TUNABLE NOTCH FILTER

Abstract

A tunable notch filter is disclosed with a first acoustic resonator 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 variable capacitance that is electronically tunable by way of 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 between the filter input node and the filter output node with high attenuation.

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 variable capacitance that is electronically tunable by way of 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; and a second capacitor coupled in parallel with the second inductive element.

2. The tunable notch filter of claim 1 wherein the second capacitor is configured to have variable capacitance that is electronically tunable by way of 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 (BAW) resonator and a surface acoustic wave (SAW) resonator.

4. The tunable notch filter of claim 1 further including: an Nth inductive element coupled in series with an Nth acoustic resonator between the filter output node and the signal ground node; and an Nth capacitor configured to have variable capacitance that is electronically tunable by way of the electronic controller and coupled in parallel with the Nth inductive element, wherein N is a natural number of 3 or more.

5. The tunable notch filter of claim 4 wherein the Nth acoustic resonator is one of a BAW resonator and a SAW resonator.

6. The tunable notch filter of claim 1 further including 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 BAW resonator and a SAW resonator.

8. 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 variable capacitance that is electronically tunable by way of an electronic controller; a second acoustic resonator and a second inductive element coupled in series between the filter input node and a signal ground node; and a second capacitor coupled in parallel with the second inductive element.

9. The tunable notch filter of claim 8 wherein the second capacitor is configured to have variable capacitance that is electronically tunable by way of the electronic controller.

10. The tunable notch filter of claim 8 wherein the first acoustic resonator and the second acoustic resonator are one of a bulk acoustic wave (BAW) resonator and a surface acoustic wave (SAW) resonator.

11. The tunable notch filter of claim 10 further including: an Nth inductive element coupled in series with an Nth acoustic resonator between the filter output node and the signal ground node; and an Nth capacitor configured to have variable capacitance that is electronically tunable by way of the electronic controller and coupled in parallel with the Nth inductive element, wherein N is a natural number of 3 or more.

12. A radio front-end comprising: a power amplifier; and 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 have variable capacitance that is electronically tunable; 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 coupled in parallel with the second inductive element.

13. The radio front-end of claim 12 further including an electronic controller configured to electronically tune the variable capacitance of the first capacitor.

14. The radio front-end of claim 13 wherein the second capacitor is configured to have variable capacitance that is electronically tunable and the electronic controller is further configured to electronically tune the variable capacitance of the second capacitor.

15. The radio front-end of claim 12 wherein the second capacitor is of a fixed capacitance type.

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

17. The radio front-end of claim 12 wherein a transmit switch is coupled between the power amplifier and the filter input node of the tunable notch filter.

18. The radio front-end of claim 12 wherein the first acoustic resonator and the second acoustic resonator are one of a bulk acoustic wave (BAW) resonator and a surface acoustic wave (SAW) resonator.

19. The radio front-end of claim 13 further including: an Nth inductive element coupled in series with an Nth acoustic resonator between the filter output node and the signal ground node; and an Nth capacitor 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 more.

20. The radio front-end of claim 19 wherein the Nth acoustic resonator is one of a BAW resonator and a SAW resonator.

21. The radio front-end of claim 13 further including an Nth acoustic resonator coupled in parallel with the second acoustic resonator, wherein N is a natural number of 3 or more.

22. The radio front-end of claim 21 wherein the Nth acoustic resonator is one of a BAW resonator and a SAW resonator.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0011] The accompanying drawing figures 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.

[0012] FIG. 1 is a schematic of related-art radio frequency front-end circuitry.

[0013] FIG. 2 is a schematic of an exemplary embodiment of a tunable notch filter that is configured in accordance with the present disclosure.

[0014] FIG. 3 is a graph of filter response of gain versus frequency for a first exemplary case in which undesired frequencies located near an upper edge of a transmit band to notch are attenuated.

[0015] FIG. 4 is a graph of filter response for a second exemplary case in which undesired transmit frequencies located at lower frequencies within the upper half of the transmit band are attenuated.

[0016] FIG. 5 is a graph of filter response for a third exemplary case in which undesirable frequencies near the center of the transmit band to notch are attenuated.

[0017] FIG. 6 is a graph of filter response for a fourth exemplary case in which undesired transmit frequencies located at frequencies within the lower half of the transmit band are attenuated.

[0018] FIG. 7 is a graph of filter response for a fifth exemplary case in which undesired transmit frequencies located at lower frequencies within the lower half of the transmit band are attenuated.

[0019] FIG. 8 is a graph of filter response for a sixth exemplary case in which undesired transmit frequencies located at lower frequencies within the lower edge of the transmit band are attenuated.

[0020] FIG. 9 is a schematic of another exemplary embodiment of a tunable notch filter that is configured in accordance with the present disclosure to have a plurality of resonators tuned by the series tuning capacitor and only one parallel tuning capacitor.

[0021] FIG. 10 is a graph of filter response for the exemplary embodiment of FIG. 9.

[0022] FIG. 11 is a schematic of yet another exemplary embodiment of a tunable notch filter that is configured in accordance with the present disclosure to have a plurality of resonators coupled to a filter input node.

[0023] FIG. 12 is a graph of filter response for the exemplary embodiment of FIG. 11.

[0024] FIG. 13 is a schematic of still another exemplary embodiment of a tunable notch filter that is configured in accordance with the present disclosure to have a plurality of resonators tuned by the series tuning capacitor and a fixed capacitance parallel tuning capacitor.

[0025] FIG. 14 is a radio front-end that incorporates any of the tunable notch filters of the present disclosure including a transmit switch coupled between a filter output node and an antenna terminal.

[0026] FIG. 15 is a radio front-end that can include any of the tunable notch filters 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

[0027] The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0028] It will be understood that, although the terms first, second, etc. may 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. For example, a first element could be termed a second element, and, similarly, a second element could be termed a 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.

[0029] It will be understood that when an element such as a layer, region, or substrate is referred to as being on or extending onto another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being directly on or extending directly onto another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being over or extending over another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being directly over or extending directly over another element, there are no intervening elements present. It will 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 the other element or intervening elements may be present. In contrast, when an element is referred to as being directly connected or directly coupled to another element, there are no intervening elements present.

[0030] Relative terms such as below or above or upper or lower or horizontal or vertical may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms a, an, and the are intended to include the plural forms as well, 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 stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0032] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0033] FIG. 2 is a schematic of an exemplary embodiment of a tunable notch filter 30 that is configured in accordance with the present disclosure. The tunable notch filter 30 includes a first acoustic resonator AR.sub.S1 and a first inductive element L.sub.TS1 coupled in series between a filter input node IN1 and a filter output node OUT1. A first capacitor C.sub.TS1 is coupled in parallel with the first acoustic resonator AR.sub.S1 and the first inductive element L.sub.TS1, wherein the first capacitor C.sub.TS1 is configured to have variable capacitance that is electronically tunable by way of an electronic controller 32. The tunable notch filter 30 further includes a second acoustic resonator AR.sub.P1 and a second inductive element L.sub.TP1 coupled in series between the filter output node OUT1 and a signal ground node G.sub.SIG, and a second capacitor C.sub.TP1 coupled in parallel with the second inductive element L.sub.TP1.

[0034] In at least some exemplary embodiments, as depicted in FIG. 2, the tunable notch filter 30 further includes an Nth inductive element L.sub.TPN coupled in series with an Nth acoustic resonator AR.sub.PN between the filter output node OUT1 and the signal ground node G.sub.SIG. An Nth capacitor C.sub.TPN is configured to have variable capacitance that is electronically tunable by way of the electronic controller 32 and is coupled in parallel with the Nth inductive element L.sub.TPN, wherein N is a natural number of 3 or more. In particular, this embodiment has an N number of capacitors including the Nth capacitor C.sub.TPN and an N number of inductive elements including the Nth inductive element L.sub.TPN that make up a plurality of electronically tunable tank circuits 34. Each of the plurality of resonators AR.sub.P1 through AR.sub.PN has a different resonant frequency.

[0035] In some embodiments, the electronic controller 32 is a baseband processor having digital control outputs that control digitally electronically tunable versions of the first capacitor C.sub.TS1, the second capacitor C.sub.TP1, and the Nth capacitor C.sub.TPN. In other embodiments, the electronic controller 32 is an analog controller having analog control signals that control analog controllable versions of the first capacitor C.sub.TS1, the second capacitor C.sub.TP1, and the Nth capacitor C.sub.TPN.

[0036] FIG. 3 is a graph of filter response of gain versus frequency for a first exemplary case in which undesired frequencies located near an upper edge of a transmit band to notch are attenuated. In this first exemplary case, the first capacitor C.sub.TS1 and the second capacitor C.sub.TP1 through the Nth capacitor C.sub.TPN are set by way of the electronic controller 32 to their minimum capacitances. A first notch depicted in long dash line is positioned at a higher frequency edge of the undesired frequencies by setting the capacitance of the first capacitor C.sub.TS1 to a minimum value. A second notch depicted in short dash line is positioned closer towards a lower edge of the transmit band to notch by setting the second capacitor C.sub.TP1 to a minimum value. A third notch depicted in dash-dot line is positioned at a lower frequency edge of the undesired frequencies by setting the capacitance of the Nth capacitor C.sub.TPN to its minimum value. A resultant frequency response is depicted in solid line. Notice that the resultant frequency response shows that the undesired transmit frequencies are greatly attenuated relative to most other frequencies within the transmit band to notch.

[0037] FIG. 4 is a graph of filter response for a second exemplary case in which undesired transmit frequencies located at lower frequencies within the upper half of the transmit band are attenuated. In this second exemplary case, the first capacitor C.sub.TS1 has increased capacitance, while the second capacitor C.sub.TP1 and the Nth capacitor C.sub.TPN remain set to their minimum capacitance values.

[0038] FIG. 5 is a graph of filter response for a third exemplary case in which undesirable frequencies near the center of the transmit band to notch are attenuated. In this third exemplary case, the first capacitor C.sub.TS1 and the Nth capacitor C.sub.TPN have increased capacitance, while the second capacitor C.sub.TP1 remains set to a minimum capacitance value.

[0039] FIG. 6 is a graph of filter response for a fourth exemplary case in which undesired transmit frequencies located at frequencies within the lower half of the transmit band are attenuated. In this fourth exemplary case, the first capacitor C.sub.TS1 has increased capacitance, while the Nth capacitor C.sub.TPN remains constant and the second capacitor C.sub.TP1 remains set to a minimum capacitance value.

[0040] FIG. 7 is a graph of filter response for a fifth exemplary case in which undesired transmit frequencies located at lower frequencies within the lower half of the transmit band are attenuated. In this fifth exemplary case, the first capacitor C.sub.TS1 has further increased capacitance, while the Nth capacitor C.sub.TPN remains constant and the second capacitor C.sub.TP1 remains set to a minimum capacitance value.

[0041] FIG. 8 is a graph of filter response for a sixth exemplary case in which undesired transmit frequencies located at lower frequencies within the lower edge of the transmit band are attenuated. In this sixth exemplary case, first capacitor C.sub.TS1 has still further increased capacitance, and the second capacitor C.sub.TP1 has increased capacitance to move the transmit band notch to the band edge while the Nth capacitor C.sub.TPN remains constant.

[0042] FIG. 9 is another exemplary embodiment of a tunable notch filter 36 that is configured in accordance with the present disclosure to have a plurality of resonators from second acoustic resonator AR.sub.P1 through Nth acoustic resonator AR.sub.PN that are electronically tuned by only the first capacitor C.sub.TS1 and the second capacitor C.sub.TP1. In other words, the plurality of electronically tunable tank circuits 34 (FIG. 2) made up of an N number of capacitors such as the Nth capacitor C.sub.TPN and an N number of inductors such as the Nth inductive element L.sub.TPN is not incorporated in this embodiment.

[0043] FIG. 10 is a graph of filter response for the exemplary embodiment of FIG. 9. In this particular example, the electronic controller 32 adjusts the capacitances of both the first capacitor C.sub.TS1 and the second capacitor C.sub.TP1 to provide the frequency response depicted in solid line adjacent to the horizontal axis representing frequency.

[0044] FIG. 11 is yet another exemplary embodiment of a tunable notch filter 38 that is configured in accordance with the present disclosure to have the plurality of resonators from second acoustic resonator AR.sub.P1 through Nth acoustic resonator AR.sub.PN that are electronically tuned by only the first capacitor C.sub.TS1 and the second capacitor C.sub.TP1. However, in this particular embodiment, the second capacitor C.sub.TP1 has fixed capacitance and the first capacitor C.sub.TS1 has capacitance that is controlled by the electronic controller 32. FIG. 12 is a graph of filter response for the exemplary embodiment of FIG. 11.

[0045] FIG. 13 is a schematic of an exemplary embodiment of a tunable notch filter 40 that is configured in accordance with the present disclosure. The tunable notch filter 40 includes the first acoustic resonator AR.sub.si and the first inductive element L.sub.TS1 coupled in series between the filter input node IN1 and the filter output node OUT1. As in the previous embodiments, the first capacitor C.sub.TS1 is coupled in parallel with the first acoustic resonator AR.sub.S1 and the first inductive element L.sub.TS1, wherein the first capacitor C.sub.TS1 is configured to have variable capacitance that is electronically tunable by way of the electronic controller 32. The tunable notch filter 40 further includes the second acoustic resonator AR.sub.pi and the second inductive element L.sub.TP1. However, in this particular embodiment, the second acoustic resonator AR.sub.P1 and the second inductive element L.sub.TP1 are coupled in series between the filter input node IN1 and the signal ground node G.sub.SIG. The second capacitor C.sub.TP1 is coupled in parallel with the second inductive element L.sub.TP1.

[0046] In at least some exemplary embodiments, as depicted in FIG. 13, the tunable notch filter 40 further includes an Nth inductive element L.sub.TPN coupled in series with an Nth acoustic resonator AR.sub.PN between the filter input node IN1 and the signal ground node G.sub.SIG. An Nth capacitor C.sub.TPN is configured to have variable capacitance that is electronically tunable by way of the electronic controller 32 and is coupled in parallel with the Nth inductive element L.sub.TPN, wherein N is a natural number of 3 or more. Frequency responses for the tunable notch filter 40 are the same as depicted in FIG. 3 through FIG. 8.

[0047] FIG. 14 is a schematic of an exemplary radio front-end 42 that incorporates a tunable notch filter 44 that can be any one of the tunable notch filters 30, 36, 38, and 40. In this particular embodiment, the tunable notch filter 44 is coupled between an output of a power amplifier PA1 and an 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 through 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 selective opening and closing of the transmit switch SW1 and the receive switch SW2.

[0048] FIG. 15 is a schematic of another exemplary radio front-end 46 that incorporates the tunable notch filter 44 that can be any one of the tunable notch filters 30, 36, 38, and 40. In this exemplary embodiment, the transmit switch SW1 is coupled between the filter input node IN1 and an output of the power amplifier PA1. In contrast to the embodiment of FIG. 14, in this embodiment the tunable notch filter 44 can also filter a receive band. The electronic controller 32 electronically tunes the tunable notch filter 44 and controls selective opening and closing of the transmit switch SW1 and the receive switch SW2.

[0049] 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 within the scope of the concepts disclosed herein and the claims that follow.