Mixed-Order Correlated Dual-loop Sturdy MASH CT ΔΣ Modulator with Distributed Signal Feed-in and VCO based Quantizer

Abstract

With the development of wireless technology, continuous time deltasigma modulator (CTDSM) have received recent attention. To increase the effective number of bits (ENOB) in CTDSM highresolution quantizers and high-order loop filters have been explored. While using high-order loop filters can improve ENOB, the increased power consumption of additional integrators and the increased risk of loop instability are serious drawbacks. On the other hand, using a quantizer with a high resolution can increase the signal-toquantization-noise ratio (SONR), but also exponentially increases the complexity of the feedback digital-to-analog converter (DAC). To address these challenges the art has focused on new topologies. Multi-loop CTDSM structures such as multi-stage noise-shaping (MASH) architecture and Sturdy MASH (SMASH) [1] structures have been developed to counter the loop stability issue in single-loop structures. The former cancels the quantization noise (ON) of the first loop by use of backend digital filters in both loops. The latter removes the backend digital filter and shapes the ON from both loops. However, the performance of the structures above is limited by the delay of the ON extraction of the first loop’s quantizer and the nonlinearity of ON extraction DAC. Noise shaping quantizers (NSO) have also been explored in CTDSM to raise the order of noise shaping. The voltage-controlled oscillator based quantizer (VCO-O) benefits from its low power consumption, technology scaling, and intrinsic dynamic element matching (DEM) characteristic. However, the nonlinearity of the VCO-O can limit performance and often prompts an increase in circuit complexity to suppress nonlinearity. A multi-loop structure without quantization error extraction and calibration-free NSO remains a challenge for the next generation of CTDSM design.