A fully integrated electroencephalogram (EEG) analog front-end IC with capacitive input impedance boosting loop

This paper presents a biopotential analog front-end (AFE) IC for measuring electroencephalogram (EEG). The AFE is based on the AC-coupled chopper stabilized instrumentation amplifier architecture to achieve the low noise. To increase the input impedance, the capacitive input impedance boosting loop (CIIBL) is proposed. The CIIBL forms a positive feedback loop between input and output of the instrumentation amplifier without additional power consumption. The CIIBL increases the input impedance from 644 MΩ to 3.5 GΩ, and enhances the CMRR from 133.4 dB to 139.1 dB, in simulation. The overall gain, the frequency response, and the input mismatches can be trimmed using programmable capacitors and programmable resistors. The AFE is fabricated in 0.18 μm 1P6M CMOS process. The core chip size of the AFE without I/O pads is 4000 by 4500 μm². The input referred noise is measured to be 0.205 μV_rms in the bandwidth from 0.5 Hz to 100 Hz. The amplifying gain of the pass band is measured to be 78 dB.