A 5 μW/channel 9b-ENOB BioADC array for electrocortical recording

We present a 4-channel integrated biopotential analog-to-digital converter (bioADC) for electrocortical recording in 180nm CMOS. The bioADC directly transduces microvolt biopotentials into a digital representation without a voltage-amplification stage. Each channel comprises a continuous-time first-order ΔΣ modulator with OTA input and current feedback, followed by a second-order comb-filter decimator. Powered from a 1.5V supply, the analog and digital circuits in each channel draw 2.1uA and 1.4uA of supply current, respectively. The bioADCs achieve an SNR of 57dB and a SFDR or 63.5dB, for 9-b ENOB. Intracranial EEG recordings from an anesthetized rat are shown and compared to simultaneous recordings from a commercial reference system to validate performance in-vivo. The micropower operation and direct digital readout make this circuit ideally suited for closed-loop neuromodulation applications.