A 96 dB SNDR current-mode continuous-time ΔΣ modulator for electrochemical sensor arrays

Abstract

A low-voltage fully differential current-mode continuous time delta-sigma modulator is presented for application in electrochemical sensor arrays. Although a first order topology is realized by using a single differential integrator, second order noise shaping is achieved. A differential quantizer based on current controlled oscillators (CCOs) allows a current-mode implementation with high noise-immunity and low-voltage compatibility. Thanks to the differential design nonlinearity impact on circuit performance is kept low. Moreover, the typical clock-jitter sensitivity for continuous time modulators is addressed by a switched shaped-current feedback DAC. The modulator implemented in 180 nm standard CMOS technology consumes 28μW and achieves an SNDR of 95dB at a signal bandwidth of 10 kHz and an oversampling ratio of 256.