Patent Publication Number: US-11647914-B2

Title: User-worn device for noninvasively measuring a physiological parameter of a user

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/659,986, filed Apr. 20, 2022, which is a continuation of U.S. patent application Ser. No. 17/410,966, filed Aug. 24, 2021, which is a continuation of U.S. patent application Ser. No. 16/449,143, filed Jun. 21, 2019, which is a continuation of U.S. patent application Ser. No. 16/409,515, filed May 10, 2019, which is a continuation of U.S. patent application Ser. No. 16/261,326, filed Jan. 29, 2019, which is a continuation of U.S. patent application Ser. No. 16/212,537, filed Dec. 6, 2018, which is a continuation of U.S. patent application Ser. No. 14/981,290 filed Dec. 28, 2015, which is a continuation of U.S. patent application Ser. No. 12/829,352 filed Jul. 1, 2010, which is a continuation of U.S. patent application Ser. No. 12/534,827 filed Aug. 3, 2009, which claims the benefit of priority under 35 U.S.C. § 119(e) of the following U.S. Provisional Patent Application Nos. 61/086,060 filed Aug. 4, 2008, 61/086,108 filed Aug. 4, 2008, 61/086,063 filed Aug. 4, 2008, 61/086,057 filed Aug. 4, 2008, and 61/091,732 filed Aug. 25, 2008. U.S. patent application Ser. No. 12/829,352 is also a continuation-in-part of U.S. patent application Ser. No. 12/497,528 filed Jul. 2, 2009, which claims the benefit of priority under 35 U.S.C. § 119(e) of the following U.S. Provisional Patent Application Nos. 61/086,060 filed Aug. 4, 2008, 61/086,108 filed Aug. 4, 2008, 61/086,063 filed Aug. 4, 2008, 61/086,057 filed Aug. 4, 2008, 61/078,228 filed Jul. 3, 2008, 61/078,207 filed Jul. 3, 2008, and 61/091,732 filed Aug. 25, 2008. U.S. patent application Ser. No. 12/497,528 also claims the benefit of priority under 35 U.S.C. § 120 as a continuation-in-part of the following U.S. Design patent application Nos. 29/323,409 filed Aug. 25, 2008 and 29/323,408 filed Aug. 25, 2008. U.S. patent application Ser. No. 12/829,352 is also a continuation-in-part of U.S. patent application Ser. No. 12/497,523 filed Jul. 2, 2009, which claims the benefit of priority under 35 U.S.C. § 119(e) of the following U.S. Provisional Patent Application Nos. 61/086,060 filed Aug. 4, 2008, 61/086,108 filed Aug. 4, 2008, 61/086,063 filed Aug. 4, 2008, 61/086,057 filed Aug. 4, 2008, 61/078,228 filed Jul. 3, 2008, 61/078,207 filed Jul. 3, 2008, and 61/091,732 filed Aug. 25, 2008. U.S. patent application Ser. No. 12/497,523 also claims the benefit of priority under 35 U.S.C. § 120 as a continuation-in-part of the following U.S. Design patent application Nos. 29/323,409 filed Aug. 25, 2008 and 29/323,408 filed Aug. 25, 2008. 
     This application is related to the following U.S. patent applications: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Filing 
                   
               
               
                 App. No. 
                 Date 
                 Title 
               
               
                   
               
             
            
               
                 12/497,528 
                 Jul. 2, 2009 
                 Noise Shielding for Noninvasive Device 
               
               
                   
                   
                 Contoured Protrusion for Improving 
               
               
                 12/497,523 
                 Jul. 2, 2009 
                 Spectroscopic Measurement of Blood 
               
               
                   
                   
                 Constituents 
               
               
                 12/497,506 
                 Jul. 2, 2009 
                 Heat Sink for Noninvasive Medical 
               
               
                   
                   
                 Sensor 
               
               
                 12/534,812 
                 Aug. 3, 2009 
                 Multi-Stream Sensor Front Ends for  
               
               
                   
                   
                 Non-Invasive Measurement of Blood 
               
               
                   
                   
                 Constituents 
               
               
                 12/534,823 
                 Aug. 3, 2009 
                 Multi-Stream Sensor for Non-Invasive 
               
               
                   
                   
                 Measurement of Blood Constituents 
               
               
                 12/534,825 
                 Aug. 3, 2009 
                 Multi-Stream Emitter for Non-Invasive 
               
               
                   
                   
                 Measurement of Blood Constituents 
               
               
                   
               
            
           
         
       
     
     The foregoing applications are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     The standard of care in caregiver environments includes patient monitoring through spectroscopic analysis using, for example, a pulse oximeter. Devices capable of spectroscopic analysis generally include a light source(s) transmitting optical radiation into or reflecting off a measurement site, such as, body tissue carrying pulsing blood. After attenuation by tissue and fluids of the measurement site, a photodetection device(s) detects the attenuated light and outputs a detector signal(s) responsive to the detected attenuated light. A signal processing device(s) process the detector(s) signal(s) and outputs a measurement indicative of a blood constituent of interest, such as glucose, oxygen, methemoglobin, total hemoglobin, other physiological parameters, or other data or combinations of data useful in determining a state or trend of wellness of a patient. 
     In noninvasive devices and methods, a sensor is often adapted to position a finger proximate the light source and light detector. For example, noninvasive sensors often include a clothespin-shaped housing that includes a contoured bed conforming generally to the shape of a finger. 
     SUMMARY 
     This disclosure describes embodiments of noninvasive methods, devices, and systems for measuring a blood constituent or analyte, such as oxygen, carbon monoxide, methemoglobin, total hemoglobin, glucose, proteins, glucose, lipids, a percentage thereof (e.g., saturation) or for measuring many other physiologically relevant patient characteristics. These characteristics can relate, for example, to pulse rate, hydration, trending information and analysis, and the like. 
     In an embodiment, the system includes a noninvasive sensor and a patient monitor communicating with the noninvasive sensor. The non-invasive sensor may include different architectures to implement some or all of the disclosed features. In addition, an artisan will recognize that the non-invasive sensor may include or may be coupled to other components, such as a network interface, and the like. Moreover, the patient monitor may include a display device, a network interface communicating with any one or combination of a computer network, a handheld computing device, a mobile phone, the Internet, or the like. In addition, embodiments may include multiple optical sources that emit light at a plurality of wavelengths and that are arranged from the perspective of the light detector(s) as a point source. 
     In an embodiment, a noninvasive device is capable of producing a signal responsive to light attenuated by tissue at a measurement site. The device may comprise an optical source and a plurality of photodetectors. The optical source is configured to emit optical radiation at least at wavelengths between about 1600 nm and about 1700 nm. The photodetectors are configured to detect the optical radiation from said optical source after attenuation by the tissue of the measurement site and each output a respective signal stream responsive to the detected optical radiation. 
     In an embodiment, a noninvasive, physiological sensor is capable of outputting a signal responsive to a blood analyte present in a monitored patient. The sensor may comprise a sensor housing, an optical source, and photodetectors. The optical source is positioned by the housing with respect to a tissue site of a patient when said housing is applied to the patient. The photodetectors are positioned by the housing with respect to said tissue site when the housing is applied to the patient with a variation in path length among at least some of the photodetectors from the optical source. The photodetectors are configured to detect a sequence of optical radiation from the optical source after attenuation by tissue of the tissue site. The photodetectors may be each configured to output a respective signal stream responsive to the detected sequence of optical radiation. An output signal responsive to one or more of the signal streams is then usable to determine the blood analyte based at least in part on the variation in path length. 
     In an embodiment, a method of measuring an analyte based on multiple streams of optical radiation measured from a measurement site is provided. A sequence of optical radiation pulses is emitted to the measurement site. At a first location, a first stream of optical radiation is detected from the measurement site. At least at one additional location different from the first location, an additional stream of optical radiation is detected from the measurement site. An output measurement value indicative of the analyte is then determined based on the detected streams of optical radiation. 
     In various embodiments, the present disclosure relates to an interface for a noninvasive sensor that comprises a front-end adapted to receive an input signals from optical detectors and provide corresponding output signals. In an embodiment, the front-end is comprised of switched-capacitor circuits that are capable of handling multiple streams of signals from the optical detectors. In another embodiment, the front-end comprises transimpedance amplifiers that are capable of handling multiple streams of input signals. In addition, the transimpedance amplifiers may be configured based on the characteristics of the transimpedance amplifier itself, the characteristics of the photodiodes, and the number of photodiodes coupled to the transimpedance amplifier. 
     In disclosed embodiments, the front-ends are employed in noninvasive sensors to assist in measuring and detecting various analytes. The disclosed noninvasive sensor may also include, among other things, emitters and detectors positioned to produce multi-stream sensor information. An artisan will recognize that the noninvasive sensor may have different architectures and may include or be coupled to other components, such as a display device, a network interface, and the like. An artisan will also recognize that the front-ends may be employed in any type of noninvasive sensor. 
     In an embodiment, a front-end interface for a noninvasive, physiological sensor comprises: a set of inputs configured to receive signals from a plurality of detectors in the sensor; a set of transimpedance amplifiers configured to convert the signals from the plurality of detectors into an output signal having a stream for each of the plurality of detectors; and an output configured to provide the output signal. 
     In an embodiment, a front-end interface for a noninvasive, physiological sensor comprises: a set of inputs configured to receive signals from a plurality of detectors in the sensor; a set of switched capacitor circuits configured to convert the signals from the plurality of detectors into a digital output signal having a stream for each of the plurality of detectors; and an output configured to provide the digital output signal. 
     In an embodiment, a conversion processor for a physiological, noninvasive sensor comprises: a multi-stream input configured to receive signals from a plurality of detectors in the sensor, wherein the signals are responsive to optical radiation from a tissue site; a modulator that converts the multi-stream input into a digital bit-stream; and a signal processor that produces an output signal from the digital bit-stream. 
     In an embodiment, a front-end interface for a noninvasive, physiological sensor comprises: a set of inputs configured to receive signals from a plurality of detectors in the sensor; a set of respective transimpedance amplifiers for each detector configured to convert the signals from the plurality of detectors into an output signal having a stream for each of the plurality of detectors; and an output configured to provide the output signal. 
     In certain embodiments, a noninvasive sensor interfaces with tissue at a measurement site and deforms the tissue in a way that increases signal gain in certain desired wavelengths. 
     In some embodiments, a detector for the sensor may comprise a set of photodiodes that are arranged in a spatial configuration. This spatial configuration may allow, for example, signal analysis for measuring analytes like glucose. In various embodiments, the detectors can be arranged across multiple locations in a spatial configuration. The spatial configuration provides a geometry having a diversity of path lengths among the detectors. For example, the detector in the sensor may comprise multiple detectors that are arranged to have a sufficient difference in mean path length to allow for noise cancellation and noise reduction. 
     In an embodiment, a physiological, noninvasive detector is configured to detect optical radiation from a tissue site. The detector comprises a set of photodetectors and a conversion processor. The set of photodetectors each provide a signal stream indicating optical radiation from the tissue site. The set of photodetectors are arranged in a spatial configuration that provides a variation in path lengths between at least some of the photodetectors. The conversion processor that provides information indicating an analyte in the tissue site based on ratios of pairs of the signal streams. 
     The present disclosure, according to various embodiments, relates to noninvasive methods, devices, and systems for measuring a blood analyte, such as glucose. In the present disclosure, blood analytes are measured noninvasively based on multi-stream infrared and near-infrared spectroscopy. In some embodiments, an emitter may include one or more sources that are configured as a point optical source. In addition, the emitter may be operated in a manner that allows for the measurement of an analyte like glucose. In embodiments, the emitter may comprise a plurality of LEDs that emit a sequence of pulses of optical radiation across a spectrum of wavelengths. In addition, in order to achieve the desired SNR for detecting analytes like glucose, the emitter may be driven using a progression from low power to higher power. The emitter may also have its duty cycle modified to achieve a desired SNR. 
     In an embodiment, a multi-stream emitter for a noninvasive, physiological device configured to transmit optical radiation in a tissue site comprises: a set of optical sources arranged as a point optical source; and a driver configured to drive the at least one light emitting diode and at least one optical source to transmit near-infrared optical radiation at sufficient power to measure an analyte in tissue that responds to near-infrared optical radiation. 
     In an embodiment, an emitter for a noninvasive, physiological device configured to transmit optical radiation in a tissue site comprises: a point optical source comprising an optical source configured to transmit infrared and near-infrared optical radiation to a tissue site; and a driver configured to drive the point optical source at a sufficient power and noise tolerance to effectively provide attenuated optical radiation from a tissue site that indicates an amount of glucose in the tissue site. 
     In an embodiment, a method of transmitting a stream of pulses of optical radiation in a tissue site is provided. At least one pulse of infrared optical radiation having a first pulse width is transmitted at a first power. At least one pulse of near-infrared optical radiation is transmitted at a power that is higher than the first power. 
     In an embodiment, a method of transmitting a stream of pulses of optical radiation in a tissue site is provided. At least one pulse of infrared optical radiation having a first pulse width is transmitted at a first power. At least one pulse of near-infrared optical radiation is then transmitted, at a second power that is higher than the first power. 
     For purposes of summarizing the disclosure, certain aspects, advantages and novel features of the inventions have been described herein. It is to be understood that not necessarily all such advantages can be achieved in accordance with any particular embodiment of the inventions disclosed herein. Thus, the inventions disclosed herein can be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as can be taught or suggested herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Throughout the drawings, reference numbers can be re-used to indicate correspondence between referenced elements. The drawings are provided to illustrate embodiments of the inventions described herein and not to limit the scope thereof. 
         FIG.  1    illustrates a block diagram of an example data collection system capable of noninvasively measuring one or more blood analytes in a monitored patient, according to an embodiment of the disclosure; 
         FIGS.  2 A- 2 D  illustrate an exemplary handheld monitor and an exemplary noninvasive optical sensor of the patient monitoring system of  FIG.  1   , according to embodiments of the disclosure; 
         FIGS.  3 A- 3 C  illustrate side and perspective views of an exemplary noninvasive sensor housing including a finger bed protrusion and heat sink, according to an embodiment of the disclosure; 
         FIG.  3 D  illustrates a side view of another example noninvasive sensor housing including a heat sink, according to an embodiment of the disclosure; 
         FIG.  3 E  illustrates a perspective view of an example noninvasive sensor detector shell including example detectors, according to an embodiment of the disclosure; 
         FIG.  3 F  illustrates a side view of an example noninvasive sensor housing including a finger bed protrusion and heat sink, according to an embodiment of the disclosure; 
         FIGS.  4 A through  4 C  illustrate top elevation, side and top perspective views of an example protrusion, according to an embodiment of the disclosure; 
         FIG.  5    illustrates an example graph depicting possible effects of a protrusion on light transmittance, according to an embodiment of the disclosure; 
         FIGS.  6 A through  6 D  illustrate perspective, front elevation, side and top views of another example protrusion, according to an embodiment of the disclosure; 
         FIG.  6 E  illustrates an example sensor incorporating the protrusion of  FIGS.  6 A through  6 D , according to an embodiment of the disclosure; 
         FIGS.  7 A through  7 B  illustrate example arrangements of conductive glass that may be employed in the system of  FIG.  1   , according to embodiments of the disclosure; 
         FIGS.  8 A through  8 D  illustrate an example top elevation view, side views, and a bottom elevation view of the conductive glass that may be employed in the system of  FIG.  1   , according to embodiments of the disclosure; 
         FIG.  9    shows example comparative results obtained by an embodiment of a sensor; 
         FIGS.  10 A and  10 B  illustrate comparative noise floors of various embodiments of the present disclosure; 
         FIG.  11 A  illustrates an exemplary emitter that may be employed in the sensor, according to an embodiment of the disclosure; 
         FIG.  11 B  illustrates a configuration of emitting optical radiation into a measurement site for measuring blood constituents, according to an embodiment of the disclosure; 
         FIG.  11 C  illustrates another exemplary emitter that may be employed in the sensor according to an embodiment of the disclosure; 
         FIG.  11 D  illustrates another exemplary emitter that may be employed in the sensor according to an embodiment of the disclosure; 
         FIG.  12 A  illustrates an example detector portion that may be employed in an embodiment of a sensor, according to an embodiment of the disclosure; 
         FIGS.  12 B through  12 D  illustrate exemplary arrangements of detectors that may be employed in an embodiment of the sensor, according to some embodiments of the disclosure; 
         FIGS.  12 E through  12 H  illustrate exemplary structures of photodiodes that may be employed in embodiments of the detectors, according to some embodiments of the disclosure; 
         FIG.  13    illustrates an example multi-stream operation of the system of  FIG.  1   , according to an embodiment of the disclosure; 
         FIG.  14 A  illustrates another example detector portion having a partially cylindrical protrusion that can be employed in an embodiment of a sensor, according to an embodiment of the disclosure; 
         FIG.  14 B  depicts a front elevation view of the partially cylindrical protrusion of  FIG.  14 A ; 
         FIGS.  14 C through  14 E  illustrate embodiments of a detector submount; 
         FIGS.  14 F through  14 H  illustrate embodiment of portions of a detector shell; 
         FIG.  14 I  illustrates a cutaway view of an embodiment of a sensor; 
         FIGS.  15 A through  15 F  illustrate embodiments of sensors that include heat sink features; 
         FIGS.  15 G and  15 H  illustrate embodiments of connector features that can be used with any of the sensors described herein; 
         FIG.  15 I  illustrates an exemplary architecture for a transimpedance-based front-end that may be employed in any of the sensors described herein; 
         FIG.  15 J  illustrates an exemplary noise model for configuring the transimpedance-based front-ends shown in  FIG.  15 I ; 
         FIG.  15 K  shows different architectures and layouts for various embodiments of a sensor and its detectors; 
         FIG.  15 L  illustrates an exemplary architecture for a switched-capacitor-based front-end that may be employed in any of the sensors described herein; 
         FIGS.  16 A and  16 B  illustrate embodiments of disposable optical sensors; 
         FIG.  17    illustrates an exploded view of certain components of an example sensor; and 
         FIGS.  18  through  22    illustrate various results obtained by an exemplary sensor of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure generally relates to non-invasive medical devices. In the present disclosure, a sensor can measure various blood constituents or analytes noninvasively using multi-stream spectroscopy. In an embodiment, the multi-stream spectroscopy can employ visible, infrared and near infrared wavelengths. As disclosed herein, the sensor is capable of noninvasively measuring blood analytes or percentages thereof (e.g., saturation) based on various combinations of features and components. 
     In various embodiments, the present disclosure relates to an interface for a noninvasive glucose sensor that comprises a front-end adapted to receive an input signals from optical detectors and provide corresponding output signals. The front-end may comprise, among other things, switched capacitor circuits or transimpedance amplifiers. In an embodiment, the front-end may comprise switched capacitor circuits that are configured to convert the output of sensor&#39;s detectors into a digital signal. In another embodiment, the front-end may comprise transimpedance amplifiers. These transimpedance amplifiers may be configured to match one or more photodiodes in a detector based on a noise model that accounts for characteristics, such as the impedance, of the transimpedance amplifier, characteristics of each photodiode, such as the impedance, and the number of photodiodes coupled to the transimpedance amplifier. 
     In the present disclosure, the front-ends are employed in a sensor that measures various blood analytes noninvasively using multi-stream spectroscopy. In an embodiment, the multi-stream spectroscopy can employ visible, infrared and near infrared wavelengths. As disclosed herein, the sensor is capable of noninvasively measuring blood analytes, such as glucose, total hemoglobin, methemoglobin, oxygen content, and the like, based on various combinations of features and components. 
     In an embodiment, a physiological sensor includes a detector housing that can be coupled to a measurement site, such as a patient&#39;s finger. The sensor housing can include a curved bed that can generally conform to the shape of the measurement site. In addition, the curved bed can include a protrusion shaped to increase an amount of light radiation from the measurement site. In an embodiment, the protrusion is used to thin out the measurement site. This allows the light radiation to pass through less tissue, and accordingly is attenuated less. In an embodiment, the protrusion can be used to increase the area from which attenuated light can be measured. In an embodiment, this is done through the use of a lens which collects attenuated light exiting the measurement site and focuses onto one or more detectors. The protrusion can advantageously include plastic, including a hard opaque plastic, such as a black or other colored plastic, helpful in reducing light noise. In an embodiment, such light noise includes light that would otherwise be detected at a photodetector that has not been attenuated by tissue of the measurement site of a patient sufficient to cause the light to adequately included information indicative of one or more physiological parameters of the patient. Such light noise includes light piping. 
     In an embodiment, the protrusion can be formed from the curved bed, or can be a separate component that is positionable with respect to the bed. In an embodiment, a lens made from any appropriate material is used as the protrusion. The protrusion can be convex in shape. The protrusion can also be sized and shaped to conform the measurement site into a flat or relatively flat surface. The protrusion can also be sized to conform the measurement site into a rounded surface, such as, for example, a concave or convex surface. The protrusion can include a cylindrical or partially cylindrical shape. The protrusion can be sized or shaped differently for different types of patients, such as an adult, child, or infant. The protrusion can also be sized or shaped differently for different measurement sites, including, for example, a finger, toe, hand, foot, ear, forehead, or the like. The protrusion can thus be helpful in any type of noninvasive sensor. The external surface of the protrusion can include one or more openings or windows. The openings can be made from glass to allow attenuated light from a measurement site, such as a finger, to pass through to one or more detectors. Alternatively, some of all of the protrusion can be a lens, such as a partially cylindrical lens. 
     The sensor can also include a shielding, such as a metal enclosure as described below or embedded within the protrusion to reduce noise. The shielding can be constructed from a conductive material, such as copper, in the form of a metal cage or enclosure, such as a box. The shielding can include a second set of one or more openings or windows. The second set of openings can be made from glass and allow light that has passed through the first set of windows of the external surface of the protrusion to pass through to one or more detectors that can be enclosed, for example, as described below. 
     In various embodiments, the shielding can include any substantially transparent, conductive material placed in the optical path between an emitter and a detector. The shielding can be constructed from a transparent material, such as glass, plastic, and the like. The shielding can have an electrically conductive material or coating that is at least partially transparent. The electrically conductive coating can be located on one or both sides of the shielding, or within the body of the shielding. In addition, the electrically conductive coating can be uniformly spread over the shielding or may be patterned. Furthermore, the coating can have a uniform or varying thickness to increase or optimize its shielding effect. The shielding can be helpful in virtually any type of noninvasive sensor that employs spectroscopy. 
     In an embodiment, the sensor can also include a heat sink. In an embodiment, the heat sink can include a shape that is functional in its ability to dissipate excess heat and aesthetically pleasing to the wearer. For example, the heat sink can be configured in a shape that maximizes surface area to allow for greater dissipation of heat. In an embodiment, the heat sink includes a metalicized plastic, such as plastic including carbon and aluminum to allow for improved thermal conductivity and diffusivity. In an embodiment, the heat sink can advantageously be inexpensively molded into desired shapes and configurations for aesthetic and functional purposes. For example, the shape of the heat sink can be a generally curved surface and include one or more fins, undulations, grooves or channels, or combs. 
     The sensor can include photocommunicative components, such as an emitter, a detector, and other components. The emitter can include a plurality of sets of optical sources that, in an embodiment, are arranged together as a point source. The various optical sources can emit a sequence of optical radiation pulses at different wavelengths towards a measurement site, such as a patient&#39;s finger. Detectors can then detect optical radiation from the measurement site. The optical sources and optical radiation detectors can operate at any appropriate wavelength, including, as discussed herein, infrared, near infrared, visible light, and ultraviolet. In addition, the optical sources and optical radiation detectors can operate at any appropriate wavelength, and such modifications to the embodiments desirable to operate at any such wavelength will be apparent to those skilled in the art. 
     In certain embodiments, multiple detectors are employed and arranged in a spatial geometry. This spatial geometry provides a diversity of path lengths among at least some of the detectors and allows for multiple bulk and pulsatile measurements that are robust. Each of the detectors can provide a respective output stream based on the detected optical radiation, or a sum of output streams can be provided from multiple detectors. In some embodiments, the sensor can also include other components, such as one or more heat sinks and one or more thermistors. 
     The spatial configuration of the detectors provides a geometry having a diversity of path lengths among the detectors. For example, a detector in the sensor may comprise multiple detectors that are arranged to have a sufficient difference in mean path length to allow for noise cancellation and noise reduction. In addition, walls may be used to separate individual photodetectors and prevent mixing of detected optical radiation between the different locations on the measurement site. A window may also be employed to facilitate the passing of optical radiation at various wavelengths for measuring glucose in the tissue. 
     In the present disclosure, a sensor may measure various blood constituents or analytes noninvasively using spectroscopy and a recipe of various features. As disclosed herein, the sensor is capable of non-invasively measuring blood analytes, such as, glucose, total hemoglobin, methemoglobin, oxygen content, and the like. In an embodiment, the spectroscopy used in the sensor can employ visible, infrared and near infrared wavelengths. The sensor may comprise an emitter, a detector, and other components. In some embodiments, the sensor may also comprise other components, such as one or more heat sinks and one or more thermistors. 
     In various embodiments, the sensor may also be coupled to one or more companion devices that process and/or display the sensor&#39;s output. The companion devices may comprise various components, such as a sensor front-end, a signal processor, a display, a network interface, a storage device or memory, etc. 
     A sensor can include photocommunicative components, such as an emitter, a detector, and other components. The emitter is configured as a point optical source that comprises a plurality of LEDs that emit a sequence of pulses of optical radiation across a spectrum of wavelengths. In some embodiments, the plurality of sets of optical sources may each comprise at least one top-emitting LED and at least one super luminescent LED. In some embodiments, the emitter comprises optical sources that transmit optical radiation in the infrared or near-infrared wavelengths suitable for detecting blood analytes like glucose. In order to achieve the desired SNR for detecting analytes like glucose, the emitter may be driven using a progression from low power to higher power. In addition, the emitter may have its duty cycle modified to achieve a desired SNR. 
     The emitter may be constructed of materials, such as aluminum nitride and may include a heat sink to assist in heat dissipation. A thermistor may also be employed to account for heating effects on the LEDs. The emitter may further comprise a glass window and a nitrogen environment to improve transmission from the sources and prevent oxidative effects. 
     The sensor can be coupled to one or more monitors that process and/or display the sensor&#39;s output. The monitors can include various components, such as a sensor front end, a signal processor, a display, etc. 
     The sensor can be integrated with a monitor, for example, into a handheld unit including the sensor, a display and user controls. In other embodiments, the sensor can communicate with one or more processing devices. The communication can be via wire(s), cable(s), flex circuit(s), wireless technologies, or other suitable analog or digital communication methodologies and devices to perform those methodologies. Many of the foregoing arrangements allow the sensor to be attached to the measurement site while the device is attached elsewhere on a patient, such as the patient&#39;s arm, or placed at a location near the patient, such as a bed, shelf or table. The sensor or monitor can also provide outputs to a storage device or network interface. 
     Reference will now be made to the Figures to discuss embodiments of the present disclosure. 
       FIG.  1    illustrates an example of a data collection system  100 . In certain embodiments, the data collection system  100  noninvasively measure a blood analyte, such as oxygen, carbon monoxide, methemoglobin, total hemoglobin, glucose, proteins, glucose, lipids, a percentage thereof (e.g., saturation) or for measuring many other physiologically relevant patient characteristics. The system  100  can also measure additional blood analytes and/or other physiological parameters useful in determining a state or trend of wellness of a patient. 
     The data collection system  100  can be capable of measuring optical radiation from the measurement site. For example, in some embodiments, the data collection system  100  can employ photodiodes defined in terms of area. In an embodiment, the area is from about 1 mm 2 -5 mm 2  (or higher) that are capable of detecting about 100 nanoamps (nA) or less of current resulting from measured light at full scale. In addition to having its ordinary meaning, the phrase “at full scale” can mean light saturation of a photodiode amplifier (not shown). Of course, as would be understood by a person of skill in the art from the present disclosure, various other sizes and types of photodiodes can be used with the embodiments of the present disclosure. 
     The data collection system  100  can measure a range of approximately about 2 nA to about 100 nA full scale. The data collection system  100  can also include sensor front-ends that are capable of processing and amplifying current from the detector(s) at signal-to-noise ratios (SNRs) of about 100 decibels (dB) or more, such as about 120 dB in order to measure various desired analytes. The data collection system  100  can operate with a lower SNR if less accuracy is desired for an analyte like glucose. 
     The data collection system  100  can measure analyte concentrations, including glucose, at least in part by detecting light attenuated by a measurement site  102 . The measurement site  102  can be any location on a patient&#39;s body, such as a finger, foot, ear lobe, or the like. For convenience, this disclosure is described primarily in the context of a finger measurement site  102 . However, the features of the embodiments disclosed herein can be used with other measurement sites  102 . 
     In the depicted embodiment, the system  100  includes an optional tissue thickness adjuster or tissue shaper  105 , which can include one or more protrusions, bumps, lenses, or other suitable tissue-shaping mechanisms. In certain embodiments, the tissue shaper  105  is a flat or substantially flat surface that can be positioned proximate the measurement site  102  and that can apply sufficient pressure to cause the tissue of the measurement site  102  to be flat or substantially flat. In other embodiments, the tissue shaper  105  is a convex or substantially convex surface with respect to the measurement site  102 . Many other configurations of the tissue shaper  105  are possible. Advantageously, in certain embodiments, the tissue shaper  105  reduces thickness of the measurement site  102  while preventing or reducing occlusion at the measurement site  102 . Reducing thickness of the site can advantageously reduce the amount of attenuation of the light because there is less tissue through which the light must travel. Shaping the tissue in to a convex (or alternatively concave) surface can also provide more surface area from which light can be detected. 
     The embodiment of the data collection system  100  shown also includes an optional noise shield  103 . In an embodiment, the noise shield  103  can be advantageously adapted to reduce electromagnetic noise while increasing the transmittance of light from the measurement site  102  to one or more detectors  106  (described below). For example, the noise shield  103  can advantageously include a conductive coated glass or metal grid electrically communicating with one or more other shields of the sensor  101  or electrically grounded. In an embodiment where the noise shield  103  includes conductive coated glass, the coating can advantageously include indium tin oxide. In an embodiment, the indium tin oxide includes a surface resistivity ranging from approximately 30 ohms per square inch to about 500 ohms per square inch. In an embodiment, the resistivity is approximately 30, 200, or 500 ohms per square inch. As would be understood by a person of skill in the art from the present disclosure, other resistivities can also be used which are less than about 30 ohms or more than about 500 ohms. Other conductive materials transparent or substantially transparent to light can be used instead. 
     In some embodiments, the measurement site  102  is located somewhere along a non-dominant arm or a non-dominant hand, e.g., a right-handed person&#39;s left arm or left hand. In some patients, the non-dominant arm or hand can have less musculature and higher fat content, which can result in less water content in that tissue of the patient. Tissue having less water content can provide less interference with the particular wavelengths that are absorbed in a useful manner by blood analytes like glucose. Accordingly, in some embodiments, the data collection system  100  can be used on a person&#39;s non-dominant hand or arm. 
     The data collection system  100  can include a sensor  101  (or multiple sensors) that is coupled to a processing device or physiological monitor  109 . In an embodiment, the sensor  101  and the monitor  109  are integrated together into a single unit. In another embodiment, the sensor  101  and the monitor  109  are separate from each other and communicate one with another in any suitable manner, such as via a wired or wireless connection. The sensor  101  and monitor  109  can be attachable and detachable from each other for the convenience of the user or caregiver, for ease of storage, sterility issues, or the like. The sensor  101  and the monitor  109  will now be further described. 
     In the depicted embodiment shown in  FIG.  1   , the sensor  101  includes an emitter  104 , a tissue shaper  105 , a set of detectors  106 , and a front-end interface  108 . The emitter  104  can serve as the source of optical radiation transmitted towards measurement site  102 . As will be described in further detail below, the emitter  104  can include one or more sources of optical radiation, such as LEDs, laser diodes, incandescent bulbs with appropriate frequency-selective filters, combinations of the same, or the like. In an embodiment, the emitter  104  includes sets of optical sources that are capable of emitting visible and near-infrared optical radiation. 
     In some embodiments, the emitter  104  is used as a point optical source, and thus, the one or more optical sources of the emitter  104  can be located within a close distance to each other, such as within about a 2 mm to about 4 mm. The emitters  104  can be arranged in an array, such as is described in U.S. Publication No. 2006/0211924, filed Sep. 21, 2006, titled “Multiple Wavelength Sensor Emitters,” the disclosure of which is hereby incorporated by reference in its entirety. In particular, the emitters  104  can be arranged at least in part as described in paragraphs [0061] through [0068] of the aforementioned publication, which paragraphs are hereby incorporated specifically by reference. Other relative spatial relationships can be used to arrange the emitters  104 . 
     For analytes like glucose, currently available non-invasive techniques often attempt to employ light near the water absorbance minima at or about 1600 nm. Typically, these devices and methods employ a single wavelength or single band of wavelengths at or about 1600 nm. However, to date, these techniques have been unable to adequately consistently measure analytes like glucose based on spectroscopy. 
     In contrast, the emitter  104  of the data collection system  100  can emit, in certain embodiments, combinations of optical radiation in various bands of interest. For example, in some embodiments, for analytes like glucose, the emitter  104  can emit optical radiation at three (3) or more wavelengths between about 1600 nm to about 1700 nm. In particular, the emitter  104  can emit optical radiation at or about 1610 nm, about 1640 nm, and about 1665 nm. In some circumstances, the use of three wavelengths within about 1600 nm to about 1700 nm enable sufficient SNRs of about 100 dB, which can result in a measurement accuracy of about 20 mg/dL or better for analytes like glucose. 
     In other embodiments, the emitter  104  can use two (2) wavelengths within about 1600 nm to about 1700 nm to advantageously enable SNRs of about 85 dB, which can result in a measurement accuracy of about 25-30 mg/dL or better for analytes like glucose. Furthermore, in some embodiments, the emitter  104  can emit light at wavelengths above about 1670 nm. Measurements at these wavelengths can be advantageously used to compensate or confirm the contribution of protein, water, and other non-hemoglobin species exhibited in measurements for analytes like glucose conducted between about 1600 nm and about 1700 nm. Of course, other wavelengths and combinations of wavelengths can be used to measure analytes and/or to distinguish other types of tissue, fluids, tissue properties, fluid properties, combinations of the same or the like. 
     For example, the emitter  104  can emit optical radiation across other spectra for other analytes. In particular, the emitter  104  can employ light wavelengths to measure various blood analytes or percentages (e.g., saturation) thereof. For example, in one embodiment, the emitter  104  can emit optical radiation in the form of pulses at wavelengths about 905 nm, about 1050 nm, about 1200 nm, about 1300 nm, about 1330 nm, about 1610 nm, about 1640 nm, and about 1665 nm. In another embodiment, the emitter  104  can emit optical radiation ranging from about 860 nm to about 950 nm, about 950 nm to about 1100 nm, about 1100 nm to about 1270 nm, about 1250 nm to about 1350 nm, about 1300 nm to about 1360 nm, and about 1590 nm to about 1700 nm. Of course, the emitter  104  can transmit any of a variety of wavelengths of visible or near-infrared optical radiation. 
     Due to the different responses of analytes to the different wavelengths, certain embodiments of the data collection system  100  can advantageously use the measurements at these different wavelengths to improve the accuracy of measurements. For example, the measurements of water from visible and infrared light can be used to compensate for water absorbance that is exhibited in the near-infrared wavelengths. 
     As briefly described above, the emitter  104  can include sets of light-emitting diodes (LEDs) as its optical source. The emitter  104  can use one or more top-emitting LEDs. In particular, in some embodiments, the emitter  104  can include top-emitting LEDs emitting light at about 850 nm to 1350 nm. 
     The emitter  104  can also use super luminescent LEDs (SLEDs) or side-emitting LEDs. In some embodiments, the emitter  104  can employ SLEDs or side-emitting LEDs to emit optical radiation at about 1600 nm to about 1800 nm. Emitter  104  can use SLEDs or side-emitting LEDs to transmit near infrared optical radiation because these types of sources can transmit at high power or relatively high power, e.g., about 40 mW to about 100 mW. This higher power capability can be useful to compensate or overcome the greater attenuation of these wavelengths of light in tissue and water. For example, the higher power emission can effectively compensate and/or normalize the absorption signal for light in the mentioned wavelengths to be similar in amplitude and/or effect as other wavelengths that can be detected by one or more photodetectors after absorption. However, the embodiments of the present disclosure do not necessarily require the use of high power optical sources. For example, some embodiments may be configured to measure analytes, such as total hemoglobin (tHb), oxygen saturation (SpO 2 ), carboxyhemoglobin, methemoglobin, etc., without the use of high power optical sources like side emitting LEDs. Instead, such embodiments may employ other types of optical sources, such as top emitting LEDs. Alternatively, the emitter  104  can use other types of sources of optical radiation, such as a laser diode, to emit near-infrared light into the measurement site  102 . 
     In addition, in some embodiments, in order to assist in achieving a comparative balance of desired power output between the LEDs, some of the LEDs in the emitter  104  can have a filter or covering that reduces and/or cleans the optical radiation from particular LEDs or groups of LEDs. For example, since some wavelengths of light can penetrate through tissue relatively well, LEDs, such as some or all of the top-emitting LEDs can use a filter or covering, such as a cap or painted dye. This can be useful in allowing the emitter  104  to use LEDs with a higher output and/or to equalize intensity of LEDs. 
     The data collection system  100  also includes a driver  111  that drives the emitter  104 . The driver  111  can be a circuit or the like that is controlled by the monitor  109 . For example, the driver  111  can provide pulses of current to the emitter  104 . In an embodiment, the driver  111  drives the emitter  104  in a progressive fashion, such as in an alternating manner. The driver  111  can drive the emitter  104  with a series of pulses of about 1 milliwatt (mW) for some wavelengths that can penetrate tissue relatively well and from about 40 mW to about 100 mW for other wavelengths that tend to be significantly absorbed in tissue. A wide variety of other driving powers and driving methodologies can be used in various embodiments. 
     The driver  111  can be synchronized with other parts of the sensor  101  and can minimize or reduce jitter in the timing of pulses of optical radiation emitted from the emitter  104 . In some embodiments, the driver  111  is capable of driving the emitter  104  to emit optical radiation in a pattern that varies by less than about 10 parts-per-million. 
     The detectors  106  capture and measure light from the measurement site  102 . For example, the detectors  106  can capture and measure light transmitted from the emitter  104  that has been attenuated or reflected from the tissue in the measurement site  102 . The detectors  106  can output a detector signal  107  responsive to the light captured or measured. The detectors  106  can be implemented using one or more photodiodes, phototransistors, or the like. 
     In addition, the detectors  106  can be arranged with a spatial configuration to provide a variation of path lengths among at least some of the detectors  106 . That is, some of the detectors  106  can have the substantially, or from the perspective of the processing algorithm, effectively, the same path length from the emitter  104 . However, according to an embodiment, at least some of the detectors  106  can have a different path length from the emitter  104  relative to other of the detectors  106 . Variations in path lengths can be helpful in allowing the use of a bulk signal stream from the detectors  106 . In some embodiments, the detectors  106  may employ a linear spacing, a logarithmic spacing, or a two or three dimensional matrix of spacing, or any other spacing scheme in order to provide an appropriate variation in path lengths. 
     The front end interface  108  provides an interface that adapts the output of the detectors  106 , which is responsive to desired physiological parameters. For example, the front end interface  108  can adapt a signal  107  received from one or more of the detectors  106  into a form that can be processed by the monitor  109 , for example, by a signal processor  110  in the monitor  109 . The front end interface  108  can have its components assembled in the sensor  101 , in the monitor  109 , in connecting cabling (if used), combinations of the same, or the like. The location of the front end interface  108  can be chosen based on various factors including space desired for components, desired noise reductions or limits, desired heat reductions or limits, and the like. 
     The front end interface  108  can be coupled to the detectors  106  and to the signal processor  110  using a bus, wire, electrical or optical cable, flex circuit, or some other form of signal connection. The front end interface  108  can also be at least partially integrated with various components, such as the detectors  106 . For example, the front end interface  108  can include one or more integrated circuits that are on the same circuit board as the detectors  106 . Other configurations can also be used. 
     The front end interface  108  can be implemented using one or more amplifiers, such as transimpedance amplifiers, that are coupled to one or more analog to digital converters (ADCs) (which can be in the monitor  109 ), such as a sigma-delta ADC. A transimpedance-based front end interface  108  can employ single-ended circuitry, differential circuitry, and/or a hybrid configuration. A transimpedance-based front end interface  108  can be useful for its sampling rate capability and freedom in modulation/demodulation algorithms. For example, this type of front end interface  108  can advantageously facilitate the sampling of the ADCs being synchronized with the pulses emitted from the emitter  104 . 
     The ADC or ADCs can provide one or more outputs into multiple channels of digital information for processing by the signal processor  110  of the monitor  109 . Each channel can correspond to a signal output from a detector  106 . 
     In some embodiments, a programmable gain amplifier (PGA) can be used in combination with a transimpedance-based front end interface  108 . For example, the output of a transimpedance-based front end interface  108  can be output to a PGA that is coupled with an ADC in the monitor  109 . A PGA can be useful in order to provide another level of amplification and control of the stream of signals from the detectors  106 . Alternatively, the PGA and ADC components can be integrated with the transimpedance-based front end interface  108  in the sensor  101 . 
     In another embodiment, the front end interface  108  can be implemented using switched-capacitor circuits. A switched-capacitor-based front end interface  108  can be useful for, in certain embodiments, its resistor-free design and analog averaging properties. In addition, a switched-capacitor-based front end interface  108  can be useful because it can provide a digital signal to the signal processor  110  in the monitor  109 . 
     As shown in  FIG.  1   , the monitor  109  can include the signal processor  110  and a user interface, such as a display  112 . The monitor  109  can also include optional outputs alone or in combination with the display  112 , such as a storage device  114  and a network interface  116 . In an embodiment, the signal processor  110  includes processing logic that determines measurements for desired analytes, such as glucose, based on the signals received from the detectors  106 . The signal processor  110  can be implemented using one or more microprocessors or subprocessors (e.g., cores), digital signal processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), combinations of the same, and the like. 
     The signal processor  110  can provide various signals that control the operation of the sensor  101 . For example, the signal processor  110  can provide an emitter control signal to the driver  111 . This control signal can be useful in order to synchronize, minimize, or reduce jitter in the timing of pulses emitted from the emitter  104 . Accordingly, this control signal can be useful in order to cause optical radiation pulses emitted from the emitter  104  to follow a precise timing and consistent pattern. For example, when a transimpedance-based front end interface  108  is used, the control signal from the signal processor  110  can provide synchronization with the ADC in order to avoid aliasing, cross-talk, and the like. As also shown, an optional memory  113  can be included in the front-end interface  108  and/or in the signal processor  110 . This memory  113  can serve as a buffer or storage location for the front-end interface  108  and/or the signal processor  110 , among other uses. 
     The user interface  112  can provide an output, e.g., on a display, for presentation to a user of the data collection system  100 . The user interface  112  can be implemented as a touch-screen display, an LCD display, an organic LED display, or the like. In addition, the user interface  112  can be manipulated to allow for measurement on the non-dominant side of patient. For example, the user interface  112  can include a flip screen, a screen that can be moved from one side to another on the monitor  109 , or can include an ability to reorient its display indicia responsive to user input or device orientation. In alternative embodiments, the data collection system  100  can be provided without a user interface  112  and can simply provide an output signal to a separate display or system. 
     A storage device  114  and a network interface  116  represent other optional output connections that can be included in the monitor  109 . The storage device  114  can include any computer-readable medium, such as a memory device, hard disk storage, EEPROM, flash drive, or the like. The various software and/or firmware applications can be stored in the storage device  114 , which can be executed by the signal processor  110  or another processor of the monitor  109 . The network interface  116  can be a serial bus port (RS-232/RS-485), a Universal Serial Bus (USB) port, an Ethernet port, a wireless interface (e.g., WiFi such as any 802.1x interface, including an internal wireless card), or other suitable communication device(s) that allows the monitor  109  to communicate and share data with other devices. The monitor  109  can also include various other components not shown, such as a microprocessor, graphics processor, or controller to output the user interface  112 , to control data communications, to compute data trending, or to perform other operations. 
     Although not shown in the depicted embodiment, the data collection system  100  can include various other components or can be configured in different ways. For example, the sensor  101  can have both the emitter  104  and detectors  106  on the same side of the measurement site  102  and use reflectance to measure analytes. The data collection system  100  can also include a sensor that measures the power of light emitted from the emitter  104 . 
       FIGS.  2 A through  2 D  illustrate example monitoring devices  200  in which the data collection system  100  can be housed. Advantageously, in certain embodiments, some or all of the example monitoring devices  200  shown can have a shape and size that allows a user to operate it with a single hand or attach it, for example, to a patient&#39;s body or limb. Although several examples are shown, many other monitoring device configurations can be used to house the data collection system  100 . In addition, certain of the features of the monitoring devices  200  shown in  FIGS.  2 A through  2 D  can be combined with features of the other monitoring devices  200  shown. 
     Referring specifically to  FIG.  2 A , an example monitoring device  200 A is shown, in which a sensor  201   a  and a monitor  209   a  are integrated into a single unit. The monitoring device  200 A shown is a handheld or portable device that can measure glucose and other analytes in a patient&#39;s finger. The sensor  201   a  includes an emitter shell  204   a  and a detector shell  206   a . The depicted embodiment of the monitoring device  200 A also includes various control buttons  208   a  and a display  210   a.    
     The sensor  201   a  can be constructed of white material used for reflective purposes (such as white silicone or plastic), which can increase the usable signal at the detector  106  by forcing light back into the sensor  201   a . Pads in the emitter shell  204   a  and the detector shell  206   a  can contain separated windows to prevent or reduce mixing of light signals, for example, from distinct quadrants on a patient&#39;s finger. In addition, these pads can be made of a relatively soft material, such as a gel or foam, in order to conform to the shape, for example, of a patient&#39;s finger. The emitter shell  204   a  and the detector shell  206   a  can also include absorbing black or grey material portions to prevent or reduce ambient light from entering into the sensor  201   a.    
     In some embodiments, some or all portions of the emitter shell  204   a  and/or detector shell  206   a  can be detachable and/or disposable. For example, some or all portions of the shells  204   a  and  206   a  can be removable pieces. The removability of the shells  204   a  and  206   a  can be useful for sanitary purposes or for sizing the sensor  201   a  to different patients. The monitor  209   a  can include a fitting, slot, magnet, or other connecting mechanism to allow the sensor  201   c  to be removably attached to the monitor  209   a.    
     The monitoring device  200   a  also includes optional control buttons  208   a  and a display  210   a  that can allow the user to control the operation of the device. For example, a user can operate the control buttons  208   a  to view one or more measurements of various analytes, such as glucose. In addition, the user can operate the control buttons  208   a  to view other forms of information, such as graphs, histograms, measurement data, trend measurement data, parameter combination views, wellness indications, and the like. Many parameters, trends, alarms and parameter displays could be output to the display  210   a , such as those that are commercially available through a wide variety of noninvasive monitoring devices from Masimo® Corporation of Irvine, Calif. 
     Furthermore, the controls  208   a  and/or display  210   a  can provide functionality for the user to manipulate settings of the monitoring device  200   a , such as alarm settings, emitter settings, detector settings, and the like. The monitoring device  200   a  can employ any of a variety of user interface designs, such as frames, menus, touch-screens, and any type of button. 
       FIG.  2 B  illustrates another example of a monitoring device  200 B. In the depicted embodiment, the monitoring device  200 B includes a finger clip sensor  201   b  connected to a monitor  209   b  via a cable  212 . In the embodiment shown, the monitor  209   b  includes a display  210   b , control buttons  208   b  and a power button. Moreover, the monitor  209   b  can advantageously include electronic processing, signal processing, and data storage devices capable of receiving signal data from said sensor  201   b , processing the signal data to determine one or more output measurement values indicative of one or more physiological parameters of a monitored patient, and displaying the measurement values, trends of the measurement values, combinations of measurement values, and the like. 
     The cable  212  connecting the sensor  201   b  and the monitor  209   b  can be implemented using one or more wires, optical fiber, flex circuits, or the like. In some embodiments, the cable  212  can employ twisted pairs of conductors in order to minimize or reduce cross-talk of data transmitted from the sensor  201   b  to the monitor  209   b . Various lengths of the cable  212  can be employed to allow for separation between the sensor  201   b  and the monitor  209   b . The cable  212  can be fitted with a connector (male or female) on either end of the cable  212  so that the sensor  201   b  and the monitor  209   b  can be connected and disconnected from each other. Alternatively, the sensor  201   b  and the monitor  209   b  can be coupled together via a wireless communication link, such as an infrared link, radio frequency channel, or any other wireless communication protocol and channel. 
     The monitor  209   b  can be attached to the patient. For example, the monitor  209   b  can include a belt clip or straps (see, e.g.,  FIG.  2 C ) that facilitate attachment to a patient&#39;s belt, arm, leg, or the like. The monitor  209   b  can also include a fitting, slot, magnet, LEMO snap-click connector, or other connecting mechanism to allow the cable  212  and sensor  201   b  to be attached to the monitor  209 B. 
     The monitor  209   b  can also include other components, such as a speaker, power button, removable storage or memory (e.g., a flash card slot), an AC power port, and one or more network interfaces, such as a universal serial bus interface or an Ethernet port. For example, the monitor  209   b  can include a display  210   b  that can indicate a measurement for glucose, for example, in mg/dL. Other analytes and forms of display can also appear on the monitor  209   b.    
     In addition, although a single sensor  201   b  with a single monitor  209   b  is shown, different combinations of sensors and device pairings can be implemented. For example, multiple sensors can be provided for a plurality of differing patient types or measurement sites or even patient fingers. 
       FIG.  2 C  illustrates yet another example of monitoring device  200 C that can house the data collection system  100 . Like the monitoring device  200 B, the monitoring device  200 C includes a finger clip sensor  201   c  connected to a monitor  209   c  via a cable  212 . The cable  212  can have all of the features described above with respect to  FIG.  2 B . The monitor  209   c  can include all of the features of the monitor  200 B described above. For example, the monitor  209   c  includes buttons  208   c  and a display  210   c . The monitor  209   c  shown also includes straps  214   c  that allow the monitor  209   c  to be attached to a patient&#39;s limb or the like. 
       FIG.  2 D  illustrates yet another example of monitoring device  200 D that can house the data collection system  100 . Like the monitoring devices  200 B and  200 C, the monitoring device  200 D includes a finger clip sensor  201   d  connected to a monitor  209   d  via a cable  212 . The cable  212  can have all of the features described above with respect to  FIG.  2 B . In addition to having some or all of the features described above with respect to  FIGS.  2 B and  2 C , the monitoring device  200 D includes an optional universal serial bus (USB) port  216  and an Ethernet port  218 . The USB port  216  and the Ethernet port  218  can be used, for example, to transfer information between the monitor  209   d  and a computer (not shown) via a cable. Software stored on the computer can provide functionality for a user to, for example, view physiological data and trends, adjust settings and download firmware updates to the monitor  209   b , and perform a variety of other functions. The USB port  216  and the Ethernet port  218  can be included with the other monitoring devices  200 A,  200 B, and  200 C described above. 
       FIGS.  3 A through  3 C  illustrate more detailed examples of embodiments of a sensor  301   a . The sensor  301   a  shown can include all of the features of the sensors  100  and  200  described above. 
     Referring to  FIG.  3 A , the sensor  301   a  in the depicted embodiment is a clothespin-shaped clip sensor that includes an enclosure  302   a  for receiving a patient&#39;s finger. The enclosure  302   a  is formed by an upper section or emitter shell  304   a , which is pivotably connected with a lower section or detector shell  306   a . The emitter shell  304   a  can be biased with the detector shell  306   a  to close together around a pivot point  303   a  and thereby sandwich finger tissue between the emitter and detector shells  304   a ,  306   a.    
     In an embodiment, the pivot point  303   a  advantageously includes a pivot capable of adjusting the relationship between the emitter and detector shells  304   a ,  306   a  to effectively level the sections when applied to a tissue site. In another embodiment, the sensor  301   a  includes some or all features of the finger clip described in U.S. Publication No. 2006/0211924, incorporated above, such as a spring that causes finger clip forces to be distributed along the finger. Paragraphs through [0105], which describe this feature, are hereby specifically incorporated by reference. 
     The emitter shell  304   a  can position and house various emitter components of the sensor  301   a . It can be constructed of reflective material (e.g., white silicone or plastic) and/or can be metallic or include metalicized plastic (e.g., including carbon and aluminum) to possibly serve as a heat sink. The emitter shell  304   a  can also include absorbing opaque material, such as, for example, black or grey colored material, at various areas, such as on one or more flaps  307   a , to reduce ambient light entering the sensor  301   a.    
     The detector shell  306   a  can position and house one or more detector portions of the sensor  301   a . The detector shell  306   a  can be constructed of reflective material, such as white silicone or plastic. As noted, such materials can increase the usable signal at a detector by forcing light back into the tissue and measurement site (see  FIG.  1   ). The detector shell  306   a  can also include absorbing opaque material at various areas, such as lower area  308   a , to reduce ambient light entering the sensor  301   a.    
     Referring to  FIGS.  3 B and  3 C , an example of finger bed  310  is shown in the sensor  301   b . The finger bed  310  includes a generally curved surface shaped generally to receive tissue, such as a human digit. The finger bed  310  includes one or more ridges or channels  314 . Each of the ridges  314  has a generally convex shape that can facilitate increasing traction or gripping of the patient&#39;s finger to the finger bed. Advantageously, the ridges  314  can improve the accuracy of spectroscopic analysis in certain embodiments by reducing noise that can result from a measurement site moving or shaking loose inside of the sensor  301   a . The ridges  314  can be made from reflective or opaque materials in some embodiments to further increase SNR. In other implementations, other surface shapes can be used, such as, for example, generally flat, concave, or convex finger beds  310 . 
     Finger bed  310  can also include an embodiment of a tissue thickness adjuster or protrusion  305 . The protrusion  305  includes a measurement site contact area  370  (see  FIG.  3 C ) that can contact body tissue of a measurement site. The protrusion  305  can be removed from or integrated with the finger bed  310 . Interchangeable, different shaped protrusions  305  can also be provided, which can correspond to different finger shapes, characteristics, opacity, sizes, or the like. 
     Referring specifically to  FIG.  3 C , the contact area  370  of the protrusion  305  can include openings or windows  320 ,  321 ,  322 , and  323 . When light from a measurement site passes through the windows  320 ,  321 ,  322 , and  323 , the light can reach one or more photodetectors (see  FIG.  3 E ). In an embodiment, the windows  320 ,  321 ,  322 , and  323  mirror specific detector placements layouts such that light can impinge through the protrusion  305  onto the photodetectors. Any number of windows  320 ,  321 ,  322 , and  323  can be employed in the protrusion  305  to allow light to pass from the measurement site to the photodetectors. 
     The windows  320 ,  321 ,  322 , and  323  can also include shielding, such as an embedded grid of wiring or a conductive glass coating, to reduce noise from ambient light or other electromagnetic noise. The windows  320 ,  321 ,  322 , and  323  can be made from materials, such as plastic or glass. In some embodiments, the windows  320 ,  321 ,  322 , and  323  can be constructed from conductive glass, such as indium tin oxide (ITO) coated glass. Conductive glass can be useful because its shielding is transparent, and thus allows for a larger aperture versus a window with an embedded grid of wiring. In addition, in certain embodiments, the conductive glass does not need openings in its shielding (since it is transparent), which enhances its shielding performance. For example, some embodiments that employ the conductive glass can attain up to an about 40% to about 50% greater signal than non-conductive glass with a shielding grid. In addition, in some embodiments, conductive glass can be useful for shielding noise from a greater variety of directions than non-conductive glass with a shielding grid. 
     Turning to  FIG.  3 B , the sensor  301   a  can also include a shielding  315   a , such as a metal cage, box, metal sheet, perforated metal sheet, a metal layer on a non-metal material, or the like. The shielding  315   a  is provided in the depicted embodiment below or embedded within the protrusion  305  to reduce noise. The shielding  315   a  can be constructed from a conductive material, such as copper. The shielding  315   a  can include one or more openings or windows (not shown). The windows can be made from glass or plastic to thereby allow light that has passed through the windows  320 ,  321 ,  322 , and  323  on an external surface of the protrusion  305  (see  FIG.  3 C ) to pass through to one or more photodetectors that can be enclosed or provided below (see  FIG.  3 E ). 
     In some embodiments, the shielding cage for shielding  315   a  can be constructed in a single manufactured component with or without the use of conductive glass. This form of construction may be useful in order to reduce costs of manufacture as well as assist in quality control of the components. Furthermore, the shielding cage can also be used to house various other components, such as sigma delta components for various embodiments of front end interfaces  108 . 
     In an embodiment, the photodetectors can be positioned within or directly beneath the protrusion  305  (see  FIG.  3 E ). In such cases, the mean optical path length from the emitters to the detectors can be reduced and the accuracy of blood analyte measurement can increase. For example, in one embodiment, a convex bump of about 1 mm to about 3 mm in height and about 10 mm 2  to about 60 mm 2  was found to help signal strength by about an order of magnitude versus other shapes. Of course other dimensions and sizes can be employed in other embodiments. Depending on the properties desired, the length, width, and height of the protrusion  305  can be selected. In making such determinations, consideration can be made of protrusion&#39;s  305  effect on blood flow at the measurement site and mean path length for optical radiation passing through openings  320 ,  321 ,  322 , and  323 . Patient comfort can also be considered in determining the size and shape of the protrusion. 
     In an embodiment, the protrusion  305  can include a pliant material, including soft plastic or rubber, which can somewhat conform to the shape of a measurement site. Pliant materials can improve patient comfort and tactility by conforming the measurement site contact area  370  to the measurement site. Additionally, pliant materials can minimize or reduce noise, such as ambient light. Alternatively, the protrusion  305  can be made from a rigid material, such as hard plastic or metal. 
     Rigid materials can improve measurement accuracy of a blood analyte by conforming the measurement site to the contact area  370 . The contact area  370  can be an ideal shape for improving accuracy or reducing noise. Selecting a material for the protrusion  305  can include consideration of materials that do not significantly alter blood flow at the measurement site. The protrusion  305  and the contact area  370  can include a combination of materials with various characteristics. 
     The contact area  370  serves as a contact surface for the measurement site. For example, in some embodiments, the contact area  370  can be shaped for contact with a patient&#39;s finger. Accordingly, the contact area  370  can be sized and shaped for different sizes of fingers. The contact area  370  can be constructed of different materials for reflective purposes as well as for the comfort of the patient. For example, the contact area  370  can be constructed from materials having various hardness and textures, such as plastic, gel, foam, and the like. 
     The formulas and analysis that follow with respect to  FIG.  5    provide insight into how selecting these variables can alter transmittance and intensity gain of optical radiation that has been applied to the measurement site. These examples do not limit the scope of this disclosure. 
     Referring to  FIG.  5   , a plot  500  is shown that illustrates examples of effects of embodiments of the protrusion  305  on the SNR at various wavelengths of light. As described above, the protrusion  305  can assist in conforming the tissue and effectively reduce its mean path length. In some instances, this effect by the protrusion  305  can have significant impact on increasing the SNR. 
     According to the Beer Lambert law, a transmittance of light (I) can be expressed as follows: I=I o *e −m*b*c , where I o  is the initial power of light being transmitted, m is the path length traveled by the light, and the component “b*c” corresponds to the bulk absorption of the light at a specific wavelength of light. For light at about 1600 nm to about 1700 nm, for example, the bulk absorption component is generally around 0.7 mm −1 . Assuming a typical finger thickness of about 12 mm and a mean path length of 20 mm due to tissue scattering, then I=I o *e (−20*0.7) . 
     In an embodiment where the protrusion  305  is a convex bump, the thickness of the finger can be reduced to 10 mm (from 12 mm) for some fingers and the effective light mean path is reduced to about 16.6 mm from 20 mm (see box  510 ). This results in a new transmittance, I 1 =I o *e (−16.6*0.7) . A curve for a typical finger (having a mean path length of 20 mm) across various wavelengths is shown in the plot  500  of  FIG.  5   . The plot  500  illustrates potential effects of the protrusion  305  on the transmittance. As illustrated, comparing I and I 1  results in an intensity gain of e (−16.6*0.7) /e (−20*0.7) , which is about a 10 times increase for light in the about 1600 nm to about 1700 nm range. Such an increase can affect the SNR at which the sensor can operate. The foregoing gains can be due at least in part to the about 1600 nm to about 1700 nm range having high values in bulk absorptions (water, protein, and the like), e.g., about 0.7 mm −1 . The plot  500  also shows improvements in the visible/near-infrared range (about 600 nm to about 1300 nm). 
     Turning again to  FIGS.  3 A through  3 C , an example heat sink  350   a  is also shown. The heat sink  350   a  can be attached to, or protrude from an outer surface of, the sensor  301   a , thereby providing increased ability for various sensor components to dissipate excess heat. By being on the outer surface of the sensor  301   a  in certain embodiments, the heat sink  350   a  can be exposed to the air and thereby facilitate more efficient cooling. In an embodiment, one or more of the emitters (see  FIG.  1   ) generate sufficient heat that inclusion of the heat sink  350   a  can advantageously allows the sensor  301   a  to remain safely cooled. The heat sink  350   a  can include one or more materials that help dissipate heat, such as, for example, aluminum, steel, copper, carbon, combinations of the same, or the like. For example, in some embodiments, the emitter shell  304   a  can include a heat conducting material that is also readily and relatively inexpensively moldable into desired shapes and forms. 
     In some embodiments, the heat sink  350   a  includes metalicized plastic. The metalicized plastic can include aluminum and carbon, for example. The material can allow for improved thermal conductivity and diffusivity, which can increase commercial viability of the heat sink. In some embodiments, the material selected to construct the heat sink  350   a  can include a thermally conductive liquid crystalline polymer, such as CoolPoly® D5506, commercially available from Cool Polymers®, Inc. of Warwick, R.I. Such a material can be selected for its electrically non-conductive and dielectric properties so as, for example, to aid in electrical shielding. In an embodiment, the heat sink  350   a  provides improved heat transfer properties when the sensor  301   a  is active for short intervals of less than a full day&#39;s use. In an embodiment, the heat sink  350   a  can advantageously provide improved heat transfers in about three (3) to about four (4) minute intervals, for example, although a heat sink  350   a  can be selected that performs effectively in shorter or longer intervals. 
     Moreover, the heat sink  350   a  can have different shapes and configurations for aesthetic as well as for functional purposes. In an embodiment, the heat sink is configured to maximize heat dissipation, for example, by maximizing surface area. In an embodiment, the heat sink  350   a  is molded into a generally curved surface and includes one or more fins, undulations, grooves, or channels. The example heat sink  350   a  shown includes fins  351   a  (see  FIG.  3 A ). 
     An alternative shape of a sensor  301   b  and heat sink  350   b  is shown in  FIG.  3 D . The sensor  301   b  can include some or all of the features of the sensor  301   a . For example, the sensor  301   b  includes an enclosure  302   b  formed by an emitter shell  304   b  and a detector shell  306   b , pivotably connected about a pivot  303   a . The emitter shell  304   b  can also include absorbing opaque material on one or more flaps  307   b , and the detector shell  306   a  can also include absorbing opaque material at various areas, such as lower area  308   b.    
     However, the shape of the sensor  301   b  is different in this embodiment. In particular, the heat sink  350   b  includes comb protrusions  351   b . The comb protrusions  351   b  are exposed to the air in a similar manner to the fins  351   a  of the heat sink  350   a , thereby facilitating efficient cooling of the sensor  301   b.    
       FIG.  3 E  illustrates a more detailed example of a detector shell  306   b  of the sensor  301   b . The features described with respect to the detector shell  306   b  can also be used with the detector shell  306   a  of the sensor  301   a.    
     As shown, the detector shell  306   b  includes detectors  316 . The detectors  316  can have a predetermined spacing  340  from each other, or a spatial relationship among one another that results in a spatial configuration. This spatial configuration can purposefully create a variation of path lengths among detectors  316  and the emitter discussed above. 
     In the depicted embodiment, the detector shell  316  can hold multiple (e.g., two, three, four, etc.) photodiode arrays that are arranged in a two-dimensional grid pattern. Multiple photodiode arrays can also be useful to detect light piping (e.g., light that bypasses measurement site  102 ). In the detector shell  316 , walls can be provided to separate the individual photodiode arrays to prevent or reduce mixing of light signals from distinct quadrants. In addition, the detector shell  316  can be covered by windows of transparent material, such as glass, plastic, or the like, to allow maximum or increased transmission of power light captured. In various embodiments, the transparent materials used can also be partially transparent or translucent or can otherwise pass some or all of the optical radiation passing through them. As noted, this window can include some shielding in the form of an embedded grid of wiring, or a conductive layer or coating. 
     As further illustrated by  FIG.  3 E , the detectors  316  can have a spatial configuration of a grid. However, the detectors  316  can be arranged in other configurations that vary the path length. For example, the detectors  316  can be arranged in a linear array, a logarithmic array, a two-dimensional array, a zig-zag pattern, or the like. Furthermore, any number of the detectors  316  can be employed in certain embodiments. 
       FIG.  3 F  illustrates another embodiment of a sensor  301   f . The sensor  301   f  can include some or all of the features of the sensor  301   a  of  FIG.  3 A  described above. For example, the sensor  301   f  includes an enclosure  302   f  formed by an upper section or emitter shell  304   f , which is pivotably connected with a lower section or detector shell  306   f  around a pivot point  303   f . The emitter shell  304   f  can also include absorbing opaque material on various areas, such as on one or more flaps  307   f , to reduce ambient light entering the sensor  301   f . The detector shell  306   f  can also include absorbing opaque material at various areas, such as a lower area  308   f . The sensor  301   f  also includes a heat sink  350   f , which includes fins  351   f.    
     In addition to these features, the sensor  301   f  includes a flex circuit cover  360 , which can be made of plastic or another suitable material. The flex circuit cover  360  can cover and thereby protect a flex circuit (not shown) that extends from the emitter shell  304   f  to the detector shell  306   f . An example of such a flex circuit is illustrated in U.S. Publication No. 2006/0211924, incorporated above (see  FIG.  46    and associated description, which is hereby specifically incorporated by reference). The flex circuit cover  360  is shown in more detail below in  FIG.  17   . 
     In addition, sensors  301   a - f  has extra length—extends to second joint on finger—Easier to place, harder to move due to cable, better for light piping. 
       FIGS.  4 A through  4 C  illustrate example arrangements of a protrusion  405 , which is an embodiment of the protrusion  305  described above. In an embodiment, the protrusion  405  can include a measurement site contact area  470 . The measurement site contact area  470  can include a surface that molds body tissue of a measurement site, such as a finger, into a flat or relatively flat surface. 
     The protrusion  405  can have dimensions that are suitable for a measurement site such as a patient&#39;s finger. As shown, the protrusion  405  can have a length  400 , a width  410 , and a height  430 . The length  400  can be from about 9 to about 11 millimeters, e.g., about 10 millimeters. The width  410  can be from about 7 to about 9 millimeters, e.g., about 8 millimeters. The height  430  can be from about 0.5 millimeters to about 3 millimeters, e.g., about 2 millimeters. In an embodiment, the dimensions  400 ,  410 , and  430  can be selected such that the measurement site contact area  470  includes an area of about 80 square millimeters, although larger and smaller areas can be used for different sized tissue for an adult, an adolescent, or infant, or for other considerations. 
     The measurement site contact area  470  can also include differently shaped surfaces that conform the measurement site into different shapes. For example, the measurement site contact area  470  can be generally curved and/or convex with respect to the measurement site. The measurement site contact area  470  can be other shapes that reduce or even minimize air between the protrusion  405  and/or the measurement site. Additionally, the surface pattern of the measurement site contact area  470  can vary from smooth to bumpy, e.g., to provide varying levels of grip. 
     In  FIGS.  4 A and  4 C , openings or windows  420 ,  421 ,  422 , and  423  can include a wide variety of shapes and sizes, including for example, generally square, circular, triangular, or combinations thereof. The windows  420 ,  421 ,  422 , and  423  can be of non-uniform shapes and sizes. As shown, the windows  420 ,  421 ,  422 , and  423  can be evenly spaced out in a grid like arrangement. Other arrangements or patterns of arranging the windows  420 ,  421 ,  422 , and  423  are possible. For example, the windows  420 ,  421 ,  422 , and  423  can be placed in a triangular, circular, or linear arrangement. In some embodiments, the windows  420 ,  421 ,  422 , and  423  can be placed at different heights with respect to the finger bed  310  of  FIG.  3   . The windows  420 ,  421 ,  422 , and  423  can also mimic or approximately mimic a configuration of, or even house, a plurality of detectors. 
       FIGS.  6 A through  6 D  illustrate another embodiment of a protrusion  605  that can be used as the tissue shaper  105  described above or in place of the protrusions  305 ,  405  described above. The depicted protrusion  605  is a partially cylindrical lens having a partial cylinder  608  and an extension  610 . The partial cylinder  608  can be a half cylinder in some embodiments; however, a smaller or greater portion than half of a cylinder can be used. Advantageously, in certain embodiments, the partially cylindrical protrusion  605  focuses light onto a smaller area, such that fewer detectors can be used to detect the light attenuated by a measurement site. 
       FIG.  6 A  illustrates a perspective view of the partially cylindrical protrusion  605 .  FIG.  6 B  illustrates a front elevation view of the partially cylindrical protrusion  605 .  FIG.  6 C  illustrates a side view of the partially cylindrical protrusion  605 .  FIG.  6 D  illustrates a top view of the partially cylindrical protrusion  605 . 
     Advantageously, in certain embodiments, placing the partially cylindrical protrusion  605  over the photodiodes in any of the sensors described above adds multiple benefits to any of the sensors described above. In one embodiment, the partially cylindrical protrusion  605  penetrates into the tissue and reduces the path length of the light traveling in the tissue, similar to the protrusions described above. 
     The partially cylindrical protrusion  605  can also collect light from a large surface and focus down the light to a smaller area. As a result, in certain embodiments, signal strength per area of the photodiode can be increased. The partially cylindrical protrusion  605  can therefore facilitate a lower cost sensor because, in certain embodiments, less photodiode area can be used to obtain the same signal strength. Less photodiode area can be realized by using smaller photodiodes or fewer photodiodes (see, e.g.,  FIG.  14   ). If fewer or smaller photodiodes are used, the partially cylindrical protrusion  605  can also facilitate an improved SNR of the sensor because fewer or smaller photodiodes can have less dark current. 
     The dimensions of the partially cylindrical protrusion  605  can vary based on, for instance, a number of photodiodes used with the sensor. Referring to  FIG.  6 C , the overall height of the partially cylindrical protrusion  605  (measurement “a”) in some implementations is about 1 to about 3 mm. A height in this range can allow the partially cylindrical protrusion  605  to penetrate into the pad of the finger or other tissue and reduce the distance that light travels through the tissue. Other heights, however, of the partially cylindrical protrusion  605  can also accomplish this objective. For example, the chosen height of the partially cylindrical protrusion  605  can be selected based on the size of the measurement site, whether the patient is an adult or child, and so on. In an embodiment, the height of the protrusion  605  is chosen to provide as much tissue thickness reduction as possible while reducing or preventing occlusion of blood vessels in the tissue. 
     Referring to  FIG.  6 D , the width of the partially cylindrical protrusion  605  (measurement “b”) can be about 3 to about 5 mm. In one embodiment, the width is about 4 mm. In one embodiment, a width in this range provides good penetration of the partially cylindrical protrusion  605  into the tissue to reduce the path length of the light. Other widths, however, of the partially cylindrical protrusion  605  can also accomplish this objective. For example, the width of the partially cylindrical protrusion  605  can vary based on the size of the measurement site, whether the patient is an adult or child, and so on. In addition, the length of the protrusion  605  could be about 10 mm, or about 8 mm to about 12 mm, or smaller than 8 mm or greater than 12 mm. 
     In certain embodiments, the focal length (f) for the partially cylindrical protrusion  605  can be expressed as: f=R/n−1, where R is the radius of curvature of the partial cylinder  608  and n is the index of refraction of the material used. In certain embodiments, the radius of curvature can be between about 1.5 mm and about 2 mm. In another embodiment, the partially cylindrical protrusion  605  can include a material, such as nBK7 glass, with an index of refraction of around 1.5 at 1300 nm, which can provide focal lengths of between about 3 mm and about 4 mm. 
     A partially cylindrical protrusion  605  having a material with a higher index of refraction such as nSF11 glass (e.g., n=1.75 at 1300 nm) can provide a shorter focal length and possibly a smaller photodiode chip, but can also cause higher reflections due to the index of refraction mismatch with air. Many types of glass or plastic can be used with index of refraction values ranging from, for example, about 1.4 to about 1.9. The index of refraction of the material of the protrusion  605  can be chosen to improve or optimize the light focusing properties of the protrusion  605 . A plastic partially cylindrical protrusion  605  could provide the cheapest option in high volumes but can also have some undesired light absorption peaks at wavelengths higher than 1500 nm. Other focal lengths and materials having different indices of refraction can be used for the partially cylindrical protrusion  605 . 
     Placing a photodiode at a given distance below the partially cylindrical protrusion  605  can facilitate capturing some or all of the light traveling perpendicular to the lens within the active area of the photodiode (see  FIG.  14   ). Different sizes of the partially cylindrical protrusion  605  can use different sizes of photodiodes. The extension  610  added onto the bottom of the partial cylinder  608  is used in certain embodiments to increase the height of the partially cylindrical protrusion  605 . In an embodiment, the added height is such that the photodiodes are at or are approximately at the focal length of the partially cylindrical protrusion  605 . In an embodiment, the added height provides for greater thinning of the measurement site. In an embodiment, the added height assists in deflecting light piped through the sensor. This is because light piped around the sensor passes through the side walls of the added height without being directed toward the detectors. The extension  610  can also further facilitate the protrusion  605  increasing or maximizing the amount of light that is provided to the detectors. In some embodiments, the extension  610  can be omitted. 
       FIG.  6 E  illustrates another view of the sensor  301   f  of  FIG.  3 F , which includes an embodiment of a partially cylindrical protrusion  605   b . Like the sensor  301 A shown in  FIGS.  3 B and  3 C , the sensor  301   f  includes a finger bed  310   f . The finger bed  310   f  includes a generally curved surface shaped generally to receive tissue, such as a human digit. The finger bed  310   f  also includes the ridges or channels  314  described above with respect to  FIGS.  3 B and  3 C . 
     The example of finger bed  310   f  shown also includes the protrusion  605   b , which includes the features of the protrusion  605  described above. In addition, the protrusion  605   b  also includes chamfered edges  607  on each end to provide a more comfortable surface for a finger to slide across (see also  FIG.  14 D ). In another embodiment, the protrusion  605   b  could instead include a single chamfered edge  607  proximal to the ridges  314 . In another embodiment, one or both of the chamfered edges  607  could be rounded. 
     The protrusion  605   b  also includes a measurement site contact area  670  that can contact body tissue of a measurement site. The protrusion  605   b  can be removed from or integrated with the finger bed  310   f . Interchangeable, differently shaped protrusions  605   b  can also be provided, which can correspond to different finger shapes, characteristics, opacity, sizes, or the like. 
       FIGS.  7 A and  7 B  illustrate block diagrams of sensors  701  that include example arrangements of conductive glass or conductive coated glass for shielding. Advantageously, in certain embodiments, the shielding can provide increased SNR. The features of the sensors  701  can be implemented with any of the sensors  101 ,  201 ,  301  described above. Although not shown, the partially cylindrical protrusion  605  of  FIG.  6    can also be used with the sensors  701  in certain embodiments. 
     For example, referring specifically to  FIG.  7 A , the sensor  701   a  includes an emitter housing  704   a  and a detector housing  706 . The emitter housing  704   a  includes LEDs  104 . The detector housing  706   a  includes a tissue bed  710   a  with an opening or window  703   a , the conductive glass  730   a , and one or more photodiodes for detectors  106  provided on a submount  707   a.    
     During operation, a finger  102  can be placed on the tissue bed  710   a  and optical radiation can be emitted from the LEDs  104 . Light can then be attenuated as it passes through or is reflected from the tissue of the finger  102 . The attenuated light can then pass through the opening  703   a  in the tissue bed  710   a . Based on the received light, the detectors  106  can provide a detector signal  107 , for example, to the front end interface  108  (see  FIG.  1   ). 
     In the depicted embodiment, the conductive glass  730  is provided in the opening  703 . The conductive glass  730  can thus not only permit light from the finger to pass to the detectors  106 , but it can also supplement the shielding of the detectors  106  from noise. The conductive glass  730  can include a stack or set of layers. In  FIG.  7 A , the conductive glass  730   a  is shown having a glass layer  731  proximate the finger  102  and a conductive layer  733  electrically coupled to the shielding  790   a.    
     In an embodiment, the conductive glass  730   a  can be coated with a conductive, transparent or partially transparent material, such as a thin film of indium tin oxide (ITO). To supplement electrical shielding effects of a shielding enclosure  790   a , the conductive glass  730   a  can be electrically coupled to the shielding enclosure  790   a . The conductive glass  730   a  can be electrically coupled to the shielding  704   a  based on direct contact or via other connection devices, such as a wire or another component. 
     The shielding enclosure  790   a  can be provided to encompass the detectors  106  to reduce or prevent noise. For example, the shielding enclosure  790   a  can be constructed from a conductive material, such as copper, in the form of a metal cage. The shielding or enclosure a can include an opaque material to not only reduce electrical noise, but also ambient optical noise. 
     In some embodiments, the shielding enclosure  790   a  can be constructed in a single manufactured component with or without the use of conductive glass. This form of construction may be useful in order to reduce costs of manufacture as well as assist in quality control of the components. Furthermore, the shielding enclosure  790   a  can also be used to house various other components, such as sigma delta components for various embodiments of front end interfaces  108 . 
     Referring to  FIG.  7 B , another block diagram of an example sensor  701   b  is shown. A tissue bed  710   b  of the sensor  701   b  includes a protrusion  705   b , which is in the form of a convex bump. The protrusion  705   b  can include all of the features of the protrusions or tissue shaping materials described above. For example, the protrusion  705   b  includes a contact area  370  that comes in contact with the finger  102  and which can include one or more openings  703   b . One or more components of conductive glass  730   b  can be provided in the openings  703 . For example, in an embodiment, each of the openings  703  can include a separate window of the conductive glass  730   b . In an embodiment, a single piece of the conductive glass  730   b  can used for some or all of the openings  703   b . The conductive glass  730   b  is smaller than the conductive glass  730   a  in this particular embodiment. 
     A shielding enclosure  790   b  is also provided, which can have all the features of the shielding enclosure  790   a . The shielding enclosure  790   b  is smaller than the shielding enclosure  790   a ; however, a variety of sizes can be selected for the shielding enclosures  790 . 
     In some embodiments, the shielding enclosure  790   b  can be constructed in a single manufactured component with or without the use of conductive glass. This form of construction may be useful in order to reduce costs of manufacture as well as assist in quality control of the components. Furthermore, the shielding enclosure  790   b  can also be used to house various other components, such as sigma delta components for various embodiments of front end interfaces  108 . 
       FIGS.  8 A through  8 D  illustrate a perspective view, side views, and a bottom elevation view of the conductive glass described above with respect to the sensors  701   a ,  701   b . As shown in the perspective view of  FIG.  8 A  and side view of  FIG.  8 B , the conductive glass  730  includes the electrically conductive material  733  described above as a coating on the glass layer  731  described above to form a stack. In an embodiment where the electrically conductive material  733  includes indium tin oxide, surface resistivity of the electrically conductive material  733  can range approximately from 30 ohms per square inch to 500 ohms per square inch, or approximately 30, 200, or 500 ohms per square inch. As would be understood by a person of skill in the art from the present disclosure, other resistivities can also be used which are less than 30 ohms or more than 500 ohms. Other transparent, electrically conductive materials can be used as the material  733 . 
     Although the conductive material  733  is shown spread over the surface of the glass layer  731 , the conductive material  733  can be patterned or provided on selected portions of the glass layer  731 . Furthermore, the conductive material  733  can have uniform or varying thickness depending on a desired transmission of light, a desired shielding effect, and other considerations. 
     In  FIG.  8 C , a side view of a conductive glass  830   a  is shown to illustrate an embodiment where the electrically conductive material  733  is provided as an internal layer between two glass layers  731 ,  835 . Various combinations of integrating electrically conductive material  733  with glass are possible. For example, the electrically conductive material  733  can be a layer within a stack of layers. This stack of layers can include one or more layers of glass  731 ,  835 , as well as one or more layers of conductive material  733 . The stack can include other layers of materials to achieve desired characteristics. 
     In  FIG.  8 D , a bottom perspective view is shown to illustrate an embodiment where a conductive glass  830   b  can include conductive material  837  that occupies or covers a portion of a glass layer  839 . This embodiment can be useful, for example, to create individual, shielded windows for detectors  106 , such as those shown in  FIG.  3 C . The conductive material  837  can be patterned to include an area  838  to allow light to pass to detectors  106  and one or more strips  841  to couple to the shielding  704  of  FIG.  7   . 
     Other configurations and patterns for the conductive material can be used in certain embodiments, such as, for example, a conductive coating lining periphery edges, a conductive coating outlaid in a pattern including a grid or other pattern, a speckled conductive coating, coating outlaid in lines in either direction or diagonally, varied thicknesses from the center out or from the periphery in, or other suitable patterns or coatings that balance the shielding properties with transparency considerations. 
       FIG.  9    depicts an example graph  900  that illustrates comparative results obtained by an example sensor having components similar to those disclosed above with respect to  FIGS.  7  and  8   . The graph  900  depicts the results of the percentage of transmission of varying wavelengths of light for different types of windows used in the sensors described above. 
     A line  915  on the graph  900  illustrates example light transmission of a window made from plain glass. As shown, the light transmission percentage of varying wavelengths of light is approximately 90% for a window made from plain glass. A line  920  on the graph  900  demonstrates an example light transmission percentage for an embodiment in which a window is made from glass having an ITO coating with a surface resistivity of 500 ohms per square inch. A line  925  on the graph  900  shows an example light transmission for an embodiment in which a window is made from glass that includes a coating of ITO oxide with a surface resistivity of 200 ohms per square inch. A line  930  on the graph  900  shows an example light transmission for an embodiment in which a window is made from glass that includes a coating of ITO oxide with a surface resistivity of 30 ohms per square inch. 
     The light transmission percentage for a window with currently available embedded wiring can have a light transmission percentage of approximately 70%. This lower percentage of light transmission can be due to the opacity of the wiring employed in a currently available window with wiring. Accordingly, certain embodiments of glass coatings described herein can employ, for example, ITO coatings with different surface resistivity depending on the desired light transmission, wavelengths of light used for measurement, desired shielding effect, and other criteria. 
       FIGS.  10 A through  10 B  illustrate comparative noise floors of example implementations of the sensors described above. Noise can include optical noise from ambient light and electro-magnetic noise, for example, from surrounding electrical equipment. In  FIG.  10 A , a graph  1000  depicts possible noise floors for different frequencies of noise for an embodiment in which one of the sensors described above included separate windows for four (4) detectors  106 . One or more of the windows included an embedded grid of wiring as a noise shield. Symbols  1030 - 1033  illustrate the noise floor performance for this embodiment. As can be seen, the noise floor performance can vary for each of the openings and based on the frequency of the noise. 
     In  FIG.  10 B , a graph  1050  depicts a noise floor for frequencies of noise  1070  for an embodiment in which the sensor included separate openings for four (4) detectors  106  and one or more windows that include an ITO coating. In this embodiment, a surface resistivity of the ITO used was about 500 ohms per square inch. Symbols  1080 - 1083  illustrate the noise floor performance for this embodiment. As can be seen, the noise floor performance for this embodiment can vary less for each of the openings and provide lower noise floors in comparison to the embodiment of  FIG.  10 A . 
       FIG.  11 A  illustrates an example structure for configuring the set of optical sources of the emitters described above. As shown, an emitter  104  can include a driver  1105 , a thermistor  1120 , a set of top-emitting LEDs  1102  for emitting red and/or infrared light, a set of side-emitting LEDs  1104  for emitting near infrared light, and a submount  1106 . 
     The thermistor  1120  can be provided to compensate for temperature variations. For example, the thermistor  1120  can be provided to allow for wavelength centroid and power drift of LEDs  1102  and  1104  due to heating. In addition, other thermistors can be employed, for example, to measure a temperature of a measurement site. The temperature can be displayed on a display device and used by a caregiver. Such a temperature can also be helpful in correcting for wavelength drift due to changes in water absorption, which can be temperature dependent, thereby providing more accurate data useful in detecting blood analytes like glucose. In addition, using a thermistor or other type of temperature sensitive device may be useful for detecting extreme temperatures at the measurement site that are too hot or too cold. The presence of low perfusion may also be detected, for example, when the finger of a patient has become too cold. Moreover, shifts in temperature at the measurement site can alter the absorption spectrum of water and other tissue in the measurement cite. A thermistor&#39;s temperature reading can be used to adjust for the variations in absorption spectrum changes in the measurement site. 
     The driver  1105  can provide pulses of current to the emitter  1104 . In an embodiment, the driver  1105  drives the emitter  1104  in a progressive fashion, for example, in an alternating manner based on a control signal from, for example, a processor (e.g., the processor  110 ). For example, the driver  1105  can drive the emitter  1104  with a series of pulses to about 1 milliwatt (mW) for visible light to light at about 1300 nm and from about 40 mW to about 100 mW for light at about 1600 nm to about 1700 nm. However, a wide number of driving powers and driving methodologies can be used. The driver  1105  can be synchronized with other parts of the sensor and can minimize or reduce any jitter in the timing of pulses of optical radiation emitted from the emitter  1104 . In some embodiments, the driver  1105  is capable of driving the emitter  1104  to emit an optical radiation in a pattern that varies by less than about 10 parts-per-million; however other amounts of variation can be used. 
     The submount  1106  provides a support structure in certain embodiments for aligning the top-emitting LEDs  1102  and the side-emitting LEDs  1104  so that their optical radiation is transmitted generally towards the measurement site. In some embodiments, the submount  1106  is also constructed of aluminum nitride (AlN) or beryllium oxide (BEO) for heat dissipation, although other materials or combinations of materials suitable for the submount  1106  can be used. 
       FIG.  11 B  illustrates a configuration of emitting optical radiation into a measurement site for measuring a blood constituent or analyte like glucose. In some embodiments, emitter  104  may be driven in a progressive fashion to minimize noise and increase SNR of sensor  101 . For example, emitter  104  may be driven based on a progression of power/current delivered to LEDs  1102  and  1104 . 
     In some embodiments, emitter  104  may be configured to emit pulses centered about 905 nm, about 1050 nm, about 1200 nm, about 1300 nm, about 1330 nm, about 1610 nm, about 1640 nm, and about 1665 nm. In another embodiment, the emitter  104  may emit optical radiation ranging from about 860 nm to about 950 nm, about 950 nm to about 1100 nm, about 1100 nm to about 1270 nm, about 1250 nm to about 1350 nm, about 1300 nm to about 1360 nm, and about 1590 nm to about 1700 nm. Of course, emitter  104  may be configured to transmit any of a variety of wavelengths of visible, or near-infrared optical radiation. 
     For purposes of illustration,  FIG.  11 B  shows a sequence of pulses of light at wavelengths of around 905 nm, around 1200 nm, around 1300 nm, and around 1330 nm from top emitting LEDs  1102 .  FIG.  11 B  also shows that emitter  104  may then emit pulses centered at around 1630 nm, around 1660 nm, and around 1615 nm from side emitting LEDs  1104 . Emitter  104  may be progressively driven at higher power/current. This progression may allow driver circuit  105  to stabilize in its operations, and thus, provide a more stable current/power to LEDs  1102  and  1104 . 
     For example, as shown in  FIG.  11 B , the sequence of optical radiation pulses are shown having a logarithmic-like progression in power/current. In some embodiments, the timing of these pulses is based on a cycle of about 400 slots running at 48 kHz (e.g. each time slot may be approximately 0.02 ms or 20 microseconds). An artisan will recognize that term “slots” includes its ordinary meaning, which includes a time period that may also be expressed in terms of a frequency. In the example shown, pulses from top emitting LEDs  1102  may have a pulse width of about 40 time slots (e.g., about 0.8 ms) and an off period of about 4 time slots in between. In addition, pulses from side emitting LEDs  1104  (e.g., or a laser diode) may have a pulse width of about 60 time slots (e.g., about 1.25 ms) and a similar off period of about 4 time slots. A pause of about 70 time slots (e.g. 1.5 ms) may also be provided in order to allow driver circuit  1105  to stabilize after operating at higher current/power. 
     As shown in  FIG.  11 B , top emitting LEDs  1102  may be initially driven with a power to approximately 1 mW at a current of about 20-100 mA. Power in these LEDs may also be modulated by using a filter or covering of black dye to reduce power output of LEDs. In this example, top emitting LEDs  1102  may be driven at approximately 0.02 to 0.08 mW. The sequence of the wavelengths may be based on the current requirements of top emitting LEDs  502  for that particular wavelength. Of course, in other embodiments, different wavelengths and sequences of wavelengths may be output from emitter  104 . 
     Subsequently, side emitting LEDs  1104  may be driven at higher powers, such as about 40-100 mW and higher currents of about 600-800 mA. This higher power may be employed in order to compensate for the higher opacity of tissue and water in measurement site  102  to these wavelengths. For example, as shown, pulses at about 1630 nm, about 1660 nm, and about 1615 nm may be output with progressively higher power, such as at about 40 mW, about 50 mW, and about 60 mW, respectively. In this embodiment, the order of wavelengths may be based on the optical characteristics of that wavelength in tissue as well as the current needed to drive side emitting LEDs  1104 . For example, in this embodiment, the optical pulse at about 1615 nm is driven at the highest power due to its sensitivity in detecting analytes like glucose and the ability of light at this wavelength to penetrate tissue. Of course, different wavelengths and sequences of wavelengths may be output from emitter  104 . 
     As noted, this progression may be useful in some embodiments because it allows the circuitry of driver circuit  1105  to stabilize its power delivery to LEDs  1102  and  1104 . Driver circuit  1105  may be allowed to stabilize based on the duty cycle of the pulses or, for example, by configuring a variable waiting period to allow for stabilization of driver circuit  1105 . Of course, other variations in power/current and wavelength may also be employed in the present disclosure. 
     Modulation in the duty cycle of the individual pulses may also be useful because duty cycle can affect the signal noise ratio of the system  100 . That is, as the duty cycle is increased so may the signal to noise ratio. 
     Furthermore, as noted above, driver circuit  1105  may monitor temperatures of the LEDs  1102  and  1104  using the thermistor  1120  and adjust the output of LEDs  1102  and  1104  accordingly. Such a temperature may be to help sensor  101  correct for wavelength drift due to changes in water absorption, which can be temperature dependent. 
       FIG.  11 C  illustrates another exemplary emitter that may be employed in the sensor according to an embodiment of the disclosure. As shown, the emitter  104  can include components mounted on a substrate  1108  and on submount  1106 . In particular, top-emitting LEDs  1102  for emitting red and/or infrared light may be mounted on substrate  1108 . Side emitting LEDS  1104  may be mounted on submount  1106 . As noted, side-emitting LEDs  1104  may be included in emitter  104  for emitting near infrared light. 
     As also shown, the sensor of  FIG.  11 C  may include a thermistor  1120 . As noted, the thermistor  1120  can be provided to compensate for temperature variations. The thermistor  1120  can be provided to allow for wavelength centroid and power drift of LEDs  1102  and  1104  due to heating. In addition, other thermistors (not shown) can be employed, for example, to measure a temperature of a measurement site. Such a temperature can be helpful in correcting for wavelength drift due to changes in water absorption, which can be temperature dependent, thereby providing more accurate data useful in detecting blood analytes like glucose. 
     In some embodiments, the emitter  104  may be implemented without the use of side emitting LEDs. For example, certain blood constituents, such as total hemoglobin, can be measured by embodiments of the disclosure without the use of side emitting LEDs.  FIG.  11 D  illustrates another exemplary emitter that may be employed in the sensor according to an embodiment of the disclosure. In particular, an emitter  104  that is configured for a blood constituent, such as total hemoglobin, is shown. The emitter  104  can include components mounted on a substrate  1108 . In particular, top-emitting LEDs  1102  for emitting red and/or infrared light may be mounted on substrate  1108 . 
     As also shown, the emitter of  FIG.  11 D  may include a thermistor  1120 . The thermistor  1120  can be provided to compensate for temperature variations. The thermistor  1120  can be provided to allow for wavelength centroid and power drift of LEDs  1102  due to heating. 
       FIG.  12 A  illustrates a detector submount  1200  having photodiode detectors that are arranged in a grid pattern on the detector submount  1200  to capture light at different quadrants from a measurement site. One detector submount  1200  can be placed under each window of the sensors described above, or multiple windows can be placed over a single detector submount  1200 . The detector submount  1200  can also be used with the partially cylindrical protrusion  605  described above with respect to  FIG.  6   . 
     The detectors include photodiode detectors 1-4 that are arranged in a grid pattern on the submount  1200  to capture light at different quadrants from the measurement site. As noted, other patterns of photodiodes, such as a linear row, or logarithmic row, can also be employed in certain embodiments. 
     As shown, the detectors 1-4 may have a predetermined spacing from each other, or spatial relationship among one another that result in a spatial configuration. This spatial configuration can be configured to purposefully create a variation of path lengths among detectors  106  and the point light source discussed above. 
     Detectors may hold multiple (e.g., two, three, four, etc.) photodiode arrays that are arranged in a two-dimensional grid pattern. Multiple photodiode arrays may also be useful to detect light piping (i.e., light that bypasses measurement site  102 ). As shown, walls may separate the individual photodiode arrays to prevent mixing of light signals from distinct quadrants. In addition, as noted, the detectors may be covered by windows of transparent material, such as glass, plastic, etc., to allow maximum transmission of power light captured. As noted, this window may comprise some shielding in the form of an embedded grid of wiring, or a conductive layer or coating. 
       FIGS.  12 B through  12 D  illustrate a simplified view of exemplary arrangements and spatial configurations of photodiodes for detectors  106 . As shown, detectors  106  may comprise photodiode detectors 1-4 that are arranged in a grid pattern on detector submount  1200  to capture light at different quadrants from measurement site  102 . 
     As noted, other patterns of photodiodes may also be employed in embodiments of the present disclosure, including, for example, stacked or other configurations recognizable to an artisan from the disclosure herein. For example, detectors  106  may be arranged in a linear array, a logarithmic array, a two-dimensional array, and the like. Furthermore, an artisan will recognize from the disclosure herein that any number of detectors  106  may be employed by embodiments of the present disclosure. 
     For example, as shown in  FIG.  12 B , detectors  106  may comprise photodiode detectors 1-4 that are arranged in a substantially linear configuration on submount  1200 . In this embodiment shown, photodiode detectors 1-4 are substantially equally spaced apart (e.g., where the distance D is substantially the same between detectors 1-4). 
     In  FIG.  12 C , photodiode detectors 1-4 may be arranged in a substantially linear configuration on submount  1200 , but may employ a substantially progressive, substantially logarithmic, or substantially semi-logarithmic spacing (e.g., where distances D1&gt;D2&gt;D3). This arrangement or pattern may be useful for use on a patient&#39;s finger and where the thickness of the finger gradually increases. 
     In  FIG.  12 D , a different substantially grid pattern on submount  1200  of photodiode detectors 1-4 is shown. As noted, other patterns of detectors may also be employed in embodiments of the present invention. 
       FIGS.  12 E through  12 H  illustrate several embodiments of photodiodes that may be used in detectors  106 . As shown in these figures, a photodiode  1202  of detector  106  may comprise a plurality of active areas  1204 . These active areas  204  may be coupled together via a common cathode  1206  or anode  1208  in order to provide a larger effective detection area. 
     In particular, as shown in  FIG.  12 E , photodiode  1202  may comprise two (2) active areas  1204   a  and  1204   b . In  FIG.  12 F , photodiode  1202  may comprise four (4) active areas  1204   c - f . In  FIG.  12 G , photodiode  1202  may comprise three (3) active areas  1204   g - i . In  FIG.  12 H , photodiode  1202  may comprise nine (9) active areas  1204   j - r . The use of smaller active areas may be useful because smaller active areas can be easier to fabricate and can be fabricated with higher purity. However, one skilled in the art will recognize that various sizes of active areas may be employed in the photodiode  1202 . 
       FIG.  13    illustrates an example multi-stream process  1300 . The multi-stream process  1300  can be implemented by the data collection system  100  and/or by any of the sensors described above. As shown, a control signal from a signal processor  1310  controls a driver  1305 . In response, an emitter  1304  generates a pulse sequence  1303  from its emitter (e.g., its LEDs) into a measurement site or sites  1302 . As described above, in some embodiments, the pulse sequence  1303  is controlled to have a variation of about 10 parts per million or less. Of course, depending on the analyte desired, the tolerated variation in the pulse sequence  1303  can be greater (or smaller). 
     In response to the pulse sequence  1300 , detectors 1 to n (n being an integer) in a detector  1306  capture optical radiation from the measurement site  1302  and provide respective streams of output signals. Each signal from one of detectors 1-n can be considered a stream having respective time slots corresponding to the optical pulses from emitter sets 1-n in the emitter  1304 . Although n emitters and n detectors are shown, the number of emitters and detectors need not be the same in certain implementations. 
     A front end interface  1308  can accept these multiple streams from detectors 1-n and deliver one or more signals or composite signal(s) back to the signal processor  1310 . A stream from the detectors 1-n can thus include measured light intensities corresponding to the light pulses emitted from the emitter  1304 . 
     The signal processor  1310  can then perform various calculations to measure the amount of glucose and other analytes based on these multiple streams of signals. In order to help explain how the signal processor  1310  can measure analytes like glucose, a primer on the spectroscopy employed in these embodiments will now be provided. 
     Spectroscopy is premised upon the Beer-Lambert law. According to this law, the properties of a material, e.g., glucose present in a measurement site, can be deterministically calculated from the absorption of light traveling through the material. Specifically, there is a logarithmic relation between the transmission of light through a material and the concentration of a substance and also between the transmission and the length of the path traveled by the light. As noted, this relation is known as the Beer-Lambert law. 
     The Beer-Lambert law is usually written as:
 
Absorbance  A=m*b*c , where:
 
     m is the wavelength-dependent molar absorptivity coefficient (usually expressed in units of M −1  cm −1 ); 
     b is the mean path length; and 
     c is the analyte concentration (e.g., the desired parameter). 
     In spectroscopy, instruments attempt to obtain the analyte concentration (c) by relating absorbance (A) to transmittance (T). Transmittance is a proportional value defined as:
 
 T=I/I   o , where:
 
     I is the light intensity measured by the instrument from the measurement site; and 
     I o  is the initial light intensity from the emitter. 
     Absorbance (A) can be equated to the transmittance (T) by the equation:
 
 A =−log  T  
 
     Therefore, substituting equations from above:
 
 A =−log( I/I   o )
 
     In view of this relationship, spectroscopy thus relies on a proportional-based calculation of −log(I/I o ) and solving for analyte concentration (c). 
     Typically, in order to simplify the calculations, spectroscopy will use detectors that are at the same location in order to keep the path length (b) a fixed, known constant. In addition, spectroscopy will employ various mechanisms to definitively know the transmission power (I o ), such as a photodiode located at the light source. This architecture can be viewed as a single channel or single stream sensor, because the detectors are at a single location. 
     However, this scheme can encounter several difficulties in measuring analytes, such as glucose. This can be due to the high overlap of absorption of light by water at the wavelengths relevant to glucose as well as other factors, such as high self-noise of the components. 
     Embodiments of the present disclosure can employ a different approach that in part allows for the measurement of analytes like glucose. Some embodiments can employ a bulk, non-pulsatile measurement in order to confirm or validate a pulsatile measurement. In addition, both the non-pulsatile and pulsatile measurements can employ, among other things, the multi-stream operation described above in order to attain sufficient SNR. In particular, a single light source having multiple emitters can be used to transmit light to multiple detectors having a spatial configuration. 
     A single light source having multiple emitters can allow for a range of wavelengths of light to be used. For example, visible, infrared, and near infrared wavelengths can be employed. Varying powers of light intensity for different wavelengths can also be employed. 
     Secondly, the use of multiple-detectors in a spatial configuration allow for a bulk measurement to confirm or validate that the sensor is positioned correctly. This is because the multiple locations of the spatial configuration can provide, for example, topology information that indicates where the sensor has been positioned. Currently available sensors do not provide such information. For example, if the bulk measurement is within a predetermined range of values, then this can indicate that the sensor is positioned correctly in order to perform pulsatile measurements for analytes like glucose. If the bulk measurement is outside of a certain range or is an unexpected value, then this can indicate that the sensor should be adjusted, or that the pulsatile measurements can be processed differently to compensate, such as using a different calibration curve or adjusting a calibration curve. This feature and others allow the embodiments to achieve noise cancellation and noise reduction, which can be several times greater in magnitude that what is achievable by currently available technology. 
     In order to help illustrate aspects of the multi-stream measurement approach, the following example derivation is provided. Transmittance (T) can be expressed as:
 
 T=e   −m*b*c  
 
     In terms of light intensity, this equation can also be rewritten as:
 
 I/I   o   =e   −m*b*c  
 
     Or, at a detector, the measured light (I) can be expressed as:
 
 I=I   o   *e   −m*b*c  
 
     As noted, in the present disclosure, multiple detectors (1 to n) can be employed, which results in I 1  . . . I n  streams of measurements. Assuming each of these detectors have their own path lengths, b 1  . . . b n , from the light source, the measured light intensities can be expressed as:
 
 I   n   =I   o   *e   −m*b     n     *c  
 
     The measured light intensities at any two different detectors can be referenced to each other. For example:
 
 I   1   /I   n =( I   o   *e   −mb     1     c )/( I   o   *e   −mb     n     c )
 
     As can be seen, the terms, I o , cancel out and, based on exponent algebra, the equation can be rewritten as:
 
 I   1   /I   n   =e   −m(b     1     −b     n     )c  
 
     From this equation, the analyte concentration (c) can now be derived from bulk signals I 1  . . . I n  and knowing the respective mean path lengths b 1  and b n . This scheme also allows for the cancelling out of I o , and thus, noise generated by the emitter  1304  can be cancelled out or reduced. In addition, since the scheme employs a mean path length difference, any changes in mean path length and topological variations from patient to patient are easily accounted. Furthermore, this bulk-measurement scheme can be extended across multiple wavelengths. This flexibility and other features allow embodiments of the present disclosure to measure blood analytes like glucose. 
     For example, as noted, the non-pulsatile, bulk measurements can be combined with pulsatile measurements to more accurately measure analytes like glucose. In particular, the non-pulsatile, bulk measurement can be used to confirm or validate the amount of glucose, protein, etc. in the pulsatile measurements taken at the tissue at the measurement site(s)  1302 . The pulsatile measurements can be used to measure the amount of glucose, hemoglobin, or the like that is present in the blood. Accordingly, these different measurements can be combined to thus determine analytes like blood glucose. 
       FIG.  14 A  illustrates an embodiment of a detector submount  1400   a  positioned beneath the partially cylindrical protrusion  605  of  FIG.  6    (or alternatively, the protrusion  605   b ). The detector submount  1400   a  includes two rows  1408   a  of detectors  1410   a . The partially cylindrical protrusion  605  can facilitate reducing the number and/or size of detectors used in a sensor because the protrusion  605  can act as a lens that focuses light onto a smaller area. 
     To illustrate, in some sensors that do not include the partially cylindrical protrusion  605 , sixteen detectors can be used, including four rows of four detectors each. Multiple rows of detectors can be used to measure certain analytes, such as glucose or total hemoglobin, among others. Multiple rows of detectors can also be used to detect light piping (e.g., light that bypasses the measurement site). However, using more detectors in a sensor can add cost, complexity, and noise to the sensor. 
     Applying the partially cylindrical protrusion  605  to such a sensor, however, could reduce the number of detectors or rows of detectors used while still receiving the substantially same amount of light, due to the focusing properties of the protrusion  605  (see  FIG.  14 B ). This is the example situation illustrated in  FIG.  14   —two rows  1408   a  of detectors  1410   a  are used instead of four. Advantageously, in certain embodiments, the resulting sensor can be more cost effective, have less complexity, and have an improved SNR, due to fewer and/or smaller photodiodes. 
     In other embodiments, using the partially cylindrical protrusion  605  can allow the number of detector rows to be reduced to one or three rows of four detectors. The number of detectors in each row can also be reduced. Alternatively, the number of rows might not be reduced but the size of the detectors can be reduced. Many other configurations of detector rows and sizes can also be provided. 
       FIG.  14 B  depicts a front elevation view of the partially cylindrical protrusion  605  (or alternatively, the protrusion  605   b ) that illustrates how light from emitters (not shown) can be focused by the protrusion  605  onto detectors. The protrusion  605  is placed above a detector submount  1400   b  having one or more detectors  1410   b  disposed thereon. The submount  1400   b  can include any number of rows of detectors  1410 , although one row is shown. 
     Light, represented by rays  1420 , is emitted from the emitters onto the protrusion  605 . These light rays  1420  can be attenuated by body tissue (not shown). When the light rays  1420  enter the protrusion  605 , the protrusion  605  acts as a lens to refract the rays into rays  1422 . This refraction is caused in certain embodiments by the partially cylindrical shape of the protrusion  605 . The refraction causes the rays  1422  to be focused or substantially focused on the one or more detectors  1410   b . Since the light is focused on a smaller area, a sensor including the protrusion  605  can include fewer detectors to capture the same amount of light compared with other sensors. 
       FIG.  14 C  illustrates another embodiment of a detector submount  1400   c , which can be disposed under the protrusion  605   b  (or alternatively, the protrusion  605 ). The detector submount  1400   c  includes a single row  1408   c  of detectors  1410   c . The detectors are electrically connected to conductors  1412   c , which can be gold, silver, copper, or any other suitable conductive material. 
     The detector submount  1400   c  is shown positioned under the protrusion  605   b  in a detector subassembly  1450  illustrated in  FIG.  14 D . A top-down view of the detector subassembly  1450  is also shown in  FIG.  14 E . In the detector subassembly  1450 , a cylindrical housing  1430  is disposed on the submount  1400   c . The cylindrical housing  1430  includes a transparent cover  1432 , upon which the protrusion  605   b  is disposed. Thus, as shown in  FIG.  14 D , a gap  1434  exists between the detectors  1410   c  and the protrusion  605   b . The height of this gap  1434  can be chosen to increase or maximize the amount of light that impinges on the detectors  1410   c.    
     The cylindrical housing  1430  can be made of metal, plastic, or another suitable material. The transparent cover  1432  can be fabricated from glass or plastic, among other materials. The cylindrical housing  1430  can be attached to the submount  1400   c  at the same time or substantially the same time as the detectors  1410   c  to reduce manufacturing costs. A shape other than a cylinder can be selected for the housing  1430  in various embodiments. 
     In certain embodiments, the cylindrical housing  1430  (and transparent cover  1432 ) forms an airtight or substantially airtight or hermetic seal with the submount  1400   c . As a result, the cylindrical housing  1430  can protect the detectors  1410   c  and conductors  1412   c  from fluids and vapors that can cause corrosion. Advantageously, in certain embodiments, the cylindrical housing  1430  can protect the detectors  1410   c  and conductors  1412   c  more effectively than currently-available resin epoxies, which are sometimes applied to solder joints between conductors and detectors. 
     In embodiments where the cylindrical housing  1430  is at least partially made of metal, the cylindrical housing  1430  can provide noise shielding for the detectors  1410   c . For example, the cylindrical housing  1430  can be soldered to a ground connection or ground plane on the submount  1400   c , which allows the cylindrical housing  1430  to reduce noise. In another embodiment, the transparent cover  1432  can include a conductive material or conductive layer, such as conductive glass or plastic. The transparent cover  1432  can include any of the features of the noise shields  790  described above. 
     The protrusion  605   b  includes the chamfered edges  607  described above with respect to  FIG.  6 E . These chamfered edges  607  can allow a patient to more comfortably slide a finger over the protrusion  605   b  when inserting the finger into the sensor  301   f.    
       FIG.  14 F  illustrates a portion of the detector shell  306   f , which includes the detectors  1410   c  on the substrate  1400   c . The substrate  1400   c  is enclosed by a shielding enclosure  1490 , which can include the features of the shielding enclosures  790   a ,  790   b  described above (see also  FIG.  17   ). The shielding enclosure  1490  can be made of metal. The shielding enclosure  1490  includes a window  1492   a  above the detectors  1410   c , which allows light to be transmitted onto the detectors  1410   c.    
     A noise shield  1403  is disposed above the shielding enclosure  1490 . The noise shield  1403 , in the depicted embodiment, includes a window  1492   a  corresponding to the window  1492   a . Each of the windows  1492   a ,  1492   b  can include glass, plastic, or can be an opening without glass or plastic. In some embodiments, the windows  1492   a ,  1492   b  may be selected to have different sizes or shapes from each other. 
     The noise shield  1403  can include any of the features of the conductive glass described above. In the depicted embodiment, the noise shield  1403  extends about three-quarters of the length of the detector shell  306   f . In other embodiments, the noise shield  1403  could be smaller or larger. The noise shield  1403  could, for instance, merely cover the detectors  1410   c , the submount  1400   c , or a portion thereof. The noise shield  1403  also includes a stop  1413  for positioning a measurement site within the sensor  301   f . Advantageously, in certain embodiments, the noise shield  1403  can reduce noise caused by light piping. 
     A thermistor  1470  is also shown. The thermistor  1470  is attached to the submount  1400   c  and protrudes above the noise shield  1403 . As described above, the thermistor  1470  can be employed to measure a temperature of a measurement site. Such a temperature can be helpful in correcting for wavelength drift due to changes in water absorption, which can be temperature dependent, thereby providing more accurate data useful in detecting blood analytes like glucose. 
     In the depicted embodiment, the detectors  1410   c  are not enclosed in the cylindrical housing  1430 . In an alternative embodiment, the cylindrical housing  1430  encloses the detectors  1410   c  and is disposed under the noise shield  1403 . In another embodiment, the cylindrical housing  1430  encloses the detectors  1410   c  and the noise shield  1403  is not used. If both the cylindrical housing  1403  and the noise shield  1403  are used, either or both can have noise shielding features. 
       FIG.  14 G  illustrates the detector shell  306   f  of  FIG.  14 F , with the finger bed  310   f  disposed thereon.  FIG.  14 H  illustrates the detector shell  306   f  of  FIG.  14 G , with the protrusion  605   b  disposed in the finger bed  310   f.    
       FIG.  14 I  illustrates a cutaway view of the sensor  301   f . Not all features of the sensor  301   f  are shown, such as the protrusion  605   b . Features shown include the emitter and detector shells  304   f ,  306   f , the flaps  307   f , the heat sink  350   f  and fins  351   f , the finger bed  310   f , and the noise shield  1403 . 
     In addition to these features, emitters  1404  are depicted in the emitter shell  304   f . The emitters  1404  are disposed on a submount  1401 , which is connected to a circuit board  1419 . The emitters  1404  are also enclosed within a cylindrical housing  1480 . The cylindrical housing  1480  can include all of the features of the cylindrical housing  1430  described above. For example, the cylindrical housing  1480  can be made of metal, can be connected to a ground plane of the submount  1401  to provide noise shielding, and can include a transparent cover  1482 . 
     The cylindrical housing  1480  can also protect the emitters  1404  from fluids and vapors that can cause corrosion. Moreover, the cylindrical housing  1480  can provide a gap between the emitters  1404  and the measurement site (not shown), which can allow light from the emitters  1404  to even out or average out before reaching the measurement site. 
     The heat sink  350   f , in addition to including the fins  351   f , includes a protuberance  352   f  that extends down from the fins  351   f  and contacts the submount  1401 . The protuberance  352   f  can be connected to the submount  1401 , for example, with thermal paste or the like. The protuberance  352   f  can sink heat from the emitters  1404  and dissipate the heat via the fins  351   f.    
       FIGS.  15 A and  15 B  illustrate embodiments of sensor portions  1500 A,  15008  that include alternative heat sink features to those described above. These features can be incorporated into any of the sensors described above. For example, any of the sensors above can be modified to use the heat sink features described below instead of or in addition to the heat sink features of the sensors described above. 
     The sensor portions  1500 A,  1500 B shown include LED emitters  1504 ; however, for ease of illustration, the detectors have been omitted. The sensor portions  1500 A,  1500 B shown can be included, for example, in any of the emitter shells described above. 
     The LEDs  1504  of the sensor portions  1500 A,  1500 B are connected to a substrate or submount  1502 . The submount  1502  can be used in place of any of the submounts described above. The submount  1502  can be a non-electrically conducting material made of any of a variety of materials, such as ceramic, glass, or the like. A cable  1512  is attached to the submount  1502  and includes electrical wiring  1514 , such as twisted wires and the like, for communicating with the LEDs  1504 . The cable  1512  can correspond to the cables  212  described above. 
     Although not shown, the cable  1512  can also include electrical connections to a detector. Only a portion of the cable  1512  is shown for clarity. The depicted embodiment of the cable  1512  includes an outer jacket  1510  and a conductive shield  1506  disposed within the outer jacket  1510 . The conductive shield  1506  can be a ground shield or the like that is made of a metal such as braided copper or aluminum. The conductive shield  1506  or a portion of the conductive shield  1506  can be electrically connected to the submount  1502  and can reduce noise in the signal generated by the sensor  1500 A,  15008  by reducing RF coupling with the wires  1514 . In alternative embodiments, the cable  1512  does not have a conductive shield. For example, the cable  1512  could be a twisted pair cable or the like, with one wire of the twisted pair used as a heat sink. 
     Referring specifically to  FIG.  15 A , in certain embodiments, the conductive shield  1506  can act as a heat sink for the LEDs  1504  by absorbing thermal energy from the LEDs  1504  and/or the submount  1502 . An optional heat insulator  1520  in communication with the submount  1502  can also assist with directing heat toward the conductive shield  1506 . The heat insulator  1520  can be made of plastic or another suitable material. Advantageously, using the conductive shield  1506  in the cable  1512  as a heat sink can, in certain embodiments, reduce cost for the sensor. 
     Referring to  FIG.  15 B , the conductive shield  1506  can be attached to both the submount  1502  and to a heat sink layer  1530  sandwiched between the submount  1502  and the optional insulator  1520 . Together, the heat sink layer  1530  and the conductive shield  1506  in the cable  1512  can absorb at least part of the thermal energy from the LEDs and/or the submount  1502 . 
       FIGS.  15 C and  15 D  illustrate implementations of a sensor portion  1500 C that includes the heat sink features of the sensor portion  1500 A described above with respect to  FIG.  15 A . The sensor portion  1500 C includes the features of the sensor portion  1500 A, except that the optional insulator  1520  is not shown.  FIG.  15 D  is a side cutaway view of the sensor portion  1500 C that shows the emitters  1504 . 
     The cable  1512  includes the outer jacket  1510  and the conductive shield  1506 . The conductive shield  1506  is soldered to the submount  1502 , and the solder joint  1561  is shown. In some embodiments, a larger solder joint  1561  can assist with removing heat more rapidly from the emitters  1504 . Various connections  1563  between the submount  1502  and a circuit board  1519  are shown. In addition, a cylindrical housing  1580 , corresponding to the cylindrical housing  1480  of  FIG.  14 I , is shown protruding through the circuit board  1519 . The emitters  1504  are enclosed in the cylindrical housing  1580 . 
       FIGS.  15 E and  15 F  illustrate implementations of a sensor portion  1500 E that includes the heat sink features of the sensor portion  1500 B described above with respect to  FIG.  15 B . The sensor portion  1500 E includes the heat sink layer  1530 . The heat sink layer  1530  can be a metal plate, such as a copper plate or the like. The optional insulator  1520  is not shown.  FIG.  15 F  is a side cutaway view of the sensor portion  1500 E that shows the emitters  1504 . 
     In the depicted embodiment, the conductive shield  1506  of the cable  1512  is soldered to the heat sink layer  1530  instead of the submount  1502 . The solder joint  1565  is shown. In some embodiments, a larger solder joint  1565  can assist with removing heat more rapidly from the emitters  1504 . Various connections  1563  between the submount  1502  and a circuit board  1519  are shown. In addition, the cylindrical housing  1580  is shown protruding through the circuit board  1519 . The emitters  1504  are enclosed in the cylindrical housing  1580 . 
       FIGS.  15 G and  15 H  illustrate embodiments of connector features that can be used with any of the sensors described above with respect to  FIGS.  1  through  15 F . Referring to  FIG.  15 G , the circuit board  1519  includes a female connector  1575  that mates with a male connector  1577  connected to a daughter board  1587 . The daughter board  1587  includes connections to the electrical wiring  1514  of the cable  1512 . The connected boards  1519 ,  1587  are shown in  FIG.  15 H . Also shown is a hole  1573  that can receive the cylindrical housing  1580  described above. 
     Advantageously, in certain embodiments, using a daughter board  1587  to connect to the circuit board  1519  can enable connections to be made more easily to the circuit board  1519 . In addition, using separate boards can be easier to manufacture than a single circuit board  1519  with all connections soldered to the circuit board  1519 . 
       FIG.  15 I  illustrates an exemplary architecture for front-end interface  108  as a transimpedance-based front-end. As noted, front-end interfaces  108  provide an interface that adapts the output of detectors  106  into a form that can be handled by signal processor  110 . As shown in this figure, sensor  101  and front-end interfaces  108  may be integrated together as a single component, such as an integrated circuit. Of course, one skilled in the art will recognize that sensor  101  and front end interfaces  108  may comprise multiple components or circuits that are coupled together. 
     Front-end interfaces  108  may be implemented using transimpedance amplifiers that are coupled to analog to digital converters in a sigma delta converter. In some embodiments, a programmable gain amplifier (PGA) can be used in combination with the transimpedance-based front-ends. For example, the output of a transimpedance-based front-end may be output to a sigma-delta ADC that comprises a PGA. A PGA may be useful in order to provide another level of amplification and control of the stream of signals from detectors  106 . The PGA may be an integrated circuit or built from a set of micro-relays. Alternatively, the PGA and ADC components in converter  900  may be integrated with the transimpedance-based front-end in sensor  101 . 
     Due to the low-noise requirements for measuring blood analytes like glucose and the challenge of using multiple photodiodes in detector  106 , the applicants developed a noise model to assist in configuring front-end  108 . Conventionally, those skilled in the art have focused on optimizing the impedance of the transimpedance amplifiers to minimize noise. 
     However, the following noise model was discovered by the applicants:
 
Noise=√{square root over ( aR+bR   2 )}, where:
 
     aR is characteristic of the impedance of the transimpedance amplifier; and 
     bR 2  is characteristic of the impedance of the photodiodes in detector and the number of photodiodes in detector  106 . 
     The foregoing noise model was found to be helpful at least in part due to the high SNR required to measure analytes like glucose. However, the foregoing noise model was not previously recognized by artisans at least in part because, in conventional devices, the major contributor to noise was generally believed to originate from the emitter or the LEDs. Therefore, artisans have generally continued to focus on reducing noise at the emitter. 
     However, for analytes like glucose, the discovered noise model revealed that one of the major contributors to noise was generated by the photodiodes. In addition, the amount of noise varied based on the number of photodiodes coupled to a transimpedance amplifier. Accordingly, combinations of various photodiodes from different manufacturers, different impedance values with the transimpedance amplifiers, and different numbers of photodiodes were tested as possible embodiments. 
     In some embodiments, different combinations of transimpedance to photodiodes may be used. For example, detectors 1-4 (as shown, e.g., in  FIG.  12 A ) may each comprise four photodiodes. In some embodiments, each detector of four photodiodes may be coupled to one or more transimpedance amplifiers. The configuration of these amplifiers may be set according to the model shown in  FIG.  15 J . 
     Alternatively, each of the photodiodes may be coupled to its own respective transimpedance amplifier. For example, transimpedance amplifiers may be implemented as integrated circuits on the same circuit board as detectors 1-4. In this embodiment, the transimpedance amplifiers may be grouped into an averaging (or summing) circuit, which are known to those skilled in the art, in order to provide an output stream from the detector. The use of a summing amplifier to combine outputs from several transimpedance amplifiers into a single, analog signal may be helpful in improving the SNR relative to what is obtainable from a single transimpedance amplifier. The configuration of the transimpedance amplifiers in this setting may also be set according to the model shown in  FIG.  15 J . 
     As yet another alternative, as noted above with respect to  FIGS.  12 E through  12 H , the photodiodes in detectors  106  may comprise multiple active areas that are grouped together. In some embodiments, each of these active areas may be provided its own respective transimpedance. This form of pairing may allow a transimpedance amplifier to be better matched to the characteristics of its corresponding photodiode or active area of a photodiode. 
     As noted,  FIG.  15 J  illustrates an exemplary noise model that may be useful in configuring transimpedance amplifiers. As shown, for a given number of photodiodes and a desired SNR, an optimal impedance value for a transimpedance amplifier could be determined. 
     For example, an exemplary “4 PD per stream” sensor  1502  is shown where detector  106  comprises four photodiodes  1502 . The photodiodes  1502  are coupled to a single transimpedance amplifier  1504  to produce an output stream  1506 . In this example, the transimpedance amplifier comprises 10 MΩ resistors  1508  and  1510 . Thus, output stream  1506  is produced from the four photodiodes (PD)  1502 . As shown in the graph of  FIG.  15 J , the model indicates that resistance values of about 10 MΩ may provide an acceptable SNR for analytes like glucose. 
     However, as a comparison, an exemplary “1 PD per stream” sensor  1512  is also shown in  FIG.  15 J . In particular, sensor  1512  may comprise a plurality of detectors  106  that each comprises a single photodiode  1514 . In addition, as shown for this example configuration, each of photodiodes  1514  may be coupled to respective transimpedance amplifiers  1516 , e.g., 1 PD per stream. Transimpedance amplifiers are shown having 40 MΩ resistors  1518 . As also shown in the graph of  FIG.  15 J , the model illustrates that resistance values of 40 MΩ for resistors  1518  may serve as an alternative to the 4 photodiode per stream architecture of sensor  1502  described above and yet still provide an equivalent SNR. 
     Moreover, the discovered noise model also indicates that utilizing a 1 photodiode per stream architecture like that in sensor  1512  may provide enhanced performance because each of transimpedance amplifiers  1516  can be tuned or optimized to its respective photodiodes  1518 . In some embodiments, an averaging component  1520  may also be used to help cancel or reduce noise across photodiodes  1518 . 
     For purposes of illustration,  FIG.  15 K  shows different architectures (e.g., four PD per stream and one PD per stream) for various embodiments of a sensor and how components of the sensor may be laid out on a circuit board or substrate. For example, sensor  1522  may comprise a “4 PD per stream” architecture on a submount  700  in which each detector  106  comprises four (4) photodiodes  1524 . As shown for sensor  1522 , the output of each set of four photodiodes  1524  is then aggregated into a single transimpedance amplifier  1526  to produce a signal. 
     As another example, a sensor  1528  may comprise a “1 PD per stream” architecture on submount  700  in which each detector  106  comprises four (4) photodiodes  1530 . In sensor  1528 , each individual photodiode  1530  is coupled to a respective transimpedance amplifier  1532 . The output of the amplifiers  1532  may then be aggregated into averaging circuit  1520  to produce a signal. 
     As noted previously, one skilled in the art will recognize that the photodiodes and detectors may be arranged in different fashions to optimize the detected light. For example, sensor  1534  illustrates an exemplary “4 PD per stream” sensor in which the detectors  106  comprise photodiodes  1536  arranged in a linear fashion. Likewise, sensor  1538  illustrates an exemplary “1 PD per stream” sensor in which the detectors comprise photodiodes  1540  arranged in a linear fashion. 
     Alternatively, sensor  1542  illustrates an exemplary “4 PD per stream” sensor in which the detectors  106  comprise photodiodes  1544  arranged in a two-dimensional pattern, such as a zig-zag pattern. Sensor  1546  illustrates an exemplary “1 PD per stream” sensor in which the detectors comprise photodiodes  1548  also arranged in a zig-zag pattern. 
       FIG.  15 L  illustrates an exemplary architecture for a switched-capacitor-based front-end. As shown, front-end interfaces  108  may be implemented using switched capacitor circuits and any number of front-end interfaces  108  may be implemented. The output of these switched capacitor circuits may then be provided to a digital interface  1000  and signal processor  110 . Switched capacitor circuits may be useful in system  100  for their resistor free design and analog averaging properties. In particular, the switched capacitor circuitry provides for analog averaging of the signal that allows for a lower smaller sampling rate (e.g., 2 KHz sampling for analog versus 48 KHz sampling for digital designs) than similar digital designs. In some embodiments, the switched capacitor architecture in front end interfaces  108  may provide a similar or equivalent SNR to other front end designs, such as a sigma delta architecture. In addition, a switched capacitor design in front end interfaces  108  may require less computational power by signal processor  110  to perform the same amount of decimation to obtain the same SNR. 
       FIGS.  16 A and  16 B  illustrate embodiments of disposable optical sensors  1600 . In an embodiment, any of the features described above, such as protrusion, shielding, and/or heat sink features, can be incorporated into the disposable sensors  1600  shown. For instance, the sensors  1600  can be used as the sensors  101  in the system  100  described above with respect to  FIG.  1   . Moreover, any of the features described above, such as protrusion, shielding, and/or heat sink features, can be implemented in other disposable sensor designs that are not depicted herein. 
     The sensors  1600  include an adult/pediatric sensor  1610  for finger placement and a disposable infant/neonate sensor  1602  configured for toe, foot or hand placement. Each sensor  1600  has a tape end  1610  and an opposite connector end  1620  electrically and mechanically interconnected via a flexible coupling  1630 . The tape end  1610  attaches an emitter and detector to a tissue site. Although not shown, the tape end  1610  can also include any of the protrusion, shielding, and/or heat sink features described above. The emitter illuminates the tissue site and the detector generates a sensor signal responsive to the light after tissue absorption, such as absorption by pulsatile arterial blood flow within the tissue site. 
     The sensor signal is communicated via the flexible coupling  1630  to the connector end  1620 . The connector end  1620  can mate with a cable (not shown) that communicates the sensor signal to a monitor (not shown), such as any of the cables or monitors shown above with respect to  FIGS.  2 A through  2 D . Alternatively, the connector end  1620  can mate directly with the monitor. 
       FIG.  17    illustrates an exploded view of certain of the components of the sensor  301   f  described above. A heat sink  1751  and a cable  1781  attach to an emitter shell  1704 . The emitter shell attaches to a flap housing  1707 . The flap housing  1707  includes a receptacle  1709  to receive a cylindrical housing  1480 / 1580  (not shown) attached to an emitter submount  1702 , which is attached to a circuit board  1719 . 
     A spring  1787  attaches to a detector shell  1706  via pins  1783 ,  1785 , which hold the emitter and detector shells  1704 ,  1706  together. A support structure  1791  attaches to the detector shell  1706 , which provides support for a shielding enclosure  1790 . A noise shield  1713  attaches to the shielding enclosure  1790 . A detector submount  1700  is disposed inside the shielding enclosure  1790 . A finger bed  1710  provides a surface for placement of the patient&#39;s finger. Finger bed  1710  may comprise a gripping surface or gripping features, which may assist in placing and stabilizing a patient&#39;s finger in the sensor. A partially cylindrical protrusion  1705  may also be disposed in the finger bed  1710 . As shown, finger bed  1710  attaches to the noise shield  1703 . The noise shield  1703  may be configured to reduce noise, such as from ambient light and electromagnetic noise. For example, the noise shield  1703  may be constructed from materials having an opaque color, such as black or a dark blue, to prevent light piping. 
     Noise shield  1703  may also comprise a thermistor  1712 . The thermistor  1712  may be helpful in measuring the temperature of a patient&#39;s finger. For example, the thermistor  1712  may be useful in detecting when the patient&#39;s finger is reaching an unsafe temperature that is too hot or too cold. In addition, the temperature of the patient&#39;s finger may be useful in indicating to the sensor the presence of low perfusion as the temperature drops. In addition, the thermistor  1712  may be useful in detecting a shift in the characteristics of the water spectrum in the patient&#39;s finger, which can be temperature dependent. 
     Moreover, a flex circuit cover  1706  attaches to the pins  1783 ,  1785 . Although not shown, a flex circuit can also be provided that connects the circuit board  1719  with the submount  1700  (or a circuit board to which the submount  1700  is connected). A flex circuit protector  1760  may be provided to provide a barrier or shield to the flex circuit (not shown). In particular, the flex circuit protector  1760  may also prevent any electrostatic discharge to or from the flex circuit. The flex circuit protector  1760  may be constructed from well known materials, such as a plastic or rubber materials. 
       FIG.  18    shows the results obtained by an exemplary sensor  101  of the present disclosure that was configured for measuring glucose. This sensor  101  was tested using a pure water ex-vivo sample. In particular, ten samples were prepared that ranged from 0-55 mg/dL. Two samples were used as a training set and eight samples were then used as a test population. As shown, embodiments of the sensor  101  were able to obtain at least a standard deviation of 13 mg/dL in the training set and 11 mg/dL in the test population. 
       FIG.  19    shows the results obtained by an exemplary sensor  101  of the present disclosure that was configured for measuring glucose. This sensor  101  was tested using a turbid ex-vivo sample. In particular, 25 samples of water/glucose/Liposyn were prepared that ranged from 0-55 mg/dL. Five samples were used as a training set and 20 samples were then used as a test population. As shown, embodiments of sensor  101  were able to obtain at least a standard deviation of 37 mg/dL in the training set and 32 mg/dL in the test population. 
       FIGS.  20  through  22    shows other results that can be obtained by an embodiment of system  100 . In  FIG.  20   , 150 blood samples from two diabetic adult volunteers were collected over a 10-day period. Invasive measurements were taken with a YSI glucometer to serve as a reference measurement. Noninvasive measurements were then taken with an embodiment of system  100  that comprised four LEDs and four independent detector streams. As shown, the system  100  obtained a correlation of about 85% and Arms of about 31 mg/dL. 
     In  FIG.  21   , 34 blood samples were taken from a diabetic adult volunteer collected over a 2-day period. Invasive measurements were also taken with a glucometer for comparison. Noninvasive measurements were then taken with an embodiment of system  100  that comprised four LEDs in emitter  104  and four independent detector streams from detectors  106 . As shown, the system  100  was able to attain a correlation of about 90% and Arms of about 22 mg/dL. 
     The results shown in  FIG.  22    relate to total hemoglobin testing with an exemplary sensor  101  of the present disclosure. In particular, 47 blood samples were collected from nine adult volunteers. Invasive measurements were then taken with a CO-oximeter for comparison. Noninvasive measurements were taken with an embodiment of system  100  that comprised four LEDs in emitter  104  and four independent detector channels from detectors  106 . Measurements were averaged over 1 minute. As shown, the testing resulted in a correlation of about 93% and Arms of about 0.8 mg/dL. 
     Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     While certain embodiments of the inventions disclosed herein have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Indeed, the novel methods and systems described herein can be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein can be made without departing from the spirit of the inventions disclosed herein. The claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of certain of the inventions disclosed herein.