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Analysis and Calibration of Nonbinary-Weighted Capacitive DAC for High-Resolution SAR ADCs
Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
2014 (English)In: IEEE Transactions on Circuits and Systems - II - Express Briefs, ISSN 1549-7747, E-ISSN 1558-3791, Vol. 61, no 9, 666-670 p.Article in journal (Refereed) Published
Abstract [en]

This brief analyzes the effect of capacitor variation on the design of high-resolution nonbinary-weighted successive-approximation-register analog-to-digital converters in terms of radix, conversion steps, and accuracy. Moreover, the limitation caused by the one-side redundancy of the nonbinary-weighted network is addressed and a corresponding solution with a mathematical derivation is provided. In order to relax the mismatch requirement on the capacitor sizing while still ensuring enough linearity, a bottom-up weight calibration technique accounting for noise and offset errors is proposed, and its effectiveness is demonstrated. This calibration approach can be easily incorporated into a charge-redistribution converter without modifying its main architecture and conversion sequence.

Place, publisher, year, edition, pages
IEEE , 2014. Vol. 61, no 9, 666-670 p.
Keyword [en]
Capacitor variation; digital error correction; nonbinary weighted; redundancy; successive approximation; successive approximation register (SAR) analog-to-digital converters (ADCs); weight calibration
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:liu:diva-110385DOI: 10.1109/TCSII.2014.2331111ISI: 000341985600006OAI: oai:DiVA.org:liu-110385DiVA: diva2:745224
Available from: 2014-09-10 Created: 2014-09-10 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Ultra-Low-Power Analog-to-Digital Converters for Medical Applications
Open this publication in new window or tab >>Ultra-Low-Power Analog-to-Digital Converters for Medical Applications
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomedical systems are commonly attached to or implanted into human bodies, and powered by harvested energy or small batteries. In these systems, analog-to-digital converters (ADCs) are key components as the interface between the analog world and the digital domain. Conversion of the low frequency bioelectric signals does not require high speed, but ultralow- power operation. This combined with the required conversion accuracy makes the design of such ADCs a major challenge. Among prevalent ADC architectures, the successiveapproximation-register (SAR) ADC exhibits significantly high energy efficiency due to its good trade-offs among power consumption, conversion accuracy, and design complexity. This thesis examines the physical limitations and investigates the design methodologies and circuit techniques for low-speed and ultra-low-power SAR ADCs.

The power consumption of SAR ADC is analyzed and its lower bounds are formulated. At low resolution, power is bounded by minimum feature sizes; while at medium to high resolution, power is bounded by thermal noise and capacitor mismatch. In order to relax the mismatch requirement on the capacitor sizing while still ensuring enough linearity for high resolution, a bottom-up weight calibration technique is further proposed. It utilizes redundancy generated by a non-binary-weighted capacitive network, and measures the actual weights of more significant capacitors using less significant capacitors.

Three SAR ADCs have been implemented. The first ADC, fabricated in a 0.13μm CMOS process, achieves 9.1ENOB with 53-nW power consumption at 1kS/s. The main key to achieve the ultra-low-power operation turns out to be the maximal simplicity in the ADC architecture and low transistor count. In addition, a dual-supply voltage scheme allows the SAR digital logic to operate at 0.4V, reducing the overall power consumption of the ADC by 15% without any loss in performance. Based on the understanding from the first ADC and motivated by the predicted power bounds, the second ADC, a single-supply 9.1-ENOB SAR ADC in 65nm CMOS process has been further fabricated. It achieves a substantial (94%) improvement in power consumption with 3-nW total power at 1kS/s and 0.7V. Following the same concept of imposing maximal simplicity in the ADC architecture and taking advantage of the smaller feature size, the ultra-low-power consumption is achieved by a matched splitarray capacitive DAC, a bottom-plate full-range input-sampling scheme, a latch-based SAR control logic, and a multi-VT design approach. The third ADC fabricated in 65nm CMOS process targets at a higher resolution of 14b and a wider bandwidth of 5KHz. It achieves 12.5ENOB  with 1.98-μW power consumption at 0.8V and 10kS/s. To achieve the high resolution, the ADC implements a uniform-geometry non-binary-weighted capacitive DAC and employs a secondary-bit approach to dynamically shift decision levels for error correction. Moreover, a comparator with bias control utilizes the redundancy to reduce the power consumption.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 114 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1611
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-110387 (URN)10.3384/diss.diva-110387 (DOI)978-91-7519-264-2 (ISBN)
Public defence
2014-10-03, Visionen, hus B, Campus Valla, Linköpings universitet, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2014-09-10 Created: 2014-09-10 Last updated: 2014-10-21Bibliographically approved

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Zhang, DaiAlvandpour, Atila

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