A Low Noise And Low Ripple Analog Front-End For Extracting Scalp EEG Signals

A low-noise and low-ripple analog front-end for extracting scalp EEG signals is presented in this work.The low-noise and low-ripple analog front-end consists of a pre-amplifier,a programmable gain amplifier and a low-pass filter.Considering the characteristics of the scalp EEG signals,such as small amplitude,low frequency and susceptibility to various types of noise interference,the pre-amplifier adopts a fully differential capacitive coupling structure,and introduces a chopping modulation technology to improve the common-mode rejection ratio(CMRR)and reduce noise at low frequency.Following the chopper modulator,a resistor-capacitor parallel network is added to suppress the ripple signal generated at the chopper frequency and the voltage offset caused by the non-ideal effect of the chopper switch.The design of the programmable gain amplifier enables the gain of the circuit adjustable.The programmable gain amplifier uses a capacitor feedback network composing of an adjustable capacitor array to realize the stepwise adjustment of the gain.The low-pass filter uses a current rudder module to achieve a lower cut-off frequency with smaller capacitance and resistance.The pre-simulation,layout,parasitic parameter extraction and post-simulation of the low-noise and low-ripple analog front-end are performed by a SMIC 0.18?m CMOS technology.The post-simulation results show that the closed-loop gain of the pre-amplifier is 40 d B,the CMRR is 132 d B and the power supply rejection ratio(PSRR)is 90 d B when the power supply voltage is 5V and the current consumption is 9 ?A.The input equivalent noise is 772 n V/sqrt(Hz)@ 100 Hz.The gain of the programmable gain amplifier is adjustable at 5d B,10 d B,20 d B and 25 d B.The cut-off frequency of the low-pass filter is 1k Hz.The ripple at the chopping frequency is suppressed with 400-fold.The total gain of the low-noise and low-ripple analog front-end is 40 d B ? 65 d B,and the passband is 1Hz ? 1k Hz.The dia area is 395?m*120?m.All parameters of the low-noise and low-ripple analog front-end meet the design specifications.