Patent US4243044A successfully refreshed from Google Patents.
US4243044A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Coupling circuit with driven guard
Assignee: HP Inc
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Filing: 1978-09-07
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Granted: 1981-01-06
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Expires: 1998-09-07
Abstract
Abstract In signal measurement circuits which are referred to a floating ground and which derive their input signals from electrodes attached to a patient's body, the effects of common mode potentials on the patient's body are minimized without requiring any patient electrodes other than those acting as signal sources, by using a unity gain amplifier to drive the floating ground toward the common mode potential on the patient's body. This process is accomplished without significantly degrading the isolation impedance between the measurement circuits and true ground. The patient is protected from hazardous electrical shock by incorporating current limiting devices in the unity gain amplifier.
Inventors
- 👤 Timothy B. Blancke
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 21:20
CPC Classifications
A; A61; A61B; A61B5/00; A61B5/24; A61B5/30; A61B5/305; A61B5/301; A61B5/307; A61B5/308; Y; Y10; Y10S; Y10S128/00; Y10S128/902
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
307 words
A circuit for coupling the difference between potentials supplied by two electrodes in contact with the body of a patient and conducted by shielded leads to the inputs thereof to an output referenced to ground in such manner as to minimize the effect of any common mode voltage and provide a high impedance between the patient and ground without requiring the attachment of another electrode to the patient, comprising a point of ground potential, a point of floating ground potential, two input terminals to which electrode leads may be respectively attached, a differential amplifier circuit having two inputs and an output, said inputs respectively coupled to said input terminals, a power supply coupled to provide operating potentials for said differential amplifier circuit, said power supply being referenced to said point of floating ground potential, output terminals, one of which is connected to said point of ground potential, means coupling the differential amplifier signals at the output of said differential amplifier to said output terminals, said coupling means maintaining a high impedance to ground for the common mode signals at the output of said differential amplifier, a terminal to which shields of electrode leads may be attached, said terminal being connected to said point of floating ground potential, and a unity gain amplifying circuit means referenced to ground, said unity gain amplifying circuit means having an input connected by means exclusive of the body of a patient to a point in said differential amplifier circuit at which common mode voltages may appear and an output connected to said point of floating ground potential, the said unity gain amplifying circuit means having means for limiting current flowing between ground and both its input and its output, said latter means limiting the current that can flow to a value that is low enough to protect the patient from electrical shock.
Claim 2
Dependent Claim
307 words
A circuit for coupling the difference between potentials supplied by two electrodes in contact with the body of a patient and conducted by shielded leads to the inputs thereof to an output referenced to ground in such manner as to minimize the effect of any common mode voltage and provide a high impedance between the patient and ground without requiring the attachment of another electrode to the patient, comprising a point of ground potential, a point of floating ground potential, two input terminals to which electrode leads may be respectively attached, a differential amplifier circuit having two inputs and an output, said inputs respectively coupled to said input terminals, a power supply coupled to provide operating potentials for said differential amplifier circuit, said power supply being referenced to said point of floating ground potential, output terminals, one of which is connected to said point of ground potential, means coupling the differential amplifier signals at the output of said differential amplifier to said output terminals, said coupling means maintaining a high impedance to ground for the common mode signals at the output of said differential amplifier, a terminal to which shields of electrode leads may be attached, said terminal being connected to said point of floating ground potential, and a unity gain amplifying circuit means referenced to ground, said unity gain amplifying circuit means having an input connected by means exclusive of the body of a patient to a point in said differential amplifier circuit at which common mode voltages may appear and an output connected to said point of floating ground potential, the said unity gain amplifying circuit means having means for limiting current flowing between ground and both its input and its output, said latter means limiting the current that can flow to a value that is low enough to protect the patient from electrical shock.
Claim 3
Dependent Claim
88 words
A circuit as set forth in claim 1 wherein said means for limiting current that can flow between ground and the input and output of the unity gain amplifying circuit means is comprised of a first current limiting means connected between the input of said unity gain amplifying circuit means and the point in said differential amplifier circuit to which the input is coupled and a second current limiting means connected between the output of said unity gain amplifying circuit means and said point of floating ground potential.
Claim 4
Dependent Claim
55 words
A circuit as set forth in claim 1 or 2 having a buffer connected between at least one of said input terminals and an input of said differential amplifier circuit and wherein the input of said unity gain amplifying means is connected to said at least one of the inputs of said differential amplifier circuit.
Claim 5
Dependent Claim
118 words
A circuit as set forth in claim 1 wherein said unity gain amplifying circuit means is comprised of an operational amplifier having a non-inverting input, an inverting input and an output and wherein a first current limiter is connected between said noninverting input and an input of said differential amplifier circuit, second and third current limiters are connected in series between the output of said operational amplifier and its inverting input, means are provided for coupling the junction of said second and third current limiters to said point of floating ground potential, and power supply means is provided that is referenced to said point of ground potential, said power supply means supplying operating potentials for said operational amplifier.
Claim 6
Dependent Claim
32 words
A circuit as set forth in claim 4 wherein at least one buffer amplifier is connected between one of said input terminals and one of the inputs of said differential amplifier circuit.
Claim 7
Dependent Claim
293 words
A circuit for coupling the difference between potentials supplied by two electrodes in contact with the body of a patient and conducted by shielded leads to the inputs thereof to an output referenced to ground in such manner as to minimize the effect of any common mode voltage and provide a high impedance between the patient and ground without requiring the attachment of another electrode to the patient, comprising a point of floating ground potential, a point of ground potential, there being an unavoidable stray impedance between said point of floating ground potential and said point of ground potential, a differential amplifier having two inputs and an output, said differential amplifier being referenced to said point of floating ground potential, means respectively coupling the inputs of said differential amplifier to said input terminals, means coupling the output of said differential amplifier to said output terminals, one of said output terminals being connected to said point of ground potential, an amplifier circuit referenced to said point of ground potential, said circuit having an input coupled to at least one of said input terminals by an all-hardware circuit and an output coupled to said point of floating ground potential for causing current to pass through said predetermined stray impedance so as to cause said point of floating ground potential to have the same potential as said one input terminal, said amplifier circuit providing sufficient impedance between said input terminal and ground and between its output and ground to protect a patient electrically coupled to said input terminals from electrical shock, and a terminal to which the shields of leads connected to said input terminals may be electrically attached, when said leads are present, said latter terminal being connected to said point of floating ground potential.
Claim 8
Dependent Claim
293 words
A circuit for coupling the difference between potentials supplied by two electrodes in contact with the body of a patient and conducted by shielded leads to the inputs thereof to an output referenced to ground in such manner as to minimize the effect of any common mode voltage and provide a high impedance between the patient and ground without requiring the attachment of another electrode to the patient, comprising a point of floating ground potential, a point of ground potential, there being an unavoidable stray impedance between said point of floating ground potential and said point of ground potential, a differential amplifier having two inputs and an output, said differential amplifier being referenced to said point of floating ground potential, means respectively coupling the inputs of said differential amplifier to said input terminals, means coupling the output of said differential amplifier to said output terminals, one of said output terminals being connected to said point of ground potential, an amplifier circuit referenced to said point of ground potential, said circuit having an input coupled to at least one of said input terminals by an all-hardware circuit and an output coupled to said point of floating ground potential for causing current to pass through said predetermined stray impedance so as to cause said point of floating ground potential to have the same potential as said one input terminal, said amplifier circuit providing sufficient impedance between said input terminal and ground and between its output and ground to protect a patient electrically coupled to said input terminals from electrical shock, and a terminal to which the shields of leads connected to said input terminals may be electrically attached, when said leads are present, said latter terminal being connected to said point of floating ground potential.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-01-06 | 1984-07-07 | 1985-01-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-01-06 | 1988-07-07 | 1989-01-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-01-06 | 1992-07-07 | 1993-01-06 | $7700.00 | Window Closed / Lapsed |