A 60-MS/s 5-MHz BW Noise-Shaping SAR ADC With Integrated Input Buffer Achieving 84.2-dB SNDR and 97.3-dB SFDR Using Dynamic Level-Shifting and ISI-Error Correction

Abstract

This article presents a 60-MS/s 5-MHz BW noise-shaping (NS) successive-approximation-register (SAR) analog-to-digital converter (ADC) with an integrated highly linear input buffer in a 40-nm CMOS process. A dynamic level-shifting (DLS) technique is proposed to adaptively adjust the output common-mode voltage of the integrated input buffer for different operation phases, achieving the optimal linearity while alleviating the voltage breakdown problem at the capacitive digital-to-analog converter (CDAC) top plate. The mismatch-error-shaping (MES) technique is utilized to minimize the CDAC mismatch, which also generates undesired inter-symbol-interference (ISI) errors as a side effect. An ISI-error correction (IEC) technique is proposed to mitigate this problem and further improve the linearity. Both foreground and background calibrations are adopted in the subranging ADC and the NS filter to improve the gain accuracy. This SAR ADC prototype, with an integrated input buffer driving a 4.4-pF CDAC within 2.7 ns, achieves signal-to-noise ratio (SNR)/signal-to-noise-and-distortion ratio (SNDR)/spurious-free dynamic range (SFDR)/dynamic range (DR)/total harmonic distortion (THD) of 85.4 dB/84.2 dB/97.3 dBc/86.4 dB/−92.9 dBc while consuming 8.06 mW from 2.5- and 1.1-V dual supply voltages. The Walden FoM (FoM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {W}}$ </tex-math></inline-formula> ) and figure-of-merit (FoM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {S}}$ </tex-math></inline-formula> ) are 60.6 fJ/conv.-step and 172.1 dB, respectively.