Improved DC Rejection with Unblocking Mechanism for EEG Acquisition System

Instrumentation for recording Electroencephalogram (EEG) signals should have arrangments to reject the undesired DC and low frequency components. These components may cause the analog part of EEG acquisition to be blocked for several seconds and also decrease the quality of acquired signals. In this paper, first is to introduce an improved highpass filtering method by using servo feedback technique. The proposed highpass filter use pseudo resistors instead of ordinary ones and presents constant group delay to avoid any phase distortion. The second design is an unblocking mechanism. This mechanism ensures stability in presence of high-level low frequency inputs. It becames possible by providing variable time constant of the highpass filter

Keywords:

DC rejection , unblocking , preamplifier , EEG , highpass filter