BIO-ISOLATED DC OPERATIONAL AMPLIFIER

• US 3,811,094 A
• Filed: 06/30/1972
• Issued: 05/14/1974
• Est. Priority Date: 06/30/1972
• Status: Expired due to Term

• Current Assignee: Robert D. Lee
• Original Assignee: Robert D. Lee
• Inventors: Lee, Robert D.
• Primary Examiner(s): Kaufman, Nathan
• Application Number:
  US05/267,862
• Time in Patent Office: 683 Days
• Field of Search: 330/59 250/217S
• US Class Current: 330/59
• CPC Class Codes: A61B 5/301 providing electrical separation, e.g. by using isolating transformers or optocouplers
• CPC Class Codes: H03F 3/087 with IC amplifier blocks H03F3/085 takes precedence

Abstract

A bio-isolated DC operational amplifier is provided for use in making bio-electrical measurements of a patient while providing isolation of the patient from electrical shocks and the like, the circuit comprising a first operational amplifier coupled to the patient and having its output coupled in a forward loop through a first optic coupler to a second operational amplifier, the output of the second operational amplifier being coupled to suitable monitoring circuitry. The output of the second operational amplifier is coupled via a feedback circuit including a second optic coupler to the input of the first operational amplifier.

Claims

1. An amplifier circuit for electrically isolating an input signal from an output signal which is an amplified version of the input signal comprising a first operational amplifier having an input and an output, a signal input terminal coupled to said amplifier input, a first light emitter, and a first photodetector capable of generating a signal when energized, said first light emitter being optically coupled to said first photodetector and electrically coupled to said output of said first operational amplifier, a second operational amplifier having an input and an output, said output signal being generated at said output of said second operational amplifier, said input of said second operational amplifier being coupled to said first photodetector, a negative voltage feedback circuit for coupling the output of said second operational amplifier to the input of said first operational amplifier, said feedback circuit comprising a second light emitter, a second photodetector capable of generating a signal when energized, and a resistor, said second light emitter being optically coupled to said second photodetector and electrically coupled to said output of said second operational amplifier, said resistor being connected between said photodetector and said input of said first operational amplifier, said feedback circuit applying a signal to said input of said first operational amplifier which is always of opposite polarity to the signal at said signal input terminal, a first power supply coupled to said first operational amplifier, said first light emitter and said second photodetector, a second power supply coupled to said first photodetector, said second operational amplifier and said second light emitter, said first power supply being electrically isolated from said second power supply and said signal input terminal being electrically isolated from said output of said second operational amplifier.

2. A circuit as claimed in claim 1 comprising a first current amplifier coupled between the output of said first operational amplifier and said first light emitter and a second current amplifier coupled between the output of said second operational amplifier and said second light emitter.

3. A circuit as claimed in claim 2 wherein each of said current amplifiers includes a transistor having a base coupled to the output of the associated operational amplifier and a collector-emitter circuit coupled to the associated light emitter.

4. A circuit as claimed in claim 1 wherein each of said photodetectors comprises a phototransistor.

5. A circuit as claimed in claim 4 wherein each photodetector further includes a transistor amplifier coupled to said phototransistor.