Patent Publication Number: US-2022224303-A1

Title: Adjustable rejection circuit with tunable impedance

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application Ser. No. 63/137,189, filed Jan. 14, 2021, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The technology of the disclosure relates generally to controlling impedance associated with transmission paths to antennas in wireless communication devices. 
     BACKGROUND 
     Mobile communication devices have become increasingly common in current society. The prevalence of these mobile communication devices is driven in part by the many functions that are now enabled on such devices. Increased processing capabilities in such devices means that mobile communication devices have evolved from being pure communication tools into sophisticated mobile multimedia centers that enable enhanced user experiences. 
     The redefined user experience requires higher data rates offered by wireless communication technologies, such as Wi-Fi, long-term evolution (LTE), and fifth-generation new-radio (5G-NR). 5G-NR, in particular, relies on multiple input-multiple output (MIMO) techniques to enable high-bandwidth communication where plural antennas may transmit multiple signals that have been shaped or steered by a beamforming circuit that adjusts relative phases of the signals. 
     Typical beamforming circuits assume relatively constant impedance at the antennas. However, temperature fluctuations or other environmental changes (e.g., how a user holds the phone in hand, near body, or on a table with speaker phone on) in the circuitry or at the antenna may cause changes of impedance outside the assumed constant impedance tolerances, resulting in variations in the beam steering which may negatively impact performance. 
     SUMMARY 
     Aspects disclosed in the detailed description include an adjustable rejection circuit with tunable impedance. In an exemplary aspect, a circuit is provided with an impedance tuner configured to match impedances for an antenna. The impedance tuner may include an LC circuit (inductor-capacitor circuit) with one or more elements of the LC circuit being variable. An adjustable rejection circuit may be placed in parallel with the impedance tuner. In an exemplary aspect, the adjustable rejection circuit may include a variable negative capacitance element that provides strong attenuation in frequencies of interest. By providing the impedance tuner and adjustable rejection circuit within a single circuit, overall performance may be improved without expanding the footprint of the device excessively. 
     In one aspect, a circuit is disclosed. The circuit comprises an input. The circuit also comprises an output. The circuit also comprises an impedance tuner. The impedance tuner comprises a first variable capacitor having a first end and a second end. The first variable capacitor is serially positioned between the input and the output. The impedance tuner also comprises a second variable capacitor coupled to a first node formed by the second end of the first variable capacitor and the output. The second variable capacitor is also coupled to a ground. The circuit also comprises an adjustable rejection circuit. The adjustable rejection circuit comprises a variable negative capacitance circuit electrically parallel to the first variable capacitor. 
     In another aspect, a circuit is disclosed. The circuit comprises an input. The circuit also comprises an output. The circuit also comprises an impedance tuner. The impedance tuner comprises a first inductor coupled to the input. The impedance tuner also comprises a second inductor serially negatively coupled to the input and the output. The impedance tuner also comprises a first variable capacitor coupled to an intermediate node between the first inductor and the second inductor and also coupled to a ground. The impedance tuner also comprises a second variable capacitor coupled to the output. The circuit also comprises an adjustable rejection circuit. The adjustable rejection circuit comprises a variable negative capacitance circuit electrically parallel to the impedance tuner. 
     Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1A  is a block diagram of a conventional impedance tuner positioned between a front end circuit and an antenna; 
         FIG. 1B  is a circuit diagram of the impedance tuner of  FIG. 1A ; 
         FIG. 2  is a partial view of a mobile communication device showing relative positions of aperture tuners, an impedance tuner, and antennas; 
         FIG. 3A  is a block diagram of a combined impedance tuner and adjustable rejection circuit capable of operating as both concurrently positioned between a front end circuit and an antenna; 
         FIG. 3B  is a block diagram of a combined impedance tuner and adjustable rejection circuit capable of operating as one or the other modalities positioned between a front end circuit and an antenna; 
         FIG. 4  is a circuit diagram of a combined impedance tuner and adjustable rejection circuit with a variable negative capacitance used to provide the adjustable rejection portion of the circuit; 
         FIG. 5  is a circuit diagram of an exemplary aspect of the combined impedance tuner and adjustable rejection circuit with negatively coupled inductors and a shunt capacitor acting as the negative capacitance element from  FIG. 4 ; 
         FIG. 6  is a diagram showing an equivalent network of two negatively coupled inductors (K&gt;0); 
         FIGS. 7A and 7B  are diagrams showing a T to π transformation and indicating that an equivalent negative capacitance is obtained; 
         FIG. 8  is diagram showing ideal negative capacitance in the case K=1 and for frequencies above 1/√(LC)/(2*π); 
         FIG. 9  is a circuit diagram of the combined impedance tuner and adjustable rejection circuit with an additional switch to disconnect the adjustable rejection circuit; 
         FIG. 10  is a circuit diagram of the combined impedance tuner and adjustable rejection circuit with two additional switches to disconnect the adjustable rejection circuit as well as remove any impedance that might exist as a function of a connection to ground therethrough; 
         FIGS. 11A and 11B  are circuit diagrams of the combined impedance tuner and adjustable rejection circuit with a plurality of adjustable rejection circuits that that may be selectively used as needed; 
         FIG. 12A  is a circuit diagram of an alternate conventional impedance matching circuit; 
         FIG. 12B  is a circuit diagram of the combined impedance tuner and adjustable rejection circuit using the impedance matching circuit of  FIG. 12A ; 
         FIG. 13  is a circuit diagram of the combined impedance tuner and adjustable rejection circuit with an expanded impedance matching circuit; 
         FIG. 14  is a block diagram of a mobile communication device showing the control link between a transceiver and a combined circuit according to an exemplary aspect of the present disclosure; 
         FIG. 15  is a block diagram of a mobile communication device showing the control link between a transceiver and a combined circuit according to an exemplary aspect of the present disclosure; and 
         FIG. 16  illustrates graphs of comparative outputs from a simulation between a conventional impedance matching circuit and a combined circuit according to an exemplary aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     Aspects disclosed in the detailed description include an adjustable rejection circuit with tunable impedance. In an exemplary aspect, a circuit is provided with an impedance tuner configured to match impedances for an antenna. The impedance tuner may include an LC circuit (inductor-capacitor circuit) with one or more elements of the LC circuit being variable. An adjustable rejection circuit may be placed in parallel with the impedance tuner. In an exemplary aspect, the adjustable rejection circuit may include a variable negative capacitance element that provides strong attenuation in frequencies of interest. By providing the impedance tuner and adjustable rejection circuit within a single circuit, overall performance may be improved without expanding the footprint of the device excessively. 
     Before addressing exemplary aspects of the present disclosure, a brief overview of conventional impedance tuners and their role in a mobile communication device are provided with reference to  FIGS. 1A-2 . A discussion of exemplary aspects of the present disclosure are provided below beginning with reference to  FIG. 3 . 
     In this regard,  FIG. 1A  illustrates a block diagram of a transmission chain  10  in a mobile communication device  12 . The transmission chain  10  may include a front end circuit  14 , which may be a radio frequency front end (RFFE) circuit included in a switch power amplifier duplexer (SPAD) module or the like. The front end circuit  14  conditions signals for transmission by one or more antennas  16 ( 1 )- 16 (N), Each antenna  16 ( 1 )- 16 (N) may have a respective aperture tuner circuit  18 ( 1 )- 18 (N). The front end circuit  14  may be connected to the antennas  16 ( 1 )- 16 (N) through a flexible connector  20 , which may be, for example, a form of coaxial cable. In an exemplary aspect, each antenna  16 ( 1 )- 16 (N) may have a respective connector  20 , although only one is shown. Because it is known that the impedance of the antennas  16 ( 1 )- 16 (N) may change, aperture tuner circuits  18 ( 1 )- 18 (N) and an impedance tuner  22  may be provided to adjust impedances presented by the antennas  16 ( 1 )- 16 (N) so as to reduce reflections and improve performance. 
       FIG. 1B  provides the circuit details of a typical impedance tuner  22 , which may include a first variable capacitor  24 , a switch  26 , and a second variable capacitor  28 . An inductor  30  may be selectively added or shorted to ground by switches  32  and  34 . Other impedance tuners do exist, but the circuit illustrated in  FIG. 1B  is typical. 
       FIG. 2  shows a partial view of the mobile communication device  12  and particularly a bottom portion  40  of a chassis  42  of the mobile communication device  12 . The impedance tuner  22  is placed proximate the antennas  16 ( 1 )- 16 (N) and may be used by all of them. Respective aperture tuner circuits  18 ( 1 )- 18 (N) are closer to the antennas  16 ( 1 )- 16 (N). Other configurations may be used by different mobile communication devices, but in general, the antennas  16 ( 1 )- 16 (N) are integrated into various positions within the chassis  42  and not part of the motherboard or printed circuit board (PCB) within the mobile communication device  12 . 
     While the impedance tuner  22  may be effective at reducing unwanted reflections and allowing impedance matching, other concerns do exist. For example, antennas by design capture signals and translate them into electrical signals. In general, the antenna does not discriminate between signals of interest and other signals. When the antenna captures signals outside the signals of interest, these additional signals may show up as noise and negatively impact performance or the user experience. Even when the antennas only capture signals of interest, ringing or harmonics of those signals may exist within the circuitry of the mobile communication device, which may also negatively impact performance or the user experience. Band pass filters and the like may be used to limit unwanted signals, but there is room for improvement in providing signal rejection at unwanted frequencies. 
     Exemplary aspects of the present disclosure reuse some of the elements of the impedance tuner and co-locate an adjustable rejection circuit with the impedance tuner. By reusing the elements of the impedance tuner, the overall footprint of the combined device is not increased excessively. Likewise, because the impedance tuner already serves all the antennas, duplicative circuits (e.g., like the aperture tuners) are not required for each antenna. 
     While the exemplary aspects discussed below primarily focus on an adjustable rejection circuit that operates concurrently with the impedance tuner, the present disclosure is not so limited, and the combined circuit may operate in one mode or another mode. These two possibilities are illustrated in  FIGS. 3A and 3B , respectively. For example,  FIG. 3A  illustrates a combined circuit  50 A that sits between a front end  52  and a connector  54 . The connector  54  may be connected to antennas  56 ( 1 )- 56 (N), each having a respective aperture tuner  58 ( 1 )- 58 (N). The combined circuit  50 A includes an impedance tuner  60  and an adjustable rejection circuit  62  that work concurrently. 
     In contrast,  FIG. 3B  illustrates a combined circuit  50 B where either an impedance tuner  64  or an adjustable rejection circuit  66  works, but not both concurrently. Such mode switching may be done with switches (not shown) as needed or desired. Individual elements may still be reused, but the functionality is limited to just a single mode. 
     Assuming an impedance tuner similar to the impedance tuner  22  of  FIG. 2 ,  FIG. 4  provides an exemplary circuit diagram of the combined circuit  50 A within a mobile communication device  80 . In particular, the mobile communication device  80  includes a front end  82 , the combined circuit  50 A, a connector  84 , antennas  86 ( 1 )- 86 (N), and aperture tuners  88 ( 1 )- 88 (N). The combined circuit  50 A includes an input  90  and an output  92 . 
     The combined circuit  50 A further includes an impedance matching circuit  94  that may include an inductor  96 , a first variable capacitor  98 , and a second variable capacitor  100 . The inductor  96  may be connected to the input  90  via a switch  102 . The inductor  96  may further be connected to a ground  104 . The input  90  is also connected to the ground  104  via a switch  106 . The second variable capacitor  100  is also connected to ground  104 . The first variable capacitor  98  is connected to the output  92  through a switch  108 . 
     The combined circuit  50 A further includes an adjustable rejection circuit  110 , which may be a frequency dependent variable negative capacitance circuit (e.g., −Ceq0(f)). While various structures can be used to create the variable negative capacitance circuit, one exemplary structure is a network made of two negatively coupled inductors with a middle node using a tunable shunt capacitor to ground as better illustrated in  FIG. 5 . 
     In particular,  FIG. 5  illustrates a mobile communication device  120  that includes a front end  82 , a connector  84 . antennas  86 ( 1 )- 86 (N), and aperture tuners  88 ( 1 )- 88 (N). The mobile communication device  120  further includes a combined circuit  122 . The combined circuit  122  includes an input  124  and an output  126 . The combined circuit  122  further includes an impedance matching circuit  128  that may include an inductor  130 , a first variable capacitor  132  (C1), and a second variable capacitor  134  (C2). The inductor  130  may be connected to the input  124  via a switch  136 . The inductor  130  may further be connected to a ground  138 . The input  124  is also connected to the ground  138  via a switch  140 . The second variable capacitor  134  is also connected to ground  138 . The first variable capacitor  132  is connected to the output  126  through a switch  142 . 
     With continued reference to  FIG. 5 , the combined circuit  122  also includes an adjustable rejection circuit  144 . The adjustable rejection circuit  144  includes a first inductor  146  and a second inductor  148  serially connected to one another with an intermediate node  150 . It should further be appreciated that the first inductor  146  and the second inductor  148  are negatively coupled. A variable capacitor  152  (−C0) is connected to the intermediate node  150  and to the ground  138 . 
     The efficaciousness of the adjustable rejection circuit  144  of  FIG. 5  may be mathematically proven. Specifically, the two negatively coupled inductors  146 ,  148  may have a K factor (K&gt;0) and thus would have an equivalent T-network  160 , as shown in  FIG. 6 . If a T to π transformation is applied, the network between the two ports of the inductors has a behavior like a negative capacitor within a specific frequency range. Thus, if a T to π transformation is applied to the network, an equivalent electrical network is obtained that has a negative capacitance between the two terminals N 1 /N 2 , as shown in  FIGS. 7A and 7B . 
     For the case of ideal coupling, K=1, and for a frequency range above the resonance pulsation of 1/√L*C0, an ideal negative capacitance of C0/4 is obtained, as shown in  FIG. 8 . 
       FIG. 9  illustrates a mobile communication device  120 A that includes a front end  82 , a connector  84 , antennas  86 ( 1 )- 86 (N), and aperture tuners  88 ( 1 )- 88 (N). The mobile communication device  120 A further includes a combined circuit  122 A. The primary difference between the combined circuit  122 A and the combined circuit  122  of  FIG. 5  is a modified adjustable rejection circuit  144 A, which includes a switch  154  that allows the adjustable rejection circuit  144 A to be selectively used. 
       FIG. 10  illustrates mobile communication device  120 B that includes a front end  82 , a connector  84 , antennas  86 ( 1 )- 86 (N), and aperture tuners  88 ( 1 )- 88 (N). The mobile communication device  120 B further includes a combined circuit  122 B, which has been modified further by adding a second switch  156  so that not only may the adjustable rejection circuit  144 B be used selectively, any impedance changes by the variable capacitor  152  coupling to ground  138  are also reduced or eliminated. Note further that the presence of the inductors  146 ,  148  also allow the inductor  130  with the switches  136 ,  140  to be eliminated as well. 
     There are additional variations that may also be used depending on design constraints. For example, as illustrated by mobile communication device  120 C in  FIG. 11A , the combined circuit  144 C may include a plurality of negative capacitance circuits  200 ( 1 )- 200 (P), which may be selected by switches  202 ( 1 )- 202 (P) and  204 ( 1 )- 204 (P). As explained above, the negative capacitance circuits  200 ( 1 )- 200 (P) may be formed from two negatively coupled inductors and a shunt variable capacitor coupled to the intermediate node. 
     Alternatively, as illustrated in  FIG. 11B , a mobile communication device  120 D may include a combined circuit  144 D which also includes a plurality of negative capacitive circuits  206 ( 1 )- 206 (Q), but instead of each circuit  206 ( 1 )- 206 (Q) having a respective tunable shunt capacitor, all the circuits  206 ( 1 )- 206 (Q) share a single shunt variable capacitor  208 . 
     While the two capacitor structure for the impedance matching circuit is common, such structure is not the only option for an impedance matching circuit. In this regard,  FIG. 12A  illustrates an impedance matching circuit  220  that includes a first inductor  222  serially connected to a second inductor  224  with an intermediate node  226  therebetween. A first variable capacitor  228  couples the intermediate node  226  to a ground  230 . A second variable capacitor  232  couples a second node  234  to ground  230  as well. A bypass switch  236  may exist to bypass the elements of the impedance matching circuit  220 . 
     To add an adjustable rejection circuit, the impedance matching circuit  220  is modified as illustrated by a combined circuit  240  in  FIG. 12B . The combined circuit  240  includes a first inductor  242  serially connected and negatively coupled to a second inductor  244  with an intermediate node  246  therebetween. A first variable capacitor  248  couples the intermediate node  246  to a ground  250 . A second variable capacitor  252  couples a second node (also an output)  254  to the ground  250  as well. The first inductor  242  is also coupled to an input  256 . A variable capacitor  258  is electrically parallel to the inductors  242 ,  244  and thus extends from the input  256  to the output  254 . A switch  260  may be included to bypass the combined circuit  240 . 
       FIG. 13  provides an alternate structure similar for a combined circuit  270 . The combined circuit  270  includes an input  272  and an output  274 . A bypass switch  276  may by be provided to create a short between the input  272  and the output  274 . An impedance matching circuit  278  may include a first inductor  280  serially connected to and negatively coupled to a second inductor  282  with a first intermediate node  284  therebetween. A first variable capacitor  286  couples the first intermediate node  284  to a ground  288 . Additionally, a third inductor  290  may be serially coupled to the second inductor  282  with a second intermediate node  292  therebetween, A fourth inductor  294  may be serially connected to and negatively coupled to the third inductor  290  with a third intermediate node  296  therebetween. A second variable capacitor  298  may couple the third intermediate node  296  to the ground  288 . 
     With continued reference to  FIG. 13 , a third variable capacitor  300  may couple the input  272  to the second intermediate node  292 , and a fourth variable capacitor  302  may couple the second intermediate node  292  to the output  274 . Still other arrangements may be possible without departing from the present disclosure. However, one of the advantages of the present disclosure is that elements of the impedance tuner are reused so as to minimize or at least reduce undesirable changes to the space required for the circuit. 
     While the above discussion focuses on various possible circuits,  FIGS. 14 and 15  show two possible control configurations for the combined circuit  50 A of  FIG. 4 . In particular, in  FIG. 14  the front end  82  may include a directional coupler  310 , which provides power measurements for forward (Pfor) and reverse directions (Prev), which are used by a transceiver  312  to calculate a voltage standing wave ratio (VSWR) and generate a control signal  314  which adjusts the variable elements within the combined circuit  50 A. Note that a control link already exists to change elements of the impedance matching portion of the combined circuit  50 A, so no additional paths need be created. Similarly, in  FIG. 15 , a control signal may be sent from the transceiver  312  to a look-up table (LUT)  316  or other circuit that generates the command for a variable capacitor (e.g., C1) as a function of the command signal for the negative capacitive element (C0). While not illustrated, the LUT  316  or function could work the other way. That is. the LUT  316  receives the command for the C1 capacitive element and generates the command for C0 capacitive element. 
     Simulations show that exemplary aspects of the present disclosure provide substantially improved rejection without materially affecting the impedance matching as shown in  FIG. 16 . Specifically, rejection and return loss are graphed for the impedance tuner  22  and the combined circuit  122 . The solid line corresponds to the return loss and rejection for the impedance tuner  22  and the dashed line corresponds to the return loss and rejection for the combined circuit  122 . 
     While various materials may be used in the fabrication of exemplary aspects of the present disclosure, two specifically contemplated structures would be fabricating using a silicon on insulator (SOI) material or using microelectromechanical systems (MEMS). 
     Those skilled in the art will recognize improvements and modifications to the 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.