Multi-Channel Analog-to-Digital Conversion Using a Delta-Sigma Modulator Without Reset and a Modulated-Sinc-Sum Filter

Abstract

A new method is presented for converting any continuously running discrete-time delta-sigma modulator (DTDSM) into a multi-channel ADC by adding only a digital filter at the output. The inputs are multiplexed and fed to the ADC directly. The crosstalk that would exist if the decimation filter output is demultiplexed directly is canceled using the proposed modulated-sinc-sum digital filter. Compared to resetting the DSM and converting it to an incremental DSM, the proposed technique is at least <inline-formula> <tex-math notation="LaTeX">$1.57\times $ </tex-math></inline-formula> more power-efficient. A prototype two-channel ADC clocked at 6.144 MHz with a channel bandwidth of 22 kHz demonstrates the proposed technique. Fabricated in a 180 nm CMOS process, the prototype chip consumes 1 mW/channel, including the digital filters, and achieves a peak SNR/DR of 94.4 dB/98.5 dB. The inter-channel crosstalk is restricted to less than &#x2212;93 dBc across the entire bandwidth and across temperature.