An 8 bit 0.3-0.8 V 0.2-40 MS/s 2-bit/Step SAR ADC With Successively Activated Threshold Configuring Comparators in 40 nm CMOS

Kentaro Yoshioka, Akira Shikata, Ryota Sekimoto, Tadahiro Kuroda, Hiroki Ishikuro

Abstract: A 0.3-0.8 V low-power 2-bit/step asynchronous successive approximation register analog-to-digital converter (ADC) is presented. A low-power 2-bit/step operation technique is proposed which uses dynamic threshold configuring comparator instead of multiple digital-to-analog converters (DACs). Power and area overhead is minimized by successively activated comparators. The comparator threshold is configured by simple Vcm biased current source, which keep the ADC free from power supply variations over 10%. Simple digital calibration is enabled by generating the reference internally. The prototype ADC fabricated in a 40 nm CMOS achieved a 44.3 dB signal-to-noise-plus-distortion ratio (SNDR) with 6.14 MS/s at a single supply voltage of 0.5 V. The ADC achieved a peak FoM of 4.8 fJ/conv-step at 0.4 V and operates down to 0.3 V.