Area-power-efficient 11-bit SAR ADC with delay-line enhanced tuning for neural sensing applications

In this paper, an area-power-efficient 11-bit hybrid analog-to-digital converter (ADC) with delay-line enhanced tuning for neural sensing applications is presented. To reduce the total amount of capacitance, this hybrid ADC is composed of a coarse tune and a fine tune by 3-bit delay-lined-based ADC and 8-bit successive approximation register (SAR) ADC, respectively. The delay-lined-based ADC is designed to detect the three most significant bits by a modified vernier structure. To relax the accuracy requirement of the coarse tune, the lifting-based searching algorithm and re-comparison procedure are proposed for the fine tune. To further achieve energy saving, split capacitor array and self-timed control are utilized in the SAR ADC. Fabricated in TSMC 0.18μm CMOS technology, an ENOB of 10.4-bit at 8KS/s can be achieved with only 0.6μW power consumption and 0.032-mm² area. The FoM of this ADC is 49.4fJ/conversion-step.