A Sixth-Order 4-2 SMASH CIFF Complex Bandpass Delta-Sigma Modulator with Delaying Digital Input Feedforward

Abstract

In this paper, a sixth-order sturdy multi-stage noise shaping (SMASH) bandpass delta-sigma (ΔΣ) modulator with delaying digital input feedforward (DFF) structure is presented. The second-order ΔΣ modulator with cascade integrators and distributed feedforward (CIFF) is utilized in each stage to reduce the signal swing. Hence, the requirement of opamp and the power consumption of circuits can be reduced due to the suppression of the signal swing and the discarding of the digital cancellation filters. One pair of complex zeros is designed within signal bandwidth to effectively suppress the noise floor of the presented modulator. The sub-sampling technique is adopted to reduce the clock frequency and the requirement of opamp. Simulation results confirm the feasibility of the proposed SMASH CIFF bandpass ΔΣ modulator with delaying DFF structure. The proposed bandpass ΔΣ modulator compared to the single-loop AFF structure, the signal-to-noise plus distortion ratio (SNDR) could be increased by 12 dB, and the dynamic range (DR) could be extended by roughly 15 dB in a 200 kHz of signal bandwidth centered at 10.7 MHz.