Reconfigurable radio frequency (RF) filter circuits

Abstract

A radio frequency (RF) filter circuit is provided. The RF filter circuit includes a first resonator communicatively coupled between a first terminal and a second terminal, a second resonator communicatively coupled to the first resonator and between the first terminal and the second terminal, and a switchable frequency adjusting circuit coupled in parallel with the first resonator. In response to the switchable frequency adjusting circuit being turned off, the RF filter circuit passes a signal in a first filtering frequency range having a first passband. In response to the switchable frequency adjusting circuit being turned on, the RF filter circuit passes the signal in a second filtering frequency range having a second passband. The second filtering frequency range has a higher attenuation at a near-band frequency outside the first passband and the second passband than the first filtering frequency range.

Description

RECONFIGURABLE RADIO FREQUENCY (RF) FILTER CIRCUITSRELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Provisional Application No. 63 / 589,237, filed October 10, 2023, which is incorporated herein by reference in its entiretyFIELD OF THE INVENTION

[0002] This disclosure relates to radio frequency (RF) devices. In particular, this disclosure relates to reconfigurable RF filter circuits.BACKGROUND

[0003] Radio frequency (RF) filters, e.g., particularly acoustic wave resonators or filters, are used in high-frequency communication applications such as 3rdGeneration (3G), 4thGeneration (4G), and 5thGeneration (5G) wireless devices. In particular, a RF filter is often employed to provide a flat passband, steep filter skirts, and squared shoulders at the upper and lower ends of the passband, and provide excellent rejection outside of the passband in a filter network. These wireless devices often support various communication means such as cellular, wireless fidelity (Wi-Fi), Bluetooth, and / or near-field communications, and accordingly, high performance of the RF filters are needed.

[0004] For example, the continuous addition of new frequency ranges or repurposing existing frequency ranges in an already crowded spectrum, while maintaining co-existing conditions, requires RF filters to achieve a very steep transition. The required filter steepness makes it difficult to achieve while maintaining desirable insertion loss. To overcome this shortcoming, a filter bank with RF filters having different roll-offs / bandwidths is used. This results in a bulky and expensive solution, in addition to the increased insertion loss since silicon (SOI) switches are needed at the input and output of the filter bank.

[0005] Therefore, there is a need to provide RF filters with a desirably high steep transition from transmission to attenuation at a near-band frequency of interest while maintaining low insertion loss.SUMMARY

[0006] Aspects of the disclosure include a RF filter circuit. The RF filter circuit includes a firstresonator communicatively coupled between a first terminal and a second terminal; a second resonator communicatively coupled to the first resonator and between the first terminal and the second terminal; and a switchable frequency adjusting circuit coupled in parallel with the first resonator. In response to the switchable frequency adjusting circuit being turned off, the RF filter circuit passes a signal in a first filtering frequency range having a first passband. In response to the switchable frequency adjusting circuit being turned on, the RF filter circuit passes the signal in a second filtering frequency range having a second passband. The second filtering frequency range has a higher attenuation at a near-band frequency outside the first passband and the second passband than the first filtering frequency range.

[0007] In some embodiments, an upper-stopband frequency of the second passband is lower than an upper-stopband frequency of the first passband.

[0008] In some embodiments, the first resonator and the second resonator each includes a series resonator.

[0009] In some embodiments, the switchable frequency adjusting circuit includes a switchable capacitor.

[0010] In some embodiments, the switchable capacitor includes a metal-insulator-metal (MIM) capacitor coupled with a silicon-on-insulator (SOI) switch.

[0011] In some embodiments, the RF filter circuit further includes another series resonator communicatively coupled to between the first terminal and the second terminal; and a shunt resonator communicatively coupled between the switchable frequency adjusting circuit and ground (GND).

[0012] In some embodiments, the switchable frequency adjusting circuit is communicatively coupled between one of the first terminal or the second terminal, and the second resonator.

[0013] In some embodiments, the RF filter circuit further includes a second switchable frequency adjusting circuit communicatively coupled to the second resonator between the first terminal and the second terminal. The second resonator is communicatively coupled between the switchable frequency adjusting circuit and the second switchable frequency adjusting circuit.

[0014] In some embodiments, the RF filter circuit further includes a third resonator communicatively coupled to the second resonator in parallel between the first terminal and the second terminal. The third resonator is communicatively coupled to the first resonator in series. The second resonator and the third resonator are each communicatively coupled to a respective switch in series or in parallel.

[0015] In some embodiments, the RF filter circuit further includes a third terminalcommunicatively coupled to the second terminal, and a filter circuit coupled between the third terminal and the second terminal, the filter circuit configured to pass a second signal in a third filtering frequency range. The third filtering frequency range is lower than or equal to the near-band frequency.

[0016] Another aspect of the present disclosure provides a RF filter circuit. The RF filter circuit includes a resonator communicatively coupled between a first terminal and a second terminal; and a switchable frequency adjusting circuit coupled in series with the resonator. In response to the switchable frequency adjusting circuit being turned off, the RF circuit passes a signal in a first filtering frequency range having a first passband. In response to the switchable frequency adjusting circuit being turned on, the RF circuit passes the signal in a second filtering frequency range having a second passband. The second filtering frequency range has a higher attenuation at a near-band frequency outside the first passband and the second passband than the first filtering frequency range.

[0017] In some embodiments, an upper-stopband frequency of the second passband is lower than an upper-stopband frequency of the first passband.

[0018] In some embodiments, the switchable frequency adjusting circuit includes a second resonator communicatively coupled in series with the resonator; and a switchable component communicatively coupled in parallel with the second resonator.

[0019] In some embodiments, the resonator and the second resonator each includes a series resonator.

[0020] In some embodiments, the switchable component includes a switchable capacitor.

[0021] In some embodiments, the switchable capacitor includes a metal-insulator-metal (MIM) capacitor coupled with a silicon-on-insulator (SOI) switch.

[0022] In some embodiments, the RF filter circuit further includes: another series resonator communicatively coupled to between the first terminal and the second terminal; and a shunt resonator communicatively coupled between the switchable frequency adjusting circuit and ground (GND).

[0023] In some embodiments, the switchable frequency adjusting circuit is communicatively coupled between one of the first terminal or the second terminal, and the resonator

[0024] In some embodiments, the RF filter circuit further includes a second switchable frequencyadjusting circuit communicatively coupled to the resonator between the first terminal and the second terminal. The resonator is communicatively coupled between the switchable frequency-adjusting circuit and the second switchable frequency-adjusting circuit.

[0025] In some embodiments, the RF filter circuit further includes a third resonatorcommunicatively coupled to the resonator in parallel between the first terminal and the second terminal. The third resonator is communicatively coupled to the second resonator in series. The resonator and the third resonator are each communicatively coupled to a respective switch in series or in parallel.

[0026] In some embodiments, the RF filter circuit further includes a third terminal communicatively coupled to the second terminal, and a filter circuit coupled between the third terminal and the second terminal, the filter circuit configured to pass a second signal in a third filtering frequency range. The third filtering frequency range is lower than or equal to the near-band frequency.

[0027] Another aspect of the present disclosure provides a RF filter device. The RF device includes a first multiplexer branch that includes a first filter circuit. The first filter circuit includes a first resonator communicatively coupled between a first terminal and a second terminal; a second resonator communicatively coupled to the first resonator and between the first terminal and the second terminal; and a switchable frequency adjusting circuit coupled in parallel with the first resonator. In response to the switchable frequency adjusting circuit being turned off, the first multiplexer branch passes a signal in a first filtering frequency range having a first passband. In response to the switchable frequency adjusting circuit being turned on, the first multiplexer branch passes the signal in a second filtering frequency range having a second passband. The second filtering frequency range has a higher attenuation at a near-band frequency outside the first passband and the second passband than the first filtering frequency range. The RF device also includes a second multiplexer branch that includes a second filter circuit communicatively coupled between a third terminal and the second terminal, the second filter circuit configured to pass a second signal in a third filtering frequency range. The third filtering frequency range is higher than or equal to the near-band frequency. The RF device also includes an antenna coupled to the second terminal.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIGS. 1A-1C each illustrates a block diagram of an exemplary configuration of a reconfigurable RF filter circuit, according to some embodiments of the present disclosure.

[0029] FIG. 2A illustrates an exemplary switchable frequency adjusting circuit, according to some embodiments of the present disclosure.

[0030] FIG. 2B illustrates an impedance-frequency diagram of the frequency adjusting circuit in FIG. 2A, according to some embodiments of the present disclosure.

[0031] FIG. 3A illustrates an exemplary RF circuit with a frequency adjusting circuit, according to some embodiments of the present disclosure.

[0032] FIG. 3B illustrates an impedance-frequency diagram of the RF circuit in FIG. 3A, according to some embodiments of the present disclosure.

[0033] FIG. 4A illustrates an exemplary reconfigurable RF filter circuit with a switchable frequency adjusting circuit, according to some embodiments of the present disclosure.

[0034] FIG. 4B illustrates part of the reconfigurable RF filter circuit in FIG. 4A, according to some embodiments of the present disclosure.

[0035] FIG. 4C illustrates a transmission-frequency diagram of the part of the reconfigurable RF filter in FIG. 4B, according to some embodiments of the present disclosure.

[0036] FIG. 4D illustrates an isolation-frequency diagram of the part of the reconfigurable RF filter in FIG. 4B, according to some embodiments of the present disclosure.

[0037] FIGS. 5 A and 5B each illustrates an exemplary reconfigurable RF filter circuit with more than one switchable frequency adjusting circuit, according to some embodiments of the present disclosure.DETAILED DESCRIPTION

[0038] The following detailed description is illustrative in nature and is not intended to limit the scope, applicability, or configuration of inventive embodiments disclosed herein in any way. Rather, the following description provides practical examples, and those skilled in the art will recognize that some of the examples may have suitable alternatives. Embodiments will hereinafter be described in conjunction with the appended drawings, which are not to scale (unless so stated), wherein like numerals / letters denote like elements. However, it will be understood that the use of a number to refer to a component in a given drawing is not intended to limit the component in another drawing labeled with the same number. In addition, the use of different numbers to refer to components in different drawings is not intended to indicate that the different numbered components cannot be the same or similar to other numbered components. Examples of constructions, materials, dimensions and fabrication processes are provided for select elements and all other elements employ that which is known by those skilled in the art.

[0039] In the present disclosure, when a number or a range of numbers is described with “about,” “approximate,” and the like, the term is intended to encompass numbers that are within a reasonable range considering variations that inherently arise during manufacturing as understood by one ofordinary skill in the art. For example, the number or range of numbers encompasses a reasonable range including the number described, such as within + / -10% of the number described, based on known manufacturing tolerances associated with manufacturing a feature having a characteristic associated with the number. For example, a material layer having a thickness of “about 5 nm” can encompass a dimension range from 4.25 nm to 5.75 nm where manufacturing tolerances associated with depositing the material layer are known to be + / -15% by one of ordinary skill in the art. Still further, the present disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed.

[0040] In the present disclosure, the term “communicatively coupled” is interchangeable with the term “coupled,” which is also interchangeable with the term “electrically coupled.”

[0041] RF filters are widely used in various electronic devices that require co-existence between multiple frequency ranges, e.g., cellular bands, connectivity bands, non-terrestrial networks (NTN) bands, etc. Often, to separate different frequency ranges and facilitate the co-existence of these frequency ranges, a conventional filter circuit can include multiple filters with fixed bandwidths. However, the use of multiple filters can be slow, bulky, costly, and lossy. A filtering circuit that can provide steep transition and rejection / attenuation at a desired wavelength, with minimum insertion loss is thus desired.

[0042] Embodiments of the present disclosure provide a reconfigurable filter circuit having a single filter with reconfigurable filtering frequency ranges, e.g., reconfigurable passbands. The reconfigurable filter circuit can separate different passbands while maintaining or improving insertion loss. The reconfigurable filter circuit requires less space in the module area than the convention filter circuit and can be more cost efficient. The reconfigurable filter circuit includes a switchable frequency adjusting circuit communicatively coupled to a plurality of filter branches. The switchable frequency adjusting circuit can be switched on and off. When switched off, the reconfigurable filter circuit allows a signal to pass a first passband. When switched on, the reconfigurable filter circuit increases the steepness of the upper skirt, and allows the signal to pass a second passband. In some embodiments, the upper-stopband frequency corresponding to the second passband is lower than the upper-stopband frequency corresponding to the first passband. The second passband has improved rejection / attenuation at a near-band frequency of interest, e.g., a frequency band near or outside the first and second passbands, and has steeper transition from transmission to attenuation at the upper skirt compared to the first passband while the first and second passbands are substantially the same / similar. In some embodiments, the reconfigurable filtercircuit is part of a multiplexer branch, and the near-band frequency is designed to be a transmission frequency or part of a transmission frequency range in another multiplexer branch. Thus, while maintaining the insertion loss, the second passband can provide improved isolation over the transmission frequency in the other multiplexer branch, and improve the co-existence of the frequency ranges in the two multiplexer branches with reduced interference.

[0043] In some embodiments, the switchable frequency adjusting circuit includes a switchable capacitor, and is coupled in parallel with a series resonator between the filter branches and a terminal of the reconfigurable filter circuit. In some embodiments, the series resonator may also be part of the switchable frequency adjusting circuit. The switchable capacitor may interact with the resonators in the reconfigurable filter circuit to change (e.g., decrease) an anti-resonance frequency (or a parallel-resonance frequency) of the resonators and thus change the frequency profile (e.g., frequency and / or steepness of the upper skirt) of the passband. In some embodiments, the enabled switchable capacitor may cause a reduced upper-stopband frequency, and result in a steeper transition between passband and stopband. Thus, by switching on and off the switchable frequency adjusting circuit, the reconfigurable filter circuit may provide improved near-band rejection over frequencies or frequency ranges of interest.

[0044] FIGS. 1A-1C each illustrates an exemplary reconfigurable filter circuit with an exemplary switchable frequency adjusting circuit, according to some embodiments. The reconfigurable filter circuits may each include a first terminal 106 communicatively coupled to a second terminal 108. Depending on the application, first terminal 106 may be the input terminal for receiving a signal and second terminal 108 may be the output terminal for outputting a filtered signal, or vice versa. A filter branch 102 and a switchable frequency adjusting circuit 104 may be communicatively coupled and may be located between first terminal 106 and second terminal 108. In some embodiments, an input signal may pass through the switchable frequency adjusting circuit and filter branch 102, and may be filtered, and outputted by the output (e.g., first terminal 106 or second terminal 108). The output signal may have a frequency range filtered by the passband formed by the switchable frequency adjusting circuit 104 and filter branch 102. In FIGS. 1A-1C, filter branch 102 may represent one of the plurality of filter branches communicatively coupled to switchable frequency adjusting circuit 104. In some embodiments, circuit branch 102 includes at least a resonator coupled in series with switchable frequency adjusting circuit 104. It should be noted that, for simplicity, FIGS. 1A-1C merely show the relative positions of a switchable frequency adjusting circuit and a filter branch, and is not meant to exclude other components (e.g., resonators, capacitors, inductors, resistors, etc.) of the circuit. For example, one or more of reconfigurable circuits lOOa-lOOc mayinclude at least one series resonator and at least one shunt resonator communicatively coupled between first terminal 106 and second terminal 108. Also, a switchable frequency adjusting circuit in FIGS. 1A-1C may represent one or more switchable frequency adjusting circuits. The specific number of switchable frequency adjusting circuits should be determined based on application and are not limited by the embodiments of the present disclosure.

[0045] FIG. 1 A illustrates a configuration of reconfigurable filter circuit 100a, according to some embodiments. Reconfigurable filter circuit 100a may include a filter branch 102 and a switchable frequency adjusting circuit 104, communicatively coupled to each other between first terminal 106 and second terminal 108. As shown in FIG. 1 A, switchable frequency adjusting circuit 104 may be located between first terminal 106 and filter branch 102, and filter branch 102 may be located between switchable frequency adjusting circuit 104 and second terminal 108. In some embodiments, filter branch 102 includes a resonator and a switch communicatively coupled to each other in series. In some embodiments, first branch 102 includes another switch communicatively coupled to the resonator in parallel. The switches can be turned on and / or to connect the resonator to switchable frequency adjusting circuit 104 or bypass the resonator, resulting in different passbands.

[0046] Switchable frequency adjusting circuit 104 may be switched on or off to adjust its component(s) in connection with filter branch 102. The different combination of active components in reconfigurable filter circuit 100a may result in different passbands or near-band rejection frequencies by reconfigurable filter circuit 100a. In operation, a signal may pass switchable frequency adjusting circuit 104 and filter branch 102 to be filtered by the passband of reconfigurable filter circuit 100a. Depending on the configuration of switchable frequency adjusting circuit 104, the passband with switchable frequency adjusting circuit 104 turned on may have a higher attenuation over a near-band frequency than the passband with switchable frequency adjusting circuit 104 turned off.

[0047] FIG. IB illustrates a configuration of reconfigurable filter circuit 100b, according to some embodiments. Reconfigurable filter circuit 100b may include switchable frequency adjusting circuit 104 and filter branch 102, communicatively coupled to each other between first terminal 106 and second terminal 108. Different from reconfigurable filter circuit 100a, in reconfigurable filter circuit 100b, filter branch 102 may be located between first terminal 106 and switchable frequency adjusting circuit 104, and switchable frequency adjusting circuit 104 may be located between filter branch 102 and second terminal 108. In some embodiments, detailed description of filter branch 102, switchable frequency adjusting circuit 104, and operation may be referred to that of FIG. 1Aand is not repeated herein.

[0048] FIG. 1C illustrates a configuration of reconfigurable filter circuit 100c, according to some embodiments. Reconfigurable filter circuit 100c may include a switchable frequency adjusting circuit 104a, a switchable frequency adjusting circuit 104b, and filter branch 102, communicatively coupled to each other between first terminal 106 and second terminal 108. In some embodiments, switchable frequency adjusting circuits 104a and 104b may each be similar to switchable frequency adjusting circuits 104. In reconfigurable filter circuit 100b, filter branch 102 may be located between switchable frequency adjusting circuits 104a and 104b, which may be located between first terminal 106 and second terminal 108. In operation, a signal may pass switchable frequency adjusting circuit 104a, filter branch 102, and switchable frequency adjusting circuit 104b to be filtered by the passband of reconfigurable filter circuit 100c. Depending on the configuration of switchable frequency adjusting circuits 104a and 104b, the passband with at least one of switchable frequency adjusting circuits 104a and 104b turned on may have higher attenuation over a near-band frequency than the passband with switchable frequency adjusting circuits 104a and 104b both turned off, and the passband with both of switchable frequency adjusting circuits 104a and 104b turned on may have higher attenuation over a near-band frequency than the passband with one of switchable frequency adjusting circuits 104a and 104b turned on.

[0049] FIG. 2A illustrates an exemplary switchable frequency adjusting circuit 200, according to some embodiments. In some embodiments, switchable frequency adjusting circuit 200 includes a switchable capacitor that can be turned on and off for different applications. In some embodiments, the switchable capacitor includes a capacitor 204 communicatively coupled in series with a switch 206. Capacitor 204 may include a metal-insulator-metal (MIM) capacitor, and switch 206 may include a silicon-on-insulator (SOI) switch. For example, the switchable capacitor may include a MIM capacitor in a SOI die. The capacitor can also be implemented in the acoustic filter die or as a surface mount technology (SMT) component on a multi-chip module (MCM). By connecting switch 206, capacitor 204 may be communicatively coupled to a resonator 202 in parallel at terminals 208a and 208b, such that an electrical signal may pass through both capacitor 204 and resonator 202. Capacitor 204 may affect the parallel-resonance (or anti-resonance) frequency fp of resonator 202. When switch 206 is open / disconnected, capacitor 204 may be bypassed and the parallel-resonance frequency fp of resonator 202 may remain unchanged.

[0050] FIG. 2B illustrates an impedance-frequency characteristics of resonator 202 with switchable frequency adjusting circuits 200 of different capacitances. FIG. 2B shows the circuit has a series resonance frequency fs corresponding to a low impedance and an anti-resonance frequency(or parallel-resonance frequency) fpl corresponding to a high impedance. Curves 201 and 202 are plots showing the electrical impedances of resonator 202 as a function of frequency. In both curves 201 and 202, capacitor 204 is closed / connected such that switchable frequency adjusting circuit 200 is communicatively coupled to a resonator (e.g., 202). Curve 201 corresponds to a lower capacitance of capacitor 204, and has a lower parallel-resonance frequency fpl. Curve 202 corresponds to a higher capacitance of capacitor, and has a higher parallel-resonance frequency fp2. FIG. 2B shows the variation of parallel-resonance frequency of the overall circuit as the capacitance of switchable frequency adjusting circuit 200 changes. In some embodiments, a higher capacitance of switchable frequency adjusting circuit 200 corresponds to a lower parallel-resonance frequency, and vice versa.

[0051] In some embodiments, switchable frequency adjusting circuit 200 may also include resonator 202, in addition to the switchable capacitor coupled in parallel. For example, switchable frequency adjusting circuit 200, including both the switchable capacitor and resonator 202, may be coupled to a circuit having one or more resonators, referring back to the description of FIGS. 1A- 1C, to modify the parallel-resonance frequency of the circuit.

[0052] FIG. 3A illustrates a circuit 300 having switchable frequency adjusting circuit 200 with switch 206 closed / connected, according to some embodiments. In some embodiments, circuit 300 includes a ladder bandpass filter which includes series resonators 302a and 302b, and shunt resonators 304. Series resonators 302a and 302b may be coupled in series, and shunt resonators 304 may each be coupled to a series resonator and a common terminal (e.g., ground). As shown in FIG. 3A, switchable frequency adjusting circuit 200 is turned on such that capacitor 204 is coupled to series resonator 302a. In some embodiments, series resonator 302a is an example of resonator 202. For simplicity, switch 206 is not shown.

[0053] FIG. 3B illustrates an impedance-frequency plot 301a and a transmission-frequency plot 301b, of circuit 300 with and without switchable frequency adjusting circuit 200. As shown in FIG. 3B, curve 303 shows the impedance-frequency characteristics of the shunt resonators (e.g., 304), curve 305 shows the impedance-frequency characteristics of the series resonators (e.g., 302a and 302b) without capacitor 204, and curve 307 shows the impedance-frequency characteristics of the series resonators (e.g., 302a and 302b) with capacitor 204 coupled in parallel with series resonator 302a. As shown in curves 303 and 305, the shunt resonators may correspond to a series resonance frequency fsl, and the series resonators (e.g., without capacitor 204) may correspond to a parallelresonance frequency fpl. Series resonance frequency fsl may be lower than parallel-resonance frequency fpl. Circuit 300 may have a passband ranging from frequency fsl and frequency fpl.

[0054] When capacitor 204 is coupled to series capacitor 302a, as shown in curve 307, parallelresonance frequency of the series resonators may be shifted to fp2, which is lower than fpl. The passband of circuit 300 may range from frequency fsl and frequency fp2. Compared to the previous passband (e.g., without capacitor 204), the passband resulted from the coupling of capacitor 204 have a slightly lower frequency and a steeper transition from transmission to attenuation, while the change to the bandwidth is none or minimum. Circuit 300 thus has a higher attenuation at a nearband frequency outside the passband (e.g., at fpl or between fpl and fp2).

[0055] FIG. 4A illustrates an exemplary reconfigurable circuit 400 having a switchable frequency adjusting circuit 200, according to some embodiments. In some embodiments, reconfigurable circuit 400 may be a multiplexer with a plurality of multiplexer branches, and switchable frequency adjusting circuit 200 may be part of one of the multiplexer branches. Each multiplexer branch may include a filter circuit with a passband configured to filter a respective signal. In some embodiments, a first multiplexer branch includes the filter circuit between a terminal 402 and a terminal 408, where terminal 408 is communicatively coupled to an antenna for receiving or transmitting a signal. Switchable frequency adjusting circuit 200 may be part of the first multiplexer branch, and may be enabled or disabled for different applications. In some embodiments, a second multiplexer branch includes the filter circuit, e.g., a ladder filter circuit, between a terminal 404 and terminal 408. In some embodiments, a third multiplexer branch, e.g., an additional n-plexer branch, includes the filter circuit between a terminal 406 and terminal 408. For example, passbands of the first multiplexer branch are configured to pass WiFi / BT bands ranging between 2402 MHz and 2482 MHz (for WiFi) and between 2402 MHz and 2450 MHz (for BT), a passband of the second multiplexer branch is configured to pass S-band ranging between 2483.5 MHz and 2500 MHz, and a passband of the third multiplexer branch is configured to pass ultra high band (UHB) ranging between 24 GHz and 100 GHz.

[0056] By turning on and off certain switches, the first multiplexer branch is configured to enable one of the circuit branches to enable a corresponding passband to filter a respective signal. In the meantime, another multiplexer branch (e.g., the second multiplexer branch) may have another passband to filter a respective signal. By enabling switchable frequency adjusting circuit 200, the interference between the two multiplexer branches can minimized. For example, the first multiplexer branch may pass the BT band while providing sufficiently high rejection / isolation over the S-band with the use of switchable frequency adjusting circuit 200. Thus, the S-band (e.g., the second frequency range) and the BT band (e.g., the first frequency range) can co-exist.

[0057] As shown in FIG. 4A, the first multiplexer branch may include a plurality of seriesresonators 422b and 422a communicatively coupled in series, and a plurality of shunt resonators 424 communicatively coupled between a series resonator and ground (GND). The first multiplexer branch may include switchable frequency adjusting circuit 200 communicatively coupled in parallel with series resonator 422a. The first multiplexer branch may also include a first filter branch and a second filter branch communicatively coupled in parallel. The first and second filter branches may be communicatively coupled in series with series resonator 422a. The first filter branch may include a resonator 412a (e.g., a series resonator) communicatively coupled in parallel with a switch 414a and in series with a switch 416a. The second filter branch may include a resonator 412b (e.g., a series resonator) communicatively coupled in parallel with a switch 414b and in series with a switch 416b. The first multiplexer branch may also include an inductors 430 coupled to the resonators and the filter branches between terminal 402 and the resonators. The second multiplexer branch may include a plurality of series resonators 426, a plurality of shunt resonators 428, a plurality of capacitors, a plurality of inductors, and a plurality of switches. The first and second multiplexer branches may both be coupled to inductors 418a and 418b. The third multiplexer branch may include a plurality of capacitors and a plurality of inductors.

[0058] In operation, the switches in the first multiplexer branch may enable reconfigurable circuit 400 to be in different states. In some embodiments, switch 416b is closed / connected, switch 414b is open / disconnected, switch 414a is closed, and switch 416a is open. Switch 206 of switchable frequency adjusting circuit 200 is also open such that switchable frequency adjusting circuit 200 is disabled. Reconfigurable circuit 400 may be in “State 1,” in which the second filter branch is selected / enabled, and switchable frequency adjusting circuit 200 and the first filter branch are disabled. A signal to be filtered may pass resonator 412b, series resonators 422a and 422b, and shunt resonators 424. The first multiplexer branch may have a first passband (e.g., the WiFi band).

[0059] In some embodiments, switch 416b is open, switch 414b is closed, switch 414a is open, and switch 416a is closed. Reconfigurable circuit 400 may be in “State 2,” in which the first filter branch is selected / enabled, and switchable frequency adjusting circuit 200 and the first filter branch are disabled. FIG. 4B illustrates an enlarged image of the first multiplexer branch when “State 2” is activated. A signal to be filtered may pass resonator 412a, series resonators 422a and 422b, and shunt resonators 424. The first multiplexer branch may have a second passband (e.g., the BT band).

[0060] In some embodiments, in “State 2,” switch 206 is closed such that switchable frequency adjusting circuit 200 is enabled. Capacitor 204 may thus be communicatively coupled to series resonator 422a and adjust the parallel-resonance frequency of the first multiplexer branch. When enabled, switchable frequency adjusting circuit 200 may adjust the parallel-resonance frequency ofthe first multiplexer branch, and thus decrease the upper-stopband frequency of the second passband. The adjusted second passband may have higher attenuation / rej ection on other frequency ranges that are undesirably close to the second passband. For example, a third passband (e.g., the S-band) of the second multiplexer branch may be close to the second passband (e.g., the BT band), and the adjusted first passband of the first multiplexer branch may enable higher rejection / isolation on the third passband.

[0061] FIG. 4C illustrates transmission-frequency characteristics of the first multiplexer branch at State 2, according to some embodiments. Curve 403 shows the transmission characteristics of the first multiplexer branch as a function of frequency when switchable frequency adjusting circuit 200 is disabled (e.g., switch 206 open), and curve 405 shows the transmission characteristics as a function of frequency when switchable frequency adjusting circuit 200 is enabled (e.g., switch 206 closed). In an embodiment, curve 403 shows the second passband, and curve 405 shows the adjusted second passband, of the first multiplexer branch. Frequency fpbl represents the lower passband frequency, and frequency fpb2 represents the upper passband frequency. In some embodiments, frequencies fpbl and fpb2 remain the same for curves 403 and 405. Frequency range f 1 -f2 represents the range of the third passband, of the second multiplexer branch. FIG. 4C shows that, the first multiplexer branch has desirably high transmission in its passband (e.g., the BT band). Without switchable frequency adjusting circuit 200, the first multiplexer branch may have undesirably high transmission in at least part of frequency range fl-f2. Switchable frequency adjusting circuit 200 may increase the attenuation of the first multiplexer branch in frequency range f 1 -f2, resulting in a steeper transition between transmission and attenuation. In some embodiments, curve 405 has higher rejection in frequency range f 1 -f2 than curve 403. The steeper transition can result in a higher rejection over a frequency range outside or close to the adjusted second passband. In the meantime, the insertion loss of the second passband and the adjusted second passband are the same or comparable, and the bandwidth of curve 403 has little or no change to the bandwidth of curve 405.

[0062] The improvement in steepness and attenuation may be described as a transition bandwidth improvement. A transition bandwidth is defined as the frequency range between the upper passband frequency and the upper stopband. In this embodiments, the frequency of the upper stopband of curve 403 is fsbl, and the frequency of the upper stopband of curve 405 is fsb2. In some embodiments, as shown in FIG. 4C, fsb2 is lower than fsbl, such that the transition bandwidth of curve 405 (e.g., with switchable frequency adjusting circuit 200 enabled) is reduced compared to that of curve 403 (e.g., with switchable frequency adjusting circuit 200 disabled), indicating steepertransition from passband to stopband. In an example, fsbl is about 2490 MHz, fsb2 is about 2483.5 MHz, the transition bandwidth for curve 403 is about 40 MHz, and the transition bandwidth for curve 405 is about 33.5 MHz. The use of switchable frequency adjusting circuit 200 facilitates about 16% improvement in transition bandwidth. In various embodiments, the capacitance of capacitor 204 may be adjusted to obtain different upper stopband frequencies and transition bandwidths.

[0063] FIG. 4D illustrates isolation-frequency characteristics of the first multiplexer branch at State 2, according to some embodiments. Curve 407 shows the isolation characteristics of the first multiplexer branch as a function of frequency when switchable frequency adjusting circuit 200 is disabled (e.g., switch 206 open), and curve 409 shows the isolation characteristics as a function of frequency when switchable frequency adjusting circuit 200 is enabled (e.g., switch 206 closed). Frequency range fl-f2 represents range of the third passband (e.g., the S-band). FIG. 4D shows that, without switchable frequency adjusting circuit 200, the first multiplexer branch may have undesirably low isolation in at least part of frequency range f 1 -f2. Switchable frequency adjusting circuit 200 may increase the attenuation of the first multiplexer branch in frequency range f 1 -f2. In some embodiments, the steeper transition from transmission to attenuation results with the use of switchable frequency adjusting circuit results in an improved isolation (e.g., in curve 409) than without switchable frequency adjusting circuit 200 (e.g., curve 407). In various embodiments, by selecting a desired capacitance of capacitor 204, the profile of the adjusted second passband may be adjusted to meet filtering requirements of various applications. For example, the capacitance may be determined at least partially based on a co-existent passband of another multiplexer branch. The switchable frequency adjusting circuit 200 may thus be flexible designed to isolate a desired frequency range.

[0064] FIG. 5A illustrates an exemplary reconfigurable circuit 500 with more than one switchable frequency adjusting circuits, according to some embodiments. Reconfigurable circuit 500 may include three filter branches, and may be a part of another circuit, such as a multiplexer branch. Reconfigurable circuit 500 may include a terminal 502 and a terminal 508. As shown in FIG. 5, between terminals 502 and 508, reconfigurable circuit 500 may include a plurality of series resonators 522a and 522b communicatively coupled in series, and a plurality of shunt resonators 524 communicatively coupled between a series resonator and ground (GND). Reconfigurable circuit 500 may include switchable frequency adjusting circuits 200a and 200b each communicatively coupled in parallel with series resonator 522a. Reconfigurable circuit 500 may include a first filter branch, a second filter branch, and a third filter branch communicatively coupledin parallel. The first, second, and third filter branches may be communicatively coupled in series with series resonator 522a and switchable frequency adjusting circuit 200b. The first filter branch may include a resonator 512a (e.g., a series resonator) communicatively coupled in parallel with a switch 514a and in series with a switch 516a. The second filter branch may include a resonator 512b (e.g., a series resonator) communicatively coupled in parallel with a switch 514b and in series with a switch 516b. The third filter branch may include a resonator 512c (e.g., a series resonator) communicatively coupled in parallel with a switch 514c and in series with a switch 516c. In some embodiments, all the switchable frequency adjusting circuits may be coupled between the filter branches and one of the terminals (e.g., terminal 502).

[0065] In operation, switches 516a, 516b, and 516c may be respectively closed to select the respective circuit branch. In some embodiments, each circuit branch, and series resonators 552a and 552b and shunt resonators 524, may form a passband for a respective frequency range. Switchable frequency adjusting circuits 200a and 200b may be turned on and off for various applications. In some embodiments, at least one of switchable frequency adjusting circuits 200a and 200b are turned on to adjust the passband profile, e.g., to increase the attenuation at a near-band frequency or frequency range and / or create a steeper transition from transmission to attenuation, to better isolate an undesired frequency band outside or near the passband. In some embodiments, compared to only one of switchable frequency adjusting circuits 200a and 200b being on, when switchable frequency adjusting circuits 200a and 200b are both on, reconfigurable circuit 500 may have higher attenuation at desired a near-band frequency and / or steeper transition from transmission to attenuation.

[0066] FIG. 5B illustrates another exemplary reconfigurable circuit 501 with more than one switchable frequency-adjusting circuits, according to some embodiments. Different from reconfigurable circuit 500, reconfigurable circuit 501 may include a switchable frequency-adjusting circuit 200a between the circuit branches and terminal 502, and a switchable frequency-adjusting circuit 200b between the circuit branches and terminal 508. Each of switchable frequency adjusting circuit 200a may be communicatively coupled in parallel to respective series resonator 522a. Series resonator 522b may be disposed between switchable frequency adjusting circuit 200b and filter branches. Shunt resonators 524 may be coupled between both terminals of switchable frequency adjusting circuit 200a and ground, while only one terminal of switchable frequency adjusting circuit 200b is coupled with shunt resonator 524, with the other terminal communicatively coupled to terminal 508 without a shunt resonator.

[0067] In operation, switches 516a, 516b, and 516c may be respectively closed to select therespective circuit branch. In some embodiments, each circuit branch, and series resonators 552a and 552b and shunt resonators 524, may form a passband for a respective frequency range. Switchable frequency adjusting circuits 200a and 200b may be turned on and off for various applications. In some embodiments, at least one of switchable frequency adjusting circuits 200a and 200b are turned on to adjust the passband profile, e.g., to increase the attenuation at a near-band frequency or frequency range and / or create a steeper transition from transmission to attenuation, to better isolate an undesired frequency band outside or near the passband. In some embodiments, compared to only one of switchable frequency adjusting circuits 200a and 200b being on, when switchable frequency adjusting circuits 200a and 200b are both on, reconfigurable circuit 501 may have a higher attenuation at a desired near-band frequency and / or steeper transition from transmission to attenuation.

[0068] In embodiments of the present disclosure, the capacitance of capacitor 204 may be selected for different applications, e.g., to meet various rejection frequencies and / or transition steepness. For example, the capacitance of capacitor 204 may be calculated by setting constraints of a passband while substituting a resonator with a Butterworth- Van Dyke (BVD) model. In various embodiments, the capacitance varies from about 0.1 pF to about 1 pF.

[0069] Reference will now be made in greater detail to various embodiments of the subject matter of the present disclosure, some embodiments of which are illustrated in the accompanying drawings.

Claims

CLAIMS:

1. A radio frequency (RF) filter circuit, comprising: a first resonator communicatively coupled between a first terminal and a second terminal; a second resonator communicatively coupled to the first resonator and between the first terminal and the second terminal; and a switchable frequency adjusting circuit coupled in parallel with the first resonator, wherein: in response to the switchable frequency adjusting circuit being turned off, the RF filter circuit passes a signal in a first filtering frequency range having a first passband; in response to the switchable frequency adjusting circuit being turned on, the RF filter circuit passes the signal in a second filtering frequency range having a second passband; and the second filtering frequency range has a higher attenuation at a near-band frequency outside the first passband and the second passband than the first filtering frequency range.

2. The RF filter circuit of claim 1, wherein an upper-stopband frequency of the second passband is lower than an upper-stopband frequency of the first passband.

3. The RF filter circuit of claim 1, wherein the first resonator and the second resonator each comprises a series resonator.

4. The RF filter circuit of claim 3, wherein the switchable frequency adjusting circuit comprises a switchable capacitor.

5. The RF filter circuit of claim 4, wherein the switchable capacitor comprises a metalinsulator-metal (MIM) capacitor coupled with a silicon-on-insulator (SOI) switch.

6. The RF filter circuit of claim 1, further comprising: another series resonator communicatively coupled to between the first terminal and the second terminal; and a shunt resonator communicatively coupled between the switchable frequency adjusting circuit and ground (GND).

7. The RF filter circuit of claim 1, wherein:the switchable frequency adjusting circuit is communicatively coupled between one of the first terminal or the second terminal, and the second resonator.

8. The RF filter circuit of claim 1, further comprising a second switchable frequency adjusting circuit communicatively coupled to the second resonator between the first terminal and the second terminal, wherein the second resonator is communicatively coupled between the switchable frequency adjusting circuit and the second switchable frequency adjusting circuit.

9. The RF filter circuit of claim 1, further comprising a third resonator communicatively coupled to the second resonator in parallel between the first terminal and the second terminal, wherein: the third resonator is communicatively coupled to the first resonator in series; and the second resonator and the third resonator are each communicatively coupled to a respective switch in series or in parallel.

10. The RF filter circuit of claim 1, further comprising a third terminal communicatively coupled to the second terminal, and a filter circuit coupled between the third terminal and the second terminal, the filter circuit configured to pass a second signal in a third filtering frequency range, wherein the third filtering frequency range is lower than or equal to the near-band frequency.

11. A radio frequency (RF) filter circuit, comprising: a resonator communicatively coupled between a first terminal and a second terminal; and a switchable frequency adjusting circuit coupled in series with the resonator, wherein: in response to the switchable frequency adjusting circuit being turned off, the RF circuit passes a signal in a first filtering frequency range having a first passband; in response to the switchable frequency adjusting circuit being turned on, the RF circuit passes the signal in a second filtering frequency range having a second passband; and the second filtering frequency range has a higher attenuation at a near-band frequency outside the first passband and the second passband than the first filtering frequency range.

12. The RF filter circuit of claim 11, wherein an upper stopband frequency of the secondpassband is lower than an upper stopband frequency of the first passband.

13. The RF circuit of claim 11, wherein the switchable frequency adjusting circuit comprises a second resonator communicatively coupled in series with the resonator; and a switchable component communicatively coupled in parallel with the second resonator.

14. The RF filter circuit of claim 13, wherein the resonator and the second resonator each comprises a series resonator.

15. The RF filter circuit of claim 13, wherein the switchable component comprises a switchable capacitor.

16. The RF filter circuit of claim 15, wherein the switchable capacitor comprises a metalinsulator-metal (MIM) capacitor coupled with a silicon-on-insulator (SOI) switch.

17. The RF filter circuit of claim 11, further comprising: another series resonator communicatively coupled to between the first terminal and the second terminal; and a shunt resonator communicatively coupled between the switchable frequency adjusting circuit and ground (GND).

18. The RF filter circuit of claim 11, wherein: the switchable frequency adjusting circuit is communicatively coupled between one of the first terminal or the second terminal, and the resonator19. The RF filter circuit of claim 11, further comprising a second switchable frequency adjusting circuit communicatively coupled to the resonator between the first terminal and the second terminal, wherein the resonator is communicatively coupled between the switchable frequency adjusting circuit and the second switchable frequency adjusting circuit.

20. The RF filter circuit of claim 13, further comprising a third resonatorcommunicatively coupled to the resonator in parallel between the first terminal and the second terminal, wherein: the third resonator is communicatively coupled to the second resonator in series; and the resonator and the third resonator are each communicatively coupled to a respective switch in series or in parallel.

21. The RF filter circuit of claim 11, further comprising a third terminal communicatively coupled to the second terminal, and a filter circuit coupled between the third terminal and the second terminal, the filter circuit configured to pass a second signal in a third filtering frequency range, wherein the third filtering frequency range is lower than or equal to the near-band frequency.

22. A radio frequency (RF) filter device, comprising: a first multiplexer branch that comprises a first filter circuit that comprises: a first resonator communicatively coupled between a first terminal and a second terminal; a second resonator communicatively coupled to the first resonator and between the first terminal and the second terminal; and a switchable frequency adjusting circuit coupled in parallel with the first resonator, wherein: in response to the switchable frequency adjusting circuit being turned off, the first multiplexer branch passes a signal in a first filtering frequency range having a first passband; in response to the switchable frequency adjusting circuit being turned on, the first multiplexer branch passes the signal in a second filtering frequency range having a second passband; and the second filtering frequency range has a higher attenuation at a near-band frequency outside the first passband and the second passband than the first filtering frequency range. a second multiplexer branch that comprises: a second filter circuit communicatively coupled between a third terminal and the second terminal, the second filter circuit configured to pass a second signal in a third filtering frequency range, wherein the third filtering frequency range is higher than or equal to the near-band frequency; and an antenna coupled to the second terminal.

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