A 4th-order continuous-time ΔΣ modulator with improved clock jitter immunity using RTZ FIR DAC

Abstract

This paper highlights the influence of the main feedback DAC non-idealities affecting the performance of Continuous-Time Delta-Sigma Modulators (CTDSMs) in radio receiver Internet-of-Things (IoT) applications. It proposes the combination of the Return-To-Zero (RTZ) DAC pulse and Finite-Impulse-Response (FIR) DAC to have inherent Inter-Symbol-Interference immunity and reduced clock jitter sensitivity, which is crucial to meet the strict linearity and Signal-To-Noise-Distortion-Ratio (SNDR) requirements for integrated IoT radio receivers. The proposed design is validated through MATLAB® Simulink® simulations, showing that a 4th order single-bit CTDSM with RTZ + FIR DAC can achieve an SNDR performance only 3dB below the ideal even in the presence of 4.2 ps rms of clock jitter at 24 MHz sampling frequency in a 250 kHz signal bandwidth.