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Power-Efficient Continuous-Time Incremental Sigma-Delta Analog-to-Digital Converters
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.ORCID iD: 0000-0002-4691-2318
2015 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

Over the past decade, there has been a growing interest in the devel- opment of integrated circuits (ICs) for wearable or implantable biosensors, aiming at providing personalized healthcare services and reducing the health-care expenses. In biosensor ICs, the analog-to-digital converter (ADC) is a key building block that acts as a bridge between analog signals and digital processors. Since most of the biosensors are attached to or implanted in hu- man bodies and powered by either portable batteries or harvested energy, ultra-low-power operation is often required. The stringent power budget im- poses challenges in designing power-efficient ADCs, especially when targeting high-resolution. Among different ADC architectures, the Sigma-Delta (Σ∆) ADC has emerged as the most suitable for low-power, high-resolution appli- cations. This thesis aims to enhance the power efficiency of continuous-time (CT) incremental Σ∆ (IΣ∆) ADCs by exploring design techniques at both architectural and circuit levels.

The impact of feedback DACs in CT IΣ∆ ADCs is investigated, so as to provide power-efficient feedback DAC solutions, suitable for biosensor ap- plications. Different DAC schemes are examined analytically considering the trade-off between timing error sensitivity and power consumption. The an- alytical results are verified through behavioral simulations covering both the conventional and incremental Σ∆ modes. Additionally, by considering a typi- cal biosensor application, different feedback DACs are further compared, aim- ing to offer a reference for selecting a power-efficient DAC scheme.

A two-step CT IΣ∆ ADC is proposed, analyzed, implemented and tested, with the objective of offering flexible and power-efficient A/D conversion in neural recording systems. By pipelining two CT IΣ∆ ADCs, the pro- posed ADC can achieve high-resolution without sacrificing the conversion rate. Power-efficient circuits are proposed to implement the active blocks of the proposed ADC. The feasibility and power efficiency of the two-step CT IΣ∆ ADC are validated by measurement results. Furthermore, enhancement techniques from both the architecture and circuit perspectives are discussed and implemented, which are validated by post-layout simulations.

A comparative study of several CT IΣ∆ ADC architectures is presented, aiming to boost the power efficiency by reducing the number of cycles per con- version while benefiting from the advantage of CT implementation. Five CT IΣ∆ ADC architectures are analyzed and simulated to evaluate their effective- ness under ideal conditions. Based on the theoretical results, a second-order CT IΣ∆ ADC and an extended-range CT IΣ∆ ADC are selected as implemen- tation case studies together with the proposed two-step CT IΣ∆ ADC. The impact of critical circuit non-idealities is investigated. The three ADCs are then implemented and fabricated on a single chip. Experimental results reveal that the three prototype ADCs improve considerably the power efficiency of existing CT IΣ∆ ADCs while being very competitive when compared to all types of the state-of-the-art IΣ∆ ADCs. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xxii, 179 p.
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2015:03
Keyword [en]
analog-to-digital conversion, sigma-delta modulation, incre- mental ADC, two-step ADC, continuous-time, biosensor applications.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-164282ISBN: 978-91-7595-507-0OAI: diva2:805219
Public defence
2015-05-18, Sal C, Electrum, Kista, School of ICT, KTH, Electrum 229, Isafjordsgatan 22, Kista, 13:00 (English)
Swedish Research Council

QC 20150422

Available from: 2015-04-22 Created: 2015-04-14 Last updated: 2015-04-22Bibliographically approved

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