Patent Publication Number: US-11024479-B2

Title: Passive wireless switch circuit and related apparatus

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/263,069, filed on Jan. 31, 2019, now U.S. Pat. No. 10,453,636, which claims the benefit U.S. provisional patent application Ser. No. 62/727,881, filed on Sep. 6, 2018, the disclosures of which are incorporated herein by reference in their entireties. 
     This application is related to U.S. patent application Ser. No. 16/263,055, filed on Jan. 31, 2019, now U.S. Pat. No. 10,529,519, and entitled “PASSIVE WIRELESS SWITCH CIRCUIT AND RELATED APPARATUS,” 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 operating microelectromechanical systems (MEMS) switches in an electrical circuit. 
     BACKGROUND 
     Wireless devices have become increasingly common in current society. The prevalence of these wireless devices is driven in part by the many functions that are now enabled on such devices for supporting a variety of applications. In this regard, a wireless device may employ a variety of circuits and/or components (e.g., filters, transceivers, antennas, and so on) to support different numbers and/or types of applications. Accordingly, the wireless device may include a number of switches to enable dynamic and flexible couplings between the variety of circuits and/or components. 
     Notably, a conventional switch, such as a silicon-on-insulator (SOI) switch, may create a relatively higher on-resistance (R ON ) when the conventional switch is closed and a relatively higher off-capacitance (C OFF ) when the conventional switch is opened. Accordingly, the conventional switch may suffer a degraded figure-of-merit (FOM) (FOM=R ON ×C OFF ) and cause unwanted insertion loss to degrade RF efficiency and/or performance of the wireless device. In contrast, a microelectromechanical systems (MEMS) switch typically has a FOM that is at least ⅓ lower than the FOM of the conventional SOI switch. As a result, it may be possible to reduce the unwanted insertion loss associated with the conventional SOI switch by replacing the conventional SOI switch with the MEMS switch, thus helping to improve RF efficiency and/or performance of the wireless device. 
     SUMMARY 
     Aspects disclosed in the detailed description include a passive wireless switch circuit and related apparatus. In examples discussed herein, an apparatus includes a smaller number of voltage circuits configured to control a larger number of microelectromechanical systems (MEMS) switches. The voltage circuits are configured to passively generate a number of constant voltages based on a number of radio frequency (RF) signals to collectively identify each of the MEMS switches. A decoder circuit is configured to decode the constant voltages to identify a selected MEMS switch and provide a selected constant voltage higher than a defined threshold voltage to close the selected MEMS switch. By passively generating the constant voltages, it may be possible to eliminate active components and/or circuits from the passive wireless switch circuit, thus helping to reduce leakage and power consumption. Further, by controlling the larger number of MEMS switches based on the smaller number of voltage circuits, it may be possible to reduce conductive traces between the voltage circuits and the MEMS switches, thus helping to reduce routing complexity and footprint of the apparatus. 
     In one aspect, an apparatus is provided. The apparatus includes a first number of voltage circuits. The first number of voltage circuits includes a first number of antenna ports coupled to a first number of antennas. The first number of antennas is configured to absorb a first number of radio frequency (RF) signals in a first number of selected frequency bandwidths and corresponding to first number of RF voltages, respectively. The first number of voltage circuits also includes a first number of bulk acoustic wave (BAW) structures coupled to the first number of antenna ports. The first number of BAW structures is configured to resonate at the first number of selected frequency bandwidths to convert the first number of RF voltages to a first number of boosted RF voltages higher than the first number of RF voltages, respectively. The first number of voltage circuits also includes a first number of rectifier circuits coupled to the first number of BAW structures. The first number of rectifier circuits is configured to generate a first number of constant voltages based on the first number of boosted RF voltages, respectively. The apparatus also includes a second number of MEMS switches. Each of the second number of MEMS switches is configured to be closed in response to receive a selected constant voltage exceeding a defined threshold voltage. The apparatus also includes a decoder circuit coupled between the first number of voltage circuits and the second number of MEMS switches. The decoder circuit is configured to receive the first number of constant voltages from the first number of voltage circuits, respectively. The decoder circuit is also configured to decode the first number of constant voltages to determine a selected MEMS switch among the second number of MEMS switches. The decoder circuit is also configured to provide a selected constant voltage among the first number of constant voltages to the selected MEMS switch to close the selected MEMS switch. 
     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 schematic diagram of an exemplary bulk acoustic wave (BAW) device; 
         FIG. 1B  is a schematic diagram of an exemplary BAW structure, which may be formed based on the BAW device of  FIG. 1A ; 
         FIG. 2  is a schematic diagram of an exemplary passive wireless switch circuit configured according to an embodiment of the present disclosure to control at least one microelectromechanical systems (MEMS) switch by harvesting a radio frequency (RF) voltage from an RF signal; 
         FIG. 3A  is a schematic diagram of an exemplary passive wireless switch circuit in which multiple MEMS switches are controlled by a single voltage circuit; 
         FIG. 3B  is a schematic diagram of an exemplary passive wireless switch circuit in which multiple MEMS switches are controlled by multiple voltage circuits, respectively; 
         FIG. 3C  is a schematic diagram of an exemplary passive wireless switch circuit in which multiple MEMS switches are controlled respectively by multiple voltage circuits sharing a common antenna; 
         FIG. 4A  is a schematic diagram of an exemplary apparatus including the passive wireless switch circuit of  FIG. 2 , the passive wireless switch circuit of  FIG. 3A , the passive wireless switch circuit of  FIG. 3B , or the passive wireless switch circuit of  FIG. 3C  for coupling/decoupling a first circuit and a second circuit; 
         FIG. 4B  is a schematic diagram of an exemplary apparatus in which the passive wireless switch circuit of  FIG. 2 , the passive wireless switch circuit of  FIG. 3A , the passive wireless switch circuit of  FIG. 3B , or the passive wireless switch circuit of  FIG. 3C  can be adapted to control multiple Internet-of-Things (IoT) circuits; and 
         FIG. 5  is a schematic diagram of an exemplary apparatus configured according to an embodiment of the present disclosure to control a larger number of MEMS switches based on a smaller number of voltage circuits. 
     
    
    
     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 a passive wireless switch circuit and related apparatus. In examples discussed herein, an apparatus includes a smaller number of voltage circuits configured to control a larger number of microelectromechanical systems (MEMS) switches. The voltage circuits are configured to passively generate a number of constant voltages based on a number of radio frequency (RF) signals to collectively identify each of the MEMS switches. A decoder circuit is configured to decode the constant voltages to identify a selected MEMS switch and provide a selected constant voltage higher than a defined threshold voltage to close the selected MEMS switch. By passively generating the constant voltages, it may be possible to eliminate active components and/or circuits from the passive wireless switch circuit, thus helping to reduce leakage and power consumption. Further, by controlling the larger number of MEMS switches based on the smaller number of voltage circuits, it may be possible to reduce conductive traces between the voltage circuits and the MEMS switches, thus helping to reduce routing complexity and footprint of the apparatus. 
     Before discussing a passive wireless switch circuit of the present disclosure, a brief overview of a bulk acoustic wave (BAW) structure, which may multiply an RF voltage to generate a boosted RF voltage higher than the RF voltage is first provided with reference to  FIGS. 1A and 1B . The discussion of specific exemplary aspects of the passive wireless switch circuit and related apparatuses of the present disclosure starts below with reference to  FIG. 2 . 
     In this regard,  FIG. 1A  is a schematic diagram of an exemplary BAW device  10  (e.g., a BAW filter). The BAW device  10  includes a piezo layer  12  (e.g., a quartz crystal), a top metal electrode  14  disposed on a top surface  16  of the piezo layer  12 , and a bottom metal electrode  18  disposed on a bottom surface  20  of the piezo layer  12 . When a voltage V IN  is applied between a top electrical port  22  and a bottom electrical port  24 , an acoustic wave  26  is excited and resonates at a resonance frequency f C  between the top surface  16  and the bottom surface  20  of the piezo layer  12 . The resonance frequency f C  may be determined by a thickness of the piezo layer  12  as well as a mass of the top metal electrode  14  and the bottom metal electrode  18 . 
     The BAW device  10  may be configured to expand the piezo layer  12  when a positive voltage V IN  is applied between top electrical port  22  and the bottom electrical port  24  and compress the piezo layer  12  when a negative voltage V IN  is applied between top electrical port  22  and the bottom electrical port  24 . Hereinafter, the BAW device  10  in which the piezo layer  12  expands and compresses respectively in response to the positive voltage V IN  and the negative voltage V IN  is referred to as a polarized BAW device  10   a.    
     Alternatively, the BAW device  10  may be configured to compress the piezo layer  12  when the positive voltage V IN  is applied between top electrical port  22  and the bottom electrical port  24  and expand the piezo layer  12  when the negative voltage V IN  is applied between top electrical port  22  and the bottom electrical port  24 . Hereinafter, the BAW device  10  in which the piezo layer  12  compresses and expands respectively in response to the positive voltage V IN  and the negative voltage V IN  is referred to as a polarized inverted BAW device  10   b.    
       FIG. 1B  is a schematic diagram of an exemplary BAW structure  28 , which may be formed based on the polarized BAW device  10   a  (e.g., a polarized BAW filter) and the polarized inverted BAW device  10   b  (e.g., a polarized inverted BAW filter) of  FIG. 1A . Common elements between  FIGS. 1A and 1B  are shown therein with common element numbers and will not be re-described herein. 
     The polarized BAW device  10   a  includes a piezo layer  12   a  (e.g., a quartz crystal), a top metal electrode  14   a,  and a bottom metal electrode  18   a  that correspond to the piezo layer  12 , the top metal electrode  14 , and the bottom metal electrode  18  of  FIG. 1A , respectively. The polarized inverted BAW device  10   b  includes a piezo layer  12   b  (e.g., a quartz crystal), a top metal electrode  14   b,  and a bottom metal electrode  18   b  that correspond to the piezo layer  12 , the top metal electrode  14 , and the bottom metal electrode  18  of  FIG. 1A , respectively. In a non-limiting example, the polarized BAW device  10   a  is stacked on top of the polarized inverted BAW device  10   b.  In this regard, the bottom metal electrode  18   a  of the polarized BAW device  10   a  is coupled to the top metal electrode  14   b  of the polarized inverted BAW device  10   b.    
     When the positive voltage V IN  is applied between the top metal electrode  14   a  and the bottom metal electrode  18   a,  the piezo layer  12   a  expands. Concurrently, when the positive voltage V IN  is applied between the top metal electrode  14   b  and the bottom metal electrode  18   b,  the piezo layer  12   b  compresses. As a result, a voltage V OUT  between the top metal electrode  14   a  and the bottom metal electrode  18   b  equals two times the voltage V IN  (V OUT =2×V IN ). In this regard, the BAW structure  28  can be said to function as a voltage multiplier. Accordingly, by interleaving an equal number of the polarized BAW device  10   a  and the polarized inverted BAW device  1   b  in a BAW structure, it may be possible to multiply the voltage V IN  to generate the voltage V OUT  based on the equation (Eq. 1) below.
 
 V   OUT =N L ×V IN   (Eq. 1)
 
     In the equation (Eq. 1) above, N L  represents a total number of the polarized BAW device  10   a  and the polarized inverted BAW device  10   b  in the BAW structure  28 . For example, if the BAW structure  28  is configured to include five (5) polarized BAW devices  10   a  that interleave with 5 polarized inverted BAW devices  10   b,  the BAW structure  28  is able to generate the voltage V OUT  that equals ten (10) times the voltage V IN  (V OUT =10×V IN ). As discussed below, the BAW structure  28  may be provided in a passive wireless switch circuit to generate a boosted RF voltage (e.g., V OUT ) based on an RF voltage (e.g., V IN ) for controlling a MEMS switch(es). 
       FIG. 2  is a schematic diagram of an exemplary passive wireless switch circuit  30  configured according to an embodiment of the present disclosure to control at least one MEMS switch  32  by harvesting an RF voltage V RF  from an RF signal  34 . As discussed in detail below, the passive wireless switch circuit  30  can be configured to multiply the RF voltage V RF  to generate a boosted RF voltage V RF1 , which is higher than the RF voltage V RF , and subsequently generate a constant voltage V C  based on the boosted RF voltage V RF1  to operate (close or open) the MEMS switch  32 . In this regard, there will be no electrical current in the passive wireless switch circuit  30  until the RF signal  34  is received. As such, the passive wireless switch circuit  30  has very little leakage in absence of the RF signal  34 , thus making it possible to provide the passive wireless switch circuit  30  in a low power apparatus (e.g., a battery-operated electronic device) for supporting such applications as the Internet-of-Things (IoT). 
     The passive wireless switch circuit  30  includes at least one voltage circuit  36  configured to generate the constant voltage V C  based on the RF voltage V RF . The MEMS switch  32  includes a gate terminal  38  that is coupled to the voltage circuit  36  to receive the constant voltage V C . When the constant voltage V C  exceeds (higher than or equal to) a defined threshold voltage (e.g., 30-50 V), the MEMS switch  32  is closed to allow an electrical current to flow from a drain terminal  40  to a source terminal  42 , or vice versa. In contrast, when the constant voltage V C  is below the defined threshold voltage, the MEMS switch  32  is opened, thus stopping the electrical current between the drain terminal  40  and the source terminal  42 . 
     The voltage circuit  36  includes at least one antenna port  43  configured to be coupled to at least one antenna  44 . The antenna  44  is configured to absorb the RF signal  34  in a selected frequency bandwidth. Herein, the phrase “frequency bandwidth” refers to a continuous RF band centered at a center frequency bounded by a lower frequency (lower than the center frequency) and an upper frequency (higher than the center frequency). Although the antenna  44  is shown to be inside the voltage circuit  36 , it should be appreciated that the antenna  44  may also be provided outside the voltage circuit  36  and coupled to the voltage circuit  36  via the antenna port  43 . 
     The voltage circuit  36  includes at least one BAW structure  46  configured to multiply the RF voltage V RF  to generate the boosted RF voltage V RF1 . In a non-limiting example, the BAW structure  46  is identical to the BAW structure  28  of  FIG. 1B . In this regard, the BAW structure  46  may include an equal number of polarized BAW devices  10   a  (e.g., polarized BAW filters) and polarized inverted BAW devices  10   b  (e.g., polarized inverted BAW filters). The polarized BAW devices  10   a  are configured to interleave with the polarized inverted BAW devices  10   b.    
     The BAW structure  46  may be so configured to pass the RF signal  34  in the selected frequency bandwidth, while rejecting the RF signal  34  outside the selected frequency bandwidth. As such, the passive wireless switch circuit  30  can be configured to respond only if the RF signal  34  falls within the selected frequency bandwidth. In this regard, the RF signal  34  can be considered as being “absent” with respect to the passive wireless switch circuit  30  when the RF signal  34  falls outside the frequency bandwidth, regardless of whether the RF signal  34  actually exists. Like the BAW structure  28  of  FIG. 1B , the BAW structure  46  is configured to multiply the RF voltage V RF  to generate the boosted RF voltage V RF1  in accordance to the equation (Eq. 1) above. 
     The voltage circuit  36  includes a rectifier circuit  48  configured to convert the boosted RF voltage V RF1  to the constant voltage V C . In a non-limiting example, the rectifier circuit  48  includes a diode  50 , a holding capacitor  52 , and a pull-down resistor  54 . The diode  50  includes an anode node  56  coupled to the BAW structure  46  and a cathode node  58  coupled to the gate terminal  38 . The holding capacitor  52  is coupled between the cathode node  58  and a ground (denoted as GND). The pull-down resistor  54  is coupled in parallel to the holding capacitor  52  between the cathode node  58  and the GND. In a non-limiting example, the pull-down resistor  54  is configured to pull the constant voltage V C  to below the defined threshold voltage (e.g., the GND), thus keeping the MEMS switch  32  open, in absence of the RF signal  34 . 
     The passive wireless switch circuit  30  can be configured in accordance to a variety of topologies, which are described next in reference to  FIGS. 3A-3C . Common elements between  FIGS. 2 and 3A-3C  are shown therein with common element numbers and will not be re-described herein. 
       FIG. 3A  is a schematic diagram of an exemplary passive wireless switch circuit  30 A in which multiple MEMS switches are controlled by a single voltage circuit, such as the voltage circuit  36  of  FIG. 2 . The passive wireless switch circuit  30 A includes at least one second MEMS switch  60  having at least one second gate terminal  62  coupled to the rectifier circuit  48  to receive the constant voltage V C . Like the MEMS switch  32 , the second MEMS switch  60  is configured to be closed when the constant voltage V C  exceeds the defined threshold voltage and opened when the constant voltage V C  is below the defined threshold voltage. In this regard, both the MEMS switch  32  and the second MEMS switch  60  can be closed or opened concurrently based on presence or absence of the RF signal  34 . 
       FIG. 3B  is a schematic diagram of an exemplary passive wireless switch circuit  30 B in which multiple MEMS switches are controlled respectively by multiple voltage circuits, such as the voltage circuit  36  of  FIG. 2 . The passive wireless switch circuit  30 B includes at least one second voltage circuit  64 , which is functionally equivalent to the voltage circuit  36 . For example, the second voltage circuit  64  includes at least one second antenna port  65  configured to be coupled to at least one second antenna  66 . The second voltage circuit  64  also includes at least one second BAW structure  68 , and at least one second rectifier circuit  70 . The second antenna port  65 , the second BAW structure  68 , and the second rectifier circuit  70  are functionally equivalent to the antenna port  43 , the BAW structure  46 , and the rectifier circuit  48 , respectively. 
     In this regard, the second antenna  66  is configured to absorb at least one second RF signal  72  in at least one second selected frequency bandwidth and corresponds to at least one second RF voltage V′ RF . The second BAW structure  68  is configured to multiply the second RF voltage V′ RF  to generate at least one second boosted RF voltage V′ RF1 . The second rectifier circuit  70  is configured to generate at least one second constant voltage V′ C  based on the second boosted RF voltage V′ RF1 . 
     Notably, the RF signal  34  and the second RF signal  72  are communicated respectively in the selected frequency bandwidth and the second selected frequency bandwidth that do not overlap with each other, the RF signal  34  and the second RF signal  72  can be concurrently provided to the passive wireless switch circuit  30 B to concurrently close the MEMS switch  32  and the second MEMS switch  60  with little interference. Alternatively, it is possible to close the MEMS switch  32  or the second MEMS switch  60  individually by communicating the RF signal  34  or the second RF signal  72  to the passive wireless switch circuit  30 B. 
       FIG. 3C  is a schematic diagram of an exemplary passive wireless switch circuit  30 C in which multiple MEMS switches are controlled respectively by multiple voltage circuits, such as the voltage circuit  36  of  FIG. 2 , sharing a common antenna, such as the antenna  44  of  FIG. 2 . By sharing the antenna  44  between the voltage circuit  36  and the second voltage circuit  64 , it may be possible to close the MEMS switch  32  and the second MEMS switch  60  either individually or concurrently. 
     In one non-limiting example, the MEMS switch  32  and the second MEMS switch  60  can be configured to be controlled based on the presence of the RF signal  34  in the selected frequency bandwidth and the second RF signal  72  in the second selected frequency bandwidth non-overlapping with the selected frequency bandwidth. In this regard, the RF signal  34  and the second RF signal  72  may be communicated based on a time-division duplex (TDD) scheme. Accordingly, it is only possible to close the MEMS switch  32  or the second MEMS switch  60  at a given time. 
     In another non-limiting example, the MEMS switch  32  and the second MEMS switch  60  can be configured to be controlled based on the presence of the RF signal  34  in the selected frequency bandwidth and the second RF signal  72  in the second selected frequency bandwidth that is at least partially overlapping with the selected frequency bandwidth. In this regard, it may be possible to concurrently close the MEMS switch  32  and the second MEMS switch  60  in the passive wireless switch circuit  30 C. 
     The passive wireless switch circuit  30  of  FIG. 2 , the passive wireless switch circuit  30 A of  FIG. 3A , the passive wireless switch circuit  30 B of  FIG. 3B , and the passive wireless switch circuit  30 C of  FIG. 3C , can be provided in an apparatus to support a variety of applications. In this regard,  FIG. 4A  is a schematic diagram of an exemplary apparatus  74 A including the passive wireless switch circuit  30  of  FIG. 2 , the passive wireless switch circuit  30 A of  FIG. 3A , the passive wireless switch circuit  30 B of  FIG. 3B , or the passive wireless switch circuit  30 C of  FIG. 3C  for coupling/decoupling a first circuit  76  and a second circuit  78 . Although only the passive wireless switch circuit  30  is illustrated in the apparatus  74 , it should be appreciated that the operations discussed herein can be enabled by the passive wireless switch circuits  30 A- 30 C as well. 
     According to previous discussions in  FIG. 2 , the MEMS switch  32  can be closed to couple the first circuit  76  to the second circuit  78  and opened to decouple the first circuit  76  from the second circuit  78 . The second circuit  78  may be activated or deactivated in response to being coupled or decoupled from the first circuit  76 . When activated, the second circuit  78  may provide an auxiliary constant voltage V AUX  to the gate terminal  38 . More specifically, the second circuit  78  may provide the auxiliary constant voltage V AUX  exceeding the defined threshold voltage to keep the MEMS switch  32  closed for a defined duration. With the auxiliary constant voltage V AUX , it may be possible to shorten the duration in which the RF signal  34  is present. 
     In one non-limiting example, the first circuit  76  is an antenna tuner circuit and the second circuit  78  is an antenna circuit configured to be tuned by the antenna tuner circuit. In this regard, the passive wireless switch circuit  30  can be configured to tune the antenna circuit by coupling the antenna tuner circuit to the antenna circuit. 
     In another non-limiting example, the first circuit  76  is a battery circuit configured to generate a battery voltage and the second circuit  78  is an IoT circuit (e.g., wireless sensor circuitry) configured to be activated in response to receiving the battery voltage. In this regard, the passive wireless switch circuit  30  can be configured to activate the IoT circuit by coupling the battery circuit to the IoT circuit or deactivate the IoT circuit by decoupling the battery circuit from the IoT circuit. 
       FIG. 4B  is a schematic diagram of an exemplary apparatus  74 B in which the passive wireless switch circuit  30  of  FIG. 2 , the passive wireless switch circuit  30 A of  FIG. 3A , the passive wireless switch circuit  30 B of  FIG. 3B , or the passive wireless switch circuit  30 C of  FIG. 3C  can be adapted to control multiple IoT circuits. Common elements between  FIGS. 4A and 4B  are shown therein with common element numbers and will not be re-described herein. 
     The apparatus  74 B includes a battery circuit  80 , which may be identical to the first circuit  76  of  FIG. 4A , an IoT circuit  82 , which may be the same as the second circuit  78  of  FIG. 4A , and a second IoT circuit  84 . The battery circuit  80  is configured to generate a battery voltage V BAT . The IoT circuit  82  and the second IoT circuit  84  are each configured to be activated in response to receive the battery voltage V BAT  and deactivated in response to losing the battery voltage V BAT . The voltage circuit  36  is coupled between the battery circuit  80  and the IoT circuit  82 . In this regard, the MEMS switch  32  is configured to couple the battery circuit  80  to the IoT circuit  82  or decouple the battery circuit  80  from the IoT circuit  82  based on the presence or absence of the RF signal  34 . When activated, the IoT circuit  82  may be configured to provide a first auxiliary constant voltage V AUX1  to the gate terminal  38  to keep the MEMS switch  32  closed for a first defined duration. 
     The apparatus  74 B includes a second voltage circuit  85 , which includes a second BAW structure  86 , a second rectifier circuit  88 , and a second MEMS switch  90  that are functionally equivalent to the BAW structure  46 , the rectifier circuit  48 , and the MEMS switch  32 , respectively. The antenna port  43  may be configured to receive a second RF signal  92  via the antenna  44  in a second selected frequency bandwidth and corresponds to a second RF voltage V′ RF . In one non-limiting example, the second selected frequency bandwidth is non-overlapping with the selected frequency bandwidth of the RF signal  34 . As such, the antenna port  43  may be configured to alternate between receiving the RF signal  34  in the selected frequency bandwidth and the second RF signal  92  in the second selected frequency bandwidth based on a TDD scheme. In another non-limiting example, the second selected frequency bandwidth is at least partially overlapping with the selected frequency bandwidth of the RF signal  34 . As such, the antenna port  43  may be configured to concurrently receive the RF signal  34  in the selected frequency bandwidth and the second RF signal  92  in the second selected frequency bandwidth, thus allowing the IoT circuit  82  and the second IoT circuit  84  to be closed concurrently. 
     The second BAW structure  86  is coupled to the antenna port  43  and configured to convert the second RF voltage V′ RF  to a second boosted RF voltage V′ RF1  higher than the second RF voltage V′ RF . The second rectifier circuit  88  is coupled to the second BAW structure  86  and configured to generate a second constant voltage V′ C  based on the second boosted RF voltage V′ RF1 . The second MEMS switch  90  has a second gate terminal  94  coupled to the second rectifier circuit  88 , a second drain terminal  96  coupled to the battery circuit  80 , and a second source terminal  98  coupled to the second IoT circuit  84 . The second MEMS switch  90  is closed to couple the battery circuit  80  to the second IoT circuit  84  in response to the second constant voltage V′ C  exceeding the defined threshold voltage. When activated, the second IoT circuit  84  may be configured to provide a second auxiliary constant voltage V AUX2  to the second gate terminal  94  to keep the second MEMS switch  90  closed for a second defined duration. 
     In a non-limiting example, it is possible to control a larger number of MEMS switches based on a smaller number of voltage circuits. In this regard,  FIG. 5  is a schematic diagram of an exemplary apparatus  100  configured according to an embodiment of the present disclosure to control a larger number of MEMS switches, such as the MEMS switch  32  of  FIG. 2 , based on a smaller number of voltage circuits, such as the voltage circuit  36  of  FIG. 2 . 
     The apparatus  100  includes a first number of voltage circuits  102 ( 1 )- 102 (M), each may be functionally equivalent to the voltage circuit  36  of  FIG. 2 . The voltage circuits  102 ( 1 )- 102 (M) include a first number of antenna ports  103 ( 1 )- 103 (M) coupled to a first number of antennas  104 ( 1 )- 104 (M), respectively. The antennas  104 ( 1 )- 104 (M) are configured to absorb a first number of RF signals  106 ( 1 )- 106 (M), respectively. Notably, the antennas  104 ( 1 )- 104 (M) may be integrated with the voltage circuits  102 ( 1 )- 102 (M) or separated from the voltage circuits  102 ( 1 )- 102 (M), respectively. The RF signals  106 ( 1 )- 106 (M) may be transmitted from an RF transmitter  108  in a first number of selected frequency bandwidths and correspond to a first number of RF voltages V RF-1 -V RF-M , respectively. The selected frequency bandwidths may be configured to not overlap with each other to help reduce potential interferences among the RF signals  106 ( 1 )- 106 (M). 
     The voltage circuits  102 ( 1 )- 102 (M) include a first number of BAW structures  110 ( 1 )- 110 (M), each may be functionally equivalent to the BAW structure  46  of  FIG. 2 . In this regard, the BAW structures  110 ( 1 )- 110 (M) are configured to generate a first number of boosted RF voltages V RF1-1 -V RF1-M  based on the RF voltages V RF-1 -V RF-M . 
     The voltage circuits  102 ( 1 )- 102 (M) include a first number of rectifier circuits  112 ( 1 )- 112 (M), each may be functionally equivalent to the rectifier circuit  48  of  FIG. 2 . In this regard, the rectifier circuits  112 ( 1 )- 112 (M) are configured to generate a first number of constant voltages V C-1 -V C-M  based on the boosted RF voltages V RF1-1 -V RF1-M . 
     The apparatus  100  includes a second number of MEMS switches  114 ( 1 )- 114 (N) (N&gt;M), each may be functionally equivalent to the MEMS switch  32  of  FIG. 2 . In this regard, the MEMS switches  114 ( 1 )- 114 (N) are configured to be closed respectively in response to receiving a second number of constant voltages V C-1 -V C-N  exceeding the defined threshold voltage. 
     Notably, the second number N is greater than the first number M. As such, to support a larger number of the MEMS switches  114 ( 1 )- 114 (N) based on a smaller number of the voltage circuits  102 ( 1 )- 102 (M), a decoder circuit  116  is provided between the voltage circuits  102 ( 1 )- 102 (M) and the MEMS switches  114 ( 1 )- 114 (N). In one non-limiting example, the constant voltages V C-1 -V C-M  can be so generated to collectively represent a second number of binary codewords that uniquely identify the MEMS switches  114 ( 1 )- 114 (N), respectively. In this regard, the relationship between the first number M and the second number N may be expressed in the equation (Eq. 2) below.
 
2 M ≥N  (Eq. 2)
 
     The decoder circuit  116  may be configured to receive the constant voltages V C-1 -V C-M  from the voltage circuits  102 ( 1 )- 102 (M), respectively. The constant voltages V C-1 -V C-M  may be so generated to uniquely identify a selected MEMS switch among the MEMS switches  114 ( 1 )- 114 (N). For example, if only the constant voltage V C-1  exceeds the defined threshold voltage while the constant voltages V C-2 -V C-M  are below the defined threshold voltage, then the selected MEMS switch collectively identified by the constant voltages V C-1 -V C-M  can be the MEMS switch  114 ( 1 ) among the MEMS switches  114 ( 1 )- 114 (N). 
     The decoder circuit  116  may include a second number of decoders (not shown) configured to decode the second number of binary codewords, respectively. Please refer to U.S. patent application Ser. No. 16/243,367, entitled “MICROELECTROMECHANICAL SYSTEMS (MEMS) SWITCHING CIRCUIT AND RELATED APPARATUS,” filed on Jan. 9, 2019, for examples of the binary codewords configured to uniquely identify the MEMS switches  114 ( 1 )- 114 (N) and an exemplary implementation of the decoder circuit  116 . In this regard, the decoder circuit  116  is configured to decode the constant voltages V C-1 -V C-M  to determine the selected MEMS switch among the MEMS switches  114 ( 1 )- 114 (N). Accordingly, the decoder circuit  116  may provide the constant voltage V C-1  to the selected MEMS switch  114 ( 1 ). 
     The apparatus  100  may include a first semiconductor die  118  and a second semiconductor die  120  that are separate from each other. In a non-limiting example, the voltage circuits  102 ( 1 )- 102 (M) can be provided in the first semiconductor die  118 , while the decoder circuit  116  and the MEMS switches  114 ( 1 )- 114 (N) are provided in the second semiconductor die  120 . 
     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.