Re-thinking Analog Integrated Circuits in Digital Terms: A New Design Concept for the IoT Era

A steady trend towards the design of mostly-digital and digital-friendly analog circuits, suitable to integration in mainstream nanoscale CMOS by a highly automated design flow, has been observed in the last years to address the requirements of the emerging Internet of Things (IoT) applications. In this context, this tutorial brief presents an overview of concepts and design methodologies that emerged in the last decade, aimed to the implementation of analog circuits like Operational Transconductance Amplifiers, Voltage References and Data Converters by digital circuits. The current design challenges and application scenarios as well as the future perspectives and opportunities in the field of digital-based analog processing are finally discussed

Analog processing by digital gates: fully synthesizable IC design for IoT interfaces

Analog integrated circuits do not take advantage of scaling and are easily the bottleneck in terms of cost and performance in Internet of Things (IoT) sensor nodes integrated in nanoscale technologies. While this challenge is most commonly addressed by devising more “digital friendly” analog cells based on traditional design concepts, the possibility to translate analog functions into digital, so that to implement them by true digital gates, is now emerging as a promising alternative. This last approach, which challenges the idea that “analog circuits will be always needed”, is presented in this tutorial starting from the theoretical background to its application in digital-based operational amplifiers, voltage references, oscillators and data converters integrated on silicon which have proposed in recent literature. The applicability of the concepts to the design of ICs which are natively portable across technology nodes and highly reconfigurable, thus enabling dynamic energy quality scaling, as well as a low design effort and a fast time-to-market will be described

Emerging Relaxation and DDPM D/A Converters: Overview and Perspectives

In this paper, two emerging, digital-intensive, matching-indifferent, bitstream digital-to-analog (D/A) conversion techniques proposed in the last years, namely: the Relaxation D/A Conversion (ReDAC) and the Dyadic Digital Pulse Modulation (DDPM)-based D/A conversion, are reviewed and compared. After the basic concepts are introduced, the main challenges and research achievements over the last years are summarized and the performance of different integrated circuit (IC), field-programmable gate array (FPGA) and microcontroller-based ReDACs and DDPM-DACs are discussed and compared, highlighting advantages and open research questions. Present applications of the two techniques in voltage and current mode A/D conversion, RF modulation, digitally controlled switching-mode power converters, and machine learning accelerators will be discussed, and future application perspectives will be outlined

Variability-aware low-power techniques for nanoscale mixed-signal circuits.

New circuit design techniques that accommodate lower supply voltages necessary for portable systems need to be integrated into the semiconductor intellectual property (IP) core. Systems that once worked at 3.3 V or 2.5 V now need to work at 1.8 V or lower, without causing any performance degradation. Also, the fluctuation of device characteristics caused by process variation in nanometer technologies is seen as design yield loss. The numerous parasitic effects induced by layouts, especially for high-performance and high-speed circuits, pose a problem for IC design. Lack of exact layout information during circuit sizing leads to long design iterations involving time-consuming runs of complex tools. There is a strong need for low-power, high-performance, parasitic-aware and process-variation-tolerant circuit design. This dissertation proposes methodologies and techniques to achieve variability, power, performance, and parasitic-aware circuit designs. Three approaches are proposed: the single iteration automatic approach, the hybrid Monte Carlo and design of experiments (DOE) approach, and the corner-based approach. Widely used mixed-signal circuits such as analog-to-digital converter (ADC), voltage controlled oscillator (VCO), voltage level converter and active pixel sensor (APS) have been designed at nanoscale complementary metal oxide semiconductor (CMOS) and subjected to the proposed methodologies. The effectiveness of the proposed methodologies has been demonstrated through exhaustive simulations. Apart from these methodologies, the application of dual-oxide and dual-threshold techniques at circuit level in order to minimize power and leakage is also explored