Patent Publication Number: US-11652462-B2

Title: Multiplexer with hybrid acoustic passive filter

Description:
CROSS REFERENCE TO PRIORITY APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR § 1.57. This application is a continuation of U.S. patent application Ser. No. 17/134,955, filed Dec. 28, 2020 and titled “HYBRID ACOUSTIC LC FILTER CASCADED WITH LC FILTER,” which is a continuation of U.S. patent application Ser. No. 16/514,857, filed Jul. 17, 2019 and titled “CASCADED FILTER CIRCUIT WITH HYBRID ACOUSTIC LC FILTER.” U.S. patent application Ser. No. 16/514,857 claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/700,142, filed Jul. 18, 2018 and titled “HYBRID ACOUSTIC LC FILTER CASCADED WITH LC FILTER;” U.S. Provisional Patent Application No. 62/700,148, filed Jul. 18, 2018 and titled “PARALLEL HYBRID ACOUSTIC PASSIVE FILTER;” and U.S. Provisional Patent Application No. 62/700,146, filed Jul. 18, 2018 and titled “HYBRID ACOUSTIC LC FILTER WITH HARMONIC SUPPRESSION.” The disclosures of each of these priority applications are hereby incorporated by reference in their entireties herein. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of this disclosure relate to a hybrid acoustic LC filter. 
     Description of Related Technology 
     An acoustic wave filter can include a plurality of acoustic resonators arranged to filter a radio frequency signal. Acoustic resonators can be arranged as a ladder filter to filter the radio frequency signal. Example acoustic wave filters include surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters. Acoustic wave filters can be implemented in radio frequency electronic systems. For instance, filters in a radio frequency front end of a mobile phone can include acoustic wave filters. 
     An LC filter includes at least an inductor and a capacitor. LC filters are non-acoustic filters that include passive components. LC filters can filter radio frequency signals. 
     Filtering relatively high frequency radio frequency signals and meeting stringent filtering specifications can be difficult. Accordingly, improved filters are desired to filter relatively high frequency signals and meet performance specifications. 
     SUMMARY OF CERTAIN INVENTIVE ASPECTS 
     The innovations described in the claims each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of the claims, some prominent features of this disclosure will now be briefly described. 
     One aspect of this disclosure is a cascaded filter for radio frequency filtering. The cascaded filter includes a hybrid acoustic LC filter and a non-acoustic LC filter cascaded with the hybrid acoustic LC filter. The hybrid acoustic LC filter is configured to filter a radio frequency signal. The hybrid acoustic LC filter includes a first acoustic resonator on an acoustic resonator die, a second acoustic resonator, a capacitor external to the acoustic resonator die, and an inductor external to the acoustic resonator die. The non-acoustic LC filter includes an LC circuit. 
     The hybrid acoustic LC filter further can further include a second inductor in parallel with the second acoustic resonator, in which the second acoustic resonator is arranged as a shunt resonator in series with the inductor. 
     The first acoustic resonator and the second acoustic resonator can be shunt resonators. The capacitor and the inductor can be arranged as an LC tank coupled between the first acoustic resonator and the second acoustic resonator. 
     The first acoustic resonator can be coupled to a node in a signal path between the LC circuit and both the inductor and the capacitor. 
     The first acoustic resonator and the second acoustic resonator can be bulk acoustic wave resonators. For example, the first acoustic resonator and the second acoustic resonator can be film bulk acoustic wave resonators. 
     The LC circuit of the non-acoustic LC filter can include integrated passive devices on an integrated passive device die. The inductor of the hybrid acoustic LC filter can be a surface mount inductor. The inductor of the hybrid acoustic LC filter can include a conductive trace of a substrate. The integrated passive devices can include an LC shunt circuit and a series LC resonant circuit. 
     The LC circuit of the non-acoustic LC filter can include a series LC resonant circuit and an LC shunt circuit. The series LC resonant circuit can include a parallel LC circuit. The LC shunt circuit can includes a series LC circuit. The LC circuit of the non-acoustic LC filter can further include a second shunt series LC circuit. 
     A passband of the cascaded filter can be set by the non-acoustic LC filter. The first acoustic resonator can be arranged to provide rejection at a frequency band outside of the passband. A lower bound of the passband can be at least 3 gigahertz. The passband can spans from at least 3.3 gigahertz to 4.2 gigahertz. 
     Another aspect of this disclosure is a multiplexer that includes a first filter coupled to a common node and a second filter coupled to the common node. The first filter is configured to filter a radio frequency signal. The first filter includes a hybrid acoustic LC filter and a non-acoustic LC filter cascaded with the hybrid acoustic LC filter. The hybrid acoustic LC filter includes a first acoustic resonator on an acoustic resonator die, a second acoustic resonator, a capacitor external to the acoustic resonator die, and an inductor external to the acoustic resonator die. 
     The multiplexer can further includes a third filter coupled to the common node. The second filter can include a second hybrid acoustic LC filter. The second filter can include a second non-acoustic LC filter. 
     Another aspect of this disclosure is a wireless communication device that includes an antenna and a radio frequency front end in communication with the antenna. The radio frequency front end includes a filter configured to filter a radio frequency signal for transmission via the antenna. The filter includes a hybrid acoustic LC filter and a non-acoustic LC filter cascaded with the hybrid acoustic LC filter. The hybrid acoustic LC filter includes acoustic resonators on an acoustic resonator die, a capacitor external to the acoustic resonator die, and an inductor external to the acoustic resonator die. 
     The wireless communication device can be a mobile phone. 
     Another aspect of this disclosure is a cascaded filter circuit for radio frequency filtering that includes a hybrid acoustic LC filter, a non-acoustic LC filter including an LC circuit, and a switch configured to selectively couple the hybrid acoustic LC filter and the non-acoustic LC filter. The hybrid acoustic LC filter is configured to filter a radio frequency signal. The hybrid acoustic LC filter includes an acoustic resonator on an acoustic resonator die, a capacitor external to the acoustic resonator die, and an inductor external to the acoustic resonator die. 
     The cascaded filter circuit can further includes a second non acoustic LC filter, in which the switch is configured to couple the hybrid acoustic LC filter and the non-acoustic LC filter in a first state, and in which the switch is configured to couple the hybrid acoustic LC filter and the second non-acoustic LC filter in a second state. The non-acoustic LC filter can be a transmit filter and the second non-acoustic LC filter can be a receive filter. 
     The cascaded filter circuit can further include a second hybrid acoustic LC filter, in which the switch is configured to couple the hybrid acoustic LC filter and the non-acoustic LC filter in a first state, and in which the switch is configured to couple the second hybrid acoustic LC filter and the non-acoustic LC filter in a second state. 
     The hybrid acoustic LC filter can further includes a second inductor in parallel with the acoustic resonator, in which the acoustic resonator is arranged as a shunt resonator in series with the inductor. 
     The hybrid acoustic LC filter can further include a second acoustic resonator. The first acoustic resonator and the second acoustic resonator can be shunt resonators. The capacitor and the inductor can be arranged as an LC tank between the acoustic resonator and the second acoustic resonator. The hybrid acoustic LC filter can further include a second inductor in series with the first acoustic resonator and a third inductor in series with the second acoustic resonator. 
     The acoustic resonator can be a bulk acoustic wave resonator. 
     The LC circuit of the non-acoustic LC filter can include integrated passive devices of an integrated passive device die. The inductor of the hybrid acoustic LC filter can be a surface mount inductor. The inductor of the hybrid acoustic LC filter can include a conductive trace of a substrate. 
     A passband of a cascaded filter that includes the non-acoustic LC filter and the hybrid acoustic LC filter can be set by the non-acoustic LC filter. A lower bound of the passband can be at least 3 gigahertz. 
     Another aspect of this disclosure is a method of filtering a radio frequency signal. The method includes coupling, with a switch, a hybrid acoustic LC filter and a non-acoustic LC filter. The hybrid acoustic LC filter includes an acoustic resonator on an acoustic resonator die, a capacitor external to the acoustic resonator die, and an inductor external to the acoustic resonator die. The method also includes filtering a radio frequency signal while the hybrid acoustic LC filter and the non-acoustic filter are coupled together. 
     The method can further include decoupling, with the switch, the hybrid acoustic LC filter from the non-acoustic LC filter; and coupling, with the switch, the hybrid acoustic LC filter and a second non acoustic LC filter. The method can further include providing, with a power amplifier, the radio frequency signal to the non-acoustic LC filter; and amplifying, with a low noise amplifier, a filtered signal provided by the second non-acoustic filter. 
     The filtering can include providing, using the acoustic resonator of the hybrid acoustic LC filter, rejection outside of a passband of a filter that includes the hybrid acoustic LC filter and the non-acoustic LC filter. 
     The radio frequency signal can have a frequency in a range from 3 gigahertz to 5 gigahertz. 
     Another aspect of this disclosure is a wireless communication device that includes an antenna and a radio frequency front end in communication with the antenna. The radio frequency front end includes a filter configured to filter a radio frequency signal for transmission via the antenna. The filter includes a hybrid acoustic LC filter, a non-acoustic LC filter, and a switch configured to selectively couple the hybrid acoustic LC filter and the non-acoustic LC filter. The hybrid acoustic LC filter includes an acoustic resonator on an acoustic resonator die and an LC component external to the acoustic resonator die. 
     The wireless communication device can be a mobile phone. 
     Another aspect of this disclosure is a parallel hybrid acoustic passive filter that includes a first sub-filter and a second sub-filter coupled in parallel with the first sub-filter. The first sub-filter includes a first acoustic resonator and a first non-acoustic passive component. The second sub-filter includes a second acoustic resonator and a second non-acoustic passive component. The first sub-filter and the second sub-filter are together arranged to filter a radio frequency signal. 
     The first sub-filter and the second sub-filter can be together arranged as a band pass filter having a passband. A frequency response of the parallel hybrid acoustic passive filter can have a first sub-passband corresponding to the first sub-filter, a second sub-passband corresponding to the second sub-filter, and a notch at a notch frequency between the first sub-passband and a second sub-passband. 
     The first sub-filter and the second sub-filter can be together arranged as a band stop filter having a stop band. The band stop filter can have a notch in the stop band. 
     The first sub-filter can includes bulk acoustic wave resonators that include the acoustic resonator. 
     The first non-acoustic passive component can include a first inductor and a second inductor, in which the first inductor is in parallel with the acoustic resonator, and in which the acoustic resonator is arranged as a shunt resonator that is in series with the second inductor. 
     The first sub-filter can further include an additional acoustic resonator, in which the first acoustic resonator and the additional acoustic resonator are shunt resonators, and in which the first non-acoustic passive component includes a capacitor and an inductor arranged as an LC tank coupled between the first acoustic resonator and the additional acoustic resonator. 
     The second non-acoustic passive component can include an integrated passive device. 
     The first sub-filter and the second sub-filter can have different passbands. A lower bound of a passband of the parallel hybrid acoustic passive filter can be at least 2 gigahertz. 
     Another aspect of this disclosure is a multiplexer with a parallel hybrid acoustic passive filter. The multiplexer includes a first filter coupled to a common node and a second filter coupled to the common node. The first filter is configured to filter a radio frequency signal. The first filter includes a first sub-filter in parallel with a second sub-filter. The first sub-filter includes a first acoustic resonator and a first non-acoustic passive component. The second sub-filter includes a second acoustic resonator and a second non acoustic passive component. 
     The first filter can be a band pass filter. A frequency response of the first filter can have a first sub-passband corresponding to the first sub-filter, a second sub-passband corresponding to the second sub-filter, and a notch at a notch frequency between the first sub-passband and a second sub-passband. The second filter can be a band stop filter. 
     The first filter can be a band stop filter having a stop band and a notch in the stop band. 
     The second filter can include another acoustic resonator and another non-acoustic passive component. 
     The first filter can have a first passband, the second filter can have a second passband, and the first passband can have a lower edge that is at a higher frequency than an upper edge of the second passband. 
     The multiplexer can further include a third filter coupled to the common node. 
     The multiplexer can further include a shared filter in series between the first filter and the common node, in which the shared filter is also in series between the second filter and the common node. The shared filter can be a high pass filter. 
     Another aspect of this disclosure is a wireless communication device that includes a radio frequency front end an antenna in communication with the radio frequency front end. The radio frequency front end includes a filter configured to filter a radio frequency signal. The filter includes a first sub-filter in parallel with a second sub filter. The first sub-filter includes a first acoustic resonator and a first non-acoustic passive component. The second sub-filter includes a second acoustic resonator and a second non acoustic passive component. 
     Another aspect of this disclosure is a multiplexer with a hybrid acoustic passive filter. The multiplexer includes a plurality of filters configured to filter respective radio frequency signals, a shared filter coupled between each of the plurality of filters and a common node, and a radio frequency filter coupled to the common node. Each filter of the plurality of filters has a different passband. At least a first filter of the plurality of filters includes acoustic resonators and a non-acoustic passive component. 
     The plurality of filters can includes the first filter, a second filter, and a third filter. The first filter can be a first band pass filter having a first passband. The second filter can be a second band pass filter having a second passband. The third filter can be a band stop filter having a stop band that includes the first passband and the second passband. 
     The shared filter can be a high pass filter. The radio frequency filter can be a low pass filter. 
     The shared filter can be a non-acoustic LC filter. The shared filter can include second acoustic resonators and an LC component. 
     The non-acoustic passive component can include an inductor arranged in parallel with a first acoustic resonator of the acoustic resonators. 
     The acoustic resonators can be embodied on an acoustic resonator die. The non-acoustic passive component can include an inductor external to the acoustic resonator die and a capacitor external to the acoustic resonator die. 
     A second filter of the plurality of filter can include second acoustic resonators and a second non-acoustic passive component. The first filter can have a first passband and the second filter can have a second passband. The first and second passbands can both be within a frequency range from 2 gigahertz to 5 gigahertz. The first and second passbands can both be within a frequency range from 2 gigahertz to 3 gigahertz. 
     The multiplexer can be arranged as a quadplexer. 
     Another aspect of this disclosure is wireless communication device that includes an antenna and a multiplexer in communication with the antenna. The multiplexer includes a plurality of filters configured to filter respective radio frequency signals, a shared filter coupled between each of the plurality of filters and a common node, and a radio frequency filter coupled to the common node. The plurality of filters includes a first filter that includes acoustic resonators and a non-acoustic passive component. 
     A second filter of the plurality of filter can include second acoustic resonators and a second non-acoustic passive component. The wireless communication device can be configured to support a carrier aggregation at the common node. The carrier aggregation can includes a first carrier and a second carrier, in which the first carrier is within a first passband of the first filter, and in which the second carrier is outside of the first passband and a second passband of the second filter. 
     Another aspect of this disclosure is a multiplexer with hybrid acoustic passive filters. The multiplexer includes a plurality of filters including a first filter and a second filter having different radio frequency passbands, a shared high pass filter coupled between each of the plurality of filters and a common node, and a low pass filter coupled to the common node. The first filter includes first acoustic resonators and a first LC circuit. The second filter includes second acoustic resonators and a second LC circuit. 
     The plurality of filters can further include a band stop filter having a stop band that includes the passbands of the first and second filters. 
     Another aspect of this disclosure is a hybrid acoustic LC filter with harmonic suppression. The hybrid acoustic LC filter includes a hybrid passive/acoustic filter configured to filter a radio frequency signal and a non-acoustic LC filter cascaded with the hybrid passive/acoustic filter. The hybrid passive/acoustic filter includes acoustic resonators and a non-acoustic passive component. The non-acoustic LC filter is configured to suppress a harmonic of the radio frequency signal. 
     The non-acoustic LC filter can be a notch filter. A frequency response of the notch filter can have a notch corresponding to a second harmonic of the radio frequency signal. A frequency response of the notch filter can have two notches corresponding to different harmonics of the radio frequency signal. 
     The non-acoustic LC filter can be a low pass filter. 
     The non-acoustic LC filter can include integrated passive devices of an integrated passive device die. 
     The acoustic resonators can include bulk acoustic wave resonators. 
     The non-acoustic passive component can include a first inductor and a second inductor. The acoustic resonators can include a first shunt acoustic resonator arranged in series with the first inductor and in parallel with the second inductor. 
     The acoustic resonators can include a first shunt acoustic resonator and a second shunt acoustic resonator. The non-acoustic passive component can include an LC tank coupled between the first shunt acoustic resonator and the second shunt acoustic resonator. 
     Another aspect of this disclosure is a multiplexer that includes a first filter configured to filter a radio frequency signal and a second filter coupled to the first filter at a common node. The first filter includes a hybrid passive/acoustic filter and a non-acoustic LC filter cascaded with the hybrid passive/acoustic filter. The hybrid passive/acoustic filter includes acoustic resonators and a non-acoustic passive component. The non-acoustic LC filter is configured to suppress a harmonic of the radio frequency signal. 
     The second filter can include second acoustic resonators and a second non-acoustic passive component. The first filter can be a mid-band filter and the second filter can be a high band filter. The multiplexer can further include a low band filter coupled to the first filter and the second filter at the common node. 
     The non-acoustic LC filter can include integrated passive devices of an integrated passive device die. 
     The non-acoustic passive component can include a first inductor and a second inductor. The acoustic resonators can include a first shunt acoustic resonator arranged in series with the first inductor and in parallel with the second inductor. 
     The acoustic resonators can include a first shunt acoustic resonator and a second shunt acoustic resonator. The non-acoustic passive component can include an LC tank coupled between the first shunt acoustic resonator and the second shunt acoustic resonator. 
     The acoustic resonators can include bulk acoustic wave resonators. 
     Another aspect of this disclosure is a wireless communication device that includes radio frequency front end and an antenna in communication with the radio frequency front end. The radio frequency front end includes a filter configured to filter a radio frequency signal. The filter includes a hybrid passive/acoustic filter and an LC filter cascaded with the hybrid passive/acoustic filter. The hybrid passive/acoustic filter includes acoustic resonators and a non-acoustic passive component. The non-acoustic LC filter is configured to suppress a harmonic of the radio frequency signal. The antenna is configured to transmit a filtered version of the radio frequency signal with the harmonic suppressed. 
     The wireless communication device can be configured as a mobile phone. 
     The wireless communication device can further include a baseband processor and a transceiver, in which the transceiver is in communication with the radio frequency front end and is also in communication with the baseband processor. 
     For purposes of summarizing the disclosure, certain aspects, advantages and novel features of the innovations have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, the innovations may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     The present disclosure relates to U.S. patent application Ser. No. 16/514,797, titled “HYBRID ACOUSTIC LC FILTER CASCADED WITH LC FILTER,” filed on Jul. 17, 2019, the entire disclosure of which is hereby incorporated by reference herein. The present disclosure relates to U.S. patent application Ser. No. 16/514,810, titled “PARALLEL HYBRID ACOUSTIC PASSIVE FILTER,” filed on Jul. 17, 2019, the entire disclosure of which is hereby incorporated by reference herein. The present disclosure relates to U.S. patent application Ser. No. 16/514,883, titled “MULTIPLEXER WITH HYBRID ACOUSTIC PASSIVE FILTER,” filed on Jul. 17, 2019, the entire disclosure of which is hereby incorporated by reference herein. The present disclosure relates to U.S. patent application Ser. No. 16/514,806, titled “HYBRID ACOUSTIC LC FILTER WITH HARMONIC SUPPRESSION,” filed on Jul. 17, 2019, the entire disclosure of which is hereby incorporated by reference herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of this disclosure will be described, by way of non-limiting example, with reference to the accompanying drawings. 
         FIG.  1 A  is a schematic block diagram of a cascaded filter that includes a hybrid acoustic LC filter and an LC filter according to an embodiment. 
         FIG.  1 B  is a schematic block diagram of a radio frequency system that includes a cascaded filter in a signal path between a power amplifier and an antenna according to an embodiment. 
         FIG.  1 C  is a schematic block diagram of a radio frequency system that includes a cascaded filter in a signal path between an antenna and a low noise amplifier according to an embodiment. 
         FIG.  2 A  is a schematic block diagram of a cascaded filter circuit that includes a hybrid acoustic LC filter coupled to LC filters by a switch according to an embodiment. 
         FIG.  2 B  is a schematic block diagram of a cascaded filter circuit that includes an LC filter coupled to hybrid acoustic LC filters by a switch according to an embodiment. 
         FIG.  3 A  is a schematic block diagram of a radio frequency system with a cascaded filter circuit according to an embodiment. 
         FIG.  3 B  is a schematic block diagram of a radio frequency system with a cascaded filter circuit according to another embodiment. 
         FIG.  3 C  is a schematic block diagram of a radio frequency system with a cascaded filter circuit according to another embodiment. 
         FIG.  4 A  is a schematic block diagram of a multiplexer that includes a cascaded filter and another filter according to an embodiment. 
         FIG.  4 B  is a schematic block diagram of a multiplexer that includes a cascaded filter and another filter according to another embodiment. 
         FIG.  5 A  is a schematic block diagram that includes a cascaded filter and another filter coupled to a common mode by a switch according to an embodiment. 
         FIG.  5 B  is a schematic block diagram of a multiplexer that includes a cascaded filter and another filter coupled to a common mode by a switch according to another embodiment. 
         FIG.  6 A  is a schematic diagram of a cascaded filter according to an embodiment. 
         FIG.  6 B  is a graph of the frequency response of the cascaded filter of  FIG.  6 A . 
         FIG.  7    is a schematic diagram of a cascaded filter according to another embodiment. 
         FIG.  8    is a schematic diagram of a cascaded filter according to another embodiment. 
         FIG.  9    is a schematic diagram of a cascaded filter according to another embodiment. 
         FIG.  10    is a schematic diagram of a cascaded filter according to another embodiment. 
         FIG.  11 A  is a schematic diagram of a hybrid resonator according to an embodiment. 
         FIG.  11 B  is a graph of a frequency response of the hybrid resonator of  FIG.  11 A . 
         FIG.  12    is a schematic diagram of a hybrid resonator according to another embodiment. 
         FIG.  13    is a schematic block diagram of a hybrid parallel band pass filter according to an embodiment. 
         FIG.  14    is a schematic block diagram of a diplexer that includes a hybrid parallel band pass filter according to an embodiment. 
         FIG.  15    is a schematic block diagram of a triplexer that includes a hybrid parallel band pass filter according to an embodiment. 
         FIG.  16    is a schematic block diagram of a triplexer that includes a shared high pass filter and a hybrid parallel band pass filter according to an embodiment. 
         FIG.  17    is a schematic block diagram of a quadplexer that includes a shared high pass filter and a hybrid band pass filter according to an embodiment. 
         FIG.  18    is a schematic diagram of a triplexer that includes a hybrid parallel band pass filter according to an embodiment. 
         FIG.  19 A  illustrates simulation results of the triplexer of  FIG.  18   . 
         FIG.  19 B  illustrates graphs of simulation results of the triplexer of  FIG.  18    compared to a previous design. 
         FIG.  20    is a schematic block diagram of a hybrid parallel band stop filter according to an embodiment. 
         FIG.  21    is a schematic diagram of a hybrid parallel band stop filter according to an embodiment. 
         FIG.  22    is a graph of a frequency response of the hybrid parallel band stop filter of  FIG.  21   . 
         FIG.  23 A  is a schematic block diagram of a radio frequency system that includes a hybrid acoustic LC filter cascaded with a low pass filter according to an embodiment. 
         FIG.  23 B  is a schematic block diagram of a radio frequency system that includes a hybrid acoustic LC filter cascaded with a second harmonic notch filter according to an embodiment. 
         FIG.  24 A  is a schematic diagram of an example low pass filter. 
         FIG.  24 B  is a schematic diagram of another example low pass filter. 
         FIG.  24 C  is a schematic diagram of an example second harmonic notch filter. 
         FIG.  24 D  is a schematic diagram of an example harmonic notch filter. 
         FIG.  24 E  is a schematic diagram of an example second harmonic notch and low pass filter. 
         FIG.  25 A  is a schematic block diagram of a triplexer that includes hybrid acoustic LC filter cascaded with a low pass filter according to an embodiment. 
         FIG.  25 B  is a schematic block diagram of a triplexer that includes a hybrid acoustic LC filter cascaded with a second harmonic notch filter according to an embodiment. 
         FIG.  26    is a schematic diagram of a radio frequency module with a transmit path that includes a filter according to an embodiment. 
         FIG.  27    is a schematic diagram of a radio frequency module with a receive path that includes a filter according to an embodiment. 
         FIG.  28    is a schematic diagram of a radio frequency module that includes a filter according to an embodiment. 
         FIG.  29    is a schematic diagram of a wireless communication device that includes a filter according to an embodiment. 
         FIG.  30    is a schematic diagram of a wireless communication device that includes a filter according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS 
     The following detailed description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein can be embodied in a multitude of different ways, for example, as defined and covered by the claims. In this description, reference is made to the drawings where like reference numerals can indicate identical or functionally similar elements. It will be understood that elements illustrated in the figures are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings. The headings provided herein are for convenience only and do not necessarily affect the scope or meaning of the claims. 
     This disclosure relates to filters that include an acoustic component and a non-acoustic passive component. Certain embodiments relate to a hybrid acoustic LC filter cascaded with an LC filter. Such filters can achieve a relatively wide passband and also meet stringent out-of-band rejection specifications. Some embodiments relate to filters with an acoustic component and a non-acoustic passive component that are arranged in parallel with each other. Such filters can achieve relatively wide bandwidth and high rejection at stopbands that are relatively close to a passband without high loss in the passband. Embodiments disclose herein relate to a non-acoustic LC filter cascaded with a hybrid passive/acoustic filter, in which the non-acoustic LC filter is arranged to suppress a harmonic of a radio frequency signal provided by the hybrid passive/acoustic filter. Such filters can achieve relatively high bandwidth and high rejection while suppressing self-created harmonics. Any suitable combination of features of the embodiments disclosed herein can be combined with each other. In various applications, two or more embodiments can be implemented together with each other. 
     Hybrid Acoustic LC Filter Cascaded with LC Filter 
     As fifth-generation (5G) wireless communications technology advances, non-acoustic wideband ultra-high band (UHB) filter designs encounter difficulties with meeting new carrier aggregation specifications. New carrier aggregation generally creates more intermodulation frequencies that can degrade receiver side sensitivity. Accordingly, carrier aggregation specifications can have more stringent intermodulation distortion (IMD) rejection specifications for the filter. 
     LC band pass filters, such as integrated passive device (IPD) band pass filters, have advantages of wide bandwidth and relatively good broad out of band rejections. However, LC band pass filters do not have particularly sharp rejections at passband-close frequencies. Non-acoustic passband filters can have significantly worse rolling-off losses at the passband edge frequencies compared to acoustic wave filters. This is generally undesirable when high rejection is desired for a stopband close to the passband. 
     Since acoustic resonator filters can provide higher rejection at passband-close frequencies without high edge rolling off loss due to higher quality factor (Q) than LC resonators, a passive non-acoustic filter can be cascaded with a hybrid acoustic LC filter to achieve both wide bandwidth and sharp rejections at the stopbands close to the passband. 
     To provide carrier aggregation IMD rejection compliant filters with relatively sharp rejections at frequencies relatively close to the passband of the filter, a hybrid acoustic LC filter that can be implemented. The hybrid acoustic LC filter can be a wideband filter that includes one or more capacitors, one or more inductors, and one or more acoustic resonators. Hybrid acoustic LC filters can include hybrid resonators that include an acoustic resonator, at least inductor, and at least one capacitor. 
     A hybrid acoustic LC filter can be cascaded with an LC filter to provide a relatively low-loss wide passband and also provide relatively sharp rejections at frequencies relatively close to the passband of the cascaded filter. The LC filter can include integrated passive devices (IPDs) on an integrated passive device die. The hybrid acoustic LC filter can include one or more bulk acoustic wave resonators. The combination of bulk acoustic wave resonators and LC circuit elements in the cascaded filter can provide a relatively wide passband and also meet relatively stringent out-of-band rejection specifications. 
     Aspects of this disclosure relate to a cascaded filter for filtering a radio frequency signal. The cascaded filter includes a hybrid acoustic LC filter and a non-acoustic LC filter cascaded with the hybrid acoustic LC filter. The hybrid acoustic LC filter includes acoustic resonators, a capacitor, and an inductor. The non-acoustic LC filter includes an LC circuit. 
     Cascaded filters discussed herein can be implemented for various frequency bands including wireless bands as long as acoustic resonators can be used. As an example, the cascaded filters can have a passband, with a lower frequency bound of at least 2.5 gigahertz (GHz) or at least 3 GHz in certain applications. The cascaded filters can have a relatively high upper bound of a passband in certain applications, such as about 4.5 GHz, about 6 GHz, about 8.5 GHz, or about 10 GHz. Cascaded filters discussed herein can be implemented in power amplifier modules, diversity receive modules, or any other suitable radio frequency front end modules. Cascaded filters discussed herein can meet the following design specifications: relatively low insertion loss (IL), relatively sharp frequency cutoff, and relatively strong suppression of intermodulation frequency and harmonics. 
       FIG.  1 A  is a schematic block diagram of a cascaded filter  10  that includes a hybrid acoustic LC filter  12  and an LC filter  14  according to an embodiment. The cascaded filter  10  has a first port RF 1  and a second port RF 2 . The hybrid acoustic LC filter  12  and the LC filter  14  are arranged in series with each other between the first port RF 1  and the second port RF 2 . A radio frequency signal can propagate from the first port RF 1  to the second port RF 2  in certain applications. A radio frequency signal can propagate from the second port RF 2  to the first port RF 1  in various applications. 
     The hybrid acoustic LC circuit  12  includes one or more acoustic resonators, one or more inductors, and one or more capacitors. The one or more acoustic resonators can be BAW resonators, such as film bulk acoustic wave resonators (FBARs). For instance, the BAW resonators can be more advantageous for filtering signals having higher frequencies, such as frequencies above 2.5 GHz. The one or more acoustic resonators can alternatively or additionally include any other suitable acoustic wave resonators, such as one or more surface acoustic wave (SAW) resonators, one or more boundary acoustic wave resonators, and/or one or more Lamb wave resonators. The hybrid acoustic LC filter  12  can include a capacitor and an inductor external to a die that include the acoustic resonator(s). The hybrid acoustic  12  can be a ladder filter. The hybrid acoustic filter  12  can be a fixed filter in certain application. A fixed filter can be implemented with lower complexity than a tunable filter in some instances. The hybrid acoustic LC filter  12  can be tunable in some applications. When the hybrid acoustic LC filter  12  is tunable, notches and/or stop bands can be tunable. 
     The LC circuit  14  includes one or more inductors and one or more capacitors. The LC circuit  14  can include one or more IPDs, one or more surface mounted components, one or more passive devices implemented on a packaging substrate, or any suitable combination thereof. Surface mounted components at some frequencies can have higher quality factor and lower insertion loss than IPDs and passive devices implemented on a packaging substrate. The one or more capacitors can be explicit capacitor(s) and/or parasitic capacitor(s). The LC circuit  14  can also implement impedance matching. 
       FIG.  1 B  is a schematic block diagram of a radio frequency (RF) system  15  that includes cascaded filter  10  in a signal path between a power amplifier  16  and an antenna  17  according to an embodiment.  FIG.  1 B  illustrates that the cascaded filter  10  can be included in a transmit signal path. In certain applications, the first port RF 1  of the cascaded filter  10  can be electrically coupled to an output of the power amplifier  16  and a second port RF 2  of the cascaded filter  10  can be electrically coupled to the antenna  17 . In some applications, the first port RF 1  of the cascaded filter  10  can be electrically coupled to the antenna  17  and the second port RF 2  of the cascaded filter  10  can be electrically coupled to the output of the power amplifier  16 . 
       FIG.  1 C  is a schematic block diagram of an RF system  18  that includes a cascaded filter  10  in a signal path between an antenna  17  and a low noise amplifier  19  according to an embodiment.  FIG.  1 C  illustrates that the cascaded filter  10  can be included in a receive signal path. In certain applications, the first port RF 1  of the cascaded filter  10  can be electrically coupled to an input of the low noise amplifier  19  and a second port RF 2  of the cascaded filter  10  can be electrically coupled to the antenna  17 . In some applications, the first port RF 1  of the cascaded filter  10  can be electrically coupled to the antenna  17  and the second port RF 2  of the cascaded filter  10  can be electrically coupled to the input of the low noise amplifier  19 . 
       FIG.  2 A  is a schematic block diagram of a cascaded filter circuit  20  that includes a hybrid acoustic LC filter  12  coupled to LC filters  14 A and  14 N by a switch  22  according to an embodiment. The cascaded filter circuit  20  can share a hybrid acoustic LC filter  12  among a plurality of LC circuits  14 A to  14 N. The switch  22  can electrically connect the hybrid acoustic LC filter  12  in series with a selected LC circuit to implement a cascaded filter. The illustrated switch  22  is a multi-throw radio frequency switch. The switch  22  can electrically couple the hybrid acoustic LC filter  12  to a selected LC filter. The switch  22  can have any suitable number of throws, and the cascaded filter circuit  20  can have a corresponding number of LC filters  14 A to  14 N. The illustrated LC filters  14 A and  14 N are each coupled to a corresponding port RF 21  and RF 2N , respectively, of the cascaded filter circuit  20 . In the cascaded filter circuit  20 , the hybrid acoustic LC filter  12  can implement relatively sharp rejection at frequencies relatively close to the passband in combination with a selected one or more of the LC filters  14 A to  14 N. In certain applications, the hybrid acoustic LC filter  12  can be tunable to tune the rejection at frequencies relatively close the passband for a selected one or more of the LC filters  14 A to  14 N that is electrically coupled thereto. 
       FIG.  2 B  is a schematic block diagram of a cascaded filter circuit  25  that includes an LC filter  14  coupled to hybrid acoustic LC filters  12 A and  12 N by a switch  22  according to an embodiment. The cascaded filter circuit  20  can share an LC filter  14  among a plurality of hybrid acoustic LC circuits  12 A to  12 N. The switch  22  can electrically connect the LC filter  14  in series with a selected hybrid acoustic LC circuit to implement a cascaded filter. The illustrated switch  22  is a multi-throw radio frequency switch. The switch  22  can electrically couple the LC filter  14  to a selected hybrid acoustic LC filter. The switch  22  can have any suitable number of throws, and the cascaded filter circuit  25  can have a corresponding number of hybrid acoustic LC filters  12 A to  12 N. The illustrated hybrid acoustic LC filters  12 A and  12 N are each coupled to a corresponding port RF 11  and RF 1N , respectively, of the cascaded filter circuit  25 . 
       FIG.  3 A  is a schematic block diagram of a radio frequency system  30 A with a cascaded filter circuit according to an embodiment. The radio frequency system  30  is an example system that can implement the cascaded circuit  20  of  FIG.  2 A . As illustrated, an antenna  32  is coupled to the hybrid acoustic LC filter  12 , the switch  22  is a transmit/receive switch, and the LC filters  14 A and  14 B are connected to a power amplifier  34  and a low noise amplifier  36 , respectively. The cascaded circuit  25  of  FIG.  2 B  can be implemented in a radio frequency system that is similar to the radio frequency system  30 A. 
       FIG.  3 B  is a schematic block diagram of a radio frequency system  30 B with a cascaded filter circuit according to another embodiment.  FIG.  3 B  illustrates that LC circuits  14 A and  14 B can be in different transmit paths with respective power amplifiers  34 A and  34 B. Accordingly, the hybrid acoustic LC filter  12  can be included in (a) a cascaded filter circuit with the LC filter  14 A between the power amplifier  34 A and the antenna  32  and (b) a cascaded filter circuit with the LC filter  14 B between the power amplifier  34 B and the antenna  32 . 
       FIG.  3 C  is a schematic block diagram of a radio frequency system  30 C with a cascaded filter circuit according to another embodiment. The cascaded filter of the radio frequency system  30 C can be implemented in a diversity receive application, for example.  FIG.  3 C  illustrates that LC circuits  14 A and  14 B can be in different receive paths with respective low noise amplifiers  36 A and  36 B. Accordingly, the hybrid acoustic LC filter  12  can be included in (a) a cascaded filter circuit with the LC filter  14 A between the low noise amplifier  36 A and the antenna  32  and (b) a cascaded filter circuit with the LC filter  14 B between the low noise amplifier  36 B and the antenna  32 . 
       FIG.  4 A  is a schematic block diagram of a multiplexer  40  that includes a cascaded filter and another filter according to an embodiment. The multiplexer  40  includes a plurality of filters coupled to a common node. As illustrated, a cascaded filter, which includes an LC filter  14  and a hybrid acoustic LC filter  12 , and other filter(s)  42  are coupled together at the common node. In the multiplexer  40 , the LC filter  14  is coupled to the common node by way of the hybrid acoustic LC filter  12 . The multiplexer  40  can be a duplexer with two filters, a triplexer with three filters, a quadplexer with four filters, etc. The other filter(s)  42  can include any suitable number of filters. The other filter(s)  42  can include one or more LC filters (e.g., IPD filters), one or more acoustic wave filters, one or more hybrid acoustic LC filters, the like, or any suitable combination thereof. 
       FIG.  4 B  is a schematic block diagram of a multiplexer  45  that includes a cascaded filter and another filter according to another embodiment. The multiplexer  45  is like the multiplexer  40  of  FIG.  4 A  except that the hybrid acoustic LC filter  12  is coupled to the common node by way of the LC filter  14 . 
     A plurality of filters can be in communication with a common node, such as an antenna node, by way of a switch.  FIG.  5 A  is a schematic diagram of a radio frequency system  50  that includes a cascaded filter and another filter  42  coupled to a common node by way of a switch  52 . The cascaded filter, the other filter  42 , and the switch  52  can implement switch-plexing. The switch-plexing can implement on-demand multiplexing. 
       FIG.  5 B  is a schematic block diagram of a radio frequency system  55  that includes a cascaded filter and another filter coupled to a common mode by a switch according to another embodiment. The radio frequency system  55  is like the radio frequency system  50  of  FIG.  5 A  except that the hybrid acoustic LC filter  12  and the LC filter  14  are arranged in a different order. 
       FIG.  6 A  is a schematic diagram of a cascaded filter  60  according to an embodiment. The cascaded filter  60  can be a band pass filter arranged to pass radio frequency signals having a frequency above 3 GHz, such as Band 42 signals and/or Band 43 signals and/or Band 48 signals. In such applications, the acoustic wave resonators of the filter  60  can be BAW resonators. The filter  60  can be used in 5th generation (5G) wireless systems applications. 5G technology can be referred to as 5G New Radio (NR). The cascaded filter  60  includes a hybrid acoustic LC filter  62  cascaded with an LC filter  64 . The hybrid acoustic LC filter  62  is an example of the hybrid acoustic LC filter  12 . The LC filter  64  is an example of the LC filter  14 . 
     The hybrid acoustic LC filter  62  includes acoustic resonators A 61  and A 62 ; inductors L 601 , L 602 , L 603 , L 604 , L 605 , and L 606 ; and capacitors C 601 , C 602 , C 603 , and C 604 . The acoustic resonators A 61  and A 62  can be BAW resonators such as FBARs. In some instances, the acoustic resonators A 61  and A 62  can include a SAW resonator, a temperature compensated SAW (TCSAW) resonator, a boundary acoustic wave resonator, a Lamb wave resonator, the like, or any suitable combination thereof. The inductors L 601 , L 602 , L 603 , L 604 , L 605 , and L 606  and capacitors C 601 , C 602 , C 603 , and C 604  are LC/non-acoustic components. The LC/non-acoustic components of the hybrid acoustic LC filter  62  can be implemented external to a die that includes the acoustic resonators A 61  and A 62 . The LC/non-acoustic components of the hybrid acoustic LC filter  62  can include one or more surface mount technology (SMT) inductors and/or capacitors. In some instances, the LC/non-acoustic components of the hybrid acoustic LC filter  62  can include one or more IPDs and/or one or more inductive traces on a packaging substrate. 
     As illustrated, the hybrid acoustic LC filter  62  includes a hybrid resonator structure with the inductor L 602  in parallel with the acoustic resonator A 62 , in which the inductor L 603  is in series with inductor and the acoustic resonator A 62 . More details about this hybrid resonator structure are provided with reference to  FIGS.  11 A and  11 B . The illustrated LC filter  62  also includes an LC tank between acoustic nodes at which acoustic resonators A 61  and A 62  are arranged in series with respective inductors L 603  and L 606  in shunt circuits, in which the LC tank includes capacitor C 604  and inductor L 605 . More details about this hybrid resonator structure are proved with reference to  FIG.  12   . 
     The LC filter  64  can be a band pass filter. For instance, the LC filter  64  can be a Band 42/Band 43 band pass filter. The LC filter  64  includes an IPD part  65  on an IPD die, a packaging substrate part  66  that includes traces on the packaging substrate, and SMT part  67  that includes SMT components. The IPD part  65  includes IPD capacitors C 605 , C 606 , C 607 , C 608 , C 609 , and C 610  and IPD inductor L 608 . The packaging substrate part  66  includes inductive traces arranged as inductors L 609 , L 610 , L 611 , and L 612 . The SMT part  67  includes SMT capacitors C 611  and C 612 . 
     As illustrated, the LC filter  64  includes bridge capacitors, LC resonant circuits, coupling capacitors, and a series LC tank. A first bridge capacitor C 610  has a first end coupled to a series LC tank and a second end coupled to an input node of the LC filter  64 . The series LC tank include the capacitor C 605  and the inductor L 608 . The first bridge capacitor C 610  is in parallel with the three coupling capacitors C 606 , C 607 , and C 608 . 
     A first LC resonant circuit is an LC shunt resonant circuit. As illustrated, the first LC resonant circuit includes a shunt inductor L 611  in parallel with a series LC circuit that includes the inductor L 612  and capacitor C 612 . A second bridge capacitor C 609  has a first end coupled to the series LC tank and a second end coupled the first LC resonant circuit. The second bridge capacitor C 609  is in parallel with two coupling capacitors C 606  and C 607 . A second LC resonant circuit is an LC shunt resonant circuit. As illustrated, the second LC resonant circuit includes a shunt inductor L 609  in parallel with a series LC circuit that includes inductor L 610  and capacitor C 611 . 
     A first coupling capacitor C 608  is coupled between an input of the filter and a node at which the first coupling capacitor C 608  is coupled to the first LC resonant circuit and a second coupling capacitor C 607 . The second coupling capacitor C 607  is coupled in series between the first coupling capacitor C 608  and the third coupling capacitor C 606 . The second coupling capacitor C 607  is also coupled between the first LC resonant circuit and the second LC resonant circuit. A third coupling capacitor C 606  is coupled between the series LC tank and a node at which the third coupling capacitor C 606  is coupled to the second LC resonant circuit and the second coupling capacitor C 607 . The illustrated series LC tank is a parallel LC circuit. 
       FIG.  6 B  is a graph of the frequency response of the cascaded filter  60  of  FIG.  6 A . The illustrated curve represents a frequency response of the cascaded filter of  60   FIG.  6 A . The stepped lines represent a design specification or filter mask. The curve in  FIG.  6 B  indicates that the frequency response of the cascaded filter  60  of  FIG.  6 A  meets the design specifications except at 9 GHz. As illustrated, the filter response has two nulls created by the shunt acoustic resonators A 61  and A 62 . The frequency response has relatively sharp roll off at edges of the passband. The non-acoustic LC filter  64  of  FIG.  6 A  can provide the relatively large bandwidth. The frequency response has a relatively wide bandwidth, which is from around 3.1 GHz to 4.2 GHz in the illustrated frequency response. Accordingly, the cascaded filter  60  of  FIG.  6 A  can have a bandwidth of at least 1 GHz. In some other embodiments, cascaded filters with a hybrid acoustic LC filter cascaded with a non-acoustic LC filter can have a bandwidth in a range significantly wider than determined by an acoustic resonator coupling factor, such as a bandwidth from about 3.3 GHz to 4.2 GHz or a bandwidth from about 4.4 GHz to 5 GHz. 
     The cascaded filter  60  of  FIG.  6 A  is an example of a non-acoustic LC filter cascaded with a hybrid acoustic LC filter. The principles and advantages discussed herein can be implemented in a variety of other filter topologies. Some example filter topologies are shown in  FIGS.  7  to  10   . These filters can be used in 5G applications, for example. These filters include acoustic resonators, such as FBARs, and inductors and capacitors. The inductors and capacitors can include one or more IPDs, one or more surface mount inductors, one or more surface mount capacitors, one or more inductive traces on a packaging substrate, the like, or any suitable combination thereof. The example filters of  FIGS.  7  to  10    illustrate filters for various applications and design specifications. Any suitable combination of features of these filters can be implemented together with each other and/or in accordance with any other principles and advantages discussed herein. 
       FIG.  7    is a schematic diagram of a cascaded filter  70  according to another embodiment. The cascaded filter  70  includes a hybrid acoustic LC filter  72  cascaded with an LC filter  74 . The hybrid acoustic LC filter  72  is an example of the hybrid acoustic LC filter  12 . The LC filter  74  is an example of the LC filter  14 . The cascaded filter  70  can be a receive filter, for example. The cascaded filter  70  can have a passband from 3.4 GHz to 3.7 GHz in certain applications. 
     The hybrid acoustic LC filter  72  includes acoustic resonators A 71 , A 72 , A 73 , A 74 , A 75 , and A 76 ; capacitors C 701 , C 702 , and C 703 ; and inductors L 701 , L 702 , L 703 , L 704 , L 705 , L 706 , L 707 , L 708 , and L 709 . The acoustic resonators A 71  to A 76  can be BAW resonators. The capacitors C 701  to C 703  can be SMT capacitors. The inductors L 701  to L 709  can include a combination of SMT inductors and conductive traces of a packaging substrate. 
     The illustrated LC filter  74  includes capacitors C 704  and C 705  and inductors L 710  and L 711 . In certain embodiments, the LC filter  74  can be implemented by IPD capacitors and inductors on an IPD die. In some other embodiments, the LC filter  74  can be implemented by SMT capacitors and inductors on an IPD die. 
       FIG.  8    is a schematic diagram of a cascaded filter  80  according to another embodiment. The cascaded filter  80  includes a hybrid acoustic LC filter  82  cascaded with an LC filter  84 . The hybrid acoustic LC filter  82  is an example of the hybrid acoustic LC filter  12 . The LC filter  84  is an example of the LC filter  14 . In an embodiment, the cascaded filter  80  can be a band pass filter having a passband from around 3.3 GHz to 4.2 GHz. According to another embodiment, the cascaded filter can have a passband from 3.4 GHz to 3.7 GHz. The cascaded filter  80  can be a receive filter, for example. 
     The hybrid acoustic LC filter  82  includes acoustic resonators A 81 , A 82 , A 83 , A 84 , and A 85 ; capacitors C 801  and C 802 ; and inductors L 801 , L 802 , L 803 , L 804 , L 805 , and L 806 . The acoustic resonators A 81  to A 85  can be BAW resonators. The capacitors C 801  and C 802  can be SMT capacitors. The inductors L 801  to L 805  can include a combination of SMT inductors and conductive traces of a packaging substrate. A hybrid resonator that includes the inductors L 802  and L 803  and acoustic resonators A 81 , A 82 , and A 83  can function similarly to the hybrid resonator described with reference to  FIGS.  11 A and  11 B . The hybrid ladder structure that includes inductors L 802  to L 805 , capacitor C 802 , and acoustic resonators A 81  to A 85  can function similarly to the hybrid ladder structure described with reference to  FIG.  12   . 
     The illustrated LC filter  84  includes capacitors C 803 , C 804 , C 805 , C 806 , and C 807  and inductors L 806 , L 807 , L 808 , and L 809 . The LC filter  84  can include one or more IPDs, one or more SMT components, one or more conductive traces of a substrate, or any suitable combination thereof. 
       FIG.  9    is a schematic diagram of a cascaded filter  90  according to another embodiment. The cascaded filter  90  includes a hybrid acoustic LC filter  92  cascaded with an LC filter  94 . The hybrid acoustic LC filter  92  is an example of the hybrid acoustic LC filter  12 . The LC filter  94  is an example of the LC filter  14 . In certain embodiments, the cascaded filter  90  can include surface mounted passive components except for shunt inductors coupled between acoustic resonators and ground, in which such shunt inductors can be printed traces on a packaging substrate. As such, in such embodiments, the cascaded filter  90  does not include an IPD. The cascaded filter  90  can be a receive filter coupled between an antenna switch and a low noise amplifier in certain instances. The cascaded filter  90  can improve insertion loss relative to previous designs. The cascaded filter  90  can be a receive filter. 
     The hybrid acoustic LC filter  92  includes acoustic resonators A 91 , A 92 , and A 93 ; capacitors C 901 , C 902 , C 903 , and C 904 ; and inductors L 901 , L 902 , L 903 , and L 904 . The acoustic resonators A 91  to A 93  can be BAW resonators. The capacitors C 901  to C 904  can be SMT capacitors. The inductors L 901  to L 904  can include a combination of SMT inductors and conductive traces of a packaging substrate. 
     The illustrated LC filter  94  includes capacitors C 903 , C 904 , and C 905  and inductors L 905 , L 906 , L 907 , and L 908 . The LC filter  94  can include one or more IPDs, one or more SMT components, one or more conductive traces of a substrate, or any suitable combination thereof. In one embodiment, the LC filter  94  consists of SMT inductors and capacitors. 
       FIG.  10    is a schematic diagram of a cascaded filter according to another embodiment. The cascaded filter  100  includes a hybrid acoustic LC filter  102  cascaded with an LC filter  104 . The hybrid acoustic LC filter  102  is an example of the hybrid acoustic LC filter  12 . The LC filter  104  is an example of the LC filter  14 . In certain embodiments, the cascaded filter  100  can include IPDs, surface mounted passive components, inductive traces on a laminate, and FBARs. The cascaded filter  100  can be a receive filter coupled between an antenna switch and a low noise amplifier in certain instances. The cascaded filter  100  can be a band pass filter with a passband from about 3.3 GHz to 4.2 GHz. The cascaded filter  100  is a receive filter in certain embodiments. 
     The hybrid acoustic LC filter  102  includes acoustic resonators A 101 , A 102 , and A 103 ; capacitors C 1001  and C 1002 ; and inductors L 1001 , L 1002 , L 1003 , L 1004 , L 1005 , and L 1006 . The acoustic resonators A 101  to A 103  can be BAW resonators. The capacitors C 1001  and C 1002  can include a SMT capacitor and/or an IPD capacitor. The inductors L 1001  to L 1006  can include one or more SMT inductors, one or more IPD inductors, one or more conductive traces of a packaging substrate, or any suitable combination thereof. In an embodiment, the inductors L 1001  to L 1006  include at least SMT inductor, at least one IPD inductor, and at least one conductive trace of a packaging substrate. 
     A hybrid resonator that includes the inductors L 1002  and L 1003  and acoustic resonator A 102  can function similarly to the hybrid resonator described with reference to  FIGS.  11 A and  11 B . A hybrid resonator that includes the inductors L 1005  and L 1006  and acoustic resonator A 103  can function similarly to the hybrid resonator described with reference to  FIGS.  11 A and  11 B . The hybrid ladder structure that includes inductors L 802  to L 806 , capacitor C 1002 , and acoustic resonators A 102  to A 103  can function similarly to the hybrid ladder structure described with reference to  FIG.  12   . 
     The illustrated LC filter  104  includes capacitors C 1003 , C 1004 , C 1005 , C 1006 , and C 1007  and inductors L 1007 , L 1008 , L 1009 , and L 1010 . The LC filter  104  can include one or more IPDs, one or more SMT components, one or more conductive traces of a substrate, or any suitable combination thereof. In an embodiment, the LC filter  104  includes at least SMT component, at least one IPD, and at least one conductive trace of a packaging substrate. 
     The hybrid acoustic LC filters discussed herein can include a variety of hybrid resonators that include an acoustic wave resonator and a non-acoustic passive component. Example hybrid resonators will be discussed with reference to  FIGS.  11 A to  12   . These hybrid resonators can be implemented in association with any suitable embodiments discussed herein. 
       FIG.  11 A  is a schematic diagram of a hybrid resonator  110  according to an embodiment. The hybrid resonator  110  includes an acoustic resonator  112 , a first inductor  114 , and a second inductor  116 . The acoustic resonator  112  is arranged as a shunt resonator. The acoustic resonator  112  can be an FBAR, for example. The acoustic resonator  112  can be any other suitable acoustic resonator. The acoustic resonator  112  is in parallel with the first inductor  114 . The acoustic resonator  112  is in series with the second inductor  116 . The combination of the inductors  114  and  116  and the acoustic resonator  112  can create a pair of notches that are relatively close to passbands without a significant impact on transmission loss. The notches can be in a range from with about 1.1 GHz to 8.5 GHz from a lower bound or an upper bound of a passband. 
       FIG.  11 B  is a graph of a frequency response of the hybrid resonator  110  of  FIG.  11 A . The frequency response illustrates the pair of notches discussed with reference to  FIG.  11 A . The frequency response also illustrates that the simulated hybrid resonator  110  does not introduce significant transmission loss. 
       FIG.  12    is a schematic diagram of a hybrid resonator  120  according to another embodiment. The hybrid resonator  120  is a hybrid ladder structure. The hybrid resonator  120  includes a first series shunt circuit, an LC tank, and a second series shunt circuit. The first series shunt circuit includes a first acoustic resonator  122  and a first inductor  123 . The second series shunt circuit includes a second acoustic resonator  124  and a second inductor  125 . The LC tank includes a capacitor  126  in parallel with a third inductor  127 . The hybrid resonator  120  includes the LC tank between acoustic nodes. This can provide both inter-resonator impedance matching and a far-end notch in a frequency response of a filter that includes the hybrid resonator  120 . The hybrid resonator  120  includes a hybrid ladder structure. The hybrid resonator  120  can be used for low pass filters and/or high pass filters, for example. The hybrid resonator  120  is a hybrid ladder topology. 
     Parallel Hybrid Acoustic Passive Filter 
     As 5G wireless communications technology advances, new carrier aggregation (CA) specifications can specify more stringent intermodulation distortion (IMD) rejection for a filter. Such new CA can involve more multiplexing filters than previous CA. To provide CA IMD rejection compliant filters with sharp rejections at passband-close frequencies, acoustic-assisted filters can be designed with hybrid resonators such as the hybrid acoustic LC resonators to provide a relatively low-loss, wide passband and also have relatively sharp rejections at passband-close frequencies. Acoustic resonators can generate harmonics when relatively high power is applied. The harmonics generated by a surface acoustic wave device or a bulk acoustic wave device can leak to a higher frequency band and/or have an emission over a standard specification. 
     To provide CA compliant multiplexing filters with sharp rejections at edge band frequencies, hybrid acoustic LC wideband filters can be included in some or all of the passband arms. To reduce and/or minimize filter acoustic die and passive component use, either the hybrid acoustic LC filter, an integrated passive devices (IPD) filter, or a passive low pass (LP) or high pass (HP) filter can be shared by two or more passband arms. In addition, to provide a specific sharp rejection in high band arm (e.g., at Wi-Fi 2.4 GHz) in a band pass filter (BPF), a parallel hybrid acoustic LC filter can be included. In some instances, the parallel hybrid acoustic LC filter can be cascaded with another filter such as a passive non-acoustic filter. 
     Hybrid acoustic LC filters with parallel hybrid acoustic LC sub-filters are disclosed. In an embodiment, a parallel acoustic LC filter includes a first sub-filter configured to filter a radio frequency signal and a second sub-filter coupled in parallel with the first sub-filter. The first sub-filter includes a first acoustic resonator and a first LC component. The second sub-filter includes a second acoustic resonator and a second LC component. The parallel hybrid acoustic LC filter can be implemented in a multiplexer that includes a plurality of filters coupled together at a common node. A parallel hybrid acoustic filter can implement any suitable principles and advantages of the acoustic LC circuits disclosed herein. As one example, a parallel hybrid acoustic LC filter can include the hybrid resonator  110  of  FIG.  11 A . As one more example, a parallel hybrid acoustic LC filter can include a hybrid ladder structure  120  of  FIG.  12   . 
     Parallel hybrid acoustic LC filters can be band pass filters. Parallel hybrid acoustic LC filters can be band stop filters. A parallel hybrid acoustic LC filter can be in a high band path. Such filters can reduce and/or minimize the design complexity. In addition, such filters can be implemented with fewer passive components and/or in less physical area in certain applications. Parallel hybrid passive filters discussed herein can meet design specifications for high band paths, such as desired rejections at specific frequencies (e.g., Wi-Fi frequency bands). This can allow the high band path to be shared by a transmit path and a receive path simultaneously. 
     A parallel hybrid acoustic LC filter can provide relatively wide bandwidth and strong rejection at a particular frequency band. The parallel hybrid acoustic LC filter can include hybrid filters for different frequency bands in parallel with each other and arranged to provide strong rejection for another frequency band. As one example, a parallel Band 40 and Band 41 hybrid acoustic LC band pass filter can provide a bandwidth sufficiently wide to passband  40  and Band 41 signals while also providing strong rejection for a 2.4 GHz Wi-Fi frequency band. In some embodiments, a passive non-acoustic filter can be cascaded with the parallel hybrid acoustic LC filter to achieve both wide bandwidth and sharp rejections in a high band path. According to certain embodiments, a triplexer can be achieved by a parallel hybrid acoustic LC filter and two other filters coupled to a common node. For instance, a triplexer for low band (LB)/mid band (MB)/high band (HB) can include a LB filter, a MB filter, and a HB filter implemented by a hybrid acoustic LC filter that includes a Band 40 filter in parallel with a Band 41 filter. Such a triplexer can effectively serve as a quadplexer to benefit system level carrier aggregation applications. 
       FIG.  13    is a schematic block diagram of a hybrid parallel band pass filter  130  according to an embodiment. The parallel hybrid band pass filter  130  includes a first band pass filter  132  and a second band pass filter  134  arranged in parallel with each other. The first band pass filter  132  and the second band pass filter  134  are arranged to filter radio frequency signals. The first band pass filter  132  is a hybrid acoustic passive filter that includes a first acoustic resonator and a first non-acoustic passive component. The first non-acoustic passive component can include at least an inductor and a capacitor. The second band pass filter  134  can be a hybrid acoustic passive filter that includes a second acoustic resonator and a second non-acoustic passive component. The second non-acoustic passive component can include at least an inductor and a capacitor. The first band pass filter  132  has a first passband and the second band pass filter  134  has a second passband. By including two filters in parallel with each other, bandwidth of the parallel filter can be increased relative to either of the individual filters that are included in the parallel filter. The hybrid parallel band pass filter  130  has a passband that includes the first passband and the second passband. A frequency response of the hybrid parallel band pass filter  130  can have a notch in its passband between the first passband and the second passband. The notch can be for a 2.4 GHz Wi-Fi band, for example. A symbol  135  for the parallel hybrid band pass filter  130  is also shown in  FIG.  13   . 
     Although embodiments are discussed with reference to parallel hybrid acoustic LC filters for high band filters, any of the suitable principles and advantages discussed herein can be applied to mid band filters, low band filters, or any other filters that could benefit from features discussed herein. 
     Parallel hybrid acoustic LC filters discussed herein can be implemented in power amplifier modules, diversity receive modules, or any other suitable radio frequency front end modules. 
     The parallel hybrid acoustic passive filters discussed herein can be implemented in multiplexers that include a plurality of filters coupled together at a common node. Such multiplexers can include a diplexer, a triplexer, a quadplexer, etc. Any suitable number of filters can be coupled together at a common node in a multiplexer. A plurality of filers can be coupled together at a common node by a multi-throw radio frequency switch to implement switch-plexing functionality. Some example multiplexers that include parallel hybrid acoustic passive filters will be described with reference to  FIGS.  14  to  16   . The example multiplexers include a parallel hybrid acoustic filter  130  of  FIG.  13    and can be implemented in accordance with any suitable principles and advantages of the parallel hybrid acoustic filter  130 . 
       FIG.  14    is a schematic block diagram of a diplexer  140  that includes a hybrid parallel band pass filter  130  according to an embodiment. The diplexer  140  includes a hybrid parallel band pass filter  130  and a second filter  144 . The parallel hybrid acoustic filter  130  can be a high band filter and the second filter  144  can be a mid-band filter as illustrated. The parallel hybrid acoustic filter  130  and the second filter  144  can be coupled together at a common node, such as the illustrated antenna node ANT. The second filter  144  can be a hybrid acoustic passive filter, a non-acoustic LC filter, or an acoustic wave filter. The second filter  144  can be a band stop filter. A stop band of the band stop filter can include some or all of the first passband of the first band pass filter  132  and/or the second passband of the second band pass filter  134 . 
       FIG.  15    is a schematic block diagram of a triplexer  150  that includes a and a hybrid parallel band pass filter  130  according to an embodiment. The triplexer  150  includes a hybrid parallel band pass filter  130 , a second filter  154 , and a third filter  156 . The parallel hybrid acoustic filter  130  can be a high band filter, the second filter  154  can be a mid-band filter, and the third filter  156  can be a low band filter as illustrated. The parallel hybrid acoustic filter  130 , the second filter  154 , and the third filter  156  can be coupled together at a common node, such as the illustrated antenna node. The second filter  154  can be a high pass and band stop filter. A stop band of the high pass and band stop filter can include some or all of the first passband of the first band pass filter  132  and/or the second passband of the second band pass filter  134 . The second filter  154  can be a hybrid acoustic LC filter, a non-acoustic LC filter, or an acoustic wave filter. The third filter  156  can be a low pass filter. The third filter  156  can be a hybrid acoustic LC filter, a non-acoustic LC filter, or an acoustic wave filter. The third filter  156  can pass frequencies below the respective passbands of the second filter  154  and the hybrid parallel band pass filter  130 . 
       FIG.  16    is a schematic block diagram of a triplexer  160  that includes a shared high pass filter  162  and a hybrid parallel band pass filter  130  according to an embodiment. The triplexer  160  is like the triplexer  150  of  FIG.  15    except that a shared high pass filter  162  is cascaded with both the hybrid parallel band pass filter  130  and the second filter  144  and the second filter  144  is a band stop filter. Accordingly, the shared high pass filter  162  is coupled between the parallel hybrid acoustic filter  130  and the common node. The shared high pass filter  162  is also coupled between the second filter  144  and the common node. The shared high pass filter  162  can be an LC filter or a hybrid acoustic LC filter, for example. In an embodiment the shared high pass filter  162  can be a non-acoustic passive filter. Such a shared high pass filter  162  together with the parallel hybrid acoustic filter  130  can achieve relatively wide bandwidth and relatively sharp rejections for a high band path. 
       FIG.  17    is a schematic block diagram of a quadplexer  170  that includes a shared high pass filter  162  and a hybrid band pass filter according to an embodiment. The quadplexer  170  is like the triplexer  160  of  FIG.  16    except that separate terminals are provided to the first band pass filter  132  and the second band pass filter  134 , respectively. This can provide more freedom in terms of carrier aggregation options. In the quadplexer  170 , the first band pass filter  132  and the second band pass filter  134  can receive signals within different frequency band and filter the respective signals. 
       FIG.  17    is an example of a multiplexer that includes a hybrid acoustic passive filter. The first band pass filter  132  and the second band pass filter  134  have different passbands and are both coupled to a common node (the antenna node ANT in  FIG.  17   ) by way of the shared high pass filter  162 . The first band pass filter  132  and/or the second band pass filter  134  can include acoustic resonators and a non-acoustic passive component. The non-acoustic passive component can include an inductor and a capacitor external to a die that includes the acoustic wave resonators. The non-acoustic passive component can include an inductor in parallel with an acoustic resonator of the acoustic resonators. The first band pass filter  132  and/or the second band pass filter  134  can include any suitable combination of features of the hybrid acoustic passive filters disclosed herein. In certain embodiments, the first band pass filter  132  and the second band pass filter  134  each have a passband within a frequency range from 2 gigahertz to 5 gigahertz, such as passbands within a frequency range from 2 gigahertz to 3 gigahertz. 
     The band stop filter  144  is coupled to the common node by way of the shared high pass filter  162 . The band stop filter  144  includes a stop band that includes the passbands of the first band pass filter  132  and the second band pass filter  134 . The low pass filter  156  is coupled to the common node. 
     With the quadplexer  170 , certain carrier aggregation performance can be improved relative to the triplexer  160  of  FIG.  16   . For example, a wireless communication device that includes the quadplexer can support a carrier aggregation at a common node that includes a first carrier and a second carrier. In this example, the first carrier can be within a passband of the first band pass filter  132  and outside of the passband of the second band pass filter  134 , and the second carrier can be outside of the passbands of both the first and second band pass filters  132  and  134 , respectively. By not filtering the first carrier with the second band pass filter  134 , there can be less insertion loss degradation in the quadplexer  170  relative to the triplexer  160 . 
       FIG.  18    is a schematic diagram of a triplexer  180  that includes a hybrid parallel band pass filter  182  according to an embodiment. In  FIG.  18   , an example multiplexer with a hybrid parallel band pass filter is illustrated. As illustrated, the triplexer  180  includes the hybrid parallel band pass filter  182 , a hybrid acoustic LC filter  184 , and a non-acoustic LC filter  186 , and a harmonic notch filter  188 . 
     The hybrid parallel band pass filter  182  is an example of the hybrid parallel band pass filter  130 . The hybrid parallel band pass filer  182  is a high band filter in the triplexer  180 . The hybrid parallel band pass filter  182  is an example filter topology of acoustic wave resonators and inductors. As illustrated, a high band signal is provided to the hybrid parallel band pass filter  182  by way of inductors L 1801  and L 1802 . The hybrid parallel band pass filter  182  includes a first sub-filter that includes acoustic resonators A 1801 , A 1802 , A 1803 , A 1804 , A 1805 , A 1806 , A 1807 , A 1808 , A 1809 , and A 1810  and inductors L 1803 , L 1804 , and L 1805 . The hybrid parallel band pass filter  182  also includes a second sub-filter that includes acoustic resonators A 1811 , A 1812 , A 1813 , A 1814 , A 1815 , A 1816 , A 1817 , A 1818 , A 1819 , and A 1820  and inductors L 1806  and L 1807 . The hybrid parallel band pass circuit  182  includes parasitic capacitances that are not illustrated in  FIG.  18   , although these parasitic capacitances are part of an LC circuit of the hybrid parallel band pass filter  182 . Inductors of the hybrid parallel band pass filter  182  can include one or more SMT inductors and/or one or more conductive traces of a substrate. Acoustic resonators of the hybrid parallel band pass filter  182  can include one or more BAW resonators, such as one or more FBARs. 
     The hybrid acoustic LC filter  184  includes acoustic resonators, inductors, and capacitors. As illustrated, the hybrid acoustic LC filter  184  includes acoustic resonators A 1821 , A 1822 , A 1823 , A 1824 , A 1825 , A 1826 , A 1827 , A 1828 , and A 1829 ; inductors L 1808 , L 1809 , L 1810 , L 1811 , and L 1812 ; and capacitors C 1801  and C 1802 . The hybrid acoustic LC filter  184  can be implemented in accordance with any suitable principles and advantages of the hybrid acoustic LC filters disclosed herein. The hybrid acoustic LC filter  184  is a mid-band filter in the triplexer  180 . 
     The non-acoustic LC filter  186  is a low band filter in the triplexer  180 . The non-acoustic LC filter  186  can be a low pass filter. Such a low pass filter can be implemented in accordance with any suitable principles and advantages of the low pass filters of  FIGS.  24 A and/or  24 B , for example. 
     The harmonic notch filter  188  can provide notches at harmonics of a radio frequency signal to filter out the harmonics. The harmonic notch filter  188  can be implemented in accordance with any suitable principles and advantages of the low pass filters of  FIG.  24 D , for example. The illustrated harmonic notch filter  188  includes capacitors C 1803 , C 1804 , C 1805 , and C 1806  and inductors L 1813  and L 1814 . The harmonic notch filter  188  can provide notches at two harmonic frequencies. 
       FIG.  19 A  illustrates simulation results of the triplexer  180  of  FIG.  18   .  FIG.  19 A  illustrates the passbands of the filters  182 ,  184 , and  186  of the triplexer  180 . The low pass filter  186  has a passband indicated by a curve with a solid line. The mid band filter  184  has a passband indicated by a first dashed curve. The parallel hybrid acoustic band pass filter  182  passbands indicated by a different dashed curve. The parallel hybrid acoustic band pass filter  182  has a notch in the middle part of its passband. This notch can correspond to a frequency range between two different frequency bands that the parallel hybrid acoustic band pass filter  182  is arranged to pass. Simulation results indicate that isolation is improved across mid band and high band filters in the triplexer  180  compared to previous designs. Reasonable insertion loss is present in simulations of the triplexer  180  of  FIG.  18    with 9:1 load pull. 
       FIG.  19 B  illustrates graphs of simulation results of the triplexer  180  of  FIG.  18    compared to a previous design. These simulation results indicate that both insertion loss and isolation are improved with the triplexer  180  compared to the previous design. 
     Although embodiments of parallel hybrid acoustic filters discussed herein relate to band pass filters, any suitable principles and advantages of parallel hybrid acoustic filters discussed herein can be applied to band stop filters. A parallel hybrid acoustic band stop filter can be implemented as a standalone filter or in a multiplexer. Example parallel hybrid acoustic band stop filters will be discussed with reference to  FIGS.  20  to  22   . 
       FIG.  20    is a schematic block diagram of a hybrid parallel band stop filter  200  according to an embodiment. The hybrid parallel band stop filter  200  can create relatively broad-band rejection at close proximity of a passband of another filter without using an LC notch filter, which can degrade in-band loss more significantly. 
     The parallel hybrid band stop filter  200  includes a first band stop filter  202  and a second band stop filter  204  arranged in parallel with each other. The first band stop filter  202  and the second band stop filter  204  are arranged to filter radio frequency signals. The first band stop filter  202  is a hybrid acoustic passive filter that includes a first acoustic resonator and a first non-acoustic passive component. The first non-acoustic passive component can include at least an inductor and a capacitor. The second band stop filter  204  is a hybrid acoustic passive filter that includes a second acoustic resonator and a second non-acoustic passive component. The second non-acoustic passive component can include at least an inductor and a capacitor. The first band stop filter  202  has a first stop band and the second band stop filter  204  has a second stop band. By including two filters in parallel with each other, stop band of the parallel hybrid band stop filter  200  can be increased relative to either of the individual filters  202  or  204  that are included in the parallel filter. 
     The hybrid parallel band stop filter  200  has a stop band that includes the first stop band and the stop passband. A frequency response of the hybrid parallel band stop filter  200  can have a notch in its stop band between the first stop band and the second stop band. A symbol  205  for the parallel hybrid band pass filter  200  is also shown in  FIG.  20   . 
       FIG.  21    is a schematic diagram of a hybrid parallel band stop filter  210  according to an embodiment. The hybrid parallel band stop filter  210  is an example of the hybrid parallel band stop filter  200  of  FIG.  20   . The hybrid parallel band stop filer  210  is an example filter topology of acoustic wave resonators and inductors. The hybrid parallel band stop filer  210  includes parasitic capacitances that are not illustrated in  FIG.  21   , although these parasitic capacitances are part of an LC circuit of the hybrid parallel band stop filter  210 . 
     As illustrated, a radio frequency signal can be provided to the hybrid parallel band stop filter  210  by way of inductors L 2101  and L 2102 . The hybrid parallel band stop filter  210  includes a first sub-filter  212  that includes acoustic resonators A 2101 , A 2102 , A 2103 , A 2104 , and A 2105  and inductors L 2103 , L 2104 , L 2105 , L 2106 , and L 2107 . The hybrid parallel band stop filter  210  also includes a second sub-filter  214  that includes acoustic resonators A 216 , A 217 , A 218 , A 219 , and A 220 ; inductors L 2108 , L 2109 , and L 2110 ; and capacitor C 2101 . Inductors of the hybrid parallel band stop filter  210  can include one or more SMT inductors and/or one or more conductive traces of a substrate. Acoustic resonators of the hybrid parallel band stop filter  210  can include one or more BAW resonators, such as one or more FBARs. 
       FIG.  22    is a graph of a frequency response of the hybrid parallel band stop filter  210  of  FIG.  21   . The frequency response in  FIG.  22    shows that a relatively wide stop-band can be achieved with the parallel hybrid acoustic band stop filter  210 . 
     Hybrid Acoustic LC Filter with Harmonic Suppression 
     As 5G wireless communications technology advances, new carrier aggregation (CA) can specify more stringent intermodulation distortion (IMD) rejection for a filter. To provide CA IMD rejection compliant filters with sharp rejections at the passband-close frequencies, acoustic-assisted filters can be designed with hybrid resonators such as the hybrid acoustic LC resonators to provide a relatively low-loss, wide passband and also have relatively sharp rejections at passband-close frequencies. Acoustic resonators can generate harmonics when relatively high power is applied. The harmonics generated by a surface acoustic device or bulk acoustic device can leak to a higher frequency band and/or have an emission over a specification for a standard. 
     Since acoustic resonator filters can generate harmonics at relatively high power, a passive non-acoustic filter can be cascaded with a hybrid acoustic LC filter to achieve both hybrid acoustic LC filter rejections and to suppress resonator generated harmonics. Accordingly, a non-acoustic LC filter, such as an integrated passive device (IPD) filter, can be cascaded with a hybrid acoustic LC filter to achieve a relatively wide bandwidth and relatively high rejections while suppressing self-created harmonics. 
     Hybrid acoustic LC filters and/or multiplexers discussed herein can include a harmonic suppression filter to suppress one or more harmonic frequencies. The harmonic suppression filter can be a low pass filter and/or a notch filter. Disclosed harmonic suppression filters include non-acoustic filters. For instance, the harmonic suppression filter can be an IPD filter. The harmonic suppression filter is cascaded with the hybrid acoustic LC filter. These cascaded filters can be coupled between a power amplifier and an antenna port. For example, the harmonic suppression filter can be coupled between an antenna port and the hybrid acoustic LC filter. 
     Aspects of this disclosure relate to a hybrid acoustic LC filter with harmonic suppression. The hybrid acoustic LC includes a hybrid passive/acoustic filter configured to filter a radio frequency signal and a non-acoustic LC filter configured to suppress a harmonic of the radio frequency signal. The hybrid passive/acoustic filter includes acoustic resonators and a non-acoustic passive component. The non-acoustic LC filter is cascaded with the hybrid passive/acoustic filter. 
     The non-acoustic LC filter can be a notch filter. A frequency response of the notch filter can have a notch corresponding to a second harmonic of the radio frequency signal. A frequency response of the notch filter can have a notch corresponding to a third harmonic of the radio frequency signal. The non-acoustic LC filter can be a low pass filter. The non-acoustic LC filter can include integrated passive devices of an integrated passive device die. 
     The hybrid passive/acoustic filter can be implemented in accordance with any suitable principles and advantages of any of hybrid resonators disclosed herein. For instance, the hybrid passive/acoustic filter can include the hybrid resonator of  FIG.  11 A  and/or the hybrid resonator of  FIG.  12   . The acoustic resonators can include bulk wave acoustic resonators. 
     Hybrid acoustic LC filters with harmonic suppression can be implemented in a variety of applications, such as standalone filters, in multiplexers that include a plurality of filters arranged to filter radio frequency signals, and wireless communication devices such as mobile phones. Hybrid acoustic LC filters with harmonic suppression discussed herein can be implemented in power amplifier modules, diversity receive modules, or any other suitable radio frequency front end modules. 
       FIG.  23 A  is a schematic block diagram of radio frequency system that includes a filter  230  that includes a hybrid acoustic LC filter  232  cascaded with a low pass filter  233  according to an embodiment. The radio frequency system also includes a power amplifier  231  and an antenna  234 . As illustrated, the hybrid acoustic LC filter  232  can receive the radio frequency signal from the power amplifier  231 . The radio frequency signal from the power amplifier  231  can have a relatively high power. Acoustic resonators of the hybrid acoustic LC filter  232  can generate one or more harmonics. The low pass filter  233  can filter out such harmonic(s). Accordingly, the filter  230  is a hybrid acoustic LC filter with harmonic suppression. As illustrated, the low pass filter  233  is coupled between an output of the hybrid acoustic LC filter  232  and the antenna  234 . The antenna  234  can transmit a filtered version of the radio frequency signal provided by the power amplifier  231 . 
     The hybrid acoustic LC filter  232  can include acoustic resonators and non-acoustic passive components. The acoustic resonators can include one or more bulk acoustic wave resonators such as FBARs, one or more SAW resonators, one or more boundary wave resonators, one or more Lamb wave resonators, the like, or any suitable combination thereof. The hybrid acoustic LC filter  232  can include an LC circuit that includes one or more inductors and one or more capacitors. The one or more capacitors can include one or more IPD capacitors, one or more surface mount capacitors, one or more parasitic capacitors, the like, or any suitable combination thereof. The one or more inductors can include one or more IPD inductors, one or more surface mount conductors, one or more inductors implemented as a conductive trace of a packaging substrate, the like, or any suitable combination thereof. The hybrid acoustic LC filter  232  can be implemented in accordance with any suitable principles and advantages of hybrid acoustic LC filters disclosed herein. In some instances, the hybrid acoustic LC filter  232  can include a hybrid resonator  110  of  FIG.  11 A . The hybrid acoustic LC filter  232  can include a hybrid ladder structure  120  of  FIG.  12    in certain applications. 
     In certain applications, the hybrid acoustic LC filter  232  can have a passband from 3.3 GHz to 4.2 GHz. According to some other applications, the hybrid acoustic LC filter  232  can have a passband from 4.4 GHz to 5 GHz. The hybrid acoustic LC filter  232  can provide rejection for (a) a carrier aggregation transmit blocker and (b) a continuous-wave out-of-band blocker in various embodiments. 
     The low pass filter  233  can pass signals below a cutoff frequency and suppress signals above a cut off frequency. Accordingly, the cutoff frequency of the low pass filter  233  can be selected so as to pass the radio frequency signal from the hybrid acoustic LC filter  232  and to suppress one or more harmonics of the radio frequency signal. For instance, the cutoff frequency could be set to a frequency that is above the frequency of the radio frequency signal and below the second harmonic of the radio frequency signal. In certain embodiments, the hybrid acoustic LC filter  232  is a band pass filter and the cutoff frequency of the low pass filter  233  is above the passband of the band pass filter and below a second harmonic of the radio frequency signal passed by the band pass filter. 
     The low pass filter  233  can be a non-acoustic LC filter. The low pass filter  233  can include one or more capacitors and one or more inductors. The low pass filter  233  can include one or more IPDs, one or more surface mount passive components, one or more passive components of a packaging substrate such as one or more inductive traces on the packaging substrate, the like, or any suitable combination thereof. Example circuit topologies for the low pass filter  233  will be discussed with reference to  FIGS.  24 A and  24 B . 
       FIG.  23 B  is a schematic block diagram of a radio frequency system that includes a filter  235  that includes a hybrid acoustic LC filter  232  cascaded with a harmonic notch filter  236  according to an embodiment. The radio frequency system of  FIG.  23 B  is like the radio frequency system of  FIG.  23 A  except that the filter  230  of  FIG.  23 A  is replaced by the filter  235  in  FIG.  23 B . The filter  235  is like the filter  230  of  FIG.  23 A  except that a harmonic notch filter  236  is included in place of the low pass filter  233  from the filter  230  of  FIG.  23 A . As illustrated, the harmonic notch filter  236  is coupled between an output of the hybrid acoustic LC filter  232  and the antenna  234 . 
     The harmonic notch filter  236  can have one or more notches in its frequency response to filter out one or more corresponding harmonics of a radio frequency signal from the hybrid acoustic LC filter  232 . The second harmonic generated by acoustic resonators of the hybrid acoustic LC filter  232  can be the most pronounced harmonic. Accordingly, the harmonic notch filter  236  can be a second harmonic notch filter that has a notch in its frequency response at a second harmonic. The harmonic notch filter  236  can have a notch at one or more other harmonics. In certain embodiments, a harmonic notch filter cascaded with the hybrid acoustic LC filter  232  can have two or more notches at any suitable harmonics. As an example, a harmonic notch filter can have notches at a second harmonic and a third harmonic. With a notch at a harmonic of a radio frequency signal provided by the hybrid acoustic LC filter  232 , the harmonic notch filter  236  can suppress the harmonic generated by acoustic resonators of the hybrid acoustic LC filter  232 . 
     The harmonic notch filter  236  can be a non-acoustic LC filter that includes one or more capacitors and one or more inductors. The harmonic notch filter  236  can include one or more IPDs, one or more surface mount passive components, one or more passive components of a packaging substrate such as one or more inductive traces on the packaging substrate, the like, or any suitable combination thereof. Example circuit topologies for the harmonic notch filter  236  and/or other suitable harmonic notch filters will be discussed with reference to  FIGS.  24 C and  24 D . 
       FIG.  24 A  is a schematic diagram of an example low pass filter  240 . The low pass filter  240  is an example of the low pass filter  233  of  FIG.  23 A . The low pass filter  240  includes a series inductor L 1  and a shunt capacitor C 1  arranged to filter out frequencies above a cutoff frequency. The inductance of the series inductor L 1  and the capacitance of the shunt capacitor C 1  can together set the cutoff frequency in the low pass filter  240 . 
       FIG.  24 B  is a schematic diagram of another example low pass filter  242 . The low pass filter  242  is an example of the low pass filter  233  of  FIG.  23 A . The low pass filter  242  includes series inductors L 1  to LN and shunt capacitors C 1  to CN. The inductances of the series inductors L 1  to LN and the capacitances of the shunt capacitors C 1  to CN can together set the cutoff frequency in the low pass filter  242 . 
       FIG.  24 C  is a schematic diagram of an example harmonic notch filter  243 . The harmonic notch filter  243  is an example of the harmonic notch filter  236  of  FIG.  23 B . The harmonic notch filter  243  includes a shunt series LC circuit. The inductor Ls and a capacitor C 1  of the shunt series LC circuit can set the frequency of the notch. Different impedances of the inductor Ls and the capacitor C 1  can together generate a notch at different respective frequencies. The notch can be provided at any suitable harmonic frequency. For instance, the notch can be set to a second harmonic of a radio frequency signal provided to the harmonic notch filter  243 . As another example, the notch can be set to a third harmonic of a radio frequency signal provided to the harmonic notch filter  243 . 
       FIG.  24 D  is a schematic diagram of an example harmonic notch filter  244 . The harmonic notch filter  244  is an example of the harmonic notch filter  236  of  FIG.  23 B . The harmonic notch filter  244  includes two shunt series LC circuits. A first shunt series LC circuit includes capacitor C 1  and inductor Ls 1 . A second shunt series LC circuit includes capacitor C 2  and inductor Ls 2 . The two shunt series LC circuits can provide notches at different harmonics, such as a second harmonic and a third harmonic. Accordingly, the illustrated harmonic notch filter  244  can provide notches at two different harmonics. The impedances of each shunt series LC can set a respective frequency of each notch. Other harmonic notch filters can provide notches at three or more harmonics. 
       FIG.  24 E  is a schematic diagram of an example harmonic notch and low pass filter  245 . The harmonic notch and low pass filter  245  can provide a low pass filter that also includes a notch in a frequency response at a harmonic. A shunt series LC circuit can provide the harmonic notch. The shunt series LC circuit includes capacitor C 1  and inductor Ls. A series inductor L 1  together with a shunt capacitor C 2  can provide low pass filter characteristics. 
     The hybrid acoustic LC filters with harmonic suppression discussed herein can be implemented in multiplexers that include a plurality of radio frequency filters coupled together at a common node. Example multiplexers include diplexers, triplexer, quadplexers, etc. Any suitable number of filters can be coupled together at a common node in a multiplexer. A plurality of filers can be coupled together at a common node by a multi-throw radio frequency switch to implement switch-plexing functionality. Some example multiplexers that include a hybrid acoustic LC filters with harmonic suppression will be described with reference to  FIGS.  25 A to  25 B . While the multiplexers are triplexers in these example embodiments, the principles and advantages associated with such embodiments can be applied to any other suitable multiplexers. Other suitable multiplexers include diplexers, quadplexers, etc. 
       FIG.  25 A  is a schematic block diagram of a triplexer  250  that includes hybrid acoustic LC filter  232  cascaded with a low pass filter  233  according to an embodiment. The triplexer  250  includes the filter  230  of  FIG.  23 A , a high band filter  252 , and a low band filter  254 . The filter  230 , the high band filter  252 , and the low band filter  254  are coupled together at a common node, which is an antenna node in the triplexer  250 . The filter  230  is a mid-band filter in the triplexer  250 . The high band filter  252  can be a band pass filter or a high pass filter. The high band filter  252  is arranged to filter high band radio frequency signals. The high band filter  252  can be a hybrid acoustic LC filter implemented in accordance with any suitable principles and advantages discussed herein. As one example, the high band filter can include parallel hybrid acoustic passive filters. In some other embodiments, the high band filter  252  can be implemented by any other suitable circuit elements, such as non-acoustic LC circuit elements. The low band filter  254  can be a low pass filter or a band pass filter. The low band filter  254  is arranged to filter low band radio frequency signals. The low band filter  254  can be a hybrid acoustic LC filter implemented in accordance with any suitable principles and advantages discussed herein. In some other embodiments, the low band filter  254  can be implemented by any other suitable circuit elements, such as non-acoustic LC circuit elements. 
       FIG.  25 B  is a schematic block diagram of a triplexer  255  that includes a hybrid acoustic LC filter  232  cascaded with a harmonic notch filter  236  according to an embodiment. The triplexer  255  is like the triplexer  250  of  FIG.  25 A  except that the filter  235  is included in place of the filter  230 . The filter  235  includes a harmonic notch filter  236  arranged to suppress a harmonic in the radio frequency signal provided by the hybrid acoustic LC filter  232 . The harmonic notch filter  236  can provide notches for two or more harmonics in some applications. In certain embodiments, a filter of a multiplexer can include a hybrid acoustic LC filter cascaded with a low pass and harmonic notch filter. 
     Radio Frequency Modules 
     The filters disclosed herein can be implemented in a variety of packaged modules. Some example packaged modules will now be disclosed in which any suitable principles and advantages of the filters and/or multiplexers disclosed herein can be implemented. The example packaged modules can include a package that encloses the illustrated circuit elements. A module that includes a radio frequency component can be referred to as a radio frequency module. The illustrated circuit elements can be disposed on a common packaging substrate. The packaging substrate can be a laminate substrate, for example.  FIGS.  26  to  28    are schematic block diagrams of illustrative packaged modules according to certain embodiments. Any suitable combination of features of these packaged modules can be implemented with each other. While filters are illustrated in the example packaged modules of  FIGS.  26  to  28   , any of such filters can be implemented in a suitable multiplexer. 
       FIG.  26    is a schematic diagram of a radio frequency module  260  with a transmit path that includes a filter  262  according to an embodiment. The illustrated module  260  includes the filter  262 , a power amplifier  263 , and a radio frequency switch  264 . The radio frequency module that includes a power amplifier can be referred to as a power amplifier module. The power amplifier  263  can amplify a radio frequency signal. The radio frequency switch  264  can be a multi-throw radio frequency switch. The radio frequency switch  264  can electrically couple an output of the power amplifier  263  to the filter  262 . The filter  262  is a transmit filter arranged to filter a transmit radio frequency signal. The filter  262  can include any suitable combination of features of the filters disclosed herein. In some other instances, a radio frequency switch can selectively electrically connect a transmit signal path to an input of the power amplifier  263 . 
       FIG.  27    is a schematic diagram of a radio frequency module  270  with a receive path that includes a filter  272  according to an embodiment. The illustrated module  270  includes the filter  272 , a low noise amplifier  274 , and a radio frequency switch  274 . The filter  272  is a receive filter arranged to filter a received radio frequency signal. The filter  272  can include any suitable combination of features of the filters disclosed herein. The low noise amplifier  274  can amplify filtered received radio frequency signal provided by the filter  272 . The radio frequency switch  274  can electrically couple an output of the low noise amplifier  274  to a receive path. In certain embodiments, the radio frequency switch  276  can be a multi-throw radio frequency switch arranged to selectively electrically couple the output of the low noise amplifier  274  to one or more selected receive paths. In such embodiments, a radio frequency splitter (not illustrated) can be coupled between the low noise amplifier  274  and the radio frequency switch  276 . 
       FIG.  28    is a schematic diagram of a radio frequency module  280  that includes a filter  282  according to an embodiment. The illustrated module  280  includes one or more filters  282 , a radio frequency switch  284 , a power amplifier  263 , and a low noise amplifier  274 . The one or more filters  282  can include any suitable combination of features of the filters disclosed herein. The radio frequency switch  284  can electrically couple the one or more filters  282  to the power amplifier  263  and/or the low noise amplifier  274 . 
     Wireless Communication Devices 
     The filters discussed herein can filter radio frequency signals in a wireless communication device. Example wireless communication devices will be discussed with reference to  FIGS.  29  and  30   . 
       FIG.  29    is a schematic diagram of a wireless communication  290  device that includes a filter  293  in a radio frequency front end  292  according to an embodiment. The wireless communication device  290  can be any suitable wireless communication device. For instance, a wireless communication device  290  can be a mobile phone, such as a smart phone. As illustrated, the wireless communication device  290  includes an antenna  291 , an RF front end  292  that includes a filter  293 , a transceiver  294 , a processor  295 , a memory  296 , and a user interface  297 . The antenna  291  can transmit RF signals provided by the RF front end  292 . Such RF signals can include carrier aggregation signals. The antenna  291  can provide received RF signals to the RF front end  292  for processing. Such RF signals can include carrier aggregation signals. 
     The RF front end  292  can include one or more power amplifiers, one or more low noise amplifiers, RF switches, receive filters, transmit filters, duplex filters, multiplexers, frequency multiplexing circuits, or any combination thereof. The RF front end  292  can transmit and receive RF signals associated with any suitable communication standards. The filter  293  can be implemented in accordance with any suitable principles and advantages of the filters discussed herein. For instance, the filter  293  can implement any suitable combination of features discussed with reference to any of  FIGS.  1  to  25 B . Two or more filters of the RF front  292  can be implemented in accordance with any suitable principles and advantages disclosed herein. 
     The transceiver  294  can provide RF signals to the RF front end  292  for amplification and/or other processing. The transceiver  294  can also process an RF signal provided by a low noise amplifier of the RF front end  292 . The transceiver  294  is in communication with the processor  295 . The processor  295  can be a baseband processor. The processor  295  can provide any suitable baseband processing functions for the wireless communication device  290 . The memory  296  can be accessed by the processor  295 . The memory  296  can store any suitable data for the wireless communication device  290 . The processor  295  is also in communication with the user interface  297 . The user interface  297  can be any suitable user interface, such as a display. 
       FIG.  30    is a schematic diagram of a wireless communication device  300  that includes a filter  293  in a radio frequency front end  292  and a second filter  303  in a diversity receive module  302  according to an embodiment. The wireless communication device  300  is like the wireless communication device  290  of  FIG.  29   , except that the wireless communication device  300  also includes diversity receive features. As illustrated in  FIG.  30   , the wireless communication device  300  includes a diversity antenna  301 , a diversity module  302  configured to process signals received by the diversity antenna  301  and including a filter  303 , and a transceiver  304  in communication with both the radio frequency front end  292  and the diversity receive module  302 . The filter  303  can be implemented in accordance with any suitable principles and advantages of the filters discussed herein. For instance, the filter  303  can implement any suitable combination of features discussed with reference to any of  FIGS.  1  to  25 B . Two or more filters of the diversity receive module  302  can be implemented in accordance with any suitable principles and advantages disclosed herein. 
     Conclusion 
     Any of the principles and advantages discussed herein can be applied to other suitable systems, modules, chips, filter assemblies, filters, wireless communication devices, and methods not just to the systems, modules, chips, filter assemblies, filters, wireless communication devices, and methods described above. The elements and operations of the various embodiments described above can be combined to provide further embodiments. Any of the principles and advantages discussed herein can be implemented in association with radio frequency circuits configured to process signals having a frequency in a range from about 30 kHz to 300 GHz, such as a frequency in a range from about 450 MHz to 8.5 GHz. 
     Aspects of this disclosure can be implemented in various electronic devices. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products such as chips and/or packaged radio frequency modules, electronic test equipment, uplink wireless communication devices, personal area network communication devices, etc. Examples of the consumer electronic products can include, but are not limited to, a mobile phone such as a smart phone, a wearable computing device such as a smart watch or an ear piece, a telephone, a television, a computer monitor, a computer, a router, a modem, a hand-held computer, a laptop computer, a tablet computer, a personal digital assistant (PDA), a vehicular electronics system such as an automotive electronics system, a microwave, a refrigerator, a stereo system, a digital music player, a camera such as a digital camera, a portable memory chip, a household appliance, etc. Further, the electronic devices can include unfinished products. 
     Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. The word “coupled,” as generally used herein, refers to two or more elements that may be either directly coupled to each other, or coupled by way of one or more intermediate elements. Likewise, the word “connected,” as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel devices, filters, filter assemblies, chips, methods, apparatus, and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods, apparatus, and systems described herein may be made without departing from the spirit of the disclosure. For example, circuit blocks described herein may be deleted, moved, added, subdivided, combined, and/or modified. Each of these circuit blocks may be implemented in a variety of different ways. The accompanying claims and their equivalents are intended to cover any such forms or modifications as would fall within the scope and spirit of the disclosure.