A 2.36μW/Ch CMOS 8-Channel EEG Acquisition Unit with Input Protection Circuits for Applications Under Transcranial Direct Current Stimulation

A 0.18um-CMOS 8-channel EEG acquisition unit with input protection circuits is designed and fabricated for EEG monitoring under the transcranial direct current stimulation (tDCS). The capacitively-coupled chopper instrumentation amplifier (CCCIA) with chopper modulation is used to suppress flicker noise and amplify input EEG signals. To filter out high frequency noise with high linearity, the switched-capacitor low-pass filter (SC-LPF) is proposed. The switched-capacitor amplifier (SC-Amp) is also proposed to drive ADC capacitor array. The input protection circuit (IPC) is implemented by I/O device to keep internal circuits from overstress and artifacts from the tDCS. A 10-bit SAR ADC with offset-calibration comparator is integrated for accurate ADC conversion. The fabricated EEG acquisition unit has programmable gain 57.5/67.6/78.5dB. The measured power dissipation of a single CCCIA circuit is 2.36μW per channel. The measured recovery time is 7.5ms after the tDCS stimulation. It has been verified that the designed chip can record real EEG signals.