of claim 1 or 2, wherein a first filter of the at least one first filter and a second filter of the at least one second filter are cascaded together in a package using at least one of:

a link electrically connecting the first filter and the second filter directly; and

a shared connection point within the package to which the first filter and the second filter are electrically connected.

10. The filter of claim 1 or 2, further comprising at least one of:

a circuit matching element for matching at least one of an input to and an output from the filter;

a circuit matching element for matching a first filter of the at least one first filter;

a circuit matching element for matching a second filter of the at least one second filter;

a circuit matching element for matching a point in the filters at which a first filter of the at least one first filter and a second filter of the at least one second filter are cascaded together.

11. A method for making a filter, comprising:

cascading at least one first filter with at least one second filter, each first filter being a band-stop type filter having a first set of filter parameters that are a function of a first material used to fabricate the respective first filter, each second filter having a second set of filter parameters that are a function of a second material used to fabricate the respective second filter, each second filter being one of:

a band-stop filter; and

a band-pass filter;

wherein the first material and the second material are different materials;

wherein the filter has a third set of filter parameters that are a function of both the first material and the second material; and wherein the first material has a smaller magnitude temperature coefficient than the second material such that each of the at least one first filter has less temperature-dependent frequency drift than each of the at least one second filter.

12. The method of claim 11, wherein cascading at least one first filter and at least one second filter comprises:

cascading a first filter of the at least one first filter and a second filter of the at least one second filter, the first filter being a narrow band stop-band type filter having at least one stop band in filter response, each stop band having a sharp transition band relative to a transition band of each of the at least one second filter.

13. The method of claim 11 or 12, wherein cascading at least one first filter and at least one second filter comprises:

concatenating a first filter of the at least one first filter and a second filter of the at least one second filter, the second filter being one of:

a wide band pass filter; and

a wideband band stop filter.

14. The method of claim 11 or 12, wherein the second material has a higher electromechanical coupling coefficient than the first material.

15. The method of claim 11 or 12, wherein cascading the at least one first filter and the at least one second filter comprises:

cascading a first filter of the at least one first filter and a second filter of the at least one second filter, wherein the first filter is fabricated using any one of:

surface Acoustic Wave (SAW) technology;

film Bulk Acoustic Resonator (FBAR) technology; and

bulk Acoustic Wave (BAW) filter technology;

wherein the second filter is fabricated using any one of:

SAW technology;

FBAR technology; and

BAW filter technology.

16. The method of claim 11 or 12, wherein:

each first filter has one of:

17. The method of claim 11 or 12, wherein cascading at least one first filter and at least one second filter comprises:

cascading a first filter of the at least one first filter and a second filter of the at least one second filter, wherein the first filter is fabricated using the first material, the first material comprising at least one of: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a AlN; and combinations thereof.

18. The method of claim 11 or 12, wherein cascading at least one first filter and at least one second filter comprises:

cascading a first filter of the at least one first filter and a second filter of the at least one second filter, wherein the second filter is fabricated using the second material, the second material comprising at least one of: quartz; langasite; SiO 2₂/ZnO/diamond; SiO 2₂AlN/diamond; li₂B₄O₇；AlN/Li₂B₄O₇；LiTaO₃；LiNbO₃；SiO₂/LiTaO₃；SiO₂/LiNbO₃(ii) a ZnO; AlN; and combinations thereof.

19. A method for filtering a signal, comprising:

providing a signal to an input of a first filter, the first filter being a band-stop type filter having a first set of filter parameters that are a function of a first material used to fabricate the first filter;

filtering the signal using the first filter, thereby producing an output of the first filter;

providing the output of the first filter to a second filter, the second filter having a second set of filter parameters that are a function of a second material used to fabricate the second filter, the second filter being one of a band-stop type filter and a band-pass type filter;

filtering the output of the first filter using the second filter, thereby producing an output of the second filter; wherein the first material and the second material are different materials;

wherein a combination of the first filter and the second filter has a third set of filter parameters that is a function of both the first material and the second material; and

wherein the first material has a smaller magnitude temperature coefficient than the second material such that each first filter has less temperature-dependent frequency drift than each second filter.