27.2 14.1-ENOB 184.9dB-FoM Capacitor-Array-Assisted Cascaded Charge-Injection SAR ADC
Kyojin Choo, Hyochan An, Dennis Sylvester, David Blaauw
Abstract
IoT sensors are in rising demand and they often require low power, yet high precision measurements. Under constrained energy, Nyquist-rate SAR ADCs are typically used for readout as they are energy efficient and easy to multiplex across many sensors. However, achieving high precision (>14b) in SAR ADCs is challenging as all factors limiting performance (resolution, mismatch, and noise) must be simultaneously addressed with minimal energy impact. In this paper, we present an energy-efficient, capacitor-array-assisted cascaded charge-injection SAR ADC (c-ciSAR) with 17b nominal resolution (14.14b ENOB) that achieves a 184.9dB Schreier FoM (SFoM) and 4.32fJ/conv with a 1V supply in 0.18μm CMOS. The ADC deploys a combination of techniques to improve resolution, mismatch, and noise performance while remaining energy-efficient, namely: 1) hybridization of a capacitor-array DAC (CDAC) with charge-injection-cell (ci-cell) based DACs (ciDACs) to achieve high resolution and flexible programmability; 2) direct analog DAC mismatch compensation and repeated LSB decisions that leverage flexible programmability; 3) a noise-efficient charge-domain preamplifier for comparator (1.66 NEF) and SNR extended ci-cell; and 4) ±2·VDD signal sampling with pre-sampling MSB decision.