(12) United States Patent
`Hanna et al.
`
`USOO6505133B1
`(10) Patent No.:
`US 6,505,133 B1
`(45) Date of Patent:
`Jan. 7, 2003
`
`(54) SIMULTANEOUS SIGNALATTENUATION
`MEASUREMENTS UTILIZING CODE
`DIVISION MULTIPLEXING
`
`SS
`(75) Inventors: RNA A. R
`ark A. Norris, Boulder, CO (US)
`(73) Assignee: Datex-Ohmeda, Inc., Madison, WI
`(US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/712,864
`(22) Filed:
`Nov. 15, 2000
`9
`(51) Int. Cl." ................................................ G06F 19/00
`(52) U.S. Cl. ............................................ 702/74; 702/79
`(58) Field of Search .............................. 702/10, 69, 74,
`702/79, 108, 110, 122, 124-126, 176-178,
`783, 189, 193, 194, 196, 197; 600/309,
`386, 310; 370/320, 535, 536, 203, 206;
`375/316, 322,329, 332, 346
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
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`1/1989 Johnson ....,
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`7/1989 Hood, Jr. ..................... 356/41
`4,930,140 A 5/1990 Cripps et al. .................. 375/1
`4,972,331 A 11/1990 Chance .........
`... 364/550
`5,122,974 A 6/1992 Chance ......
`... 364/550
`5,193.543 A 3/1993 Yelderman ....
`... 128/633
`5,204.874 A * 4/1993 Falconer et al. .....
`... 370/209
`5,277,181 A
`1/1994 Mendelson et al. ......... 128/633
`5,320,098 A 6/1994 Davidson .................... 128/630
`5,343.818 A 9/1994 McCarthy et al. .......... 128/633
`5,349,952 A * 9/1994 McCarthy et al. ............ 356/41
`
`5,349.953 A * 9/1994 McCarthy et al. .......... 600/323
`5,387,259 A
`2/1995 Davidson .................... 128/630
`5,460,182 A 10/1995 Goodman et al. .......... 128/664
`5,766,127 A 6/1998 Pologe et al. ............... 600/310
`5,769,791. A 6/1998 Benaron et al. ............ 600/473
`5,772,597 A
`6/1998 Goldberger et al. ........ 600/473
`5,774.213 A 6/1998 Trebino et al. ............. 356/320
`5,782,758. A
`7/1998 Ausec et al. ................ 600/336
`5,785,658 A 7/1998 Benaron et al. ............ 600/473
`5,800,348 A
`9/1998 Kaestle ....................... 600/322
`5,805,583 A
`9/1998 Rakib ......................... 370/342
`5,807.261 A 9/1998 Benaron et al. ............ 600/473
`5,891,022 A 4/1999 Pologe ....................... 600/323
`5,891,024 A 4/1999 Jarman et al. .............. 600/323
`5,919,134 A
`7/1999 Diab .......................... 600/323
`5,921,921. A * 7/1999 Potratz et al. .............. 600/323
`5,934,277 A
`8/1999 Mortz ........................ 128/633
`5,995,858 A 11/1999 Kinast ........................ 600/323
`6,097,712 A * 8/2000 Secord et al. ............... 600/323
`6,229,856 B1
`5/2001 Diab et al. .................. 375/316
`6,269,267 B1
`7/2001 Brady et al. ................... 607/5
`* cited by examiner
`Primary Examiner Marc S. Hoff
`Assistant Examiner-Craig Steven Miller
`(74) Attorney, Agent, or Firm Marsh Fischmann &
`Breyfogle LLP
`ABSTRACT
`(57)
`A pulse oximeter (100) includes two or more light sources
`(102) for transmitting optical signals through an appendage
`(103) of patient. The sources (102) are operated to transmit
`code division multiplexed (CDM) signals. That is, the
`sources (102) are driven by drives (104) in response to
`Signals from a digital processing unit (116) Such that the
`Sources (102) are modulated using different code sequences.
`The code Sequences are preferably non-periodic and may be
`orthogonal to one another. The use of Such CDM signals
`provides certain advantages related to noise reduction.
`
`24 Claims, 5 Drawing Sheets
`
`500
`
`M
`
`SELECTA
`MEASUREMEN
`INTERWAL
`
`502
`
`SELECACLOCKRAE
`
`504.
`
`DWDEACLOCKBLOCK
`INO CARRERPARS
`
`DEFINEEACHCODEBIT
`INTERMS OFA
`CARRIERPAR
`
`FORFRSSOURCE,
`USE RANDOMBTPAIR
`TODETERMINE
`SOURCESTATE
`
`FORSECOND SOURCE
`NNERSECONDETR
`RANDOMBPAR
`
`DRIVESOURCES IN
`ACCORDANCE WITH
`MODUATED, CODED
`CLOCKBLOCK
`
`506
`
`508
`
`50
`
`512
`
`514
`
`REPEAFORALL
`CLOCKELOCKSN
`MEASUREMENT
`NTERWAL
`
`RECEIVECODE
`SEQUENCE FOREACH
`SOURCE
`
`APPLYFILERING
`WAJES
`
`GENERATE
`EMODULATING
`SIGNALS
`
`APPLY DEMODULANG
`SIGNALSTOBETECTOR
`SIGNAL
`
`NTEGRATERESULTING
`WALUESTOCEAN
`INENSITY RELATED
`WALUES
`
`
`
`USENTENSTY
`RELATEDVALUESTO
`DETERMINEBLOOD
`OXYGENATION
`
`56
`
`518
`
`520
`
`522
`
`524
`
`526
`
`528
`
`Petitioner Apple Inc. – Ex. 1007, p. 1
`
`

`

`U.S. Patent
`
`Jan. 7, 2003
`
`Sheet 1 of 5
`
`US 6,505,133 B1
`
`106
`
`110
`
`100
`112 f
`
`DETECTOR
`
`AMPLIFER
`
`FAST ADC
`
`POSITIONER
`
`
`
`DSP WITH
`SOFTWARE
`
`
`
`LIGHT
`SOURCE
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Petitioner Apple Inc. – Ex. 1007, p. 2
`
`

`

`U.S. Patent
`
`Jan. 7, 2003
`
`Sheet 2 of 5
`
`US 6,505,133 B1
`
`
`
`CDM CODES
`
`202
`
`
`
`TWO ORMORE
`ORTHAGONAL BINARY
`SEQUENCES
`
`DRIVERS
`
`204
`
`
`
`200
`
`
`
`
`
`DiSEEN
`DATA
`
`212
`
`DEMODULATOR
`
`TRANSMITTERNI
`
`MEDIUM
`
`
`
`
`
`RECEIVER
`
`210
`
`FIG.2
`
`Petitioner Apple Inc. – Ex. 1007, p. 3
`
`

`

`U.S. Patent
`
`Jan. 7, 2003
`
`Sheet 3 of 5
`
`US 6,505,133 B1
`
`RED AND IRDRIVE SIGNALS, BASEBAND CODE DIVISION MULTIPLEX
`
`
`
`º SHONENDESZ , !cS
`
`100
`
`400
`30
`O
`200
`TIME (ARBITRARY UNITS)
`
`500
`
`600
`
`FIG.3
`
`Petitioner Apple Inc. – Ex. 1007, p. 4
`
`

`

`U.S. Patent
`
`Jan. 7, 2003
`
`Sheet 4 of 5
`
`US 6,505,133 B1
`
`
`
`RED AND IRDRIVE SIGNALS, CARRIER CODE DIVISION MULTIPLEX
`1 - O - 1
`1
`0 - 1 - O - O - O - O - 1 - O - 1 - O
`
`O
`
`1
`|
`1
`1 ||
`0 |
`O | 0 ||
`1 0 1 0 1 1 0 1 0 1 0 1 0
`
`O
`
`100
`
`400
`300
`200
`TIME (ARBITRARY UNITS)
`
`500
`
`600
`
`FG4
`
`Petitioner Apple Inc. – Ex. 1007, p. 5
`
`

`

`U.S. Patent
`
`Jan. 7, 2003
`
`Sheet 5 of 5
`
`US 6,505,133 B1
`
`5 O O
`
`cities
`
`START
`
`SELECT A
`MEASUREMENT
`INTERVAL
`
`502
`
`SELECT ACLOCKRATE
`SELECTAClockRATE-
`
`DVDEACLOCKBLOCK
`INTO CARRIER PARS
`
`DEFINE EACH CODEBT
`INTERMS OFA
`CARRIERPAR
`
`
`
`FORFIRST SOURCE,
`USE RANDOM BIT PAR
`TO DETERMINE
`SOURCE STATE
`
`RESSEESR
`
`RANDOM BIT PAR
`
`DRIVE SOURCES IN
`ACCORDANCE WITH
`MODULATED, CODED
`
`506
`
`508
`
`510
`
`512
`
`514
`
`516
`
`518
`
`520
`
`522
`
`524
`
`526
`
`528
`
`
`
`
`
`REPEAT FOR ALL
`CLOCK BLOCKS IN
`MEASUREMENT
`INTERVA
`RECEIVE CODE
`SEQUENCE FOREACH
`SOURCE
`
`APPLY FILTERING
`VALUES
`
`GENERATE
`DEMODULATING
`SIGNALS
`
`APPLY DEMODULATING
`SIGNALSTODETECTOR
`SIGNAL
`
`INESSESSING
`
`INTENSITY RELATED
`VALUES
`
`REENESIS to
`DETERMINE BLOOD
`
`END
`
`FIG.5
`
`Petitioner Apple Inc. – Ex. 1007, p. 6
`
`

`

`US 6,505,133 B1
`
`1
`SIMULTANEOUS SIGNALATTENUATION
`MEASUREMENTS UTILIZING CODE
`DIVISION MULTIPLEXING
`
`2
`and techniques can be utilized to extract information about
`the different frequency components.
`In order to accurately determine information regarding the
`Subject, it is desirable to minimize noise in the detector
`Signal. Such noise may arise from a variety of Sources. For
`example, one Source of noise relates to ambient light inci
`dent on the detector. Another Source of noise is electronic
`noise generated by various Oximeter components. Many
`Significant Sources of noise have a periodic component.
`Various attempts to minimize the effects of Such noise
`have been implemented in hardware or software. For
`example, various filtering techniques have been employed to
`filter from the detector Signal frequency or wavelength
`components that are not of interest. However, because of the
`periodic nature of many Sources of noise and the broad
`Spectral effects of associated harmonics, the effectiveness of
`Such filtering techniques is limited. In this regard, it is noted
`that both TDM signals and FDM signals are periodic in
`nature. Accordingly, it may be difficult for a filter to dis
`criminate between Signal components and noise components
`having a similar period.
`SUMMARY OF THE INVENTION
`The present invention is directed to a simultaneous signal
`attenuation measurement System employing code division
`multiplexing (CDM). The invention allows for analysis of a
`multiplexed signal to distinguish between two or more
`Signal components thereof based on codes modulated into
`the Signal components. The CDM codes are nonperiodic
`thereby facilitating various processing techniques for dis
`tinguishing the Signals of interest from noise or other
`interference. Moreover, the invention allows for a variety of
`hardware and processing options that may reduce costs,
`Simplify System operation and improved accuracy of the
`attenuation measurements.
`According to one aspect of the present invention, codes
`are modulated into the transmitted Signals of a Signal attenu
`ation measurement System. The System includes at least two
`Signal Sources (e.g., having different wavelengths) that are
`pulsed by Source drives to a medium under analysis. One or
`more detectorS receive the first and Second Signal from the
`medium (e.g., after transmission through or reflection from
`the medium) and output a composite signal reflecting con
`tributions corresponding to each of the transmitted Source
`Signals. The detector Signal is thus a multiplexed signal
`composed of at least two signal components. In accordance
`with the present invention, the Source drives are operated to
`modulate each of the Source Signals based on a code. For
`example, each drive may pulse a corresponding one of the
`Signal Sources between a high output or “on' State and a low
`value or “off State. It will be appreciated that, depending on
`the Sources employed, Substantial photonic energy may be
`transmitted in the nominal “off State. Accordingly, in the
`context of the Source signals, a code may be conceptualized
`as a bit stream of “0s” and “1s”, where “0” corresponds to
`an off State, “1” corresponds to an on State, and the bit length
`corresponds to a base unit of time that generally reflects the
`Shortest pulse length utilized in driving the Sources.
`The codes define Source Signals that have nonperiodic
`characteristics. That is, due to the codes, there is at least a
`component of each Source Signal that is not described by a
`regularly repeating temporal pattern. AS will be understood
`from the description below, however, the codes themselves
`may be concatenated in the Source Signal and a periodic
`modulating Signal may carry the coded Signal.
`A number of preferred characteristics have been identified
`for the codes. Among these are:
`
`FIELD OF THE INVENTION
`The present invention relates in general to Simultaneous
`Signal attenuation measurement Systems and, in particular,
`to the use of code division multiplexing in Such Systems to
`identify attenuation characteristics associated with indi
`vidual signal components.
`BACKGROUND OF THE INVENTION
`Signal attenuation measurements generally involve trans
`mitting a signal towards or through a medium under
`analysis, detecting the Signal transmitted through or
`reflected by the medium and computing a parameter value
`for the medium based on attenuation of the Signal by the
`medium. In Simultaneous Signal attenuation measurement
`Systems, multiple signals are simultaneously transmitted
`(i.e., two or more signals are transmitted during at least one
`measurement interval) to the medium and detected in order
`to obtain information regarding the medium.
`Such attenuation measurement Systems are used in vari
`ous applications in various industries. For example, in the
`medical or health care field, optical (i.e., visible spectrum or
`other wavelength) signals are utilized to monitor the com
`position of respiratory and anesthetic gases, and to analyze
`tissue or a blood Sample with regard to oxygen Saturation,
`analyte values (e.g., related to certain hemoglobins) or other
`composition related values.
`The case of pulse oximetry is illustrative. Pulse oximeters
`determine an oxygen Saturation level of a patient's blood, or
`related analyte values, based on transmission/absorption
`characteristics of light transmitted through or reflected from
`the patient's tissue. In particular, pulse Oximeters generally
`include a probe for attaching to a patient's appendage Such
`as a finger, earlobe or nasal Septum. The probe is used to
`transmit pulsed optical Signals of at least two wavelengths,
`typically red and infrared, to the patient's appendage. The
`transmitted Signals are received by a detector that provides
`an analog electrical output signal representative of the
`received optical Signals. By processing the electrical Signal
`and analyzing Signal values for each of the wavelengths at
`different portions of a patient pulse cycle, information can be
`obtained regarding blood oxygen Saturation.
`Such pulse Oximeters generally include multiple Sources
`(emitters) and one or more detectors. A modulation mecha
`nism is generally used to allow the contribution of each
`Source to the detector output to be determined. Conventional
`pulse Oximeters generally employ time division multiplex
`ing (TDM) signals. As noted above, the processing of the
`electrical Signals involves Separate consideration of the
`portions of the Signal attributable to each of the Sources.
`Such processing generally also involves consideration of a
`dark current present when neither Source is in an “on” State.
`In TDM oximeters, the sources are pulsed at different times
`Separated by dark periods. Because the first Source “on”
`period, the Second Source “on” period and dark periods
`occur at Separate times, the associated Signal portions can be
`easily distinguished for processing.
`Alternatively, pulse Oximeters may employ frequency
`division multiplexing (FDM) signals. In the case of FDM,
`each of the Sources is pulsed at a different frequency
`resulting in detector Signals that have multiple periodic
`components. Conventional signal processing components
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Petitioner Apple Inc. – Ex. 1007, p. 7
`
`

`

`US 6,505,133 B1
`
`1O
`
`3
`1. the codes for the different sources are preferably
`mathematically orthogonal;
`2. the numbers of 1S and OS in a code should be about the
`Same,
`3. the distribution of 1 S and OS within a code should be
`fairly even; and
`4. the distribution of transitions between 1s and OS within
`a code should be fairly even.
`These preferences and Some bases therefor are described in
`detail below. The codes utilized in accordance with the
`present invention preferably have one or more of these
`characteristics and, more preferably, have all of the noted
`characteristics.
`According to another aspect of the invention, a detector
`15
`Signal is processed in a signal attenuation measurement
`System to demultiplex the detector Signal and extract com
`ponent information therefrom based on nonperiodic codes.
`In particular, the detector Signal is first processed to provide
`a processed signal for demultiplexing and the processed
`Signal is then demultiplexed using at least one coded demul
`tiplexing Signal that includes a Series of values defining a
`nonperiodic code. Information is thereby obtained regarding
`first and Second Signal components of the detector Signal.
`This information can be utilized in an attenuation analysis to
`determine an attenuation related parameter of a medium
`under analysis.
`The initial processing of the detector Signal may include
`various processing Steps and components depending on the
`Specific application and implementation. For example,
`where the detector Signal is an analog signal, initial pro
`cessing may involve analog to digital conversion.
`Preferably, Such conversion is implemented using a fast
`analog to digital converter that digitally Samples the detector
`Signal multiple times per Source cycle. Such a convertor in
`combination with processing techniques enabled by code
`division multiplexing allows for improved measurement
`accuracy and hardware implementation options for certain
`attenuation measurement applications. The initial processing
`may further or alternatively include Signal filtering to reduce
`undesired components, signal amplification including, e.g.,
`DC rectification to remove or avoid amplifying DC or low
`frequency components especially in the case of DC coupled
`Sources, and/or other Signal enhancement processing.
`Preferably, the demultiplexing process involves the use of
`a unique demultiplexing Signal for each Signal component of
`interest, e.g., corresponding to each Signal Source. In this
`regard, the same codes used for modulating the Source
`Signals may be used to demodulate the detector Signal.
`However, for mathematical convenience, the demodulating
`codes may be conceptualized as a Series of -1S and +1S
`rather than 0s and 1S as discussed above in relation to the
`modulating codes. The coded demodulating Signal may be
`filtered to compensate for certain wave shape distortions
`resulting from bandwidth limitations and non-linearities
`and/or to reduce response at certain frequencies. In addition,
`the codes may be pre-computed to reduce Storage and
`processing requirements.
`
`25
`
`35
`
`40
`
`4
`FIG. 2 is a block diagram illustrating a code division
`multiplexing System in accordance with the present inven
`tion;
`FIG. 3 illustrates two drive signals reflecting codes that
`may be used in the code division multiplexing System of the
`present invention;
`FIG. 4 illustrates two drive signals, reflecting codes
`transmitted using a carrier wave in accordance with the
`present invention; and
`FIG. 5 is a flowchart illustrating a code division multi
`plexing proceSS in accordance with the present invention.
`DETAILED DESCRIPTION OF THE
`INVENTION
`The code division multiplexing System of the present
`invention may be used in a variety of Signal attenuation
`measurement devices. In the following description, the
`invention is Set forth in the context of a pulse Oximeter used
`to measure blood oxygen Saturation or related blood analyte
`values. As will be described below, the invention has par
`ticular advantages in the context of pulse OXimetry including
`allowing for improved noise reduction and OXimeter com
`ponent options. However, while pulse OXimetry represents a
`particularly advantageous application of the present
`invention, it will be understood that various aspects of the
`present invention are more broadly applicable in a variety of
`Simultaneous Signal attenuation measurement contexts.
`In the following description, the pulse oXimetry environ
`ment is first described with reference to a specific pulse
`Oximeter embodiment. Thereafter, Specific implementations
`of the code division multiplexing System of the present
`invention are described.
`Referring to FIG. 1, a pulse OXimeter in accordance with
`the present invention is generally identified by the reference
`numeral 100. The pulse oximeter 100 includes two or more
`light Sources 102 for transmitting optical Signals through an
`appendage 103 of a patient. In the illustrated embodiment,
`two light sources 102 are shown. For example, the light
`Sources 102 may include a red LED and an infrared LED.
`The light sources 102 are driven by light source drives 104
`in response to drive signals from a digital Signal processing
`unit 116. In the illustrated embodiment, as will be described
`in more detail below, the signals from the light sources 102
`are modulated using different code Sequences. For example,
`the source drive 104 associated with the red light source 102
`may pulse the red light Source in accordance with a first code
`Sequence and the light Source drive 104 associated with the
`infrared light Source 102 may pulse the infrared light Source
`102 in accordance with a Second code Sequence different
`from the first code Sequence. It will be appreciated that Such
`a multiplexing System does not result in a periodic signals
`Such as in the case of time division multiplexed or frequency
`division multiplexed Signals. In particular, the pulsing of the
`Sources 102 between “on” and “off” states does not define a
`regularly repeating waveform. It should also be noted that
`although the following description references “on” and “off”
`cycles for each of the Sources 102, in reality, the optical
`Signals associated with each Source 102 do not define an
`ideal Square wave. For example, Substantial photonic energy
`is emitted even in the “off” state in the case of DC coupled
`Sources. In addition, the intensity transmitted by each of the
`Sources 102 can vary substantially within an “on” cycle. The
`ability to recognize and address Such non-ideal characteris
`ticS is an advantage of the present invention.
`The optical signals transmitted by the light sources 102
`are transmitted through the patient's appendage 103 and
`
`45
`
`50
`
`55
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`For a more complete understanding of the present inven
`tion and further advantages thereof, reference is now made
`to the following detailed description, taken in conjunction
`with the drawings, in which:
`FIG. 1 is a Schematic diagram of a pulse OXimeter in
`connection with which the present invention may be imple
`mented;
`
`60
`
`65
`
`Petitioner Apple Inc. – Ex. 1007, p. 8
`
`

`

`S
`impinge upon a detector 106. In this regard, a positioner 108
`provides for proper alignment of the Sources 102 and the
`detector 106. Various different types of positioners 108 are
`available depending, for example, on the appendage to be
`irradiated and on the patient (e.g. different positioners 108
`may be provided for neonatal and adult patients). One
`typical type of positioner 108 is provided in the form of a
`clothespin-like clamp which engages a patient's fingertip.
`When the positioner 108 is engaged on the patient's
`fingertip, the light Sources are positioned on one side of the
`patient's finger and the detector 106 is positioned on the
`opposite Side in alignment with the light Sources So as to
`receive the optical Signals transmitted through the patient's
`finger. It will be appreciated that, in alternative
`implementations, a reflective pulse oXimeter may be
`employed whereby the Sources and detector are located on
`the Same side of the patient's appendage So as to receive
`optical Signals reflected back from the patient's tissue.
`The detector 106 receives the optical signals transmitted
`through the patient's appendage 103 and provides an analog
`Signal representative of the received optical Signals. In the
`illustrated embodiment, the detector 106 outputs an analog
`current signal where the magnitude of the current at any
`given time is proportional to the cumulative intensity of the
`received optical Signals. The detector Signal in the illustrated
`embodiment is then processed by an amplifier circuit 110.
`The amplifier circuit may serve a number of functions. First,
`the illustrated amplifier circuit is operative for converting
`the input analog current signal from the detector 106 into an
`analog Voltage Signal. The amplifier circuit 110 may also be
`operative for Subtracting certain DC and low frequency
`components from the detector Signal. For example, one DC
`component which may be Subtracted from-the detector Sig
`nal relates to photonic energy transmitted by the Sources 102
`during "dark periods.” That is, as noted above, practical
`Source implementations generally transmit a signal of Some
`intensity even during off periods. In addition, low frequency
`ambient light may be Subtracted from the detector Signal.
`The amplifier circuit 110 may also filter out certain high
`frequency electronic noise and provide other signal proceSS
`ing functionality.
`The amplifier circuit 110 outputs an analog Voltage Signal
`which is representative of the optical signals (or frequency
`division multiplexed signal) from the sources 102. This
`analog Voltage Signal is received by a fast A/D converter 112
`which Samples the analog Voltage Signal to generate a digital
`Voltage Signal which can be processed by the digital Signal
`processing unit 116. In particular, the converter 112 prefer
`ably takes multiple digital Samples per cycle of each of the
`Sources 102. That is, the sampling rate of the converter 112
`is Sufficiently fast to take multiple Samples, for example, at
`least about 20 samples per “on” period of each of the sources
`102. Such multiple Sampling per cycle allows the Oximeter
`to track the shape of the detector Signal, to allow for reduced
`noise processing of the resulting digital Signal and to iden
`tify phase components of interest within a signal cycle.
`Multiple samples per dark period are also obtained. It will
`thus be appreciated that the values output by the converter
`112 are not integrated or aggregate values corresponding to
`a Source cycle period or dark period, but rather, are Sub
`Stantially instantaneous values reflecting the detector Signal
`at a moment within a cycle.
`The digital Signal processor 116 implements a number of
`functions. Of particular importance to the present invention,
`and as will be described in more detail below, the processor
`116 includes a demultiplexer module, i.e., the processor
`executes a variety of demultiplexing Software/logic func
`
`6
`tions including generating or otherwise obtaining a coded
`demultiplexing Signal corresponding to each Signal compo
`nent associated with each Source, processing the composite
`Signal using each of the demultiplexing Signals to obtain a
`Set of values reflecting the contribution of each Source, and
`using these value Sets to obtain instantaneous intensity
`related values for each of the sources. The processor 116 also
`includes a parameter calculation module for calculating
`blood oxygen Saturation or related parameter values using
`known algorithms.
`FIG. 2 illustrates a code division multiplexing system 200
`that can be implemented in the pulse oximeter 100 of FIG.
`1 in accordance with the present invention. The system 200
`includes a code module 202 for providing codes that are
`used to modulate the Sources and demultiplex the detector
`Signal. A number of preferred criteria have been identified
`with respect to the codes employed. First, these codes are
`preferably Selected, relative to one another, in a manner that
`allows for processing So as to accurately distinguish the
`contributions of each of the Sources. In this regard, the codes
`may be Substantially orthogonal to reduce any interference
`between the two signal components, or “channels', corre
`sponding to the two different Sources and their wavelengths/
`Spectral composition. AS noted above, the codes may be
`conceptualized as binary Sequences. In the context of the
`Sources it is convenient to conceptualize the code Sequence
`in terms of 0 and 1 bits corresponding to the off or low
`output State, on the one hand, and the on or high output State
`on the other. In the case of the demultiplexing Signal, the bits
`are conceptualized as -1 and +1 for mathematical conve
`nience. In the following discussion, the -1 and +1 conven
`tion is used. The following Sequences illustrate the concept
`of code orthogonality as well as the mathematical conve
`nience of +1S and -1S for a particular processing technique:
`
`1
`-1
`- 1 - 1
`1 - 1
`
`1 - 1
`1
`1
`1 - 1
`
`The first line above is a first code Sequence and the Second
`line above is a Second code Sequence. These two code
`Sequences are orthogonal in that half the time that the bit
`value of the first code is -1, the bit value of the second code
`is -1 and vice versa. The other half of the time the bit values
`are opposite. A similar relationship holds for bit values of 1.
`The third line above is the bit-by-bit product of the first two
`code Sequences. Because the corresponding bits of the codes
`are the same half of the time (producing a product of +1) and
`different the other half of the time (producing a product of
`-1), the sum of the bits in the third line above is 0. By
`contrast, the Sum of the products of two identical codes
`would be equal to the number of bits in the code. As will be
`described below, this property facilitates isolation of the
`portion of the multiplexed detector Signal attributable to
`each of the Sources and obtainment of a value indicative of
`the intensity of that received signal at a given time or time
`period.
`For example, the use of the following eight code Segments
`in equal numbers will allow for generation of a number of
`Suitable orthogonal code Sequences:
`
`US 6,505,133 B1
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Petitioner Apple Inc. – Ex. 1007, p. 9
`
`

`

`US 6,505,133 B1
`
`7
`
`- 1 - 1 - 1 - 1
`- 1 - 1
`1
`1
`-1
`1 - 1
`1
`-1
`1
`1 - 1
`1 - 1 - 1
`1
`1 - 1
`1 - 1
`1
`1 - 1 - 1
`1
`1
`1
`1
`
`8
`code. In this case, a 10 carrier pair is used to transmit a +1
`code bit and a 01 carrier pair is used for a 0 code bit. The
`corresponding carrier pairs and associated code bit values
`for each code Sequence are shown in FIG. 4. Such carrier
`code modulation has a number of advantages in the illus
`trated implementation. First, Such modulation Simplifies the
`process of Satisfying the above noted code criteria as Such
`criteria can be Satisfied by the modulated code Sequences
`rather than the base code Sequences. In this regard, Since
`each code bit is half 0 and half 1 and includes one transition,
`the transmitted code will automatically satisfy all of the
`above noted criteria except for orthogonality. The preferred
`code Selection process therefore reduces to Satisfying
`orthogonality.
`Additionally, the carrier code takes the coded Signal
`further away from DC or low frequency interference. By
`using higher frequency carriers (e.g., multiple carrier pairs
`per code bit), the resulting signal can be taken further away
`from DC or low frequency interference so that 1/f noise and
`power line noise (e.g., ambient light) have a reduced impact
`on the desired measurements. These higher frequency car
`riers produce nulls (noise minima) for several harmonics
`above the carrier frequency. By appropriate Selection of the
`carrier frequency, these nulls can be used to ease anti
`aliasing requirements.
`Referring again to FIG. 2, the resulting Signals transmitted
`by the sources 206 travel through the medium 208 in the
`illustrated embodiment. In this case, the medium may be, for
`example, a patient's finger, ear lobe or nasal Septum.
`Alternatively, in the case of a reflective oximeter, the Signal
`portions reflected from the medium may be detected to
`obtain information about the medium.
`The signals are received by one or more detectors 210 that
`provide an electrical detector Signal proportional to the
`received optical Signal. Such a signal may be an analog
`current Signal. In the illustrated embodiment, a Single detec
`tor 210 receives the signals from both sources 206, thereby
`reducing components and costs as is desirable, particularly
`when the detector 210 is provided as part of a disposable or
`Short lifespan probe. Accordingly, the detector Signal is a
`composite Signal including contributions from each of the
`Sources 206. AS discussed above, the detector Signal may be
`processed by an amplifier circuit and an analog to digital
`circuit that are not shown in FIG. 2.
`In particular, the amplifier circuit outputs an analog
`Voltage Signal which is representative of the optical Signals
`(or code division multiplexed signal) from the Sources. This
`analog Voltage Signal is received by a fast A/D converter
`which Samples the analog Voltage Signal to generate a digital
`Voltage Signal which can be processed by the digital Signal
`processing unit. The converter 112 takes multiple digital
`Samples per time period corresponding to a code value or
`value of the carrier wave. That is, the Sampling rate of the
`converter is Sufficiently fast to take one or more Samples and,
`more preferably at least about 3 Samples and, even more
`preferably at least about 20 samples per “on” or “off” period
`of each of the Sources 102. Such multiple Sampling per cycle
`allows the Oximeter to track the shape of the detector Signal,
`to allow for reduced noise processing of the resulting digital
`Signal, to reduce the required A/D converter word length and
`to identify phase components of interest within a signal
`cycle. In one implementation, information regarding the
`shape of the Signal may be used in filtering the demodulating
`Signal as discussed below. The code modulated composite
`Signal may be Sampled by the converter, for example, at a
`frequency of about 41,667 Hz. It will thus be appreciated
`that the values output by the converter 112 are not integrated
`
`It will be observed that these four bit segments include even
`numbers of -1S and/or +1S allowing for generation of codes
`based on combinations of these Segments that are orthogonal
`as discussed above. Similar Segments of different bit lengths
`may be used as a basis for generating orthogonal code
`Sequences.
`In addition to Orthogonality, preferred codes for the illus
`trated implementation of the invention have a Substantially
`equal number of