I 1111111111111111 11111 111111111111111 111111111111111 lllll 111111111111111111
`5,827,969
`
`United States Patent
`[11]Patent Number:
`[19J
`Oct. 27, 1998
`[45]Date of Patent:
`
`
`
`Lee et al.
`
`US005827969A
`
`[54]PORTABLE HAND HELD DOPPLER FETAL
`[56]
`HEART RATE PROBE WITH SELECTIVE
`POWER SETTINGS
`
`
`
`References Cited
`
`
`
`U.S. PATENT DOCUMENTS
`
`4,413,629 11/1983 Durley III ............................... 600/453
`
`
`
`
`William Del D. Fisher,[75]Inventors: C. Lee, Orinda;
`
`
`
`
`
`4,819,652 4/1989 Micco .................................. 73/861.25
`
`5,313,947 5/1994 Micco ..................................... 600/455
`
`
`Santa Cruz; Andras Boross, Belmont,
`all of Calif.
`
`Primary Examiner-Christine K. Oda
`
`
`
`
`
`Attorney, Agent, or Firm----Fliesler, Dubb, Meyer & Lovejoy
`MedaSonics, Inc., Newark, Calif.[73]Assignee:
`[57]
`
`
`
`
`ABSTRACT
`
`
`
`[21]Appl. No.: 662,049
`
`[22] Filed:Jun. 12, 1996
`
`. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
`
`A probe in a hand held ultrasonic Doppler fetal heart beat
`
`
`
`
`
`
`detector and monitoring system comprising a crystal for
`
`
`
`transmitting ultrasonic energy, a variable power source
`[51]Int. Cl.6
`A61B 8/06
`
`
`
`
`connected to said crystal for driving the crystal at a selected
`
`73/627; [52]U.S. Cl. ........................ 073/861.25; 600/455
`
`
`
`
`
`power setting and a microprocessor for selecting a power
`
`
`
`[58]Field of Search ......................... 128/661.07, 661.09,
`
`
`setting for the variable power source.
`
`
`
`128/698; 073/627, 861.25; 364/413.25,
`
`
`413.02; 600/453, 455, 446, 457
`
`
`
`16 Claims, 5 Drawing Sheets
`
`55
`
`MICRO
`
`PROC.
`
`57
`
`MASIMO 2004
`Apple v. Masimo
`IPR2020-01523
`
`

`

`U.S. Patent
`
`Oct. 27, 1998
`
`Sheet 1 of 5
`
`5,827,969
`
`
`
`FIG. 1
`
`P
`
`58
`
`46
`
`DETECTOR
`
`VOL CTL
`
`87
`
`81
`
`18
`
`19
`
`20
`
`FIG. 2
`
`P
`
`5
`
`7-49
`7
`
`50
`
`51 _ 52
`A
`_[NOISE CTL
`
` 59= 86 P
`FRsol*=e
`a4
`So
`
`

`

`U.S. Patent
`
`Oct. 27, 1998
`
`Sheet 2 of 5
`
`5,827,969
`
`HIGH POWER
`
`STATE 1 a2
`
`TRANSEANT?
`
`TRANSEANT?
`
`LOW POWER
`
`STATE 2
`
`

`

`U.S. Patent
`
`Oct. 27, 1998
`
`Sheet 3 of 5
`
`5,827,969
`
`
`
`
`
`
`
`
`
`
`TIME OUT ?
`LOW oe TRANSEANT7/6!
`
`
`YES
`| FIG 5
`YES
`
`TRANSEANT?
`
`TIME OUT ? FO
`
`—
`TRANSEANT7
`
`HIGH POWER
`
`76
`
`LOW
`
`HIGH
`
`POWER
`
`FIG. 6
`
`

`

`U.S. Patent
`
`Oct. 27, 1998
`
`Sheet 4 of 5
`
`5,827,969
`
`KEY
`
`A POWER DEPRESSED
`
`B POWER AND VOL. UP
`DEPRESSED
`
`C POWER AND VOL. DOWN
`DEPRESSED
`
`D VOL. DOWN AND VOL. UP
`DEPRESSED
`
`
`
`
`
`
`
`
`FIG. 7
`
`

`

`U.S. Patent
`
`Oct. 27, 1998
`
`Sheet 5 of 5
`
`5,827,969
`
`iCOMPARATOR|
`
`80
`
`REFERENCE
`
`FROM
`DETECTOR51
`
`46
`
`VOLTAGE
`
`
`
` MUTING
`
`
`
`FILTER
`
`VAR. GAIN AMP
`VOUT 83
`
`R2
`
`T1
`
`Tl=:T2T3 T4 TS
`
`
`a
`TIME
`
`FIG. 9
`
`FIG. 10
`
`PULSE WIDTH
`
`MODULATION
`
`CIRCUIT
`82
`
` 81
`
`

`

`5,827,969
`
`1
`PORTABLE HAND HELD DOPPLER FETAL
`HEART RATE PROBE WITH SELECTIVE
`POWERSETTINGS
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention generally relates to a portable, hand
`held probe in a Doppler fetal heart beat detection and
`monitoring system for detecting the fetal heart beat using
`Doppler ultrasound techniques in general and more specifi-
`cally to a method and a probe capable of changing the
`applied ultrasonic field strength thereby increasing the sen-
`sitivity of the probe.
`2. Description of the Related Art
`The Doppler effect was first described in the 19th century
`by Christian Doppler, an Austrian scientist from Salzburg. A
`hand held ultrasonic Doppler fetal heart beat detection and
`monitoring system includes a probe for detecting the fetal
`heart beat and for providing an analog signal to a headset
`and/or to an auxiliary unit (hereinafter referred to as a
`calculation or Calc. unit). The probe includes one or more
`crystals that transmits and receives ultrasonic sound waves.
`In use, the detector is held against the mothers abdomen and
`directed towards the fetus. The transmitter crystal generates
`an ultrasonic wave that passes into the mothers body. The
`transmitted ultrasonic waveis reflected by the movementof
`the fetal heart as a reflected ultrasonic waveto the receiving
`crystal. The frequency of reflected ultrasonic wave is
`changed as a function of the velocity of movement of the
`fetal heart. This frequency shift is detected and processed by
`the probe into an analog signal that can be heard as the fetal
`heart beat through the headset and the speaker in the Calc.
`unit. The Calc. unit also processes the analog signalto derive
`a fetal heart rate and displays the same.
`A probe 11 having a single energy level transmitter and a
`detector 51, volume controller 52, power supply 54 and of
`FIG. 2 is available from MedaSonics, Inc. as Part No.
`101-0135-010. A Calc. unit suitable for use with probe 11 is
`available from MedaSonics,
`Inc., 47233 Fremont
`Boulevard, Fremont, Calif. 94538, and is identified as
`FETAL CALC. SPEAKER/HEART DISPLAY, Part No.
`101-0238-010. A headset 10 compatible for use with probe
`11 can also be purchased from MedaSonics, Inc., and is
`identified as HEADSET, Part No. 101-0008-010.
`During the later stage of the first trimester and the early
`stage of the secondtrimester, the heart of the fetus is so small
`that the conventional hand held Doppler fetal heart beat
`detection and monitoring systems encounter difficulty in
`detecting the fetal heart beat due to the very low level of
`ultrasonic energy in the reflected ultrasonic wave from the
`fetal heart.
`
`One approach to this problem was to provide a set of
`interchangeable probes where each probe emits ultrasound
`energy at a different ultrasonic frequency to improve the
`sensitivity of the probe in detecting the fetal heart beat. The
`disadvantageof this solution is that the user has to have easy
`and immediate access to the set of probes, the necessity of
`physically having to change the probes during the
`examination,
`the potential of one or more probes being
`damaged and the increase cost of having more than one
`probe.
`Other approaches have been directed to methods of pro-
`cessing ofthe reflected ultrasonic wave by the detectorin the
`probeto distinguish the low level fetal heart beat component
`from the noise componentofthe reflected ultrasonic waves.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`55
`
`60
`
`65
`
`2
`Typically a medium, such as an aqueous based acoustic
`gel or petroleum based gelatin, is applied to the probe. The
`medium acts as an acoustic impedance matching interface
`between the probe and the insonated area, which is the skin
`surface. Application of the medium to the probe generates
`unwanted noise, referred to as break noise, which appears as
`a high amplitude signal componentin the output signal of
`the detector and is heard as a loud sound in the head set or
`from a speaker in the Calc. unit. Break noise is also
`generated when the probe is moved across the skin surface
`causing the probe/medium/skin interface to be broken.
`SUMMARYOF THE INVENTION
`
`An object of the present invention is to provide a probe
`that can detect the fetal heart beat during the late part of the
`first trimester and the first part of the second trimester of
`pregnancy.
`Another object of the present invention is to provide a
`portable hand held Doppler fetal heart beat detection and
`monitoring system that uses only one probe and which has
`variable powersettings for controlling the level ultrasonic
`energy in the ultrasonic wave being transmitted by the probe
`thereby increasing the level of reflected ultrasound energy
`from the fetal heart so as to increase the sensitivity of the
`probe.
`The present invention is a method and a probe in a hand
`held Doppler fetal heart beat detection and monitoring
`system for detecting the fetal heart beat and for measuring
`fetal heart rate. The hand held probe comprises a transmit-
`ting crystal, a variable power meansfor selectively driving
`the transmitting crystal to produce an ultrasonic wave hav-
`ing variouslevels of ultrasonic energy and a selection means
`for selecting the power level of the power means.
`Specifically, a plurality of power drivers is provided which
`can be interconnected to drive the transmitting crystal at
`different power levels. A microcontroller controls the selec-
`tion of which powerdrivers are to be used, either singularly
`or in combination with each other, and monitors one or more
`buttons on the probe such that the user, by depressing one or
`more buttons, can cause the power level to be changed.
`The reflected ultrasound energy from the fetal heart is
`proportional to the transmitted ultrasound energy from the
`detector. The sensitivity or signal to noise ratio of the probe
`depended,in the first order determination, upon the probe’s
`internal generated noise, reflected ultrasonic noise in the
`reflected ultrasonic wave received by the receiving crystal,
`commonly referred to as tissue cluttering, and the strength of
`reflected ultrasound energy reflected by the fetal heart. It has
`been found that the ratio of an increase in the transmitted
`
`energy of the ultrasonic wave is almost entirely translated
`into an increase in the sensitivity (signal to noise ratio) of the
`probe.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`to the
`The invention will be described with respect
`particular embodiments therefore and reference will be
`made to the drawings, in which:
`FIG. 1 is an illustration depicting a hand held Doppler
`fetal heart beat detection and monitoring system including
`the probe of the invention;
`FIG. 2 is a block diagram of the probe of the invention;
`FIG. 3 is a block diagram ofa plurality of selective power
`drivers for driving the transmitting crystal at two different
`powersettings;
`FIG. 4 isa state diagram illustrating the sequence of steps
`for the selection of one of the two power modesfor the probe
`of the invention;
`
`

`

`5,827,969
`
`3
`FIG. 5 is a state diagram illustrating another sequence of
`steps for the selection of one of the two power modesfor the
`probe of the invention;
`FIG. 6 is a block diagram of a plurality of selective power
`drivers for driving the transmitting crystal at seven different
`powersettings;
`FIG. 7 is a state diagram illustrating the sequenceof steps
`for the selection of one of seven power modesfor the probe
`of the invention;
`FIG. 8 is a block diagram of the automatic break noise
`detection and attenuation portion of the probe of the inven-
`tion;
`FIG. 9 is a circuit diagram of a current sink circuit of the
`attenuation portion of the probe of the invention; and
`FIG. 10 is a chart illustrating the gain of the variable gain
`amplifier as a function of the occurrence of break noise is
`detected.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`FIG. 1 illustrates an ultrasonic Doppler fetal heart beat
`detection and monitoring system embodying a probe 11, a
`head set 10 and a Calc. unit 12. Probe 11 generates ultrasonic
`waves and then receives and processesreflected ultrasonic
`waves to generate an analog signal of the fetal heart beat.
`Probe 11 also includes a power button 18, volume down
`button 19 and a volumeup button 20. The volumelevel of
`the sound generated by headset 10 and speaker 14 in Calc.
`unit 12 is controlled by volume buttons 19 and 20. Crystals
`that produce and receive ultrasonic wavesare located in the
`base 21 of probe 11. Headset 10 is connected to probe 11 via
`jack 15 for receiving the analog signal and for generating an
`audible fetal heart beat. Calc. unit 12 is connected to probe
`11 by multi-line cable 22 via plugs 16 and 17 and includes
`electronic circuitry for processing the analog signal from
`probe 11 into an audio fetal heart beat which is emitted from
`speaker 14 and further calculates and displays the fetal heart
`rate on a display means 13.
`A fetal stethoscope is formed by the combination of probe
`11 and headset 10 or probe 11 and Calc. unit 12. Headset 10
`allowsthe doctorto solely hear the fetal heart beat during an
`examination. Calc. unit 12 is used when the doctor wishes
`
`the patient to hear the fetal heart beat and/or when the doctor
`wishes to obtain a read-out on the fetal heartrate.
`
`In use a medium,typically an aqueous based acoustic gel
`or petroleum based gelatin is applied to base 21 of probe 11.
`The medium acts as an acoustic impedance matching device
`to aid in the transmission of ultrasonic waves generated by
`probe 11 into the body of the mother and in the transmission
`of reflected ultrasonic waves from the mother, such as the
`fetal heart, to probe 11. Probe 11 is then placed against the
`outer skin of the mother with the medium betweenthe probe
`and the skin. Ultrasonic waves generated by a crystal within
`probe 11 enters the mothers body. The transmitted ultrasonic
`wavesare reflected by the movementof the fetal heart which
`changes the frequency of the ultrasonic wave as a function
`of the velocity of movement of the fetal heart. The energy
`level of the reflected ultrasonic wave from the fetal heart is
`
`directly proportional to the energy level of the transmitted
`ultrasonic wave from probe 11. The reflected ultrasonic
`waves pass through the medium andare sensed by a second
`crystal in probe 11.
`the energy of other reflected
`It has been found that
`ultrasonic waves from within the mother’s body, which is
`referred to as tissue clutter, is independent of the energy
`
`10
`
`15
`
`20
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`level of ultrasonic waves transmitted by probe 11. Further,
`the internal noise generated by the electronics within probe
`11 is, for the most part, independent of the energy level of
`ultrasonic waves being generated by crystal 50. A first
`approximation for the signal to noise ratio of the probe 11 is
`derived from the magnitude of the noise generated by tissue
`clutter, the magnitude of the noise generated by the elec-
`tronics within probe 11 and the magnitude of the energy of
`the reflected ultrasonic wave from the fetal heart. Therefore
`an increase in the ultrasonic power in the transmitted ultra-
`sonic wavewill increase the signal to noise ratio of the probe
`in that the energy level of the reflected ultrasonic wave from
`the fetal heart will be increased whiletissue clutter noise and
`noise generated in the probe will remain at the same level.
`Tests have shown that by increasing the energy level of the
`transmitted ultrasonic wave by 6 dBthat the signal to noise
`ratio will be increase by approximately 6 dB.
`FIG. 2 is a block diagram of the major components within
`probe 11. A transmitter 56 drives crystal 50 at a frequency
`of the square waveclock signal of clock 55. Microcontroller
`57 is commercially available from Microchip Technology,
`Inc., 2355 West Chandler Blvd, Chandler, Ariz. 85224, as
`part number PIC 16C622. Microcontroller 57 provides a
`transmitter power setting signal on bus 67 to transmitter 56
`for setting the power level of transmitter 56. Power supply
`54 receives a power off signal on line 47 from microcon-
`troller 57 which places microcontroller 57 in a SLEEPstate
`and turns off powerto the other components within probe 11.
`Powersupply 54 receives a power on signal on line 47 from
`microcontroller 57 which places microcontroller 57 in a
`WAKE state and turns on powerto the other components
`within probe 11. In the SLEEPstate, microcontroller 57
`monitors power button 18 and upon sensing the depression
`of power button 18 will send the power on signal to power
`supply 54.
`Receiving crystal 49 responds to the reflected ultrasonic
`energy in the reflected ultrasonic waves and provides a input
`signal, derived from the received reflected ultrasonic energy,
`to detector 51. Detector 51 is well known in the art and
`examples of detector 51 are provided in Section 14 of the
`Electronics’ Engineers Handbook, Donald G. Fink and
`Donald Christiansen, McGraw Hill Book Company, 1989,
`ISSN 0-07-020982-0.
`
`The output signal of detector 51 is provided to a volume
`controller 52 via line 46 that in turn provides an analog
`signal at sockets 58 and 59. Socket 58 receives jack 15 from
`headset 10 and socket 59 receives plug 16 on cable 22 from
`Calc. unit 12. Socket 59 also provides power from power
`supply 54 via cable 17 to Calc. unit 12. Microcontroller 57
`generates a pulse width modulated signal on line 87 to
`volume controller 52 for controlling the amplitude of the
`analog signal generated by volumecontroller 52. When the
`volume down button 19 is depressed, the pulse width of the
`pulse width modulated signal is decreased, thereby causing
`the amplitude of the analog signal from volume controller 52
`to be decreased. Similarly, when the volume up button 20 is
`depressed, the pulse width of the width modulation signalis
`increased thereby causing the amplitude of the analog signal
`from volume controller 52 to be increased.
`
`A noise controller 53 is provided for detecting break
`noise. Microcontroller 57 monitors the output of noise
`controller 53 on line 84 and uponsensing break noise being
`detected by noise controller 53 generates a signal on line 85
`to noise controller 53 that activates circuitry within noise
`controller 53 for reducing the amplitude of the analog signal
`from volume controller 52.
`
`FIG. 3 is a block diagram of the transmitting portion of
`probe 11. Transmitter 56 consists of six power drivers 60,
`
`

`

`5,827,969
`
`5
`61, 62, 63, 64 and 65 connected in pairs, where each power
`drive is an AC or ACTlogic tristate inverting buffer. Drivers
`60 and 65 area first pair, drivers 61 and 64 are a second pair,
`and drivers 62 and 63 are a third pair. Transmitter 56 is a
`continuous wave (CW) transmitter. Clock 56 provides a
`square waveclock signalvia line 68 to drivers 60, 61 and 62
`and to inverter 66 that in turn provides the inverted square
`wave clock signal to drivers 63, 64 and 65. When poweris
`turned on drivers 60prod 65 are always activated and
`providing a driving signal to crystal 50. When the square
`wave clock signal is high driver 60 will act as a current
`source and driver 65 will act as a current sink and whenthe
`square wave clock signal is low driver 60 will act as a
`current sink and driver 65 will act as a current source. This
`results in crystal 50 generating an ultrasonic wave at the
`frequency of the square waveclock signal appearing on line
`68 from clock 55. The energy or strength of the ultrasonic
`wavecreated by crystal 50 is a function of the magnitude of
`the poweror current driving crystal 50.
`Microcontroller 57 monitors the state of power button 18
`via line 69. The low power mode is selected by holding
`down powerbutton 18 for a first period of time and the high
`power modeis selected by holding down the power button
`18 for a second period of time, where the first period is
`shorter than the second period. When microcontroller 59
`determines that power button 18 was depressed for the
`second period of time for the high power mode, microcon-
`troller 57 conditions drivers 61, 62, 63 and 64 via a signal
`on line 67. Drivers 61 and 62 are in parallel with driver 60
`and drivers 63 and 64 are in parallel with driver 65. When
`drivers 61, 62, 63 and 64 are activated, the power driving
`crystal 50 is increased by a factor of four which adds 6 dB
`to the energy of the ultrasonic wave being transmitted by
`probe 11.
`FIG. 4 is a state diagram illustrating the process that
`microcontroller 57 follows when monitoring power button
`18. Starting with probe 11 in STATE 0,the of f state, when
`powerbutton 18 is depressed microcontroller 57 will start a
`timer to assess whether the incoming signal generated by the
`depressing of power button 18 is a transient signal. When-
`ever microcontroller 57 determines the occurrence of a
`transient signal the STATE of probe 11 will not be changed.
`The remaining discussion will be made assuming that the
`signal generated by depressing the power button 18,
`the
`volume down button 19 and the volume up button 20 is a
`non transient signal.
`When microcontroller 57 determinesthat signal generated
`by the depression of power button 18, microcontroller 57
`will switch probe 11 to STATE 1, low powerstate, resulting
`in crystal 50 being driven only by drivers 60 and 65. The
`microcontroller 57 will continue to monitor the period that
`powerbutton 18 is depressed after entering STATE 1 andif
`the power button 18 has been held down for the second
`period the microcontroller 57 will switch the probe 11
`STATE1, low power, to STATE 2., high power. This task is
`accomplished by microcontroller 57 initiating a counter with
`a count value of the second period when probe 11 is in
`STATE0, off state, and power button 18 is first depressed
`and then counts downthat counter for as long as the power
`button 18 remains depressed. If the counter reaches zero
`indicating the end of the second period, microcontroller 57
`will switch probe 11 from STATE 1, low power, to STATE
`2, high powerby issuing a signal on line 67 that will turn on
`drivers 61, 62, 63 and 64 effectively placing drivers 61 and
`62 in parallel with driver 60 and drivers 63 and 64 in parallel
`with driver 65. Whendrivers 61, 62, 63 and 64 are notin the
`on state in response to the signal on line 67 from microcon-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`troller 57, the four drivers 61, 62, 63 and 64 are in a high
`impedancestate rather than in an off state. If power button
`18 is released prior to the counter reaching zero, then the
`probe 11 will remain in STATE 1, low power. When probe
`11 is in either STATE 1 or STATE 2 and microcontroller 57
`
`again detects that power button 18 is depressed, microcon-
`troller 57 will switch probe 11 to STATE 0,off state.
`With this sequence of operation for probe 11, probe 11 can
`go from the off state to the low powerstate, or from the off
`state through the low power state to the high powerstate.
`Probe 11 cannot switch between the low powerstate and the
`high powerstate without going through the off state.
`FIG. 5 is a alternate state diagram illustrating the process
`that microcontroller 57 follows when monitoring power
`button 18. Again, assuming that probe 11 is in STATE 0,off
`state, microcontroller 57 sensing the depressing of power
`button 18 switches probe 11 from STATE 0 to STATE 1, low
`power. Upon the next depression of power button 18,
`microcontroller 57 enters into a time-out phase. Microcon-
`troller 57 loads a counter with a count for recognizing a
`request for STATE 0, the off state, and counts down the
`counter as long as the power button 18 is depressed. If the
`counter does not reach zero before the power button 18 is
`released then the microcontroller 57 will switch probe 11
`from STATE1, low power, to STATE 2, high power. If the
`counter reaches zero before the power button 18 is released,
`then microcontroller 57 will switch probe 11 from STATE 1,
`low power, to STATE 0,off.
`If the probe 11 is in STATE 2, high power, and power
`button 18 is depressed, microcontroller 57 will enter into the
`time-out phase. The microcontroller 57 again loads the
`counter and counts down the counter as long as the power
`button 18 is depressed. If the counter does not reach zero
`before the power button 18 is released then the microcon-
`troller 57 will switch probe 11 from STATE 2, high power,
`to STATE 1, low power. If the counter reaches zero before
`the power button 18 is released, then microcontroller 57 will
`switch probe 11 from STATE2, high power, to STATE0,off.
`With this sequence of operation, probe 11 can switch back
`and forth between the high power and low powerstates
`without first passing through the off state.
`FIG. 6 is an alternate embodiment of the transmitting
`portion of probe 11. Transmitter 56 is again shownas having
`six powerdrivers 70, 71, 72, 73, 74 and 75 connected in
`pairs where each power driver is an AC or ACT logic
`tri-state inverting buffer. Drivers 70 and 75 will drive crystal
`50 with one unit of ultrasonic energy, drivers 71 and 74 will
`drive crystal 50 with two units of ultrasonic energy and
`drivers 72 and 73 will drive crystal 50 with four units of
`ultrasonic energy. By selecting the power driver pairs that
`are active, the energy driving crystal 50 can be between one
`unit and seven units of ultrasonic energy. Again clock 50
`produces a square wave clock signal on line 68 connected
`directly to drivers 70, 71 and 72 and to drivers 73, 74, 75
`through inverter 66. Again, when any of the drivers are not
`selected that driver will be in the high impedancestate rather
`thanthe off state thereby not causing any loading effect upon
`crystal 50. Microcontroller 57 selects the power state by
`monitoring the state of power button 18, via line 69, volume
`down button 19 via line 80, and volume up button via line
`81. A display unit 76 (not shown in FIG. 1) in probe 11 is
`provided to show the selected powerlevel for probe 11.
`FIG. 7 is a state diagram for controlling the power level
`of probe 11 in accordance with commands received via
`power button 18, volume down button 19 and volume up
`button 20. In FIG. 7, condition A represents that only power
`
`

`

`5,827,969
`
`8
`generates the analog signal provided by probe 11 to headset
`10 and Calc. unit 12. Pulse width modulation filter 81 cannot
`
`change the gain control voltage fast enough to attenuate the
`portion of the analog signal associated with the occurrence
`of break noise in the output signal of detector 51.
`FIG. 9 is a circuit diagram of muting circuit 82. Upon
`detecting the occurrence of break noise, microcontroller 57
`generates a voltage on line 85 to muting circuit 82 which
`effectively, immediately lowers the gain control voltage on
`line 83 at the output of pulse width modulation filter 81 to
`variable gain amplifier 83 thereby effectively attenuating the
`break noise from being emitted through head set 10 or
`through speaker 14 on Calc. unit 12.
`The output of the pulse width modulation filter 81 is
`connected to the collector of transistor T1 via line 86. When
`
`10
`
`15
`
`7
`button 18 is depressed; condition B represents that power
`button 18 and volume up button 20 are simultaneously
`depressed; condition C represents that power button 18 and
`volume down button 19 are simultaneously depressed; and
`condition D represents that volume down button 19 and
`volume up button 20 are simultaneously depressed.
`Again, assumethat the microcontroller 57 is in STATE 0,
`the off state. When microcontroller 57 senses that only the
`power button 18 is depressed,then microcontroller 57 will
`switch probe 11 from STATE0, off, to STATE 1, powerlevel
`1. In powerlevel 1 (PLL), microcontroller 57 will initiate a
`signal on line 19 to turn on drivers 70 and 75 such that
`crystal 50 is driven with one unit of ultrasonic power.
`Microcontroller 57 includes a three stage up/down binary
`counter, which counts from 1 to 7. The count in the up/down
`counter determines which pairs of drivers are turned by
`microcontroller 57 via signals on lines 77, 78 and 79. For
`example, when the up/down counter has a count of five,
`driver pair 70 and 75 and driver pair 72 and 73 will be turn
`of thereby by driving crystal 50 with five units of ultrasonic
`energy.
`
`the voltage is placed on line 85, transistor T2 controls the
`current flow through transistor T1 such that transistor T1
`acts as a current sink on the output of pulse width modulator
`filter 81. The muting circuit of is designed to provide two
`different levels of attenuation during the attenuation period
`after break noise is detected. Microcontroller 50 has another
`timer for timing the time that has elapsed since the last break
`During Condition B, power button 18 and volume up
`noise has been detected and maintain the voltage on line 87
`buttons 20 are simultaneously depressed,
`the up/down
`to muting circuit 82 until the timer indicates that the attenu-
`counter will be continuously stepped up to a maximum
`ation period is over. A typical attenuation period for muting
`count of seven or until either the power button 18 or volume
`the output signal is 500 ms.
`up button 20 is released. The rate of stepping the up/down
`counter is slow enough such that the user, by observing the
`Referring to FIG. 10, as soon as break noise is detected at
`powerindicator, can stop the count at a desired powerlevel
`T1, the current sink will lower the value of the gain control
`PL1-PL7for probe 11.
`voltage at the output of the pulse width modulation filter 81
`such that the output analog signal of variable gain amplifier
`During condition C, power button 18 and volume down
`83 will drop by 30 dB. This level of attenuation will change
`buttons 19 are simultaneously depressed,
`the up/down
`from -—30 dB to -10 dB, at time T2, under the control of
`counter will be continuously stepped down to a minimum
`capacitor Cl and resistor R1. When capacitor C1 is fully
`count of one or until either the power button 18 or volume
`charged at T2, the attenuation will be at a level of -10 dB.
`up button 20 is released. The rate of stepping the up/down
`The period between Ti and T2 is 300 ms. After T2, the
`counter is slow enough such that the user, by observing the
`attenuation will remain at -10 dB until the timer indicates
`powerindicator, can stop the count at a desired powerlevel
`the end of the attenuation period at T4. Microcontroller 57
`PL7-PL1for probe 11.
`will
`then remove the voltage from the muting circuit,
`During condition D, volume up button 20 and volume
`thereby removing the current sink from the output of the
`down button 18 are simultaneously depressed, the micro-
`pulse width modulator filter 81 and returning the set gain
`controller 57 will switch probe 11 from the present power
`control voltage generated by the pulse width modulation
`STATE (PL1-PL7) to STATE0,off, and reset the up/down
`filter 81 to variable gain amplifier 83.
`counter a binary count of 1.
`Break noise can occur during an attenuation period.
`In this embodiment, the probe 11 can be turned on and off
`Assumein FIG. 10 that a second occurrence of break noise
`and once tuned on can be stepped up and down between
`occurred at time T3. Under this condition the timer for the
`seven powerlevel.
`break noise would be reset for another 500 ms and the
`FIG. 8 is a block diagram of noise controller 53 and the
`attenuation of -10 dB would be held for a full 500 msuntil
`volume controller 52. Noise controller 53 comprises a
`TS which would be 900 msafter the detection of the first
`comparator 18 that monitors the output signal of detector 51
`break noise.
`50
`on line 46. The output of comparator 80 will be inafirst state
`While the invention has been particularly shown and
`wheneverthe instantaneous magnitude of the output signal
`described with reference to the preferred embodiments
`from detector 51 is greater than the magnitude of a reference
`thereof, it will be understood by those skilled in the art that
`voltage and will be in a second state wheneverthe instan-
`changes in form a detail may be made therein without
`taneous magnitude of the output signal from detector 51 is
`departing from the spirit and scope of the invention. Given
`less than the magnitude of the reference voltage. As previ-
`the above disclosure of general concepts and specific
`ously stated, break noise is exhibited as a high amplitude
`embodiments, the scope of the protection sought is defined
`signal that is greater in amplitude than the amplitude of the
`by the following.
`output signal normally expected to be generated by detector
`Whatis claimedis:
`51. Microcontroller 57 monitors the output of comparator 80
`1. A probe in a hand held ultrasonic Doppler fetal heart
`and whenever comparator 80 indicates that the output signal
`beat detection and monitoring system comprising:
`from detector 51 is greater than the reference voltage,
`a crystal for transmitting ultrasonic energy;
`microcontroller 57 conditions muting circuit 82. Volume
`controller 52 includes a pulse width modulation filter 81
`a variable power source, connectedto said crystal, having
`which generates a gain control voltage on line 86 as a
`a plurality of powersettings for driving said crystal at
`function of the pulse width of the pulse width signal gen-
`a selected power setting wherein said variable power
`erated by microcontroller 57. Variable gain amplifier 83 gain
`source comprises a plurality of pairs of powerdrivers;
`and
`is controlled by the magnitude of the gain control signal and
`
`20
`
`25
`
`30
`
`40
`
`45
`
`55
`
`60
`
`65
`
`

`

`5,827,969
`
`10
`during said HIGH POWERstate upon detecting a non
`transient signal generated by depression of said
`POWERbutton switching to said LOW POWERstate
`when said POWER button is depressed for said first
`period of time and to said OFF state when said POWER
`button is depressed for said second period of time.
`10. The probe of claim 5 wherein said selection means
`comprises:
`a POWERbutton, a VOL UPbutton and a VOL DOWN
`button operable by a user for generating said power
`signals by depressing said POWER button and the
`combination of any two of said POWERbutton, said
`POWERUPbutton and said POWER DOWNbutton;
`and
`
`a microprocessor for monitoring said POWER button,
`said VOL UPbutton and said VOL DOWNbutton and
`for selecting a powersetting for said power meansas a
`function of said powersignals.
`11. The probe of claim 10 wherein said probe has multiple
`states