This paper presents a third-order single-loop delta-sigma modulator of a biomedical micro-system for portable electroencephalogram(EEG) monitoring applications.To reduce the power consumption,the loop filter of the proposed modulator is implemented by applying a switched-capacitor structure.The modulator is designed in a 0.35-μm 2P4M standard CMOS process,with an active area of 365×290μm^2.Experimental results show that this modulator achieves a 68 dB dynamic range with an input sinusoidal signal of 100 Hz signal bandwidth under a 64 over-sampling ratio.The whole circuit consumes 515μW under a 2.5 V power supply,which is suitable for portable EEG monitoring.
A fully-differential bandpass CMOS(complementary metal oxide semiconductor) preamplifier for extracellular neural recording is presented.The capacitive-coupled and capacitive-feedback topology is adopted.The preamplifier has a midband gain of 20.4 dB and a DC gain of 0.The -3 dB upper cut-off frequency of the preamplifier is 6.7 kHz.The lower cut-off frequency can be adjusted for amplifying the field or action potentials located in different bands. It has an input-referred noise of 8.2μVrms integrated from 0.15 Hz to 6.7 kHz for recording the local field potentials and the mixed neural spikes with a power dissipation of 23.1μW from a 3.3 V supply.A bandgap reference circuitry is also designed for providing the biasing voltage and current.The 0.22 mm^2 prototype chip,including the preamplifier and its biasing circuitry,is fabricated in the 0.35-μm N-well CMOS 2P4M process.
