An 8.6 ENOB 900MS/s time-interleaved 2b/cycle SAR ADC with a 1b/cycle reconfiguration for resolution enhancement

Abstract

By taking advantage of the merits of the low power consumption and hardware simplicity of SAR ADCs, 2b/cycle conversion structures in SAR ADCs have been actively studied in recent years for enhanced conversion rates and excellent FoM [1-3]. However, many error sources in the 2b/cycle SAR ADCs, such as mismatches between DACs and comparators, and the signal-dependent errors from comparators, namely kickback noise and offset, make it difficult to achieve high resolution. To date, pure 2b/cycle structures operating above hundreds of MS/s have shown a somewhat limited resolution with an ENOB lower than 7 at Nyquist rates [1,2]. As a derivation of the structure, a sub-ADC could be implemented using the 2b/cycle SAR ADC structure for high resolution as in [4], at the cost of increased circuit complexity and static current flow. In this work, we present a resolution-enhancing design technique for 2b/cycle SAR ADCs with negligible hardware overhead, while relieving the requirements for the aforementioned errors: Reconfiguration from a 2b/cycle structure to a normal 1b/cycle SAR ADC with error-correction capability achieves an 8.6 ENOB from a 9b ADC.