as United States
`a2) Patent Application Publication (10) Pub. No.: US 2003/0033102 Al
` Dietiker (43) Pub. Date: Feb. 13, 2003
`
`
`
`US 20030033102A1
`
`(54) SYSTEM AND METHOD FORA
`SELF-CALIBRATING NON-INVASIVE
`SENSOR
`
`(86) PCT No.:
`
`PCT/US01/25109
`
`Publication Classification
`
`(76)
`
`Inventor: Thomas Dietiker, Torrance, CA (US)
`
`Tint, C07 cicccccccccccccccccccccscscsessesecsesscsteseenees GOLD 18/00
`(51)
`(52) US. C0. eee ecsecssecssesseesnessnsenceasessrenssenssnscenseeses 702/85
`
`Correspondence Address:
`Mark Krietzman
`Sonnenschein Nath & Rosenthal
`Wacker Drive Station Sears Tower
`PO Box 061080
`Chichago, IL 60606 (US)
`
`(21)
`
`Appl. No.:
`
`10/149,779
`
`(22)
`
`PCT Filed:
`
`Aug. 9, 2001
`
`67)
`
`ABSTRACT
`
`A non-invasive emitter-photodiode sensor which is able to
`provide a data-stream corresponding to the actual wave-
`length of light emitted thereby allowing calibration of the
`sensor signal processing equipment and resulting in accurate
`measurements over a wider variation in emitter wavelength
`ranges.
`
`
` PROBE LIGHT SOURCE 200
`
` FIRST LIGHT
`SOURCE
`
`SECOND LIGHT
`SOURCE
`
`
`
`204
`
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`WAVELENGTH
`
`SENSOR
`
` 202
`
`PROBE 102
`
`
`1
`
`APPLE 1009
`
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`
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`

`

`Patent Application Publication
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`Feb. 13, 2003 Sheet 1 of 13
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`Feb. 13,2003 Sheet 10 of 13
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`US 2003/0033102 Al
`
`Feb. 13, 2003
`
`SYSTEM AND METHOD FOR A
`SELF-CALIBRATING NON-INVASIVE SENSOR
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`[0001] This application claims the benefit of Provisional
`Patent Application Serial No. 60/225,021 filed on Aug. 11,
`2000 and entitled SELF CALIBRATING NON-INVASIVE
`BLOOD COMPONENT SENSOR.
`
`BACKGROUND OF THE INVENTION
`
`[0002]
`
`1. Technical Field
`
`[0003] This invention relates generally to non-invasive
`sensing devices, and in particularly to calibrating these
`non-invasive sensing devices.
`
`[0004]
`
`2. Related Art
`
`[0005] Coherentlight sources are utilized in a broad range
`of applications in many distinctfields of technology includ-
`ing the consumer, industrial, medical, defense and scientific
`fields. In the medical field an emitter-receiver pair of coher-
`ent light sources in form oflight-emitting diodes (LEDs) are
`often utilized in medical sensing devices to obtain accurate
`non-invasive measurements. An example application of such
`a medical sensing device may include a blood constituent
`monitoring system and/or a non-invasive oximeter that may
`be utilized to monitor arterial oxygen saturation.
`
`In non-invasive oximetry, coherent light having a
`[0006]
`knownspecific wavelength is typically transmitted from an
`emitter LED through a target, such as biological
`tissue
`carrying blood,
`to a photodetector. The photodetector
`receives and measuresa portion of transmitted coherentlight
`that is neither absorbed norreflected from the blood in the
`
`tion, will typically degrade over time, vary with tempera-
`ture, and the drive circuit may become unstable and cause a
`wavelength shift.
`
`[0009] Attempts to solve the wavelength shift problem
`have included systemsthat correlate the wavelength shift to
`a change in drive circuit current. The change in drive circuit
`current drives the LED to a specific wavelength. Typically,
`these systems include a scheme for determining the wave-
`length shift of the photodiodesvia a seriesoffilters, diffusers
`and a plurality of photodetectors. Unfortunately,
`this
`approach is too complex and expensive for practical manu-
`facturing techniques.
`
`[0010] Therefore, there is a need for a non-invasive sensor
`system that is capable of measuring the wavelengthofa light
`source without requiring prior knowledge of the wavelength
`of the light source and is not complex or expensive to
`manufacture.
`
`SUMMARY
`
`[0011] This invention is a self-calibrating sensor system
`“SCSS” capable of determining the actual wavelength of
`light emitted from a light source resulting in accurate
`measurements over a wide variation of wavelength ranges.
`In an example operation, the SCSS is capable of receiving
`incident light radiation from the at least one light source at
`a sensor probe and producinga calibrated signal correspond-
`ing to the received incident light radiation at the sensor
`probe.
`
`[0012] As an example implementation of the SCSSarchi-
`tecture,
`the SCSS may include a sensor probe receiving
`incident light radiation from at least one light source and a
`calibration circuit in signal communication with the sensor
`probe. The calibration circuit may produce a calibrated
`signal corresponding to the received incident light radiation
`biological tissue in order to determine the oxygen saturation
`at the sensor probe. The sensor probe may include a wave-
`(SP02) within the blood Similarly, an example of an indus-
`length sensor. The wavelength sensor may includeafirst
`trial application may include a non-invasive sensor system
`diode configured to receive short wavelengths from the
`having a coherent light of a known specific wavelength
`incident
`light radiation and produce a first photocurrent
`transmitted from a coherent light source (such as an LED
`signal and a second diode configured to receive long wave-
`emitter) through a target, such as a fluid or material,
`to
`lengths from the incident
`light radiation and produce a
`photodetector.
`second photocurrent signal.
`
`[0007] Unfortunately, these types of non-invasive sensor
`systems utilizing a coherent light source require accurate
`prior knowledge of the wavelength of the coherent light
`source in order to determine the amount of coherent light
`that is absorbedorreflected through the target. One way of
`having the prior knowledge of the wavelength is to select
`coherentlight source emitters that have wavelengths within
`a certain range of tolerance. As such, attempts at determin-
`ing the wavelength have included a binning process of
`selecting LEDs within the required nominal wavelength
`specifications.
`
`[0008] However,it is appreciated by those skilled in the art
`and familiar with the production of emitter-photodiode
`sensing devices that there is a need to be able to select from
`a wider variation of emitter output wavelengths in reducing
`the production costs and defect rates of the sensing devices.
`As an example, typical production techniques require selec-
`tion of an emitter within 2 nm of a target wavelength, which
`maylead to rejection of 40-60% of the component emitters.
`Moreover, an additional problem is that a selected emitter,
`which was within the target wavelength at time of produc-
`
`15
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`[0013] The invention may be better understood with ref-
`erence to the following figures. The components in the
`figures are not necessarily to scale, emphasis instead being
`placed upon clearly illustrating the principles of the inven-
`tion. Moreover,
`in the figures,
`like reference numerals
`designate corresponding parts throughout the several views.
`
`FIG.1 illustrates a block diagram of an example
`[0014]
`implementation of a self-calibrating sensor system (SCSS).
`
`FIG.2 illustrates a block diagram of an example
`[0015]
`implementation of the probe block of the SCSS shown FIG.
`1.
`
`[0016] FIG. 3 illustrates a cross-sectional view of an
`example implementation of the probe shown in FIG.2.
`
`[0017] FIG. 4A illustrates a cross-sectional view of
`another example implementation of the probe shown in
`FIG.2.
`
`15
`
`

`

`US 2003/0033102 Al
`
`Feb. 13, 2003
`
`[0018] FIG. 4B illustrates a cross-sectional view of
`example reflective implementation of the probe shown in
`FIG.2.
`
`[0019] FIG. 5 is a top view of an example implementation
`of the probe shown in FIG.4.
`
`[0020] FIG. 6 is a cross-sectional view of the probe
`implementation of FIG.5.
`
`[0021] FIG. 7 illustrates an example implementation of
`the probe block shown in FIG.2 utilizing photodiodes.
`
`[0022] FIG. 8 illustrates a cross-sectional view of an
`example implementation of the wavelength sensor block
`shown in FIG. 7 utilizing a double diffusion photodiode.
`
`[0023] FIG. 9 is a graph of the response curve of the
`wavelength sensor shown in FIG.8.
`
`[0024] FIG. 10 is schematic diagram depicting an exem-
`plary implementation of the calibration circuit block shown
`in FIG. 1.
`
`[0025] FIG. 11 is schematic diagram depicting another
`exemplary implementation of the calibration circuit block
`shown in FIG.1.
`
`[0026] FIG. 12 is a flow chart illustrating the process
`performed by the SCSS shown in FIG.1.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`[0027] FIG. 1 illustrates a block diagram of a self-cali-
`brating sensor system (SCSS) 100. The SCSS 100 may
`include a probe 102, a calibration circuit 104, a controller
`106, software 108 located on in memory (not shown) and
`optional lookup table (“LUT”) 110. The probe 102 is in
`signal communication,via signal path 112, to the calibration
`circuit 104. The calibration circuit 106 may be a divider
`and/or comparatorcircuit.
`
`[0028] The calibration circuit 104 is in signal communi-
`cation to the controller 106 and an external output device
`(not shown) via signal paths 114 and 116, respectively. The
`controller 106 is in signal communication to software 108
`and optional LUT 110 via signal paths 118 and 120, respec-
`tively.
`
`[0029] The controller 106 may be any general-purpose
`processor such as an Intel XXX86, Motorola 68XXX or
`PowerPC, DEC Alpha or other equivalent processor. Alter-
`natively, a specific circuit or oriented device mayselectively
`be utilized as the controller 106. Additionally, the controller
`106 mayalso be integrated into a signal semiconductor chip
`such as an Application Specific Integrated Chip (ASIC) or
`Reduced Instruction Set Computer (RISC), or may be imple-
`mented via a Digital Signal Processor (DSP) chip. Examples
`of a specific circuit or oriented device for the controller 106
`may also be a mixed sionac ASIC.
`
`[0030] The software 108 may be resident in memory (not
`shown)located either internally or externally to the control-
`ler 106. The software 108 includes both logic enabling the
`controller 106 to operate and also logic for self-calibrating
`the SCSS 100.
`
`[0031] An example of the external output device may be
`an oximeter such as a NPB40 manufactured by Nellcor of
`
`Pleasanton, Calif., a 9840 Series pulse oximeter manufac-
`tured by Nonin Medical, Inc. of Plymouth, Minn., or an
`equivalent device.
`
`[0032] FIG. 2 shows an example implementation of probe
`102. Probe 102 may include a probe light source 200 and
`wavelength sensor 202. Probe light source 200 may include
`a first light source 204 and second light source 206. First
`light source 204 and second light source 206 may be
`implemented utilizing light-emitting diodes (LEDs). As an
`example implmentation in oximeter application, first light
`source 204 may be an LED emitting light radiation at a
`wavelength of approximately 660 nm and second light
`source 206 may be an LED emitting light radiation at a
`wavelength of approximately 880 nm. Wavelength sensor
`202 may be implemented utilizing a double diffusion pho-
`todiode. It is appreciated by those of skill in the art that
`probe light source 200 may also include multiple light
`sources in the order of three or more.
`
`In FIG. 3, a cross-sectional view of an example
`[0033]
`implementation of the probe 300 is shown. In this example,
`probe 300 may be a medical device such as a transmissive
`blood oxygen saturation and pulse rate sensor. However,it
`would be appreciated by one skilled in the art that probe 300
`mayalso be a reflective sensor. Additionally, probe 300 may
`also be utilized for measuring other blood constituents
`including, but not
`limited to, oxyhemoglobin, bilirubin,
`carboxy-hemoglobin, and glucose. Probe 300 may include a
`rigid casing 302 having a cavity 304 and casing butt 306,
`first light source 204, second light source 206 and wave-
`length sensor 202. Probe 300 is connected to calibration
`circuit 104, FIG.1, via signal path 112. A material 308, FIG.
`3, such as a finger may be inserted into the cavity 304.
`
`[0034] As an example,first light source 204 and second
`light source 206 may be two LED emitters that produce light
`radiation at a wavelength of approximately 660 nm and 880
`nm, respectively. Wavelength sensor 202 is supported within
`the rigid casing 302 opposite first light source 204 and
`second light source 206. First light source 204 and second
`light source 206 and wavelength sensor 202 maybe in signal
`communication with a control cable (not shown). The con-
`trol cable is in signal communication with an oximeter (not
`shown) via signal path 112. The oximeter determines the
`oxygen saturation of the blood in the material 308 (in this
`example a finger) by measuring and processing the amount
`of incident light radiation reaching wavelength sensor 202
`from a pulse of light radiation from first light source 204.
`
`In operation, the SCSS 100, FIG. 1, performs a
`[0035]
`self-calibration procedure prior to measuring any of the
`properties of the material 308, FIG. 3. This self-calibration
`procedure includes emitting a pulse of light radiation from
`the first light source 204 that is received as incident light
`radiation by wavelength sensor 202 prior to inserting mate-
`rial 308 into the cavity 304. The oximeter utilizes the
`measured incident light radiation received by wavelength
`sensor 202 to determine the operating wavelength of thefirst
`light source 204. Once the operating wavelength ofthe first
`light source 203 is known, the SCSS 100, FIG.1, is utilized
`in combination with the oximeter to accurately determine
`blood oxygen saturation of the material 308.
`
`Theself-calibration procedure is beneficial because
`[0036]
`it is appreciated by those skilled in the art that light radiation
`output by first light source 204 of 660 nm in this example
`
`16
`
`16
`
`

`

`US 2003/0033102 Al
`
`Feb. 13, 2003
`
`is the
`It
`region.
`implementation is in the red spectral
`absorption of this red light radiation that
`the oximeter
`utilizes to determine the oxygen saturation of the blood. As
`such, a relatively small variation in operating wavelength
`may results in inaccurate readings at the oximeter. As an
`example, without the self-calibration procedure, if the light
`radiation output by first light source 204 varied in excess of
`+2 nm from an operating wavelength required by the oxime-
`ter, the results would be inaccurate.
`[0037] FIG. 4A illustrates a cross-sectional view of
`another example implementation of probe 400.
`In this
`example, probe 400 may include a rigid or flexible casing
`402 having a cavity 404,first light source 204, second light
`source 206 and wavelength sensor 202. Similar to the
`previous example implementation, probe 400 is connected
`to calibration circuit 104, FIG. 1, via signal path 112,
`however, probe 400, FIG. 4A, does not have a cavity butt.
`A material 406 may be inserted into the cavity 404.
`[0038] Similar to the previous example,first light source
`204 and second light source 206 may be two LED emitters
`that produce light radiation at different wavelengths. Wave-
`length sensor 202 is supported within the rigid casing 402
`opposite first light source 204 and second light source 206.
`First
`light source 204 and second light source 206 and
`wavelength sensor 202 may be in signal communication
`with a control cable (not shown). The control cable is in
`signal communication with a measuring device (not shown)
`via signal path 112. The measuring device determines the
`properties in the material 406 by measuring and processing
`the amount of incident light radiation reaching wavelength
`sensor 202 from a pulse of light radiation from first light
`source 204.
`
`[0039] As an industrial example, the material 406 may be
`a fluid, liquid or solid material that exhibits optical trans-
`missive characteristics that may be measured and utilized to
`determine the properties of the material. An example imple-
`mentation would include measuring the properties of the
`material for process or quality control purposes.
`[0040] Again in operation, the SCSS 100, FIG. 1, per-
`formsa self-calibration procedure prior to measuring any of
`the properties of the material 406, FIG. 4A. This self-
`calibration procedure includes emitting a pulse of light
`radiation from the first light source 204 that is received as
`incident light radiation by wavelength sensor 202 prior to
`inserting material 406 into the cavity 404. The measuring
`device utilizes the measured incidentlight radiation received
`by wavelength sensor 202 to determine the operating wave-
`length of the first light source 204. Once the operating
`wavelength of thefirst light source 204 is known, the SCSS
`100, FIG.1, is utilized in combination with the measuring
`device to accurately determine the properties of the material
`406.
`
`[0041] FIG. 4B illustrates a cross-sectional view of an
`example reflective implementation of probe 408. In this
`example, probe 408 may include a rigid or flexible casing
`410 having a cavity 412, first light source 204, second light
`source 206 and wavelength sensor 202. Similar to the
`previous example implementation, probe 408 is connected
`to calibration circuit 104, FIG. 1, via signal path 112,
`however, probe 408, FIG. 4B, does not have a cavity butt.
`A material 412 may be inserted into the cavity 412.
`[0042] Similar to the previous example,first light source
`204 and second light source 206 may be two LED emitters
`
`that produce light radiation at different wavelengths. How-
`ever, in this example, wavelength sensor 202 is supported
`within the rigid casing 410 adjacentto first light source 204
`and second light source 206. First light source 204 and
`second light source 206 and wavelength sensor 202 may be
`in signal communication with a control cable (not shown).
`The control cable is in signal communication with a mea-
`suring device (not shown) via signal path 112. The measur-
`ing device determines the properties in the material 412 by
`measuring and processing the amount of incident
`light
`radiation reflected by material 412 and reaching wavelength
`sensor 202 from a pulse of light radiation from first light
`source 204.
`
`[0043] Again, as an industrial example, the material 412
`may bea fluid, liquid or solid material that exhibits optical
`transmissive characteristics that may be measured and uti-
`lized to determinethe properties of the material. An example
`implementation would include measuring the properties of
`the material for process or quality control purposes.
`
`[0044] Again in operation, the SCSS 100, FIG. 1, per-
`formsa self-calibration procedure prior to measuring any of
`the properties of the material 412, FIG. 4B. This self-
`calibration procedure includes emitting a pulse of light
`radiation from thefirst light source 204 that is reflected by
`flexible casing 410 and later received as incident
`light
`radiation by wavelength sensor 202 prior to inserting mate-
`rial 412 into the cavity 410. The measuring device utilizes
`the measured incident light radiation received by wave-
`length sensor 202 to determine the operating wavelength of
`the first light source 204. Once the operating wavelength of
`the first light source 204 is known, the SCSS 100, FIG.1,
`is utilized in combination with the measuring device to
`accurately determine the properties of the material 412.
`
`It is appreciated by of skill in the art that it is
`[0045]
`possible to generate signals from the wavelength sensor 202,
`FIG. 2 during operation of the light sources 204 and 206
`through the medium (i.e., material 308, FIG. 3, 406, FIG.
`4A, and/or 414, FIG. 4B) being inspected. It is also possible
`to generate the same signals using light reflected off the
`medium. Therefore, it is not necessary to couple the light
`sources 204, FIG. 2 and 206 directly to the wavelength
`sensor 202 as long as the medium either transmitsor reflects
`enoughlight to generate processable signals from the wave-
`length sensor 202.
`
`In FIG. 5, a top view of an example medical
`[0046]
`implementation of probe 500 having a flexible casing (i.e.,
`flexible strip) 502 is shown. Probe 500 may include first
`light source 204, second light source 206 and wavelength
`sensor 202. In this example implementation, probe 500 is a
`blood oxygen saturation and pulse rate sensor that utilizes
`the flexible strip 502 to attach to a material, such as a body
`part (not shown). The probe 500 is connected to an oximeter
`(not shown) via signal path 112. The flexible strip 502 may
`be wrapped around the body part and affixed to itself via an
`attachmentstrip (such as an adhesive strip) 504. Example
`body parts would includea finger, toe, ear-lobe, arm, leg or
`other similar parts.
`
`[0047] As an example,first light source 204 and second
`light source 206 may be two LED emitters that produce light
`radiation at a wavelength of approximately 660 nm and 880
`nm, respectively. Wavelength sensor 202 is supported within
`the flexible strip 502 and placed opposite first light source
`
`17
`
`17
`
`

`

`US 2003/0033102 Al
`
`Feb. 13, 2003
`
`204 and second light source 206 whenthe flexible strip 502
`is wrapped around a body part. First light source 204 and
`second light source 206 and wavelength sensor 202 may be
`in signal communication with a control cable (not shown).
`The control cable is in signal communication with an
`oximeter (not shown) via signal path 112. The oximeter
`determines the oxygen saturation of the blood in the body
`part by measuring and processing the amount of incident
`light radiation reaching wavelength sensor 202 from a pulse
`of light radiation from first light source 204.
`
`[0048] As before, in operation, the SCSS 100, FIG. 1,
`performsa self-calibration procedure prior to measuring any
`of the properties of the body part. This self-calibration
`procedure includes, prior to wrapping flexible strip 502
`around the body part, bending the flexible strip 502 so that
`the first light source 204 and second light source 206 are
`opposite in special orientation to wavelength sensor 202 and
`then emitting a pulse of light radiation from the first light
`source 204 that is received as incident light radiation by
`wavelength sensor 202. The oximeter utilizes the measured
`incident light radiation received by wavelength sensor 202
`to determine the operating wavelength of the first
`light
`source 204. Once the operating wavelength of thefirst light
`source 204 is known, placed around a body part and the
`wavelength sensor 202 measures the incidentlight radiation
`emitted by the first light source 204 and passing through the
`blood flowing within the body part. The SCSS 100, FIG.1,
`is then utilized in combination with the oximeter to accu-
`
`rately determine blood oxygensaturation of the body part. In
`FIG.6, a cross-sectional view of the probe 500 is shown in
`a wrap type position.
`
`In FIG. 7, an example implementation of the probe
`[0049]
`700 is shownutilizing photodiodes. Similar to FIG. 2, Probe
`700, FIG.7, includes probe light source 702 and wavelength
`sensor 704. Probe light source 702 includesfirst light source
`706 and second light source 708. First light source 706 may
`include LED 710 and second light source may include LED
`712. Wavelength sensor 704 is a double diffusion photo-
`diode.
`
`[0050] As an example of operation, LED 710 and LED
`712 may have their cathodes grounded in commonat signal
`path 714 and may emit light radiation 716 at wavelengths
`660 nm and 880 nm, respectively, when a voltage is applied
`at anodes 718 and 720, respectively. The emitted light
`radiation 716 is incident on material 722. A part of the
`emitted light radiation 716 is transmitted through material
`722 and is received as incident
`light radiation 724 by
`wavelength sensor 704. As before,
`in order to properly
`measure the properties of the material 722 from the received
`incident light radiation 724, the SCSS 100, FIG. 1 performs
`a self-calibration procedure.
`
`[0051] The SCSS 100, FIG.1, performsa self-calibration
`procedure prior to measuring any of the properties of the
`material 722. This self-calibration procedure includes emit-
`ting a pulse of light radiation 716 from LED 710 that is
`received as incident
`light radiation 724 by wavelength
`sensor 704 prior to inserting material 722 between the probe
`light source 702 and wavelength sensor 704. The oximeter
`utilizes the measured incident light radiation 724 received
`by wavelength sensor 704 to determine the operating wave-
`length of LED 710. Once the operating wavelength of LED
`710 is known, the SCSS 100, FIG. 1, is utilized in combi-
`
`nation with the oximeter to accurately determine blood
`oxygen saturation of the material 722.
`
`[0052] FIG. 8 illustrates a cross-sectional view of the
`wavelength sensor 704 receiving incident light radiation 724
`utilizing a double diffusion photodiode (also known as a
`double junction photodiode). Photodiodes with double dif-
`fusion are typically utilized to accurately measure the cen-
`troid wavelength of light sources such as LEDs 710 and 712.
`Double diffusion photodiodes are processed with two junc-
`tions, one on the top surface and one on the back surface of
`a semiconductor photodiode (such as a Si-photodiode), each
`junction typically exhibits a different and well-defined spec-
`tral response. As result, by measuring the quotient of signals
`generated by the two junctions, the centroid wavelength of
`any given monochromatic light source may be determined.
`
`[0053] The wavelength sensor 704 has two p-n junctions
`constructed vertically on a commonsilicon substrate. The
`wavelength sensor 704 includesa first anode 800, common
`cathode 802, first diode 804 (also known as an upperdiode),
`second diode 806 (also known as a lower diode), second
`anode 808, and a thin active region 810. Thefirst anode 800
`is positioned on the top surface above the common cathode
`802 forming the first diode 804. The thickness of the first
`diode 804 is chosen so that
`the energy of the shortest
`wavelength being measured from the incident light radiation
`724 is absorbed entirely therein. The second diode 806 is
`formed between the common cathode 802 and the second
`
`anode 808 that placed on the bottom surface with the thin
`active region 810 between the commoncathode 802 and the
`second anode 808. The thickness of the thin active region
`810 is selected to allow for absorption of substantially all of
`the longest measured wavelength of incident light radiation
`724.
`
`FIG.9 illustrates a typical plot 900 of the spectral
`[0054]
`response of the wavelength sensor 704, FIG. 8. The plot
`900, FIG. 9, has a vertical axes 902 representing relative
`response, in percentage, of the wavelength sensor 704, FIG.
`8, and a horizontal axis 904, FIG. 9, representing the
`wavelength of the incident light radiation 724, FIG. 8. The
`plot 900, FIG. 9, shows two response curves 906 and 908
`representing the relative response versus wavelength for the
`first diode 804, FIG. 8, and the second diode 806, respec-
`tively.
`
`[0055] As an example of operation of the wavelength
`sensor 704, the first diode 804 may have an enhanced blue
`response and the second diode 806 may have an enhanced
`red response. In this example, the absorbed radiation of the
`incident
`light radiation 724 between the red and blue
`responses (such as between 456 and 900 nm) generates two
`photocurrent signals proportional to the wavelength of the
`incident light radiation 724. The quotient of these photocur-
`rent signals is independent of the light
`level up to the
`saturation point of the wavelength sensor 704. Utilizing this
`example, the wavelength of either monochromatic incident
`light radiation 724 or the spectral density peak of polychro-
`matic incident light radiation 724 may be determined. An
`example of the wavelength sensor 704 may be a PSS
`WS-7.56 wavelength sensor produced by Pacific Silicon
`Sensor, Inc. of Westlake Village, Calif.
`
`In FIG. 10, a schematic diagram depicting an
`[0056]
`exemplary implementation of the calibration circuit 1000 is
`shown. The calibration circuit 1000 is in signal communi-
`
`18
`
`18
`
`

`

`US 2003/0033102 Al
`
`Feb. 13, 2003
`
`cation with the probe 1002 and controller 106, FIG.1, via
`signal paths 112 and 114, respectively. The calibration
`circuit 1000 may include a pair of amplifiers 1004 and 1006
`(such as log amplifiers) in signal communication with first
`anode 800, FIG. 8 and second anode 808 of wavelength
`sensor 1008, FIG. 10, and a differential amplifier 1010, via
`signal paths 1010, 1012 and 1014, respectively. The differ-
`ential amplifier 1008 is in signal communication with the
`controller 106, FIG. 1, via signal path 112.
`
`In operation, the wavelength sensor 1004 produces
`[0057]
`two photocurrent signals from the two junctions(i.e., pho-
`todiodes 804 and 806) in the double diffusion photodiode.
`Each junction in the wavelength sensor 1004 exhibits a
`different and well-defined spectral response, which is know
`to the controller 106, FIG. 1, and the magnitude of these two
`resulting photocurrent signals are proportional to the wave-
`length of the measured incident light radiation 724, which
`corresponds to one of the light sources (either 204 or 206,
`FIG.2) in probe 1002, FIG. 10. The photocurrent signals
`are amplified by amplifiers 1004 and 1006 via signal paths
`1010 and 1012, respectively, and input into the differential
`amplifier 1008 via signal path 1018 and 1020. If the ampli-
`fied photocurrent signals 1018 and 1020 are approximately
`equal the corresponding differential output signal 1022 of
`the differential amplifier 1008 is almost equal to zero. Once
`the differential output signal 1022 is almost equalto zero the
`wavelength of the incident light radiation is determined and
`the SCSS 100, FIG. 1, is calibrated.
`
`[0058] When the amplified photocurrent signals 1018 and
`1020 are not approximately equal the corresponding differ-
`ential output signal 1022 will vary according to the differ-
`ence in magnitude value between the amplified photocurrent
`signals 1018 and 1020. The differential output signal 1022 is
`the utilized as a reference by the controller 106, FIG. 1. The
`controller 106 determines the wavelength of the incident
`light radiation 724 by knowing the spectral response of the
`photodiodes 804 and 806, FIG. 8. The controller 106 either
`determines the wavelength ofthe incident light radiation 724
`utilizing software 108 or other hardware (not shown) located
`in the SCSS 100. The software 108 may include logic that
`allows the controller 106 to calculate the wavelength values
`in real-time from the measure values received from the
`
`wavelength sensor 1004.
`
`[0059] Alternatively, the controller 106 may determine the
`wavelength of the incident light radiation 724 utilizing the
`lookup (“LUT”)table 110. The LUT 110 mayberesident in
`memory (not shown)residenteither internally or externally
`to the controller 106. The LUT 110 includes a ta