Tunable notch filter and radio front end

Abstract

A tunable notch filter and radio front end are disclosed in which a first acoustic resonator is coupled in series with a first inductive element between a filter input node and a filter output node. A first capacitor is coupled in parallel with the first acoustic resonator and the first inductive element. In at least one embodiment, the first capacitor is configured to have a variable capacitance that is electronically tunable by an electronic controller. A second acoustic resonator is coupled in series with a second inductive element between the filter output node and a signal ground node. A second capacitor is coupled in parallel with the second inductive element. In at least one embodiment, the second capacitor is electronically tunable. The tunable notch filter is configured to provide a highly selective notch filter response with high attenuation between the filter input node and the filter output node.

Description

[0001] Related Applications

[0002] This application claims the benefit of provisional patent application serial number 62 / 633,356 filed on February 21, 2018, the disclosure of which is hereby incorporated by reference in its entirety. This application also relates to U.S. Patent No. 9,698,839, the disclosure of which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present disclosure relates to tunable notch filters, and more particularly to tunable notch filters for use in radio frequency receivers. Background Art

[0004] As wireless communication standards continue to evolve to provide higher data rates, reliability, and network capacity, technologies such as carrier aggregation and multiple-input, multiple-output (MIMO) have become commonplace. Wireless communication devices that utilize carrier aggregation and / or MIMO use multiple antennas to simultaneously transmit and receive signals within different wireless operating bands. These wireless communication devices require specialized filtering circuits to separate signals within different wireless operating bands, which typically adds significant complexity and size to the radio frequency (RF) front-end circuitry within the device.

[0005] Figure 1 1 is a schematic diagram of a conventional RF front-end circuit 10 capable of operating in a carrier aggregation and / or MIMO configuration. The conventional RF front-end circuit 10 includes a main antenna 12A, an auxiliary antenna 12B, an antenna switching circuit 14, a main transceiver circuit 16, and an auxiliary receiver circuit 18. The main transceiver circuit 16 and the auxiliary receiver circuit 18 are coupled to the main antenna 12A and the auxiliary antenna 12B via the antenna switching circuit 14. Figure 1 As shown, the antenna switching circuit 14 is a double-pole double-throw switch configured to couple the main transceiver circuit 16 to one of the main antenna 12A and the auxiliary antenna 12B, and to couple the auxiliary receiver circuit 18 to the antenna 12 that is not coupled to the main transceiver circuit 16. In normal operation, the main transceiver circuit 16 is coupled to the main antenna 12A to transmit and receive main RF transmit signals and main RF receive signals therefrom, and the auxiliary receiver circuit 18 is coupled to the auxiliary antenna 12B to receive auxiliary RF receive signals. However, when the performance of the auxiliary antenna 12B is better than the performance of the main antenna 12A, the antenna switching circuit 14 can swap the main antenna 12A and the auxiliary antenna 12B. For example, when the voltage standing wave ratio associated with the auxiliary antenna 12B is less than the voltage standing wave ratio associated with the main antenna 12A, the antenna switching circuit 14 can swap the main antenna 12A and the auxiliary antenna 12B.

[0006] The auxiliary receiver circuit 18 includes a filtering circuit 20, a receiver switching circuit 22, and a plurality of low noise amplifiers (LNAs) 24. The filtering circuit 20 is coupled to the antenna switching circuit 14, and the receiver switching circuit 22 is coupled between the filtering circuit 20 and the LNAs 24. The filtering circuit 20 is configured to isolate signals within a particular operating band or set of operating bands received from the primary antenna 12A or the auxiliary antenna 12B so that they can be processed separately. The receiver switching circuit 22 is configured to couple the output of the filter or filter bank in the filtering circuit 20 to one of the LNAs 24, where the isolated signal is then amplified for further processing, such as baseband conversion. Each of the LNAs 24 can be designed to amplify a particular operating band or set of operating bands efficiently and with low distortion.

[0007] The filtering circuit 20 may include a plurality of acoustic filters 26, which may be isolated or grouped together with additional acoustic filters to form an RF multiplexer 28. In its simplest form, the filtering circuit 20 includes an isolated acoustic filter 26 for each operating band supported by the auxiliary receiver circuit 18. However, performance improvements and area reductions may be achieved by grouping the acoustic filters 26 into the RF multiplexer 28. Typically, an acoustic filter is a bandpass filter configured to pass one or more desired operating bands while attenuating all signals outside the desired operating bands. The acoustic filter 26 must provide high attenuation at all frequencies outside the desired passband to reduce undesirable distortion while providing low insertion loss within the passband. The largest source of undesirable distortion in a conventional RF front end circuit 10 typically comes from antenna-to-antenna coupling in the signal path of the main RF transmit signal to the auxiliary receiver circuit 18. The main RF transmit signal is a high power signal compared to the auxiliary RF receive signal, and therefore may cause a number of problems, such as desensitization of the auxiliary receiver circuit 18. Therefore, the primary purpose of each acoustic filter 26 is to attenuate the primary RF transmit signal in the auxiliary receiver signal path while passing the auxiliary RF receive signal with as little attenuation as possible.

[0008] As the number of operating frequency bands supported by modern wireless communication standards continues to increase, the complexity and size of the filtering circuit 20, the receiver switching circuit 22, and the LNA 24 increase in turn. Since the area of ​​the RF front-end circuit is a major concern in portable wireless communication devices, there is a need for the RF front-end circuit to be configured to operate in a carrier aggregation and / or MIMO configuration with reduced size and complexity. Summary of the invention

[0009] A tunable notch filter is disclosed, wherein a first acoustic resonator is coupled in series with a first inductive element between a filter input node and a filter output node. A first capacitor is coupled in parallel with the first acoustic resonator and the first inductive element. In at least one embodiment, the first capacitor is configured to have a variable capacitance that is electronically tunable by an electronic controller. A second acoustic resonator is coupled in series with a second inductive element between the filter output node and a signal ground node. The second capacitor is coupled in parallel with the second inductive element. In at least one embodiment, the second capacitor is electronically tunable. The tunable notch filter is configured to provide a highly selective notch filter response with high attenuation between the filter input node and the filter output node.

[0010] In at least one embodiment, an Nth inductive element is coupled in series with the Nth acoustic resonator between the filter output node and the signal ground node, and an Nth capacitor is coupled in parallel with the Nth inductive element, where N is a natural number of 3 or greater. In at least one embodiment, the Nth capacitor is electronically tunable.

[0011] After reading the following detailed description of the preferred embodiments in conjunction with the accompanying drawings, those skilled in the art will understand the scope of the present disclosure and implement additional aspects thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0013] Figure 1 It is a schematic diagram of a radio frequency front-end circuit of the related art.

[0014] Figure 2 is a schematic diagram of an exemplary embodiment of a tunable notch filter configured in accordance with the present disclosure.

[0015] Figure 3 is a graph of the filter response of gain versus frequency for a first exemplary case, in which undesired frequencies located near the upper edge of the transmit band of the notch are attenuated.

[0016] Figure 4 is a graph of the filter response for a second exemplary case, wherein undesired transmit frequencies at lower frequencies within the upper half of the transmit band are attenuated.

[0017] Figure 5 is a graph of the filter response for a third exemplary case, in which undesired frequencies near the center of the notched transmit band are attenuated.

[0018] Figure 6is a graph of filter response for a fourth exemplary case, in which undesired transmit frequencies at frequencies within the lower half of the transmit band are attenuated.

[0019] Figure 7 is a graph of a filter response for a fifth exemplary case in which undesired transmit frequencies at lower frequencies within the lower half of the transmit band are attenuated.

[0020] Figure 8 is a graph of the filter response for a sixth exemplary case, in which undesired transmit frequencies at lower frequencies within the lower edge of the transmit band are attenuated.

[0021] Fig. 9 is a schematic diagram of another exemplary embodiment of a tunable notch filter configured in accordance with the present disclosure to have multiple resonators tuned by series tuning capacitors and only one parallel tuning capacitor.

[0022] Fig.10 yes Fig. 9 A graph of the filter response of an exemplary embodiment of the invention.

[0023] Fig.11 is a schematic diagram of yet another exemplary embodiment of a tunable notch filter configured in accordance with the present disclosure with a plurality of resonators coupled to a filter input node.

[0024] Fig.12 yes Fig.11 A graph of the filter response of an exemplary embodiment of the invention.

[0025] Fig.13 is a schematic diagram of yet another exemplary embodiment of a tunable notch filter configured in accordance with the present disclosure to have multiple resonators tuned by series tuning capacitors and fixed capacitance shunt tuning capacitors.

[0026] Fig.14 is a radio front end incorporating any of the tunable notch filters of the present disclosure, including a transmit switch coupled between a filter output node and an antenna terminal.

[0027] Fig.15 A radio front end may include any tunable notch filter of the present disclosure, including a transmit switch coupled between a filter input node of the tunable notch filter and an output of a power amplifier. DETAILED DESCRIPTION

[0028] The embodiment described below represents the necessary information that enables those skilled in the art to practice the embodiment, and shows the best mode of practicing the embodiment. When reading the following description according to the accompanying drawings, those skilled in the art will understand the concept of the present disclosure and will recognize the application of these concepts that are not particularly proposed herein. It should be understood that these concepts and applications all fall within the scope of the present disclosure and the appended claims.

[0029] It should be understood that although the terms first, second, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, the first element can be referred to as the second element, and similarly, the second element can be referred to as the first element without departing from the scope of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0030] It should be understood that when an element such as a layer, region or substrate is referred to as being "on" another element or extending "on" another element, it can be directly on another element or extend directly to another element or there can also be an intermediate element. In contrast, when an element is referred to as being "directly on" another element or extending "directly" to another element, there is no intermediate element. Similarly, it should be understood that when an element such as a layer, region or substrate is referred to as being "above" another element or extending "above" another element, it can be directly above another element or extend directly above another element or there can also be an intermediate element. In contrast, when an element is referred to as being "directly above" another element or extending "directly above" another element, there is no intermediate element. It should also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to another element or there can be an intermediate element. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there is no intermediate element.

[0031] Relative terms such as "below" or "above" or "up" or "lower" or "horizontal" or "vertical" may be used herein to describe the relationship of one element, layer or region to another element, layer or region as shown in the figures. It should be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation shown in the figures.

[0032] The terms used herein are only used for the purpose of describing specific embodiments and are not intended to limit the present disclosure. As used herein, the singular forms "a", "an", and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises, comprising, includes, and / or including" when used herein specify the presence of the features, integers, steps, operations, elements, and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups thereof.

[0033] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those commonly understood by those of ordinary skill in the art to which the present disclosure belongs. It will be further understood that the terms used herein should be interpreted as having a meaning consistent with the meaning in the context of this specification and the relevant art, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0034] Figure 2 is a schematic diagram of an exemplary embodiment of a tunable notch filter 30 configured in accordance with the present disclosure. The tunable notch filter 30 includes a first acoustic resonator AR coupled in series between a filter input node IN1 and a filter output node OUT1. S1 and the first inductor element L TS1 The first capacitor C TS1 With the first acoustic resonator AR S1 and the first inductor element L TS1 The first capacitor C is coupled in parallel TS1 The notch filter 30 is configured to have a variable capacitance that is electronically tunable by an electronic controller 32. The tunable notch filter 30 also includes a capacitor between the filter output node OUT1 and the signal ground node G SIG The second acoustic resonator AR is coupled in series between P1 and the second inductor element L TP1 , and the second inductor element L TP1 The second capacitor C coupled in parallel TP1 .

[0035] In at least some exemplary embodiments, Figure 2 As shown, the tunable notch filter 30 also includes a filter output node OUT1 and a signal ground node G SIG Between the Nth acoustic resonator AR PN The Nth inductor element L coupled in series TPN . The Nth capacitor C TPNis configured to have a variable capacitance that is electronically tunable by an electronic controller 32 and is connected to the Nth inductor element L TPN In particular, the embodiment has a configuration including an Nth capacitor C TPN The N capacitors and the Nth inductor element L TPN N inductance elements constitute multiple electronically tunable oscillation circuits 34. Multiple resonators AR P1 To AR PN Each of them has a different resonant frequency.

[0036] In some embodiments, the electronic controller 32 is a baseband processor having a digital control output that controls the first capacitor C TS1 , the second capacitor C TP1 and the Nth capacitor C TPN In other embodiments, the electronic controller 32 is an analog controller having an analog control signal that controls the first capacitor C TS1 , the second capacitor C TP1 and the Nth capacitor C TPN A simulated controllable version of .

[0037] Figure 3 is a graph of the filter response of gain versus frequency for a first exemplary case, in which undesired frequencies located near the upper edge of the transmit band of the notch are attenuated. In this first exemplary case, the first capacitor C TS1 and the second capacitor C TP1 To the Nth capacitor C TPN The first capacitor C is set to its minimum capacitance by the electronic controller 32. TS1 The capacitance of the second capacitor C is set to the minimum value, and the first notch depicted by the long dashed line is located at the higher frequency edge of the undesired frequency. TP1 is set to the minimum value, the second notch depicted by the short dashed line is positioned closer to the lower edge of the transmit band of the notch. TPN With the capacitance of the notch set to its minimum value, the third notch, depicted by the dash-dotted line, is located at the lower frequency edge of the undesired frequency. The resulting frequency response is depicted by the solid line. Note that the resulting frequency response shows that the undesired transmit frequency is greatly attenuated relative to most other frequencies within the transmit band of the notch.

[0038] Figure 4 is a graph of the filter response for a second exemplary case, in which undesired transmission frequencies at lower frequencies within the upper half of the transmit band are attenuated. In this second exemplary case, the first capacitor C TS1has an increased capacitance, and the second capacitor C TP1 and the Nth capacitor C TPN Keep set to its minimum capacitance value.

[0039] Figure 5 is a graph of the filter response for a third exemplary case, in which undesired frequencies near the center of the transmit band of the notch are attenuated. In this third exemplary case, the first capacitor C TS1 and the Nth capacitor C TPN has an increased capacitance, and the second capacitor C TP1 Keep set to minimum capacitance value.

[0040] Figure 6 is a graph of the filter response for a fourth exemplary case, in which undesired transmission frequencies at frequencies within the lower half of the transmit band are attenuated. In this fourth exemplary case, the first capacitor C TS1 With increased capacitance, the Nth capacitor C TPN Keep constant and the second capacitor C TP1 Keep set to minimum capacitance value.

[0041] Figure 7 is a graph of the filter response for a fifth exemplary case, in which undesired transmission frequencies at lower frequencies within the lower half of the transmit band are attenuated. In this fifth exemplary case, the first capacitor C TS1 With further increased capacitance, the Nth capacitor C TPN Keep constant and the second capacitor C TP1 Keep set to minimum capacitance value.

[0042] Figure 8 is a graph of the filter response for a sixth exemplary case, in which undesired transmission frequencies at lower frequencies within the lower edge of the transmit band are attenuated. In this sixth exemplary case, the first capacitor C TS1 Also has a further increased capacitance, and the second capacitor C TP1 With increased capacitance to move the transmit band notch to the band edge, the Nth capacitor C TPN Keep it constant.

[0043] Fig. 9 is configured according to the present disclosure to have a first capacitor C TS1 and the second capacitor C TP1 Electronically tuned second acoustic resonator AR P1 To the Nth acoustic resonator AR PNAnother exemplary embodiment of a tunable notch filter 36 having multiple resonators. In other words, in this embodiment, no capacitor such as the Nth capacitor C is included. TPN N capacitors and an Nth inductor element such as L TPN A plurality of electronically tunable oscillation circuits 34 ( Figure 2 ).

[0044] Fig.10 yes Fig. 9 Graph of the filter response of an exemplary embodiment of FIG. 1 . In this particular example, the electronic controller 32 adjusts the first capacitor C TS1 and the second capacitor C TP1 The capacitances of the two are combined to provide a frequency response depicted by a solid line adjacent to the horizontal axis representing frequency.

[0045] Fig.11 is configured according to the present disclosure to have a first capacitor C TS1 and the second capacitor C TP1 Electronically tuned second acoustic resonator AR P1 To the Nth acoustic resonator AR PN 38. However, in this particular embodiment, the second capacitor C TP1 has a fixed capacitance, and the first capacitor C TS1 It has a capacitance that is controlled by the electronic controller 32 . Fig.12 yes Fig.11 A graph of the filter response of an exemplary embodiment of the invention.

[0046] Fig.13 is a schematic diagram of an exemplary embodiment of a tunable notch filter 40 configured in accordance with the present disclosure. The tunable notch filter 40 includes a first acoustic resonator AR coupled in series between a filter input node IN1 and a filter output node OUT1. S1 and the first inductor element L TS1 As in the previous embodiment, the first capacitor C TS1 With the first acoustic resonator AR S1 and the first inductor element L TS1 The first capacitor C is coupled in parallel TS1 The notch filter 40 is configured to have a variable capacitance that is electronically tunable by the electronic controller 32. The tunable notch filter 40 also includes a second acoustic resonator AR P1 and the second inductor element L TP1 However, in this particular embodiment, the second acoustic resonator AR P1 and the second inductor element L TP1 The filter input node IN1 and the signal ground node G are coupled in series.SIG The second capacitor C TP1 The second inductor L TP1 Parallel coupling.

[0047] In at least some exemplary embodiments, Fig.13 As shown, the tunable notch filter 40 also includes a filter input node IN1 and a signal ground node G SIG Between the Nth acoustic resonator AR PN The Nth inductor element L coupled in series TPN . The Nth capacitor C TPN is configured to have a variable capacitance which is electronically tunable by an electronic controller 32 and which is connected to the Nth inductor element L TPN The frequency response of the tunable notch filter 40 is similar to Figures 3 to 8 Same as depicted in .

[0048] Fig.14 is a schematic diagram of an exemplary radio front end 42 incorporating a tunable notch filter 44, which may be any of the tunable notch filters 30, 36, 38, and 40. In this particular embodiment, the tunable notch filter 44 is coupled between the output of the power amplifier PA1 and the antenna terminal ANT1. A transmit switch SW1, depicted in a closed position, is coupled between the filter output OUT1 and the antenna terminal ANT1. A low noise amplifier LNA1 is selectively coupled to the antenna terminal ANT1 via a second switch, a receive switch SW2 (depicted in an open position). The electronic controller 32 electronically tunes the tunable notch filter 44 and controls the selective opening and closing of the transmit switch SW1 and the receive switch SW2.

[0049] Fig.15 is a schematic diagram of another exemplary radio front end 46 incorporating a tunable notch filter 44, which may be any of the tunable notch filters 30, 36, 38, and 40. In this exemplary embodiment, a transmit switch SW1 is coupled between the filter input node IN1 and the output of the power amplifier PA1. Fig.14 In contrast to the embodiment of FIG. 4 , in this embodiment, the tunable notch filter 44 can also filter the receive frequency band. The electronic controller 32 electronically tunes the tunable notch filter 44 and controls the selective opening and closing of the transmit switch SW1 and the receive switch SW2.

[0050] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered to be within the scope of the concepts disclosed herein and the following claims.

Claims

1. A tunable notch filter, comprising: a first acoustic resonator and a first inductive element coupled in series between a filter input node and a filter output node; a first capacitor coupled in parallel with the first acoustic resonator and the first inductive element, wherein the first capacitor is configured to have a variable capacitance that is electronically tunable via an electronic controller; a second acoustic resonator and a second inductive element coupled in series between the filter output node and a signal ground node; as well as A second capacitor is coupled in parallel with the second inductive element in a resonant circuit configuration.

2. The tunable notch filter of claim 1, wherein the second capacitor is configured to have a variable capacitance, the variable capacitance being electronically tunable by the electronic controller.

3. The tunable notch filter of claim 1, wherein the first acoustic resonator and the second acoustic resonator are one of a bulk acoustic wave resonator and a surface acoustic wave resonator.

4. The tunable notch filter according to claim 1, further comprising: an Nth inductive element coupled in series with the Nth acoustic resonator between the filter output node and the signal ground node; as well as An Nth capacitor is configured to have a variable capacitance electronically tunable by the electronic controller and is coupled in parallel with the Nth inductive element, where N is a natural number of 3 or greater. 5 . The tunable notch filter of claim 4 , wherein the Nth acoustic resonator is one of a bulk acoustic wave resonator and a surface acoustic wave resonator. 6 . The tunable notch filter of claim 1 , further comprising an Nth acoustic resonator coupled in parallel with the second acoustic resonator, wherein N is a natural number of 3 or more. 7 . The tunable notch filter of claim 6 , wherein the Nth acoustic resonator is one of a bulk acoustic wave resonator and a surface acoustic wave resonator.

8. A radio front end comprising: Power amplifier; as well as a tunable notch filter coupled between an output of the power amplifier and an antenna terminal, wherein the tunable notch filter comprises: a first acoustic resonator and a first inductive element coupled in series between a filter input node and a filter output node; a first capacitor coupled in parallel with the first acoustic resonator and the first inductive element, wherein the first capacitor is configured to have an electronically tunable variable capacitance; a second acoustic resonator and a second inductive element coupled in series between the filter output node and a signal ground node; and A second capacitor is coupled in parallel with the second inductive element in a resonant circuit configuration.

9. The radio front end of claim 8, further comprising an electronic controller configured to electronically tune the variable capacitance of the first capacitor.

10. The radio front end of claim 9, wherein the second capacitor is configured to have an electronically tunable variable capacitance, and the electronic controller is further configured to electronically tune the variable capacitance of the second capacitor.

11. The radio front end according to claim 8, wherein the second capacitor is of a fixed capacitance type.

12. The radio front end of claim 8, wherein a transmit switch is coupled between the filter output node of the tunable notch filter and the antenna terminal.

13. The radio front end of claim 8, wherein a transmit switch is coupled between the power amplifier and the filter input node of the tunable notch filter.

14. The radio front end of claim 8, wherein the first acoustic resonator and the second acoustic resonator are one of a bulk acoustic wave resonator and a surface acoustic wave resonator.

15. The radio front end of claim 9, further comprising: an Nth inductive element coupled in series with the Nth acoustic resonator between the filter output node and the signal ground node; as well as An Nth capacitor is configured to be controlled by the electronic controller and coupled in parallel with the Nth inductive element, wherein N is a natural number of 3 or greater.

16. The radio front end of claim 15, wherein the Nth acoustic resonator is one of a bulk acoustic wave resonator and a surface acoustic wave resonator.

17. The radio front end of claim 9, further comprising an Nth acoustic resonator coupled in parallel with the second acoustic resonator, wherein N is a natural number of 3 or greater.

18. The radio front end of claim 17, wherein the Nth acoustic resonator is one of a bulk acoustic wave resonator and a surface acoustic wave resonator.

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