A Second-Order Sigma-Delta Modulator with Extended Dynamic Range for Electroencephalogram Detection

This paper presents a 2nd-order Discrete-Time Sigma-Delta Modulator (DT SDM), which can be applied to electroencephalogram (EEG) detection. The DT SDM uses bootstrap switches to improve linearity, also utilizes chopper technique to remove DC offset and low frequency noise of amplifier in first stage integrator. A multi-group summing circuit is proposed, which achieves the same proportional attenuation of the input signal of the summing circuit and the reference voltage, thus improving the accuracy of the quantizer. Designed in a 0.18µm CMOS process, the proposed DT SDM achieves a DR of 127.4 dB, a peak-SNDR of 124.6 dB, and ENOB of 20.4 bit at 250 Hz bandwidth.