On the Robustness of Discrete-Time and Continuous-Time ΣΔ Modulators to Conducted RFI

Sigma-Delta Analog-to-Digital Converters (ADCs) are widely adopted in sensor signal acquisition circuits for their ability to achieve high resolution with minimal hardware complexity. The heart of these ADCs is the modulator, which can be implemented using either continuous time (CT) or discrete time (DT) techniques. While DT modulators are typically preferred due to their robustness against nonidealities, their immunity to external noise, particularly from radiofrequency (RF) interference when integrated with noisy circuit blocks like RF transceivers, becomes crucial for overall system performance. In this article, the impact of RF interference on the operation of second-order DT and CT modulators is investigated, employing approximated analytical techniques and computer simulations. Moreover, direct power injection experimental tests have been carried out, and the measurement results provide an immunity comparison between the two modulator types.