An adaptive DAC settling waiting time optimized ultra low voltage asynchronous SAR ADC in 40 nm CMOS

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

Research output: Contribution to journalArticle

1 Citation (Scopus)


An ultra low power and low voltage successive-approximation-register (SAR) analog-to-digital converter (ADC) with timing optimized asynchronous clock generator is presented. By calibrating the delay amount of the clock generator, the DAC settling waiting time is adaptively optimized to counter the device mismatch. This technique improved the maximum sampling frequency by 40% keeping ENOB around 7-bit at 0.4 V analog and 0.7 V digital power supply voltage. The delay time dependency on power supply has small effect to the accuracy of conversion. Decreasing of supply voltage by 9% degrades ENOB only by 0.1-bit, and the proposed calibration can give delay margins for high voltage swing. The prototype ADC fabricated in 40 nm CMOS process achieved figure of merit (FoM) of 8.75-fJ/conversion-step with 2.048 MS/s at 0.6 V analog and 0.7 V digital power supply voltage. The ADC can operates from 50 S/s to 8 MS/s keeping ENOB over 7.5-bit.

Original languageEnglish
Pages (from-to)820-827
Number of pages8
JournalIEICE Transactions on Electronics
Issue number6
Publication statusPublished - 2013 Jun



  • ADC
  • Asynchronous
  • SAR
  • Ultra low power

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Electronic, Optical and Magnetic Materials

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