AQTANA
`US005396893A
`Patent Number:
`p19
`United States Patent
`5,396,893
`Mar. 14, 1995
`[45] Date of Patent:
`Oberg et al.
`
`[11]
`
`54[54]
`
`[76]
`
`METHOD AND APPARATUS FOR
`ANALYZING HEART AND RESPIRATORY
`FREQUENCIES
`PHOTOPLETHYSMOGRAPHICALLY
`
`Inventors: Ake P. Oberg, Ugglebovagen 79,
`S-590 60 Ljungsbro; Lars-Giran
`Lindberg, Knektgatan 18, S-582 65
`Linkdping, both of Sweden
`
`920,274
`[21] Appl. No.:
`Feb. 14, 1991
`[22] PCT Filed:
`PCT/SE91/00106
`[86] PCT No::
`Aug. 3, 1992
`§ 371 Date:
`Aug. 3, 1992
`§ 102(e) Date:
`.
`[87] PCT Pub. No; WO91/11956
`PCT Pub. Date: Aug. 22, 1991
`.
`. _.
`Foreign Application Priority Data
`[30]
`Feb. 16, 1990 [SE]
`Sweden ....ccsscssssessscecseessereeees 9000564
`
`Tint, C16eee ects eeeeeneenenees A61B 5/0205
`[SL]
`[52] U.S. C1. eeeeeeeeseeeseeteseeenenee 128/671; 128/687;
`128/666
`[58] Field of Searelt ..........cccssereee 128/633, 664-667,
`128/670-671, 668, 687-690
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,183,360
`1/1980 Carlson et al.
`.
`4,379,460 4/1983 Tudell .o...ccsssssssrsrssenerees 128/671
`4,781,201 11/1988 Wright et ab. 0.0... cee 128/671
`4,788,982 12/1988 Gedeon etal. .
`4,934,372 6/1990 Corenman etal............. 128/666 X
`§,078,136
`1/1992 Stone et al.- 128/666 X
`
`FOREIGN PATENT DOCUMENTS
`0109826 5/1984
`European Pat. Off.
`.
`319158 6/1989
`European Pat. Off.
`.
`0341327 11/1989
`European Pat. Off.
`.
`0349755
`1/1990 European Pat. Off.
`.
`Seiiess a,jos European Pat. Off.
`.
`ermany -
`03211
`8/1985 WIPO.
`Primary Examiner—Angela D. Sykes
`Attorney, Agent, or Firm—Sughrue, Mion, Zinn,
`Macpeak & Seas
`[57]
`ABSTRACT
`A pulse-frequency analyzing monitor whichis provided
`with an optical sensor and whichis intended for measur-
`ing
`photoplethysmographically the blood circulation of
`a subject,suchas 2body part of a human being or an
`animal, includes a light source, preferably a light-emit-
`ting diode for infraredlight, fibre optics, a detector unit
`for detecting the alternating voltage, or AC-component
`of a generated PPG-signal for the purpose of determin-
`ing the heart frequency of the subject, an electronic
`amplifying unit and a presentation unit, for instance an
`oscilloscope of a display unit. The apparatus also in-
`cludes meansfor separating from the detected PPG-sig-
`nal a signal component which indicates the respiration
`frequency of the subject. The PPG-signal is coupled to
`a filter, preferably a digital filter, which enables limit
`frequencies and the degree of amplification to be set.
`Thedigital filter may be a component of a microproces-
`sor which is able to eliminate disturbances, for instance
`disturbances emanating from 50 Hzstraylight, in addi-
`tion to separating signals concerning the heart and res-
`piration frequency of the subject. The invention also
`relates to a method of carrying out such photople-
`thysomographic measuring processes.
`
`11 Claims, 4 Drawing Sheets
`
`
`
` SAMPLE
`AND HOLD
`
`
`AMPLIFICA-
`TION 1-500
`TIMES
`
`
`
`
`
`
`LP-FILTER
`10 Hz
`
`
`
` P-FILTER
`0 Hz
`
`L2
`
`OUTPUT
`SIGNAL
`
`OUTPUT
`SIGNAL
`
`0001
`
`Apple Inc.
`APL1062
`8,923,941
`
`U.S. Patent No.
`
`FITBIT,
`
`Ex. 1062
`
`Apple Inc.
`APL1062
`U.S. Patent No. 8,923,941
`
`0001
`
`FITBIT, Ex. 1062
`
`

`

`U.S. Patent
`
`Mar. 14, 1995
`
`Sheet 1 of 4
`
`5,396,893
`
`MEASURING
`PROBE
`
`200 Hz
`
`
` LP-FILTER
`TIMES
`
`AMPLIFICA-
`TION 1-500
`
`LP-FILTER
`20 Hz
`
`LP-FILTER
`10 Hz
`
`OUTPUT
`SIGNAL
`
`QUT PUT
`SIGNAL
`
`FIG. 6
`
`
`
`0002
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`FITBIT, Ex. 1062
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`0002
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`FITBIT, Ex. 1062
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`

`

`U.S. Patent
`
`Mar. 14, 1995
`
`Sheet 2 of 4
`
`5,396,893
`
`mM
`
`FIG. 2
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`
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`0003
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`FITBIT, Ex. 1062
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`
`
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`

`

`U.S. Patent
`
`Mar, 14, 1995
`
`Sheet 3 of 4
`
`5,396,893
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`

`

`U.S. Patent
`
`Mar. 14, 1995
`
`Sheet 4 of 4
`
`5,396,893
`
`
`
`0005
`
`FITBIT, Ex. 1062
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`0005
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`FITBIT, Ex. 1062
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`

`

`1
`
`5,396,893
`
`METHOD AND APPARATUS FOR ANALYZING
`HEART AND RESPIRATORY FREQUENCIES
`PHOTOPLETHYSMOGRAPHICALLY
`
`TECHNICAL FIELD
`
`Thepresent invention relates to monitoring apparatus
`provided with an optical sensor and functioning to ana-
`lyze pulse frequencies by measuring the blood circula-
`tion of a measuring object, such as a part of the human
`body or an animal body using photoplethysmography
`(PPG-measuring), said apparatus being of the kind set
`forth in the preamble of claim 1. The invention also
`relates to a method of taking such measurements.
`Photoplethysmography (hereinafter abbreviated to
`PPG)has been knownto the art for more than 50 years
`and is applied technically for measuring peripheral
`blood circulation. The method is primarily used for
`measuring heart frequencies and blood circulation when
`performing surgery. The method has many advantages,
`since, among other things, it is non-invasive and does
`not subject the patient to any appreciable trauma. Fur-
`thermore, the method requires no highly expensive or
`complicated equipment in order to be putinto effect.
`When light from a suitable light source impinges on
`the skin, the light is dampened or attenuated according
`to the nature of the tissue on which the light impinges.
`This light attenuation is assumed to be constant. The
`light also passes through a numberof blood vessels and
`is also attenuated by the blood present. The light is
`attenuated as a result of a number of complex processes,
`such as absorption, reflection and different forms of
`scattering. The PPG-technique is based on the assump-
`tion that the more blood that is present in the volume
`investigated, the more the light is attenuated. This re-
`sults in two signal components of interest, namely a
`DC-component which correspondsto the total amount
`of blood in the investigated volume and an AC-compo-
`nent which signifies pulsation of the blood flow.
`In order to study the aforedescribed phenomenon,it
`is necessary to use a light source, a light detector, ampli-
`fying electronics and a display unit, for instance an
`oscilloscope or a printer.
`Thelight source and the detector may be placed on a
`respective side of the object on which blood circulation
`is to be measured, and the detector consequently mea-
`sures the light transmitted. This techniqueis, at times,
`referred to as transmission-photoplethysmography and
`can only be applied to a few skin surfaces, such as fin-
`gers, ear lobes and toes.
`A more general method is to place both the light
`source and the detector in one and the same probe and
`measure the light reflected. This technique is known as
`reflection * and is the dominating technique. It has long
`been understood that the pulsating component or AC-
`componentof the PPG-signal is contingent on changes
`in blood volume during each heart beat. The greater the
`volume of blood, the less light will impinge on the de-
`tector.
`It is obvious, however, that this is not the whole
`truth. Tests have been carried out in which blood has
`been allowed to pulsate in rigid glass tubes, where
`changes in volume are impossible and wheresolely the
`flow rate pulsates. A pulsating PPG-signal is also ob-
`tained in this case, which can be explained by the detec-
`tion of changes in orientation of the erythrocytes,
`which varies during each heart beat.
`
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`In summary, there are at least two reasons for the
`AC-component, namely a change in blood volume and
`the orientation of the erythrocytes.
`A typical PPG-signal has, in the time plane, the form
`of a blood-pressure curve having the same periodicity
`as the heart beats. The signal also includes a number of
`low frequencies.
`The present invention is based on the realization that
`the lower frequencies occur as a result of changes in
`blood flow caused by the sympathetic nerve system and
`by respiration,
`this realization being based on the
`knownfact that the intrathoracic pressure is lowered
`when breathing-in, or inspiring. This subpressure is
`utilized to “suck” the venous blood into the atrium and
`ventricle.
`The invention departs from this starting point and
`assumes that this subpressure causes variations in blood
`flow in venousplexus andalso that it should be possible
`to detect this variation with the aid of the PPG-tech-
`nique, particularly by using a technique which enables
`measurements to be made in the venous plexus.
`Nerve signals in the sympathetic nerve system also
`influence the blood flow. The smooth muscle around
`the vessels pulsates at a frequency whichlies close to
`the respiration frequency. This pulsation is normally
`referred to as Traube-Hering’s waves, after the scien-
`tists’ Traube-Hering. Waves of a still lower frequency
`are also found, these waves normally being referred to
`as Mayer’s waves.
`The blood also pulsates through the so-called arterio-
`venous anastomises, so as to control body temperature.
`This normally occurs at a frequency of about 0.3 Hz and
`is designated Burton waves.
`DISCLOSURE OF THE INVENTION
`
`The present invention is based on the aforesaid real-
`ization and on measurements, or assays, carried out with
`the aid of apparatus that has been constructed in accor-
`dance with the theory on which the present invention is
`based.
`The inventive monitoring apparatus intended for
`measuring blood circulation is of the kind set forth in
`the preamble of claim 1 and has the characterizing fea-
`tures set forth in the characterizing clause ofsaid claim.
`The exhaustive experimentation, which forms the
`basis of the invention and which is briefly described
`herebelow, has shown that respiration is the totally
`dominating low-frequency component of the PPG-sig-
`nal.
`It was found from the series of experiments per-
`formed that the extracted signal can be encountered
`substantially irrespective of where in the body the
`probe is placed. This leads to the conclusion that the
`extracted PPG-signal constitutes a measurement of var-
`iations in blood pressure caused by respiration, and
`therewith also variations in the flow of blood through
`the object under examination.
`It is expected that the inventive monitoring apparatus
`will find universal use within human care establish-
`ments. In the case ofpatients in intensive care wards or
`under anaesthetic or under postoperative conditions, it
`is important to monitor heart and respiration frequen-
`cies. When these two physiological variables are
`known, the doctor or nursing syster will have a good
`picture ofthe patient’s general condition. Monitoring of
`these variables under anaesthetic conditions can facili-
`tate the assessment of the depth of anaesthesia.
`
`0006
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`

`4
`adapt to the prevailing heart and/or respiration fre-
`quency, so as to optimize the filter properties.
`Furthermore, the monitoring apparatus will prefera-
`bly be provided with means for DC-compensating the
`PPG-signal, so as to balance-out the low frequency
`components of said signal automatically, without expe-
`riencing harmful energy losses.
`In the case of one embodimentof the invention which
`is particularly beneficial in practical application, the
`monitoring apparatus includes a probe which is in-
`tended to be placed on a suitable part of the body, for
`example a finger, and which includes means for deliver-
`ing light to said body part and meansfor capturing light
`which passes through said body part or which is re-
`flected therein, for the purpose of passing this light to
`the detector unit. This monitoring apparatus is charac-
`terized by optical fibres connected to the probe and
`functioning to conduct light from a light source to the
`skin and from the skin to the detector unit respectively.
`By conducting, in said apparatus, the light through
`optical fibres to and from the skin, there is obtained a
`system which is highly resistant to electromagnetic
`disturbances or interference, a feature which is ex-
`tremely important within the sphere of medical treat-
`ment. This particular feature enables the heart fre-
`quency andrespiration frequency to be recorded during
`surgery in which diathermyis applied. An apparatus of
`this kind which is insensitive to disturbances during
`surgery represents a very important step forwards in the
`30 art
`
`oy0
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`25
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`3
`Aboveall, the invention avoids those serious disad-
`vantages that are associated with respiratory frequency
`monitoring methods and apparatus hitherto used, all of
`which are normally unreliable, besides being both stren-
`uous and complex.
`It is generally more important to monitor respiration
`parameters in the case of infant care than in the case of
`adults under intensive care. In this regard, the inventive
`monitoring apparatus is superior to the technique which
`has been used most frequently hitherto, namely the use
`of impedance plethysmography with the aid of ECG-
`electrodes placed on the surface of the skin, among
`other things because such electrodes (normally three)
`take-up a relatively large area of the thorax. When
`requiring to make X-ray examinations,it is necessary to
`removethe electrodes, since they are not transparent to
`X-rays.
`Furthermore, light disturbances from peripheral elec-
`trical apparatus are induced in ECG-cables with associ-
`ated input amplifiers. The signal cables are coupled both
`inductively and capacitively. When carying out sur-
`gery, it is impossible to carry out ECG-recordings and
`to measure heart frequencies over prolonged periods of
`time, due to the surgical application of diathermy.
`ECG-electrodes and the paste used together there-
`with cause irritation of the skin, particularly when mon-
`itoring is effected over a prolonged period and particu-
`larly in the case of infants whose skin is very tender and
`sensitive. The electrodes and associated leads or cables
`also limit the ability of the child to move.
`The present invention provides important direct ad-
`vantages in relation to the aforesaid, and also affords
`indirect advantages with respect to methods of measur-
`ing respiration frequency.
`For example, the inventive monitoring apparatus can
`be applied and handled with ease; it avoids the aforesaid
`problems associated with prolonged use of skin elec-
`trodes; it is free from disturbances during surgery in
`which diathermy is applied; and affords a wide degree
`of freedom with regard to positioning of the sensor. For
`example, a sensor-provided probe can be placed on a
`finger or on a toe, at a distance from the thorax region
`where another investigation is being made. Further-
`more, the sensor element can be made very small, such
`as not to interfere with X-ray examinations to any ap-
`preciable extent.
`An additional, very important advantage afforded by
`the inventive monitoring apparatus is that it can be
`integrated with a number of different medical instru-
`ments of the kind where heart frequency and respiration
`frequency are important parameters, for instance pul-
`soxymetry and defibrillators.
`In order to enable measurements to be taken directly
`on patients, it is necessary to equip the monitoring appa-
`ratus with one or morefilters. This will result, however,
`in difficulty in selecting limit frequencies, since the
`signal can exhibit pronounced variations.
`Accordingly, one preferred embodiment of the in-
`vention is characterized in that the apparatus includes
`one or morefilters, preferably digital filters, which have
`means for setting limit frequencies and the degree of
`amplification. Filters of this kind are suitably incorpo-
`rated in the apparatus, which will also preferably in-
`clude means for electronically detecting the frequency
`content of the signal for selection and setting of limit
`frequencies.
`According to another embodiment of the monitoring
`apparatus, the filters are adaptive and are constructed to
`
`53,396,893
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`40
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`45
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`60
`
`The inventive monitoring apparatus preferably in-
`cludes a microprocessor which is programmedto calcu-
`late the Fourier transform, and/or to separate signals
`concerning the heart and respiration frequencies of the
`object by digital filtration, and/or to eliminate disturb-
`ances, emanating, for example, from stray light of fre-
`quency 50 Hz.
`A further possibility afforded by the use of micro-
`processor technology is that of combining the measur-
`ing process with SaO2-measuring with pulsoxymetry.
`The present invention also relates to a method of
`carrying out photoplethysmographic measuring pro-
`cesses, this method being characterized mainly by the
`characteristic features set forth in claim 9.
`
`DISCLOSURE OF THE EXPERIMENTS
`PERFORMED
`
`,
`
`With the intention of confirming the aforedescribed
`theory scientifically, namely the theory that it is also
`possible to separate from a PPG-signal whose dominat-
`ing component forms a measurement of the heart fre-
`quency of the object being examined, a signal compo-
`nent which discloses the respiration frequency of said
`object, a simple photoplethysmograph was constructed.
`Fourdifferent measuring probes were mounted on the
`photoplethysmograph,all of which probes useda light-
`emitting diode as a light source. One probe utilized the
`wavelength 875 nm, two utilized the wavelength 940
`nm and one utilized the wavelength 950 nm. All probes
`measured reflected light. The photoplethysmograph
`operated either within the frequency range of 0.2-10 Hz
`or the frequency range 0.2-20 Hz.
`The photoplethysmograph was used to measure the
`blood circulation of dogs, cats, adult males aged 35
`years and infants in incubators. In order to show both
`the respiration frequency and heart frequency in the
`photoplethysmograph signal, the heart frequency and
`respiration frequency of the adults and the infants were
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`5
`recorded separately with the aid of other methods. In
`the case of the animals used in this experiment, solely
`the respiration frequency was recorded separately.
`These measurements were used as reference signals in
`the measuring-data analysis. All measurements were
`recorded on a measurement tape-recorder.
`The measurement data was analyzed partly in the
`time plane, where the two components in the photople-
`thysmographsignal were filtered out, and partly in the
`frequency plane, wherein the power spectrum was cal-
`culated?. A cross-correlation function for the photople-
`thysmograph signal and the reference signals was also
`calculated. The following conclusions can be drawn
`from these analyses:
`The apparatus functions well on adults. The heart
`frequency and respiration frequency can be separated
`by means offilter techniques. The heart frequencyis the
`dominant signal component. The two components are
`clearly evident in the power spectrum and the cross-
`correlation function shows correlation with the refer-
`ence signals.
`In the case of infants in respirators, respiration is the
`totally dominant component.It is slightly more difficult
`to filter-out the two components in the case of infants
`than in the case of adults. Although the two frequencies
`are evident in the power spectrum, respiration domi-
`nates the spectrum totally. The cross-correlation func-
`tion showscorrelation with the reference signals.
`The respiration frequency is the dominant signal
`component in the case of animals. Although a high
`frequency component can be filtered-out, it cannot be
`guaranteed that this componentis the heart frequency.
`Wavelength
`Probe
`Light Power
`The powerspectrum has a broad band with many peaks
`0.5 mW
`875 nm
`Philips CQY 58
`A
`or spikes whose origin cannot readily be established.
`
`B,C=Telefunken TSUS 5400 950 nm 15 mw
`
`35
`The cross-correlation function was constructed solely
`(corresponds to
`for respiration, where correlation can be shown.
`Philips CQY 99)
`Hewlett-Packard HEMT
`BRIEF DESCRIPTION OF THE DRAWINGS
`£001
`
`6
`beneath 20 Hz. The pulse frequency selected was 1 kHz,
`which fulfils the sampling theorem more than well. The
`diode illuminating time was 40 ys, which constitutes a
`fraction of the period time | ms. Since the illuminating
`time is so short in relation to the dark time,it is possible
`to use a very high diode current without destroying the
`light-emitting diode.
`For the purpose of obtaining a continuous measure-
`ment response,
`the measuring values are maintained
`constant between each new measuring process, with the
`aid of a sample-and-hold circuit. In order to guarantee
`that a measurement value is obtained when the diode
`emits light at full intensity, the sample-and-hold circuit
`is closed (and therewith holds the measurement value)
`before extinguishing the light-emitting diode.
`The signal from the sample-and-hold circuit is equal-
`ized by passing said signal through a low-passfilter.
`Theprinciple construction of the measuring electron-
`ics will be seen from FIG. 1. References are madeto the
`circuit diagram shown in FIG. 4.
`
`The Measuring Probe
`
`Four different measuring probes, referenced A-D,
`were constructed during the experimental period. All of
`these measuring probes included a detector in the form
`of a light-emitting diode model S-4C from United De-
`tector Technology.
`Three different
`namely:
`
`light-emitting diodes were used,
`
`5,396,893
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`D
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`940 nm
`
`2.5 mW
`
`A more detailed account of the experiments carried
`out is given below, with reference to the accompany
`drawings, in which
`FIG. 1 is a block schematic which illustrates the
`principle construction of the measuring electronics
`used;
`FIGS. 2 and 3 are schematic views of measuring
`probes used in the experimentseries;
`FIGS. 4 and § are circuit diagrams; and
`FIG.6 illustrates the principle of transmission mea-
`suring with the aid of fibre optics and with the aid of a
`probefitted to one finger of the object.
`DETAILED DESCRIPTION OF THE
`DRAWINGS
`
`Infrared light-emitting diodes were used as the light
`source. Light-emitting diodes are small, mechanically
`insensitive and have a light intensity which is propor-
`tional to the diode current. The AC-component of the
`PPG-signal is weak and must be greatly amplified. The
`light intensity should be high, in order to obtain a high
`signal level. This is achieved by pulsating the light-emit-
`ting diode with a high current. This enables a much
`higher diode current to be used than in the case of con-
`tinuous light. The use of pulsated light results in time-
`discrete measurement of a time-continuous signal.
`According to the sampling theorem, it is necessary
`for the pulse frequency to be twice as large as the fre-
`quency content of the signal, in order to recreate the
`continuous signal. This frequency content should be
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`It should be observedin this respect that the light was
`comparitively broad-bandlight and that the wavelength
`values refer to maximum intensity. The power value
`denotes the powerradiated totally in a hemisphere and
`is estimated from existing data sheets in the case of
`HEMT1001.It should also be mentioned that the light-
`emitting diodes spread light differently.
`FIGS. 2 and 2g illustrate a measuring probe compris-
`ing an acrylic tube 4 in which a light-emitting diode 1
`and a detector in the form of a light-emitting diode 2 are
`embodied or cast with epoxy resin 5. The tube 4 has a
`diameter of 8 mm and is surrounded by a tube 3 of
`diameter 12 mm.
`Theprobeillustrated in FIG.3 differs from the probe
`illustrated in FIG. 2, in that the detector 2 is angied in
`relation to the detector surface.
`The following light-emitting diodes were used with
`the different probes:
`Probe A uses light-emitting diode CQy 58
`Probes B and C uses light-emitting diode HEMT
`1001
`Probe D useslight-emitting diode TSUS 5400
`Probes A and D were constructed in the same way as
`the probe B shown in FIG.2.
`The cables used between probes and electronic de-
`vices were very thin and flexible, screened four-con-
`ductor cables sold by Telko under the trade name Pick-
`uptrad PU 402.
`
`0008
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`

`The pulse electronics used had two functions,firstly
`to drive the light-emitting diodes and secondly to gen-
`erate and deliver controlsignals to the sample-and-hold
`TABLE1
`circuit. The fundamental componentof the pulse elec-
`tronics is a bistable flip-flop which generates a square
`value or type
`value or type
`component
`component
`wave having a frequency of 1 kHz. This flip-flop is
`10M
`4011
`RI
`Ici
`15k
`4050
`Ic2
`R2
`constructed around two Nand-gates (IC 1A andBin the
`Ic3
`4538
`R3
`3.9k
`circuit diagrarn of FIG. 4), and a buffer circuit (IC 2).
`Ica
`TLO71
`R4
`3.3k
`The clock frequency is proportional to the product R2
`Ics
`NES37
`RS
`22k
`and Cl. The capacitor C24 is required, to lead away
`ICc6
`TLO72
`R6
`180
`Ic7 .
`TLO71
`R7
`0-100k
`disturbing high frequencies.
`Ic8
`TLO72
`R8
`ik
`The control pulses are generated by a monostable
`Ico
`TLO72
`Rg
`27k
`flip-flop (IC3), which is triggered on positive flanks by
`1C10
`TLO71
`R10
`2.2k
`Cll
`ADS580
`Ril
`39k
`flanks of the square wave.
`RI2
`39k
`Those times at which the monostable flip-flop is
`R13
`2.2k
`“high” is determined by the product R3 and C2 for the
`RM
`39k
`light-emitting diode, and by the product R4 and C3 for
`R15
`39k
`Ri6
`1002
`the sample-and-hold circuit.
`R17
`1.8M.
`Current
`is supplied to the light-emitting diode
`R18
`3.9M
`through a transistor stage built around a Darlington
`RI9
`15M
`transistor (T1 in FIG. 4). A Darlington transistor is
`R20
`480k
`R21
`150k
`actually two transistors connected in series and has the
`R22
`4.7K
`positive property of having a very high current-ampli-
`R23
`0-100k
`fying factor.
`R24
`75k
`The voltage drop across collector and emitter
`R25
`822
`reached about 1.4 V.
`R26
`2.7k
`R27
`480k
`Thelight-emitting diode control pulse was connected
`R28
`150k
`to the base of the transistor via a resistor (R5), which
`R29
`4.7k
`was dimensioned so that the transistor would bottom at
`R30
`0-50k
`high pulse values and throttle at low pulse values.
`R31
`92k
`R32
`33k
`The resistor R41 was coupled in parallel with the
`R33
`680
`collector resistor R6 by means of a switch on the front
`R34
`2.2k
`R35
`tk
`panel of the apparatus used, such as to obtain a high
`R36
`0-500k
`collector current and a high light intensity. The collec-
`R37
`1k
`tor current was 130 mA in position “low” and 180 mA
`R38
`10k
`R39
`8.2k
`in position “high”.
`R40
`8.2k
`R41
`18
`R42
`360k
`R43
`560k
`R44
`560k
`R45
`1M
`R46
`IM
`R47
`1M
`R48
`0-100k
`
`R49 L5k
`
`15
`
`20
`
`25
`
`30
`
`35
`
`Ti
`
`PHO
`
`LED
`
`Cl
`C2
`C3
`C4
`C5
`C6
`C7
`cs
`co
`C10
`Cll
`C12
`C13
`ci4
`Cis
`Ci6
`C17
`C18
`c19
`C20
`C21
`C22
`C23
`C24
`C25
`
`BD6674
`
`UDT S-4C
`
`probe A:CQY 58
`probe BsHEMT 1001
`probe C:HEMT 1001
`probe D:CQY 99
`22 nF
`10 nF
`10 nF
`0-40 pF
`33 nF
`150
`0.22 wF
`6.8 nF
`10 pF
`0.22 uF
`0.22 uF
`47 nF
`47 uF
`47 oF
`22 nF
`22 oF
`22 nF
`22 oF
`1nF
`0.1 pF
`22 nF
`1nF
`0.1 pF
`15 nF
`1.0 pF
`
`7
`FIGS.4 and 5 are circuit diagrams of embodiments of
`the pulse electronics circuity employed in the present
`invention. Exemplary values for the components used
`in these embodiments are set forth in Tables 1 and 2 as
`follows:
`
`5,396,893
`
`8
`
`Pulse Electronics
`
`The digital IC-circuits are supplied with a voltage
`+Vcc of +5 V whereas the OP-amplifiers are supplied
`with + Vcc and a voltage — Vcc of —5 V. Also, each of
`the digital circuits are provided with a switch-offcapac-
`itor of 0.1 uF between “Vcc and ground. The OP ampli-
`fiers have similar switch-off capacitors between +-Vcc
`and ground as well as between — Vcc and ground.
`TABLE 2
`value or type
`component
`Tradania
`;
`type TD3701
`50 mA
`PBDF104
`ed HE
`pF
`1000 pF
`1000 yF
`7805
`78105
`
`value or type
`
`50 mA
`PBDF104
`O.1 WF
`0.33 pF
`0.1 pF
`0.33 pF
`79L05
`LOS
`
`$2
`Ic2
`2
`c4
`C6
`cs
`REG2
`REG¢4
`
`component
`io
`Taal
`
`$1
`Ic]
`&
`cs
`c7
`REG
`REGS
`
`The Current-Voltage Converter
`The light-emitting diode in the measuring probe was
`biased electrically with +2.5 V in the reverse direction.
`This voltage was produced by IC11, which is a preci-
`sion regulator and which held the voltage stable. A
`linear detector response was guaranteed in this way.
`The light-emitting diode now delivered a reverse cur-
`rent which was proportional to the detected light inten-
`sity. This current was converted to a voltage, by a cur-
`rent-voltage converter constructed around an opera-
`tional amplifier (IC4).
`It shall be noted that the current-voltage converter
`was an inverting circuit.
`
`The Sample-and-Hold Circuit (C5)
`Thecircuit functioned to hold the time-discrete mea-
`surement values constant between each new measuring
`process. Sample-and-hold circuits, however, are en-
`:
`‘
`cumbered with the disadvantage that disturbances in
`60 the form of spikes from the control logic leak through
`to the measurement value. This is particularly pro-
`nounced in respect of the weak AC-component. In
`order to reduce this disturbance, the amplitude of the
`:
`control signal was scaled down to about 2 V over the
`65 resistors R39 and R40. An external holding capacitor
`C15 on 1.0 82 F was connected to the circuit. This
`capacitor also assisted in damping the disturbance
`spikes.
`
`0009
`
`FITBIT, Ex. 1062
`
`0009
`
`FITBIT, Ex. 1062
`
`

`

`9
`Low-Pass Filter 200 Hz
`
`5,396,893
`
`The purpose of the first low-pass filter was to elimi-
`nate the disturbance spikes deriving from the sample-
`and-hold circuit. The filter was an active Tjebychev
`filter of the fourth order, followed by a passive RC-link.
`Thefilter had been designed to permit 0.5 dB ripple in
`the pass band and to have a cut-off frequency of 200 Hz.
`The filter was built-up around two cascade-coupled
`operational amplifiers (IC 6A and B) and the RC-link
`R16 and C9.
`
`The High-Pass Filter 0.1 Hz
`The high-passfilter eliminated the DC-component,
`thereby enabling amplification of the AC-component.
`Thefilter was an active Tjebychevfilter of the second
`order, constructed around an operational amplifier
`(IC7). Thefilter was designed to permit 0.5 dB ripplein
`the pass band andto have a cut-off frequency of 0.1 Hz.
`
`Amplification 1-500 Times
`The amplifier was a non-inverting amplifier con-
`structed around a offset-compensated operational am-
`plifier (IC10). The amplification was varied with the aid
`of a potentiometer positioned on the front panel.
`Notch Filter 50 and 100 Hz
`
`The weak AC-component was greatly disturbed by
`the net frequency 50 Hz,andalso by disturbances from
`lamps and fluorescent tubes at 100 Hz. These disturb-
`ances were eliminated in two cascade-coupled notch
`filters. The notch filters were constructed around two
`operational amplifiers (C 8A for 50 Hz and IC 8B for
`100 Hz). The filters could be adjusted in the frequency
`direction?, with the aid of potentiometers R29 for the 50
`Hz-filter and R30 for the 100 Hz-filter, such as to filter-
`off precisely the desired frequency.
`
`Amplification 10 Times
`The signal was amplified a further 10 timés in a non-
`inverting amplifier constructed around an operational
`amplifier (IC9A).
`Low-Pass Filter 20 Hz
`
`Thesignal passed through an active Tjebychevfilter
`of the third order, having a cut-off frequency of 20 Hz.
`This construction permitted a 0.3 dB ripple in the pass
`band. Thefilter was constructed around an operational
`amplifier (IC9B). The output signal was coupled to a
`BNC-switch labelled “Output 20 Hz” located on the
`front panel.
`
`Low-Pass Filter 10 Hz
`
`20
`
`25
`
`35
`
`Thesignal finally passed through a low-passfilter of
`the same kind as that described in the aforegoing, with
`the cut-off frequency of 10 Hz. The signal was then
`coupled to a BNC-switch labelled “Output 10 Hz”lo-
`cated on the front panel.
`The Net Part
`
`35
`
`The measuring electronics comprised a digital pulse
`part, and an analogue amplifying and filtering part. One
`problem which readily occurs when mixing digital
`technique with analogue techniqueis that disturbances
`occur in the form of spikes from the digital side to the
`analogue side. This disturbance can be reduced by using
`a separate supply voltage on the two parts. Accord-
`ingly, the built-in power unit was constructed around a
`
`65
`
`10
`transformer which had two secondary windings, each
`producing a secondary voltage of 12 V. This alternating
`voltage wasrectified to +5 V with the aid of rectifying
`bridges, smoothing and disturbance-eliminating capaci-
`tors and integrated regulators. Particular mention can
`be made to the fact that the light-emitting diode of the
`probe was powered by a current of between 100 and
`200 mA. Consequently, there was used a more powerful
`regulator capable of delivering more current to the
`digital +5 V-side (cf the circuit diagram shown in FIG.
`5).
`
`The Light Intensity of the Probes
`The following measuring process was carried out in
`order to obtain an estimation of the mutual intensity
`relationship between the various probes.
`The probes were connected and a photometer was
`held directly against the probes. The luminousintensity
`of the probes was observed from the photometer. It
`shall be noted that this is an integrated measurement
`value and not the intensity when the diodesare illumi-
`nated. The measurement values are shown in the fol-
`lowing table.
`
`Probe
`A
`B
`¢c
`D
`
`Intensity
`
`“Low”
`25.1 pW
`15.2 pW
`18.4 pW
`32.1 pW
`
`“High”
`_—
`19.0 pW
`22.7 pW
`38.7 pW
`
`It was foun