Abstract
Frequency domain analysis of EEG signals is highly useful for biofeedback and detecting various sleep stages. A simple spectrum analyser circuit has been described in this paper to display the autospectra on a CRO or an X-Y recorder.The circuit uses a digitally controlled band-pass filter whose centre frequency is variable by digital signals. Output of band-pass filter is fullwave rectified and filtered to give absolute value of amplitude of the frequency component present at a particular moment. The instrument covers whole of the low frequency spectrum of EEG signals (0.2 Hz to 28 Hz). This instrument has hold facility also, which enables one to note time variations of the amplitude of a particular frequency.
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