The Linearity-Improvement Sigma-Delta Modulator for Single-ended Biomedical Sensors

A sigma-delta modulator which can improve the linearity of input original signal is proposed in this paper. The inverting and double sampling techniques are used in proposed modulator to convert the single-ended signal to fully differential signal. Therefore, the signal´s linearity could be modified by the suppression of the even mode harmonic in fully differential circuit. With the proposed technique, the sensing biomedical signals could be more accurately acquired. The proposed modulator is designed in standard 0.18 mum 1P6M CMOS technology. The simulation results show that the linear errors of the CMOS thermal sensor and the PH electrochemical sensor are improved from 42.5% to 20.17%, 8.06% to 3.11%.