A Low-Noise Low Input Impedance Amplifier for Magnetic Measurements of Nerve Action Currents

Author

Wikswo, John P. ; Samson, Philip C. ; Giffard, Robin P.

Author_Institution

Department of Physics and Astronomy, Vanderbilt University

Issue

4

fYear

1983

fDate

4/1/1983 12:00:00 AM

Firstpage

215

Lastpage

221

Abstract

We have developed a low-noise solid-state current-to-voltage amplifier to measure the magnetic fields produced by nerve action currents. The amplifier senses the EMF induced in a toroidal, ferrite-core pickup coil surrounding the nerve by the circumferential magnetic field associated with the axial nerve action currents which propagate past the toroid. In order to obtain low input voltage noise, the input stage of the amplifier consists of 20 preamplifiers in parallel, each containing a discrete bipolar transistor pair. The complete amplifier has an input impedance of 1.33 Â¿and a minimum noise figure of 15 dB at 100 Hz for a source resistance of 50 Â¿. The amplifier has sufficient sensitivity to detect the magnetic field of the action potential propagating along a single giant axon.

Keywords

Coils; Current measurement; Impedance; Low voltage; Low-noise amplifiers; Magnetic field measurement; Magnetic noise; Magnetic variables measurement; Solid state circuits; Toroidal magnetic fields; Action Potentials; Animals; Axons; Decapodiformes; Electromagnetic Fields; Electronics, Medical;

fLanguage

English

Journal_Title

Biomedical Engineering, IEEE Transactions on

Publisher

ieee

ISSN

0018-9294

Type

jour

DOI

10.1109/TBME.1983.325220

Filename

4121609