Patent Publication Number: US-11399238-B2

Title: Microphone device with inductive filtering

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/702,317, filed Jul. 23, 2018, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Microphones are deployed in various types of devices such as personal computers, cellular phones, mobile devices, headsets, headphones, and hearing aid devices. The microphones are often used proximate to other components that can send and receive acoustic signals. Accordingly, the microphones can include filter components for preventing the acoustic signals from other components from causing noise in the microphone signal. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a cross-sectional view of a microphone device according to some implementations of the present disclosure. 
         FIG. 2  is a top view of a substrate of the microphone device of  FIG. 1  according to some implementations of the present disclosure. 
         FIG. 3  is a schematic representation illustrating connections between an application specific integrated circuit (ASIC) and an inductor on the substrate of  FIG. 2  according to some implementations of the present disclosure. 
         FIG. 4  is a flowchart illustrating a process for trimming an ASIC of the microphone device of  FIG. 1  according to some implementations of the present disclosure. 
         FIG. 5  is a plot illustrating inductor impedance versus signal frequency. 
     
    
    
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not meant to be limiting. Other implementations may be utilized, and other drawings may be made, without departing from the sprit or scope of the subject matter presented here. It will be readily understood that aspects of the present disclosure, as generally described herein, and illustrated in the figures can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure. 
     DETAILED DESCRIPTION 
     The present disclosure describes devices and techniques for a microphone device that includes an inductive radio frequency (RF) filter. More specifically, one or more inductors used to form an inductive RF filter are positioned within a back volume of the microphone device. The microphone device includes an application specific integrated circuit (ASIC) that is embedded within a substrate of the microphone device such that the inductors can be positioned in the back volume, such as in a portion of the back volume of the microphone device that is traditionally occupied by the ASIC, without requiring changes in the dimensions of the back volume. 
     The inductive RF filters used in the microphone device of the present disclosure improve the performance of the microphone device relative to microphone devices that include resistive-capacitive (RC) or capacitive RF filters. For example, the resistors utilized in RC filters can reduce a voltage delivered to a digital microphone device, thus reducing the drive capacity of the microphone device. Furthermore, resistors and/or capacitors used in RC or capacitive filters can filter out a portion of an acoustic signal sent using digital communication protocols, such as pulse density modulation (PDM) and SoundWire protocols. Inductive filters pass acoustic signals sent according to PDM and/or SoundWire protocols, while filtering out undesirable RF signals. 
       FIG. 1  illustrates a cross-sectional view of a microphone device  10  according to an exemplary implementation of the present disclosure. The microphone device  10  includes a substrate  14 , a microelectromechanical (MEMS) transducer  18 , an application specific integrated circuit (ASIC)  22 , one or more inductors  26 , and a cover  30 . In  FIG. 1 , the inductor(s)  26  is illustrated schematically. The substrate  14  includes a front (first) surface  34  and a back (second) surface  38 . The MEMS transducer  18  is mounted to the front surface  34  of the substrate  14 . The ASIC  22  is embedded within the substrate  14  such that the ASIC  22  is positioned between the front surface  34  and the back surface  38  of the substrate  14 . The inductor(s)  26  is mounted to the front surface  34  of the substrate  14  generally above the ASIC  22 . The MEMS transducer  18 , the ASIC  22 , and the substrate  14  can include conductive bonding pads to which wires can be bonded. In some implementations, the wires can be bonded to the appropriate bonding pads using a solder. For example, a first set of wires electrically connect the MEMS transducer  18  to the ASIC  22 , while a second set of wires electrically connect the ASIC  22  to conducive traces (not shown) on substrate  14 , in some implementations. Additional wires electrically connect the plurality of inductors  26  to the ASIC  22  as discussed in greater detail below. 
     The substrate  14  can include, without limitation, a printed circuit board, a semiconductor substrate, or a combination thereof. A portion of the substrate  14  adjacent the MEMS transducer  18  defines a through-hole that forms a sound port  50  of the microphone device  10 . Acoustic signals enter the microphone device  10  through the sound port  50  and cause displacement of a portion of the MEMS transducer  18 . The MEMS transducer  18 , based on its response to the displacement, can generate electrical signals corresponding to the incident audio. 
     The cover  30  can be mounted on the substrate  14  to form an enclosed volume (back volume)  54  between the cover  30  and the front surface  34  of the substrate  14 . The cover  30  encloses and protects the MEMS transducer  18 , the ASIC  22 , and wires forming electrical connections therebetween, such as the first wires and the second wires. The cover  30  can include materials such as plastic or metal. The cover  30 , the substrate  14 , the MEMS transducer  18 , and the ASIC  22  define the enclosed back volume  54 , dimensions of which can be factored into selecting performance parameters of the MEMS transducer  18 . In some implementations, the cover  30  is affixed to the substrate  14  and, in some implementations, the back volume  54  is hermetically sealed. 
     The MEMS transducer  18  can include a conductive diaphragm  58  spaced apart from a conductive back plate  60 . The diaphragm  58  is configured to move relative to the back plate  60  in response to incident acoustic signals. The movement of the diaphragm  58  in relation to the back plate  60  causes a capacitance of the MEMS transducer  18  between the diaphragm  58  and the back plate  60  to vary. The change in capacitance of the MEMS transducer  18  in response to the acoustic signals can be measured and converted into a corresponding electrical signal. Accordingly, the spatial relationship between the MEMS transducer  18  and the cover  30  can be sized for specific microphone performance parameters (i.e., microphone performance may be modified by increasing or decreasing a size of one or both of the back volume  54  and the diaphragm  58 ). In various implementations, the MEMS transducer  18  can include multiple diaphragms and/or backplates. 
     The ASIC  22  can include a package that encloses analog and/or digital circuitry for processing electrical signals received from the MEMS transducer  18 . In one or more implementations, the ASIC  22  can be an integrated circuit package having a plurality of pins or bonding pads that facilitate electrical connectivity to components outside of the ASIC  22  via wires. Referring to  FIG. 2 , the ASIC  22  can include bonding pads (not shown) to which the first set of wires  42 , the second set of wires  46 , and additional wires can be connected. The analog or digital circuitry can include amplifiers, filters, analog-to-digital converts, digital signal processors, polyfuses, and other electrical circuitry for processing the electrical signal received from the MEMS transducer  18  and other components on the substrate  14 . Polyfuses are memory components that can be programmed to store information such as calibration data, chip identification numbers, and/or memory repair data. Polyfuses can be programmed (e.g., trimmed) by applying high currents (e.g., trimming currents). In other implementations, the ASIC  22  can include EEPROM and/or flash memory. The use of inductive filters in microphone devices  10  that include EEPROM and/or flash memory increases an impedance on the line including the inductor that is higher than a resistance generated by a resistor in a RC filter. Accordingly, the use of inductive filters is advantageous over using a RC filter. 
     Referring back to  FIG. 1 , in some implementations, the ASIC  22  is embedded within the substrate  14  such that the ASIC  22  is positioned between the front surface  34  and the back surface  38  of the substrate  14 . Embedding the ASIC  22  within the substrate  14  can facilitate the dissipation of heat generated by operation of the ASIC  22 . In some implementations, embedding the ASIC  22  fills the space in which RC filter components (e.g., resistors and capacitors) could otherwise be embedded in the microphone device  10 . Embedding the ASIC  22  within the substrate  14  provides additional space within the back volume  54  of the microphone device  10  without changing the dimensions of the back volume  54  of the microphone device  10 . As shown in  FIG. 1 , embedding the ASIC  22  within the substrate  14  provides additional space within the back volume  54  of the microphone device  10  for receiving the plurality of inductors  26 . 
     The inductor(s)  26  is secured to the front surface  34  of the substrate  14  generally above the embedded ASIC  22 . The inductor(s)  26  is positioned in the space typically occupied by the ASIC in prior art microphone devices in which the ASIC is secured to the front surface of substrate. As is shown schematically in  FIG. 1 , a height H I  of the inductor(s)  26  is higher than a height H T  of the MEMS transducer  18 , but lower than a height H BV  of the back volume  54 . For example, in the illustrated implementation, the height H BV  of the back volume  54  is approximately 457 μm, the height H I  is approximately 300 μm, and the height H T  is approximately 200 μm. Embedding the ASIC  22  in the substrate  14  provides sufficient space for the inductor(s)  26  without changing the dimensions of the back volume  54  of the microphone device  10 . As indicated in  FIG. 1 , a height HA of the ASIC  22  is approximately 100 μm. A combined height of the ASIC  22  and the inductor(s)  26  is therefore larger than the height H BV  of the back volume  54 . Accordingly, embedding the ASIC  22  allows the inductor(s)  26  to be positioned within the back volume  54 . Expanding the back volume  54  to receive the inductor(s)  26  mounted on the ASIC  22  without embedding the ASIC  22  could cause the height of the cover  30  and/or microphone device  10  to be undesirably tall. The inductor(s)  26  can be ceramic chip inductors, ferrite bead inductors, or silicon chip-based inductors. In the illustrated implementation, the inductor(s)  26  are SMT 01005 chip inductors. In other implementations of microphone devices having differently shaped back volumes, SMT 0201 chip inductors or SMT 0402 chip inductors can be used. The SMT 01005 chip inductors, SMT 0201 chip inductors, and/or SMT 0402 chip inductors can be ceramic chip inductors or ferrite bead inductors. In such implementations, the chip inductors can be selected based on the dimensions of the back volume such that the inductors fit within the back volume of the microphone device. In implementations that include silicon chip-based inductors, the silicon chip-based inductors can be custom-sized to fit within the back volume of the microphone device. 
       FIG. 2  illustrates a top view of the substrate  14  of the microphone device  10  with the cover  30  removed. In the illustrated implementation, the inductor(s)  26  includes a first inductor  62 , a second inductor  66 , and a third inductor  70 . The inductors  62 ,  66 ,  70  are mounted above the ASIC. In some implementations, the inductors  62 ,  66 ,  70  can be the same size. In other implementations, the inductors  62 ,  66 ,  70  can be different sizes. For example, larger inductors may be used on the microphone power (e.g., VDD) line and smaller inductors can be used on the digital clock and/or digital output lines. In other implementations, the microphone device  10  may include more or fewer inductors. The front surface  34  of the substrate  14  completely covers the ASIC. As indicated in  FIG. 2 , the first set of wires  42  and the second set of wires  46  have an end that is connected to the MEMS transducer  18  and an end that extends beneath the front surface  34  of the substrate  14  to reach the ASIC. A first pair of pads  74  is adjacent the first inductor  62 , a second pair of pads  78  is adjacent the second inductor  66 , and a third pair of pads  82  is adjacent the third inductor  70 . A third pair of wires  86  extends between the first inductor  62  and the ASIC. A fourth pair of wires  90  extends between the second inductor  66  and the ASIC. A fifth pair of wires  94  extends between the third inductor  70  and the ASIC. 
       FIG. 3  illustrates a schematic representation of the electrical connections to and from the ASIC  22  for a microphone device  98  according to another implementation of the present disclosure in which the plurality of inductors  26  includes a fourth inductor  102 . The implementation illustrated in  FIG. 3  is substantially similar to the implementation illustrated in  FIG. 2 . Accordingly, like parts are illustrated using like numbers. The ASIC  22  of the microphone device  10  can have similar electrical connections to those shown in  FIG. 3 . The ASIC  22  is connected to the MEMS transducer  18  by the first wire  42  and the second wire  46 . The third pair of wires  86  extends between a first pad  106  and the ASIC  22 . The first inductor  62  is positioned along the third pair of wires  86  to act as a filter and prevent radiofrequency (RF) signals from traveling to the ASIC  22  along the third pair of wires  86 . The fourth pair of wires  90  extends between a second pad  110  and the ASIC  22 . The second inductor  66  is positioned along the fourth pair of wires  90  to act as a filter and prevent RF signals from traveling to the ASIC  22  along the fourth pair of wires  90 . The fifth pair of wires  94  extends between a third pad  114  and the ASIC  22 . The third inductor  70  is positioned along the fifth pair of wires  94  to act as filter and prevent RF signals from traveling to the ASIC  22  along the fifth pair of wires  94 . A sixth pair of wires  118  extends between a fourth pad  122  and the ASIC  22 . The fourth inductor  102  is positioned along the sixth pair of wires  118  to act as a filter and prevent RF signals from traveling to the ASIC  22  along the sixth pair of wires  118 . The first pad  106 , the second pad  110 , the third pad  114 , and the fourth pad  122  can be positioned on the back surface of the substrate (not shown). 
     In implementations including ceramic chip inductors and/or ferrite inductors, any of the inductors  62 ,  66 ,  70 ,  102  can be coated with an epoxy layer to prevent the coated inductors  62 ,  66 ,  70 ,  102  from vibrating. 
     In implementations in which the microphone device  98  is a digital microphone, one of the pairs of wires  86 ,  90 ,  94 ,  118  can be a microphone power (e.g., VDD) line, one of the pairs of wires  86 ,  90 ,  94 ,  118  can be a clock input line, and one of the pairs of wires  86 ,  90 ,  94 ,  118  can be a digital output line. In implementations in which the microphone device  98  is an analog microphone, one of the pairs of wires  86 ,  90 ,  94 ,  118  can be a VDD line and at least one of the pairs of wires  86 ,  90 ,  94 ,  118  can be an output line. In some implementations in which the microphone device  98  is an analog microphone, one of the pairs of wires  86 ,  90 ,  94 ,  118  can be a digital interface line. In some implementations, the digital interface line can be connected to a digital output pin of the ASIC  22 , such as an inter-integrated circuit (I2C) pin. 
     In some implementations, the microphone device  98  can have more or fewer inductors based on the type of microphone, the size of the microphone, and/or the number of input and/or outputs to the ASIC  22 . For example, analog microphones can have two inductors, with one of the inductors positioned on the VDD line and one of the inductors positioned on the microphone output line. Trimmable analog microphones can have three inductors, with one of the inductors positioned on the VDD line, one of the inductors positioned on the output line, and one of the inductors positioned on the trim lime. Digital or differential microphones can have four or more inductors, with one of the inductors positioned on the VDD line, one of the inductors positioned on the output line, one of the inductors positioned on a digital clock input line, and one of the inductors positioned on the digital output line. 
     In implementations where the microphone device  98  may be positioned proximate other devices that send and/or receive acoustic signals, this can result in noisy ground conditions. For example, noisy ground conditions can occur when the microphone device  98  is positioned at a bottom of a phone near an antenna of the phone. The radiofrequency (RF) energy from the antenna is coupled onto the ground plane that is also coupled to the microphone device  98 . The RF energy of the antenna can conduct back into the microphone device  98  along the ground plane, causing noise in the microphone device  98  (e.g., “noisy ground”). Under noisy ground conditions, communication signals from a nearby antenna can cause RF signals to radiate along wires connected between the ASIC  22  and pads on the substrate  14 , such as the third pair of wires  86 , the fourth pair of wires  90 , the fifth pair of wires  94 , and the sixth pair of wires  118 . Accordingly, in the illustrated implementation, the first inductor  62 , the second inductor  66 , the third inductor  70 , and the fourth inductor  102  are positioned along the third pair of wires  86 , the fourth pair of wires  90 , the fifth pair of wires  94 , and the sixth pair of wires  118 , respectively, to act as RF filters. In the illustrated implementation, the inductor(s)  26  improves the performance of the ASIC  22  by 10-15 decibels (dB) relative to unfiltered configurations of the ASIC  22 . The implementation illustrated in  FIG. 3  is a non-limiting, exemplary configuration of the connections to and from the ASIC  22 . Other implementations may include different configurations of the connections to and from the ASIC  22 . 
     In some implementations, the ASIC  22  can be calibrated by trimming one or more trimmable components within the ASIC  22 . In some implementations, the trimmable components are polyfuses.  FIG. 4  illustrates a flowchart of a process  126  for trimming the ASIC  22  according to an exemplary implementation. A first step in the trimming process  126  is to measure acoustic data of the untrimmed ASIC  22  ( 130 ). The measured acoustic data is compared to a predetermined threshold ( 134 ). A next step is to determine how much to trim at least one polyfuse of the ASIC  22  based on a difference between the measured acoustic data and the predetermined threshold ( 138 ). The difference between the measured acoustic data and the predetermined threshold can be indicative of a sensitivity in the ASIC  22 . A trimming current (e.g., current spike) is then applied to one or more of the pads  106 ,  110 ,  114 ,  122  to trim one or more polyfuses in the ASIC  22  ( 142 ). The wire (e.g., between the pad  106 ,  110 ,  114 ,  122  and the ASIC  22 ) forms a conductive path between the current source, the ASIC  22 , and the polyfuse(s) that are being trimmed. In some implementations, the trimming current can be up to 100 mA. 
     In implementations in which RC filters are used, a resistor of the RC circuit is positioned on the wire between a location at which the trimming current is provided and the ASIC. Accordingly, the resistor prevents the trimming current from reaching the ASIC, so voltages high enough to burn the polyfuse cannot be generated with the ASIC in such implementations including RC filters. In contrast, the microphone device  10  according to the present disclosure can include an inductor(s)  26  positioned on the wire (e.g., along the conductive path) connected to the ASIC  22  and the polyfuse(s). The inductor  26  allows the trimming current to pass to the ASIC  22  without being filtered. Accordingly, polyfuses within the ASIC  22  and connected to wires (conductive paths) that include any of the plurality of inductors  26  can be trimmed. 
     In other implementations, the trimmable components can include ASICs, digital signal processors (DSPs), temperature sensors, and/or other types of sensors embedded in the microphone or integrated into a single chip. 
       FIG. 5  illustrates a plot  146  of the impedance v.s. frequency for the plurality of inductors  26 . As shown in the plot  146 , the inductor(s)  26  has an impedance that increases as a signal frequency increases until approximately 2.5 GHz and then decreases. An audio frequency range is between approximately 20 Hz-20 KHz. As illustrated in the plot  146 , the inductor(s)  26  has a very low resistance (e.g., less than 0.1Ω) in the acoustic frequency range. Accordingly, the inductor(s)  26  allow substantially all of the signals in the acoustic frequency range to pass to the ASIC  22 . Radiofrequency (RF) signals are often sent and received proximate the microphone device  10 . Such RF signals are often antenna communication signals, such as Bluetooth signals, WiFi signals, and cellular signals. The Bluetooth frequency band is approximately 2.4 GHz-2.5 GHz and is indicated on the plot  146 . As indicated in the plot  146 , the impedance in the Bluetooth range is higher than the acoustic frequency range. For example, as indicated in the plot  146 , the impedance in the Bluetooth range is between approximately 1000Ω-approximately 10,000Ω, which is several orders of magnitude higher than the resistance in the acoustic range. The cellular (e.g., 2G, 3G, 4G, and/or 5G) frequency band ranges between approximately 600 MHz-3 GHz. As indicated in the plot  146 , the inductor(s)  26  has an impedance ranging from approximately 100Ω-approximately 10,000Ω. Accordingly, substantially all signals in the cellular frequency range are prevented from reaching the ASIC  22 . The WiFi frequency bands are indicated in  FIG. 5  and are approximately 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, and 5.9 GHz. The plurality of inductors  26  has an impedance of at least approximately 100Ω-approximately 1500Ω in the WiFi frequency range. Accordingly, substantially all signals in the WiFi frequency range are prevented from reaching the ASIC  22 . In summary,  FIG. 5  indicates that the inductor(s)  26  has an impedance of less than 0.1Ω in the audio frequency range and the inductor(s) has an impedance of greater than 100Ω for RF signals. Accordingly, the inductor(s)  26  effectively filter the RF signals while allowing audio frequency signals to pass. 
     In the illustrated implementations, the plurality of inductors  26  replaces RC filters or capacitive (C) filters that are used in some microphone devices. The use of the inductor(s)  26  as inductive filter(s) as described in the present disclosure improves the microphone device  10  with respect to the existing microphone devices. For example, the microphone device  10  can be configured to operate according to a pulse density modulation (PDM) protocol. The PDM protocol includes a digital clock input and digital data output. Positioning a RC filter or a C filter on a line having a digital clock input, a digital data output, or a microphone power line can reduce performance of the microphone device. For example, positioning a resistor on the clock digital input line and/or on the digital output line can cause the resistor to round the digital signal, which can damage and/or remove at least part of the microphone signal. Positioning a resistor on the microphone power line can reduce a voltage supplied to the microphone device, which can reduce a drive capability of the microphone device. Similarly, with respect to both RC filters and capacitive filters, capacitors large enough to be effective RF filters are large enough to filter the digital clock input and/or the digital data output signals used in the PDM protocol, which can damage and/or remove at least part of the microphone signal. Inductors, however, do not round the digital clock input or the digital data output signals. Furthermore, inductors do not reduce an amount of voltage supplied to the microphone device  10 . Accordingly, using the plurality of inductors  26  as inductive filters improves both the quality of the microphone signal and the performance of the microphone device  10  as compared to prior art microphone devices that include capacitive filters and/or RC filters. 
     In some implementations, the microphone device  10  can be configured to operate according to the SoundWire protocol. The SoundWire protocol includes a digital microphone input and a digital microphone output. Again, positioning a RC filter or a capacitive filter on a line having a digital input, a digital output, or a microphone power line can reduce performance of the microphone device  10 . The frequency of signals sent according to the SoundWire protocol can have frequencies as high as tens of MHz. Resistors and/or capacitors large enough to filter out RF signals also filter out Soundwire signals sent at such frequencies, which can damage and/or remove at least part of the microphone signal. Furthermore, positioning a resistor on the microphone power line can reduce a voltage supplied to the microphone device, which can reduce a drive capability of the microphone device. The plurality of inductors  26 , however, will pass signals in the tens of MHz range, as indicated above in  FIG. 5 . Inductive filters, therefore, improve the performance of the microphone device  10  relative to prior art microphones that include RC filters and/or capacitive filters when operating according to the SoundWire protocol. 
     One implementation relates to a microphone device including a substrate having a first surface and a second surface, a cover secured to the first surface of the substrate to form an enclosed back volume, an application specific integrated circuit (ASIC) embedded between the first surface and the second surface of the substrate, a microelectromechanical systems (MEMS) transducer mounted on the first surface of the substrate, and an inductor mounted on the first surface of the substrate. 
     Another implementation relates to a method of manufacturing a microphone device. The method includes embedding an application specific integrated circuit (ASIC) into a substrate of the microphone device. The ASIC includes a trimmable component. The substrate includes a first surface and a second surface and the ASIC is embedded between the first surface and the second surface. The method further includes mounting an inductor on the first surface of the substrate, electrically coupling the ASIC and the inductor, which is positioned along a conductive path, and applying a trimming current to the conductive path to trim the trimmable component. The trimming current passes through the inductor before the trimming current enters ASIC and trims the trimmable component. 
     The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are illustrative, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. 
     With respect to the use of plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including by not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). 
     It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g. “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two functions,” without other modifiers, typically means at least two recitations, or two or more recitations). 
     Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g. “a system having at least one of A, B, or C: would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” Further, unless otherwise noted, the use of the words “approximate,” “about,” “around,” “substantially,” etc., means plus or minus ten percent. 
     The foregoing description of illustrative elements has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed implementations. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.