A 0.5-V Fully Synthesizable SAR ADC for On-Chip Distributed Waveform Monitors

This paper presents a fully synthesizable successive-approximation-register (SAR) analog-to-digital converter (ADC) for on-chip distributed waveform monitoring in a low-power system-on-chip (SoC). All blocks in the proposed ADC are designed using only standard digital cells, enabling an auto-generation based on regular digital design tools. Therefore, the proposed ADC provides enhanced portability and reusability which facilitate integration into various functional blocks requiring testing and diagnosis. To implement the SAR ADC, a synthesizable voltage digital-to-analog converter (VDAC) and a rail-to-rail hybrid comparator are proposed in this paper. An inherited nonlinearity of the standard-cell-based VDAC is compensated by a histogram-based soft calibration which can be easily embedded in a waveform reconstruction module. In addition, an oversampling technique with a redundant error correction method is employed to realize the fully synthesizable design without a sample-and-hold (S/H) circuit. The proposed ADC was fabricated in 28-nm CMOS technology, occupying an active area of 0.002 mm
²
. The ADC achieves 5.39-bit effective-number-of-bit (ENOB) at 500-kS/s sampling rate. The power consumption of the ADC is 92.2 μW with a supply voltage of 0.5 V.