United States Patent [19]
`Conlan
`
`IIIIIILIIIILIIII IIIII
`5,573,013
`*Nov. 12, 1996
`
`US005573013A
`[11] Patent Number:
`[45]. Date of Patent:
`
`[54] METHOD OF MONITORING BODY
`MOVEMENTS USING ACTIVITY
`MONITORING APPARATUS
`
`[75] Inventor: Robert W. Conlan, Niceville, Fla.
`[73] Assignce: Precision Control Design, Inc., Fort
`Walton Beach, Fla.
`The portion of the term of this patent
`subsequent to Jun. 17, 2011, has been
`disclaimed.
`
`[*] Notice:
`
`[21] Appl. No.: 479,822
`[22] Filed:
`Jun. 7, 1995
`Related U.S. Application Data
`
`4/1991 Thornander ............................. 128/696
`5,010,887
`4/1991 Sholder ....
`. 128/782
`5,010,893
`6/1991 Niwa ....................................... 128/670
`5,025,791
`5,031,614 7/1991 Alt ................................ 128/419 OPG
`5,036,856
`8/1991 Thornton ................................. 128/670
`5,044,365
`9/1991 Webb et al
`... 128/419 PG
`5,074,303 12/1991 Hauck ......
`. 128/419 PG
`5,197,489
`3/1993 Conlan .................................... 128/782
`OTHER PUBLICATIONS
`Experimental Prototype (AM-16) Block Diagram (date
`unknown).
`Redmond, D. and Hegge, F., “Observations on the design
`and specification of a wrist—worn human activity monitoring
`system” Behavior Res. Methods, Instruments & Computer,
`(1985).
`Primary Examiner—Guy V. Tucker
`Attorney, Agent, or Firm—Lockwood, Alex, Fitzgibbon &
`Cummings
`[63) Continuation of Ser. No. 341,316, Nov. 16, 1994, aban
`doned, which is a continuation of Ser. No. 38,629, Mar. 29,
`ABSTRACT
`[57]
`1993, abandoned, which is a continuation of Ser. No.
`716,853, Jun. 17, 1991, Pat. No. 5,197,489.
`An activity monitor adapted to be worn on the non-dominant
`wrist of a subject includes a bimorphous beam motion
`[51] Int. Cl* … A61B 5/103
`sensor. The output signal of the sensor is amplified in an
`[52] U.S. Cl. .........................…. 128782
`amplifier circuit having a selectable amplification factor, and
`[58] Field of Search ..................................... 128/782, 774,
`filtered by highpass and lowpass filter circuits having indi
`128/721, 722, 670, 671, 687, 713, 714;
`vidually selectable cut-off frequencies to obtain an analog
`340/573
`signal for processing having a bandpass and amplitude
`characteristic corresponding to a particular body activity
`under observation. A control and processing circuit within
`the monitor includes a microprocessor which responds to
`either resident internal operating instructions or to externally
`supplied operating instructions, or to designated data signal
`parameters, to provide configuration control signals to the
`amplifier and filter circuits, and processing of the collected
`data, appropriate to the particular activity being monitored.
`The processed data is digitally stored in an internal memory
`for subsequent transfer through a data port to an associated
`computer for display or further processing.
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,807,388 4/1974 Orr et al. ................................ 128/690
`5/1978 Auerbach .........
`... 128/419 PT
`4,088,139
`4,117,834 10/1978 McPartland et al.
`... 128/782
`4,202,350 5/1980 Walton .................
`... 128/690
`4,353,375 10/1982 Colbrun et al. ..
`... 128/782
`4,425,921
`1/1984 Fujisaki et al. ......
`... 128/690
`4,428,378
`1/1984 Anderson et al. .......
`. 128/419 PG
`4,819,652 4/1989 Micco ..............
`... 128/661.09
`4,830,021
`5/1989 Thornton ..........
`... 128/707
`4,945,916 8/1990 Kretschmer et al.
`... 128/671
`4,989,612 2/1991 Fore ........................................ 128/721
`
`
`
`7 Claims, 8 Drawing Sheets
`
`FITBIT, INC. v. LOGANTREE LP
`Ex. 1009 / Page 1 of 20
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`U.S. Patent
`U.S. Patent
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`Nov. 12, 1996
`Nov. 12, 1996
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`Sheet 1 of 8
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`U.S. Patent
`U.S. Patent
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`Nov. 12, 1996
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`Sheet 3 of 8
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`5,573,013
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`Ex. 1009/ Page 4 of 20
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`U.S. Patent
`U.S. Patent
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`Nov. 12, 1996
`Nov. 12, 1996
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`Sheet 4 of 8
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`U.S. Patent
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`Nov. 12, 1996
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`Sheet 5 of 8
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`5,573,013
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`Ex. 1009 / Page 6 of 20
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`U.S. Patent
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`Nov. 12, 1996
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`Sheet 6 of 8
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`5,573,013
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`Freq.-Hertz
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`VL Lower Threshold
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`WITH COM PENSAT| ON
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`WITHOUT COMPENSAT|ON
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`Ex. 1009 / Page 7 of 20
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`U.S. Patent
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`Nov. 12, 1996
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`Sheet 7 of 8
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`5,573,013
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`U.S. Patent
`U.S. Patent
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`Nov. 12, 1996
`Nov. 12, 1996
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`Sheet 8 of 8
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`Ex. 1009 / Page 9 of 20
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`5,573,013
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`1
`METHOD OF MONITORING BODY
`MOVEMENTS USING ACTIVITY
`MONITORING APPARATUS
`
`This application is a continuation of application Ser. No.
`08/341,316, filed Nov. 16, 1994, now abandoned, which is
`a continuation of application Ser. No. 08/038,629, filed Mar.
`29, 1993, now abandoned, which is a continuation of appli
`cation Scr. No. 716,853, filed Jun. 17, 1991, now U.S. Pat.
`No. 5,197,489.
`
`5
`
`2
`that, for the period of time over which the subject was being
`monitored, exceeded the capacity of the memory.
`This problem was aggravated because prior activity moni
`tors were not selectively configurable to collect data only for
`a particular activity, so that unusable or irrelevant data was
`often allowed to occupy memory space along with usable
`data. Prior monitors did not have the capability to be
`reconfigured according to preset instructions and/or in
`response to the data collected by the monitor.
`Prior monitors typically utilized sensors to detect body
`movement which, because of the need to suppress harmon
`ics and other artifacts from the limited memory, lacked the
`sensitivity to detect small scale, visually imperceptible
`movements such as those caused by breathing, the beat of
`the hearl, and the flow of blood.
`A demand therefore exists for an activity monitor and
`method by which the activity of a subject, even that activity
`which includes movements that are not necessarily visually
`perceptible, can be selectively observed and accurately
`quantified. The present invention satisfies this demand.
`Accordingly, it is a general object of the present invention
`is to provide an improved apparatus, system and methods for
`selectively observing and accurately quantifying certain
`aspects of the motion of a subject.
`An object of the present invention is to provide an activity
`monitor having a size and construction such that the monitor
`may be conveniently worn on the subject.
`Another object of the present invention is to provide an
`activity monitor which can collect data regarding a subject’s
`activity automatically and according to instructions initial
`ized in the monitor.
`Another object of the present invention is to provide an
`activity monitor having a memory in which operating
`instructions and collected data are stored.
`Another object of the present invention is to provide an
`activity monitor with which data regarding a subject’s
`movement can be processed automatically and according to
`instructions initialized in the monitor.
`Another object of the present invention is to provide an
`activity monitor wherein the type of data collected and the
`processing of the data by the monitor can be automatically
`changed.
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`BACKGROUND OF THE INVENTION
`The subject invention relates to apparatus and methods for
`monitoring activity of the human body. More particularly,
`the invention relates to apparatus, systems and methods by
`which the occurrence and length of certain types of body
`movements which form activity phenomenon can be selec
`tively observed and accurately quantified.
`A human subject engages in a wide range of body
`movements. Such movements can range from the voluntary
`and visually perceptible—such as the movement of legs,
`arms and head, to the involuntary and visually impercep
`tible, such as the slight changes in elevation of skin caused
`by the rhythmic pulsations of blood and breathing.
`The observation of body movement can provide much
`information useful to physicians and researchers. For
`example, by observing a subject’s movements, the occur
`rence and length of natural phenomenon, such as wakeful
`ness, rest and sleep can be determined. By observing the
`nature of a subject’s movement, the occurrence and severity
`of disorders and the effects of drugs or other therapy can be
`assessed. In many cases quantification of the subject’s
`movement is preferred so that the movement pattern of one
`subject can be compared with the movement pattern of
`others.
`Direct visual observations of body movement are labor
`intensive, time consuming and tedious. Moreover, direct
`visual observations provide only a limited range of qualita
`tive information, such as subjective descriptions of a sub
`ject’s visually perceptible movements. Little, if any, quan
`tification in readily comparable values, such as degree,
`strength, and/or violence of a subject’s activity, and no
`information, either qualitative or quantitative, of a subject’s
`visually imperceptible movements is obtained. Furthermore,
`the value of qualitative information obtained by directly
`observing a subject is subject to question as such observa
`tions themselves may cause the subject to become conscious
`of and thereby alter his or her movements.
`Activity monitors have been developed for observing and
`quantifying certain aspects of movement without the
`involvement of an observer. However, such monitors had
`disadvantages which limited their usefulness. For example,
`such prior monitors were typically of a size which interfered
`with free movement of the subject, and typically had either
`little or no internal memory and/or little or no data process
`ing capabilities. In order that data produced by many of
`these activity monitors could be stored and/or processed it
`was necessary to connect the monitors through cables to
`external data storage and processing devices. Tethering the
`monitor in this way to an external device also tethered the
`subject to the device, thereby restricting the subject’s move
`ment and biasing the results.
`In those prior activity monitors which had internal
`memory, saturation of the memory occurred when the sub
`ject engaged in activity which produced a volume of data
`
`SUMMARY OF THE INVENTION
`The present invention is directed to an activity monitor
`and methods by which both visually perceptible and visually
`imperceptible movement can be selectively observed and
`accurately quantified.
`The apparatus includes an activity monitor, or actigraph,
`having a size, shape and construction that allows the monitor
`to be worn on the surface of the skin of a subject and which
`functions reliably and without restriction of the subject’s
`movement. One preferred embodiment of the monitor of the
`present invention is configured for wearing on a subject’s
`non-dominant wrist. The monitor may be configured to be
`worn on other parts of a subject’s body as well.
`In particular, the activity monitor of the present invention
`includes a movement sensor by which the full range of a
`subject’s movement, even that which is visually impercep
`tible, can be detected. A preferred sensor is a cantilever
`piezoelectric bimorph beam. The use of a bimorph beam as
`a sensor is advantageous in that it provides high sensitivity
`and operates without requiring any operating power, such as
`from a battery, thereby conserving this generally limited
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`resource. Furthermore, such a sensor operates in the absence
`of a gravitational field thereby expanding the applications in
`which the monitor can be utilized.
`The bimorph beam in response to an applied force pro
`duces a signal whose frequency varies according to the
`movement to which the monitor is subjected. When the
`monitor is secured adjacent to the surface of the skin of a
`subject, such as on the subject’s non-dominant wrist, the
`monitor produces signals having frequencies ranging from
`approximately 0.16 hertz to 9 hertz. Within this frequency
`range, certain activities of the subject produce frequencies
`falling within certain specific narrow frequency ranges. For
`example, breathing produces a signal having a frequency
`range of 0.2 to 1 hertz, the beat of the heart produces a signal
`having a range of 2 to 3 hertz, and the typical night time
`activity of a subject produces a signal having a range
`between 0.2 and 3 hertz. Disorders, such as tremor activity,
`typically produce a signal having a range of 2 to 9 hertz.
`So that such specific frequency ranges among the wide
`range of frequencies which a subject’s many movements
`produce can be selectively observed and quantified, the
`activity monitor includes signal processing means which
`amplify, shape and filter the signal produced by the sensor.
`In particular, so that a low amplitude signal, such as those
`produced by breathing and heart beats, can be isolated for
`later processing, the activity monitor includes signal condi
`tioning means in the form of a motion signal amplifier
`having an amplification factor selectable by an applied
`configuration control signal, and a highpass filter circuit
`having a threshold selectable by another applied configura
`tion signal below which motion sensor signals are greatly
`attenuated. This is advantageous in that it allows observa
`tions to be made of a subject both during a high activity
`period, when a relatively high amplitude high frequency
`signal is produced by the sensor, and during a low activity
`period, such as during the night, when the subject is typically
`producing a relatively low amplitude and low frequency
`signal.
`To eliminate DC drift in the motion signal amplifier the
`signal processing means preferably include a drift compen
`sation circuit which compares the dc level of the amplified
`motion signal developed by the amplifier with a fixed dc
`reference voltage to develop a drift corrected voltage at the
`motion detector which nulls out any drift.
`To eliminate artifacts present in the sensor output signal,
`such as those caused by the natural resonance of the motion
`sensor, and to obtain in conjunction with the highpass filter
`a desired frequency spectrum for analysis and quantification,
`the activity monitor includes a low pass filter circuit having
`a threshold frequency selectable by applied configuration
`signals.
`The activity monitor further includes an analog-to-digital
`converter which samples the analog signal developed by the
`motion sensor, after processing by the amplifier, high-pass
`filter and low-pass filter, and passes the resultant digital
`values to internal memory means in the monitor for storage
`and later retrieval.
`The activity monitor also includes a window detector
`which compares the voltage level of the processed motion
`signal to upper and lower voltage thresholds selectable by an
`applied configuration signal, and provides an activity count
`each time the signal voltage level crosses the thresholds.
`Preferably, the signal voltage level is compared to both a
`high threshold voltage level and a low threshold voltage
`level which are symmetrically positioned opposite the regu
`lated reference voltage. Preferably, the amount by which the
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`upper and lower thresholds differ exceeds the amount of
`noise which the system normally generates so that counts
`gencrated by the detector are caused by variations in the
`motion detector output signal and not by monitor noise.
`The activity monitor further includes a temporary internal
`memory for recording the activity counts generated by the
`activity detector over a selectable observation period, or
`epoch. At the end of the epoch, the total number of events
`occurring during the epoch is stored, and the temporary
`memory is crased for use during the next epoch. Advanta
`geously, the epoch time period is selected according to the
`type of activity to which the observation is directed. For
`cxample, because a subject engages in generally less move
`ment while asleep, the epoch used during such an observa
`tion period can be generally of greater duration than that, for
`example, used when a subject is monitored while awake. A
`Selectable epoch period avoids the memory saturation prob
`lem that prior monitors had in collecting data for periods of
`time inappropriate to a particular type of movement.
`The activity monitor also includes an internal micro
`processor having resident software by which the configura
`tion of the various circuits of the monitor are controlled. The
`microprocessor is preferably capable of powering up and
`shutting down the processing circuits at selected times to
`conserve battery power.
`The microprocessor has associated with it memory in
`which software to control the monitor components is resi
`dent and in which data obtained from the operation of the
`monitor is stored. Specifically, the memory includes a read
`only memory (ROM) which contains instructions to operate
`the monitor. Preferably, the ROM includes an operating
`system by which the monitor’s signal processing compo
`ments can be initially configured so that, for example, certain
`aspects of a subject’s movement can be initially observed,
`from which the monitor’s signal processing components can
`be reconfigured so that other aspects of a subject's move
`ment can be observed, and by which the data that is collected
`is stored.
`Advantageously, to provide an activity monitor which is
`fully adaptable and which can be altered to collect data
`regarding activity patterns not initially envisioned, the moni
`tor memory includes a random-access memory (RAM) for
`storing instructions, for example, different from those stored
`in the ROM. Advantageously, the monitor can operate off
`either, or a combination of those instructions stored in the
`ROM or in the RAM.
`Communication between the activity monitor and, for
`example, a personal computer, with which the data obtained
`by the monitor be stored, evaluated, and further processed,
`and from which new instructions to be stored in the monitor
`RAM can be prepared, is facilitated by an interface unit
`providing electrical connections between the monitor and
`the computer. To this end, the interface unit preferably
`includes a receptacle for receiving the monitor, and the
`monitor is provided with an electrical connector on the
`surface of its housing which engages a complementary
`connector in the receptacle.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The features of the present invention which are believed
`to be novel are set forth with particularity in the appended
`claims. The invention, together with the further objects and
`advantages thereof, may best be understood by reference to
`the following description taken in conjunction with the
`accompanying drawings, in the several figures of which like
`reference numerals identify like elements, and in which:
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`FIG. 1 is a perspective view of a wrist-mounted activity
`monitor constructed in accordance with the invention as
`worn on the wrist of a subject.
`FIG. 2 is an activity monitoring system including a
`computer, interface and wrist-mounted activity monitor con
`structed in accordance with the invention.
`FIG. 3 is an enlarged perspective view of a portion of the
`interface unit shown in FIG. 2 showing the positioning of the
`wrist-mounted activity monitor therein.
`FIG. 4 is a functional block diagram showing the principal
`components of the activity monitoring system of FIG. 2.
`FIG. 5 is an enlarged plan view of the control panel of the
`wrist-mounted activity monitor of FIGS. 1–3.
`FIG. 6 is an exploded perspective view of the wrist
`mounted activity monitor showing certain principal compo
`nents thereof.
`FIG. 7 is an enlarged perspective view of the piezoelectric
`bimorph beam motion detector utilized in the activity moni
`tor of FIGS. 1–3.
`FIG. 8 is a functional block diagram showing the principal
`components and circuits of the activity monitor of FIGS.
`1–3.
`FIG. 9 is a simplified schematic diagram of the activity
`monitor described in FIG. 8.
`FIG. 10 is an illustrative plot of the frequency spectrum
`of five different activities of the human body.
`FIG. 11 is a simplified depiction of the frequency spec
`trum and signal characteristics of five specific activities of
`the human body.
`FIG. 12 is a simplified schematic diagram and plot
`illustrating the characteristics of the piezoelectric bimorph
`beam sensor utilized in the activity monitor of the invention.
`FIG. 13 is a graphical depiction of certain voltage rela
`tionships associated with the window detector utilized in the
`activity monitor of the invention.
`FIG. 14 is a graphical depiction of certain bandpass
`characteristics associated with the high-pass filter utilized in
`the activity monitor shown in FIGS. 8 and 9.
`FIG. 15 is a depiction of a sinusoidal waveform illustrat
`ing certain parameters thereof.
`FIG. 16 is a depiction of a repetitive waveform showing
`certain zero-crossing parameters thereof.
`FIG. 17 is a three-dimensional depiction of certain axes
`useful in analyzing activity of the human body.
`FIG. 18 is a 3-dimensional depiction of certain activities
`of the human body viewed along the axes of FIG. 14.
`
`6
`a personal computer 13 which, except for containing nec
`essary software for accomplishing the down-loading of data
`from the monitor and the uploading of operating instructions
`to the monitor, may be entirely conventional in construction
`and operation. Communication between the activity monitor
`10 and computer 13 is facilitated by an interface unit 14,
`which is connected to a data port of computer 13 by means
`of a conventional RS-232 cable 15 or the like. The interface
`unit 14 preferably includes a receptacle 16 (FIG. 3) on its top
`surface dimensioned to receive the monitor housing 12. An
`electrical connector 17 located along one side of receptacle
`16 engages a connector 18 on housing 12 when the monitor
`is seated within the receptacle. With this arrangement the
`monitor can be quickly and conveniently installed and
`removed from interface unit 14. A plurality of controls 20 on
`the top surface of interface unit 14 assist the operator in
`accomplishing the downloading and uploading functions.
`Activity monitor 10, personal computer 13 and interface
`unit 14 together comprise a system for collecting and
`analyzing human activity data. Depending on the particular
`software resident in personal computer 13 a wide variety of
`written reports and displays may be generated from the data
`collected by the monitor.
`In this regard, and with reference to FIG. 4, data is
`exchanged between personal computer 13 and interface unit
`14 in both directions, and between interface unit 14 and
`activity monitor 10 in both directions. This provides com
`plete flexibility in that necessary operating instructions may
`be provided to monitor 10 through interface unit 14 from
`personal computer 13. When the monitor is removed from
`interface unit 14, these resident instructions control the
`operation of the monitor in a subsequent data collection
`assignment. As will be seen, a number of operating param
`eters in the monitor can be configured for either an entire
`data collection period, or for portions of a data collection
`period, or for single epochs, providing activity data and an
`activity monitor of optimum utility.
`Referring to FIG. 5, the top surface of activity monitor 10
`includes a pair of user-input pushbutton switches 22 and 23.
`These switches, which are preferably membrane type
`switches, allow the subject to indicate the occurrence of a
`particular event. For example, upon the occurrence of diz
`ziness or pain, the subject may be instructed to depress one
`of the push button switches to cause that occurrence to be
`recorded in the internal memory of the monitor. To enable
`these switches to be readily identified, the right switch may
`be one color, such as red, may be provided with a single
`raised dimple for tactile feedback, and may be accompanied
`by a single audible beep. The left pushbutton switch 22 may
`be provided with two raised dimples, may be another color,
`such as green, and may cause two audible beeps when
`actuated.
`Referring to FIG. 6, the housing 12 of activity monitor 10
`is seen to include a side panel 24 on which electrical
`connector 18 is positioned for engaging the electrical con
`nector 17 of receptacle 16. The other side of housing 12
`includes a sliding tray assembly 25 within which a coin-type
`battery cell 26 is mounted for insertion into housing 12.
`Within housing 12 a first circuit board 27 and a second
`parallel-spaced circuit board 28 provide mounting and con
`nection means for a major portion of the circuitry of the
`monitor, and also provide mounting means for motion
`sensing means in the form of a cantilever piezoelectric
`bimorph beam motion sensor 30.
`Referring to FIG. 7, motion sensor 30 is seen to comprise
`a bimorph beam 31 fixedly positioned relative to circuit
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`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`Referring to the Figures, and particularly to FIGS. 1 and
`2, a wrist-mounted activity monitor or actigraph 10 con
`structed in accordance with the invention may be similarly
`shaped and sized to a wrist-watch, having a flexible band 11
`securing a generally rectangular housing 12 against the skin
`surface of a subject being monitored. Typically, in this form
`the monitor is mounted on the non-dominant wrist, the
`activity of which has been found to correlate with body
`activity, muscle movement and brain waves.
`In use, the activity monitor 10 is worn by the subject for
`a predetermined collection period which may extend over
`one or more days. Data collected by the monitor over the
`collection period is downloaded at the end of the period to
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`Ex. 1009 / Page 12 of 20
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`7
`board 27 at one end by a metallic clamp 32 and compression
`contact 33. The compression contact 33 forces one face of
`beam 31 against clamp 32, completing one electrical con
`nection to the beam through a conductor 34. The other
`electrical connection to beam 31 is established through
`compression contact 33, which bears against the other face
`of the beam and a metallic pad 35 on circuit board 27 to
`which a conductor 36 is connccted. Thus, the bimorph beam
`is electrically connected on opposite faces to the circuitry of
`the monitor by mounting means which fixedly position the
`connected cnd relative to circuit board 27. The distal end of
`beam 31 may be fitted with a proof mass 37 to impart desired
`electro-mechanical characteristics to the bimorph beam
`assembly 30. This method of making connections to the
`bimorph beam has the advantage of avoiding solder con
`nections to the beam, and their attendant cracking or dete
`rioration with time.
`Referring to FIG. 8, within activity monitor 10 the
`bimorph beam assembly 30 is incorporated in a sensor
`circuit 40. Within this circuit the motion signal v developed
`by the bimorph beam is added to a voltage V, provided by
`a drift correction circuit 41.
`-
`Since the motion signal v generated by the beam contains
`harmonics at the beam resonant frequency, has relatively
`poor low frequency response and is of low amplitude, it is
`necessary that the motion signal be conditioned prior to
`analysis and storage. To this end, the resulting sensor output
`signal v-V, is applied to a conditioning circuit 42 compris
`ing a configurable threshold high pass filter and configurable
`gain signal amplifier. Within conditioning circuit 42 the
`signal is AC and DC amplified, typically by AC factors of
`from 5–25 and a DC factor of 75–375, to provide a signal of
`sufficient amplitude that even visually imperceptible move
`ments can be recognized and quantified without corruption
`due to DC drift. Undesired low frequency components
`resulting from other than body activity to be monitored,
`which are typically below 0.16 hertz, are attenuated. Since
`virtually all movement of a subject produces signals having
`frequencies that are above 0.16 hertz, valid data is not
`affected. Low level signals, such as result from heart beats
`or blood flow, are both above 0.16 hertz and are amplified
`for subsequent processing.
`In accordance with one aspect of the invention, the low
`frequency threshold of the high pass filter amplifier 40 is
`configurable to either 0.16 hertz or 2 hertz to permit selec
`tive attenuation of low frequency signals associated with
`body activities such as breathing, which typically produce a
`signal between 0.2 and 1 hertz. Selection of the desired
`threshold is accomplished over a configuration control line
`LCF which receives an appropriate configuration signal
`from a processing and control circuit 43 contained within the
`activity monitor. Similarly, the gain of conditioning ampli
`fier 42 is controlled by a configuration signal provided on a
`configuration control line GAN extending from processor
`circuit 43 to the amplifier. The effect of this configuration
`signal is to vary the AC gain of the conditioning amplifier
`from a high level, typically on the order of 25, to a low gain,
`typically in the order of 5. As will be seen presently, this is
`particularly useful in reconfiguring the activity monitor to
`analyze very low level motion signals, such as those asso
`ciated with sleep.
`The output of conditioning amplifier 42 (vrºv,) is applied
`to a low pass amplifier 44 and to a dc drift correction circuit
`45. Within drift correction circuit 45 the amplifier output is
`compared with a fixed reference voltage Vºo, which com
`65
`prises a virtual ground for the amplifier and filter circuitry,
`to generate the drift compensated signal V, for application
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`8
`to sensor circuit 40. In this way, the DC output level of
`conditioning amplifier 42 is continuously compared with a
`fixed reference voltage, and the voltage applied to the
`motion sensor is varied to prevent any deviation between the
`DC output level of the amplifier and the reference voltage.
`Consequently, any DC drift within the high gain condition
`ing amplifier circuit is eliminated. This makes it possible for
`the conditioning amplifier to operate at the high gains
`required for successful low level body activity detection and
`analysis.
`The output of conditioning amplifier 42 is applied to a low
`pass filter 44 wherein high frequency components of the
`signal, such as produced by the natural resonance of the
`bimorph beam sensor, are attenuated. Low pass filter 44, in
`accordance with one aspect of the invention, can be config
`ured by configuration signals applied on configuration con
`trol lines 30D, 40D and HCF by processor circuit 43 to
`obtain three different high frequency cutoff frequencies. In a
`preferred embodiment of the invention, filter 44 is config
`urable for thresholds of 1, 3 or 9 hertz.
`Since the high pass filter of conditioning amplifier 42 can
`be configured with a threshold of either 0.2 or 2 hertz, and
`filter 44 can be configured with a threshold of either 1, 3 or
`9 hertz, the monitor is advantageously able to collect infor
`mation within a selected one of five distinct frequency
`ranges: 0.16 to 1 hertz; 0.16 to 3 hertz; 0.16 to 9 hertz; 2 to
`3 hertz; and 2 to 9 hertz. This is illustrated in FIG. 10. As
`previously stated, and as illustrated in FIG. 11, the motion
`sensor when exposed to certain specific types o