27.3 A 13.8-ENOB 0.4pF-C<sub>IN</sub> 3<sup>rd</sup>-Order Noise-Shaping SAR in a Single-Amplifier EF-CIFF Structure with Fully Dynamic Hardware-Reusing kT/C Noise Cancelation
Tzu-Han Wang, Ruowei Wu, V.K. Gupta, Shaolan Li
Abstract
Noise-shaping SAR (NS-SAR) ADCs are attracting rising attention for their low-power high-resolution capability. In most recent arts, a substantial focus is placed on improving the loop filter design by using techniques such as passive SC and dynamic amps (DAs) [1-2]. While some demonstrate power efficiency reaching 180dB FoMs with medium-high ENOB (~13), NS-SARs targeting >13-ENOB needs have yet to attain this leading efficiency. It calls for further efforts in two key aspects when pushing for higher ENOB. The first is to realize high-order (≥3) NS without significant overhead, so it can use a low OSR and avoid excess digital power. Recent work reports a 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -order NS-SAR by cascading two 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order EF structures, showing better simplicity over classic single-loop designs [3]. However, the use of static amps keeps power high. Also, due to the fact that its residue voltages (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RES</sub> ) contain the DC offsets from the comparator/amp, the amp gain needs to be mild, which penalizes the thermal noise. The second need is to minimize the total kT/C noise. kT/C noise is largely unshaped and thus requires large capacitance, especially in the CDAC, to be reduced when high OSR is not desired. This makes the DAC area/power hungry and hard to drive. In the context of standard SAR, ref [4] realizes a kT/C noise cancelling scheme. Nonetheless, it cannot be directly applied to an NS-SAR. Moreover, it needs a power-hungry preamp.