A 13.8-ENOB Fully Dynamic Third-Order Noise-Shaping SAR ADC in a Single-Amplifier EF-CIFF Structure With Hardware-Reusing kT/C

Abstract

To design noise-shaping successive approximation register (NS-SAR) analog-to-digital converters (ADCs) with high resolution and good power efficiency, two key bottlenecks need to be addressed. One is to realize a high-order loop filter with low circuit overhead, and the other is to mitigate the thermal noise. This article presents an NS-SAR ADC that synergistically addresses both challenges. To achieve high-order efficiency, it proposes an innovative error feedback-cascaded integrator feedforward (EF-CIFF) structure that realizes third-order noise shaping using only a single amplifier. It combines the merits of both structures, showing improved robustness, and is free of dc offset concern. On reducing the kT/C noise, this work features a sampling kT/C noise cancellation (SNC) technique that reuses the native hardware of the EF-CIFF structure. An open- loop self-quenching floating-inverter dynamic amplifier (FIDA) is used to support all amplification with low noise and power. Prototyped in 65-nm CMOS, this work achieves 84.8-dB signal- to-noise-distortion ratio (SNDR) with 625-kHz bandwidth (BW) (OSR = 8) and 119 μW, leading to 182-dB Schreier Figure of Merit (FoM). It uses only 0.8-pF input capacitance, which is 5× smaller than prior NS-SAR ADCs with similar oversampling ratio (OSR) and SNDR.