Active Electrode IC for EEG and Electrical Impedance Tomography With Continuous Monitoring of Contact Impedance

The IC presented integrates the front-end for EEG and Electrical Impedance Tomography (EIT) acquisition on the electrode, together with electrode-skin contact impedance monitoring and EIT current generation, so as to improve signal quality and integration of the two techniques for brain imaging applications. The electrode size is less than 2 cm(2) and only 4 wires connect the electrode to the back-end. The readout circuit is based on a Differential Difference Amplifier and performs single-ended amplification and frequency division multiplexing of the three signals that are sent to the back-end on a single wire which also provides power supply. Since the system's CMRR is a function of each electrode's gain accuracy, an analysis is performed on how this is influenced by mismatches in passive and active components. The circuit is fabricated in 0.35 mu m CMOS process and occupies 4 mm(2), the readout circuit consumes 360 mu W, the input referred noise for bipolar EEG signal acquisition is 0.56 mu V-RMS between 0.5 and 100 Hz and almost halves if only EEG signal is acquired.