A 9-bit 100 MS/s SAR ADC with Digitally Assisted Background Calibration

Xiaolei ZHU
Yanfei CHEN
Tadahiro KURODA

IEICE TRANSACTIONS on Electronics   Vol.E95-C    No.6    pp.1026-1034
Publication Date: 2012/06/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E95.C.1026
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuits and Related SoC Integration Technologies)
ADC,  successive approximation,  split capacitor DAC,  charge redistribution,  nonlinearity,  digital background calibration,  

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The performance of successive approximation register (SAR) analog-to-digital converter (ADC) is well balanced between power and speed compare to the conventional flash or pipeline architecture. The nonlinearities suffer from the CDAC mismatch and comparator offset degrades SAR ADC performance in terms of DNL and INL. An on chip histogram-based digitally assisted background calibration technique is proposed to cancel and relax the aforesaid nonlinearities. The calibration is performed using the input signal, watching the digital codes in the specified vicinity of the decision boundaries, and feeding back to control the compensation capacitor periodically. The calibration does not require special calibration signal or additional analog hardware which is simple and amenable to hardware or software implementations. A 9-bit SAR ADC with split CDAC has been implemented in a 65 nm CMOS technology and it achieves a peak SNDR of 50.81 dB and consumes 1.34 mW from a 1.2-V supply. +0.4/-0.4 LSB DNL and +0.5/-0.7 LSB INL are achieved after calibration. The ADC has input capacitance of 180 fF and occupies an area of 0.10.13 mm2.