Electronic stethoscope
First Claim
1. An electronic stethoscope comprising:
- a microphone;
an active filter coupled to said microphone, said active filter having a center frequency continuously variable within the range of 1 hz to 1500 hz and a bandwidth continuously variable between 1 hz and 3000 hz, wherein said center frequency and said bandwidth are varied indedendently of each other;
an amplifier coupled to said active filter; and
an inverse filter coupled to said amplifier, said inverse filter having a frequency response which is the inverse of the frequency response of the human ear.
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Accused Products
Abstract
An electronic stethoscope includes a microphone mounted in a resilient collar in a hand-held case. The microphone is coupled to an active filter having independently and continuously adjustable bandwidth and center frequency. A switch bypasses the active filter when the user wishes to hear all of the sounds detected by the microphone. The controls for bandwidth and center frequency are located on one side of the case and can be manipulated by the hand holding the stethoscope. The volume or gain of the stethoscope is adjusted by a third control located on the one side of the stethoscope. The controls can be linear or rotary or combinations thereof. The output signal from the active filter passes through a filter having a frequency response inverse to that of the human ear, is amplified, and is coupled to headphones which plug into a socket on the rear of the case. The active filter is either a state variable filter or a Butterworth filter, has a maximum bandwidth of at least ten octaves, and is stable at all settings of the controls.
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Citations
17 Claims
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1. An electronic stethoscope comprising:
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a microphone; an active filter coupled to said microphone, said active filter having a center frequency continuously variable within the range of 1 hz to 1500 hz and a bandwidth continuously variable between 1 hz and 3000 hz, wherein said center frequency and said bandwidth are varied indedendently of each other; an amplifier coupled to said active filter; and an inverse filter coupled to said amplifier, said inverse filter having a frequency response which is the inverse of the frequency response of the human ear. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A state variable filter having a bandwidth of at least ten octaves, unity gain or less, and continuously and independently adjustable bandwidth and center frequency, said filter comprising:
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an input terminal and an output terminal; a first amplifier having an input and an output; a second amplifier having an input and an output, wherein the output of said second amplifier is coupled to said outout terminal; a third amplifier having an input and an output; a fourth amplifier having an input and an output; a first variable resistance coupling said input terminal to the input of said first amplifier; a second variable resistance coupling the output of the first amplifier to the input of the second amplifier; a third variable resistance coupling the output of the second amplifier to the input of the third amplifier; a fourth variable resistance coupling the output of the second amplifier to the input of the fourth amplifier; wherein said first and fourth variable resistances control the bandwidth and said second and third variable resistances control the center frequency of said filter; a first resistance coupling the output of said first amplifier to the input of said first amplifier; a second resistance coupling the output of said fourth amplifier to the input of said first amplifier; a third resistance coupling the output of said third amplifier to the input of said first amplifier; wherein the resistances of said first resistance to said second resistance to said third resistance are in the approximate ratio of 1;
10;
100. - View Dependent Claims (9, 10)
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11. A Butterworth filter having a bandwidth of at least ten octaves and continuously and independently adjustable bandwidth and center frequency, said filter comprising:
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an input terminal and an output terminal; a first amplifier having an input and an output, wherein the output of said first amplifier is coupled to said output terminal; a second amplifier having an input and an output; a first resistor coupling the output of said first amplifier to the input of said second amplifier; a first potentiometer coupling the output of the second amplifier to the input of the first amplifier, said first potentiometer controlling the center frequency of said filter; a second potentiometer coupling said input terminal to the input of said first amplifier, said second potentiometer controlling the bandwidth of said filter; a capacitor and a second resistor connected in series and coupled between the input of said first amplifier and electrical ground, whereby said active filter has less than unity gain at all settings of center frequency and bandwidth.
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12. A hand-held electronic stethoscope comprising:
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a case having a front and a back interconnected by a first side, a second side, a top, and a bottom, said case fitting within a hand; an hole in said top; a resilient collar in said hole; a microphone fitting within said resilient collar and insulated from vibrations in said case by said collar; electronic circuitry within said case and coupled to said microphone for amplifying sounds received by said microphone; three controls coupled to said circuitry, said controls located in either said first side or said second side; whereby said stethoscope can be held in one hand and said controls adjusted by said hand. - View Dependent Claims (13, 14, 15, 16, 17)
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Specification