From spikes to EEG: integrated multichannel and selective acquisition of neuropotentials

Electrical signals recorded from the brain cover a wide range of amplitudes, frequencies, and spatial scales, from spikes and local field potentials (LFP) inside the brain to electrocorticograms (ECoG) and electroencepalograms (EEG) outside. Each of these signal modalities represent different aspects of neural dynamics that can be combined to infer brain state and function in a broader context.We present a 16-channel interface circuit fabricated in a 0.5 mum CMOS process for the selective acquisition and digitization of any of the modalities. Each channel features a fixed gain bandpass amplifier with a tunable frequency response which allows isolation of the signal of interest without hardware modification and a programmable gain/resolution analog to digital converter (ADC). The bandpass amplifier analog front end has an input referred noise of 1.94 microV(rms) for a bandwidth of 8.2 kHz while drawing 12.2 microA of current from a 3.3 V supply. Experimental recordings with the system show spike signals in rat somatosensory cortex as well as alpha EEG activity in a human subject.