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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:29 |
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Conference: Bucharest University Faculty of Physics 2010 Meeting
Section: Biophysics and Medical Physics;Electricity and Magnetism
Title:
An Improved Amplifier for Recording Ultrafast EEG and Evoked Potentials
Authors:
Cristian Donos(1), Marian Mocanu(2), Liviu Giurgiu(1)
Affiliation:
1Faculty of Physics, 405 Atomistilor Street, Bucharest-Magurele, 077125, University of Bucharest
2"Ilie Murgulescu” Institute of Physical Chemistry, 202 Splaiul Independentei, 060021
P.O. Box 12-197, Bucharest
E-mail
cristidonos@yahoo.com
Keywords:
EEG signals, instrumentation amplifier, JFET-BJT noise
Abstract:
In a clinical context, EEG refers to recording the brain’s spontaneous electric activity, using small electrodes placed on the scalp. The signal collected is an electric “potential” measured between two electrodes. The usual signal characteristics are: small voltage (10µV to 100 µV for a healthy adult) and frequencies in the 0-40 Hz range. Evoked potentials can be measured when the subject is under the influence of a stimulus. Evoked potentials are usually recorded by multiple measurements under the same conditions and adding all the recorded signals, in order to cancel unwanted noises and the apparently random spontaneous brain activity. Also, both for spontaneous activity and evoked potentials, the higher the frequency of the signal, the lower the amplitude. In order to record signals with frequencies higher than 40 Hz, we designed a prototype EEG amplifier. It is an instrumentation amplifier with differential inputs. For each input signal, a cascode consisting of 2x2 JFET-BJTs is used, in order to obtain high input impedance, higher input-output isolation and a larger bandwidth. An integrated circuit (LT1028) with a negative feedback loop is used to maintain extremly low noise values and obtain a low output impedance. With this new designed amplifier prototype, we are able to measure, with precision, the high frequency Fourier components of the EEG signals in the nV range.
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