A chopped ultra-low-power, low-noise wearable EEG amplifier with pseudo-resistor calibration

This paper presents an ultra-low power, low noise chopper stabilized amplifier which is suitable for wearable EEG applications. The topology used is fully differential so as to have increased immunity to supply noise, and increased dynamic range. The amplifier is designed to handle +/- 50mV dc electrode offset, while preserving the EEG signal. A dc servo loop (DSL) is used to reject the dc offset and the chopping ripple is reduced through a dc offset calibration loop. A new resistor calibration technique is proposed for reducing the variation in pseudo-resistor value from 5000% to 8.25%. The amplifier is implemented in 0.18 mu m CMOS technology, and can operate with a total current of 1.8 mu A, achieving NEF of 3.31. The amplifier achieved a PSRR of 120.5dB and a CMRR of 131.62dB. The current consumption of 1.8 mu A affirms suitability of this implementation for coin cell battery operated wearable EEG recording headset. The achieved input referred noise of 0.45 mu V in the frequency band of 0.5-50Hz is desirable for EEG systems.