Low Power Techniques For High Performance Pipelined Analog To Digital Converter

Low-power and small size analog to digital converters (ADCs) are the strategic building blocks in state of the art mobile wireless communication systems. Various techniques have been developed to reduce both power consumption and die area of the ADC. Among these, the opamp-sharing technique shows the most promise. In opamp-sharing, power and die area are saved by sharing one opamp between two successive pipeline stages. However, this technique suffers from the well-known memory effect drawback due to the absence of the reset phase that discharges the opamp's input parasitics. In this dissertation, this drawback is solved by introducing a discharge phase before the opamp is used for the pipeline stages without compromising speed and resolution of the ADC. Further power and area reduction is achieved by using a capacitor-sharing technique. This technique reduces the effective load capacitance of the opamp by reusing the charge on the feedback capacitor for the MDAC operation of the following stage, resulting in faster settling without increasing opamp power. The proposed low input-capacitance variable-gm opamp also helps to reduce the memory effect and improves the settling behavior of the stage output by increasing the bandwidth of the opamp while input parasitics of the opamp are kept small. The prototype designs of a 10-bit 50MSample/s pipelined ADC and a 14-bit 100MSample/s pipelined ADC implemented in 0.181m CMOS technology demonstrate the effectiveness of the proposed techniques. The first ADC achieves 56.2dB SNDR and 72.7dB SFDR for a Nyquist input at full sampling rate while consuming 12 mW from a 1.8-V supply. The FOM, defined as, [power/2[superscript ENOB]. Fs], is 0.46 pJ/step with Fin = 24.5MHz at 50MS/s. The second ADC achieves 72.4dB SNR and 88.5dB SFDR at 100MS/s with a 46MHz input and consumes 230mW from a 3V supply. The FOM of the second ADC is 0.69 pJ/step with Fin = 46MHz at 100MS/s.

Hand-held devices are among the most successful consumer electronics in modern society. Behind these successful devices, lies a key analog design technique that involves high-performance analog-to-digital conversion combined with very low power consumption. This dissertation presents two different approaches to achieving high power efficiency from a two-step pipelined architecture, which is generally known as one of the most power-consuming analog-to-digital converters. In the first approach, an analog feedback loop of a residue amplifier in a two-step pipelined analog-to-digital converter is reconfigured digitally using a single comparator and an R-2R digital-to-analog converter. This comparator-based structure can reduce power consumption of a conventional two-step pipelined analog-to-digital converter which consists of an opamp-based residue amplifier followed by a second- stage analog-to-digital converter. In addition, this dissertation includes circuit design techniques that provide a digital offset correction for the comparator-based two-step structure, binary-weighted switching for an R-2R digital-to-analog converter, and reference trimming for a flash analog-to-digital converter. A 10-b prototype analog-to-digital converter achieves an FOM of 121 fJ/conversion-step under 0.7-V supply. The second approach provides a way to achieve low power consumption for a high-resolution two-step pipelined analog-to-digital converter. An opamp is designed to consume optimized static power using a quarter-scaled residue gain together with minimized loading capacitance from the proposed second stage. A 14-b prototype analog-to-digital converter achieves an FOM of 31.3 fJ/conversion-step with an ENOB of 11.4 b, which is the lowest FOM in high-resolution analog-to-digital converters having greater than an ENOB of 10 b. Finally, the potential for further power reduction in a two-step pipelined analog-to-digital converter is discussed as a topic for future research.

This book shows that digitally assisted analog to digital converters are not the only way to cope with poor analog performance caused by technology scaling. It describes various analog design techniques that enhance the area and power efficiency without employing any type of digital calibration circuitry. These techniques consist of self-biasing for PVT enhancement, inverter-based design for improved speed/power ratio, gain-of-two obtained by voltage sum instead of charge redistribution, and current-mode reference shifting instead of voltage reference shifting. Together, these techniques allow enhancing the area and power efficiency of the main building blocks of a multiplying digital-to-analog converter (MDAC) based stage, namely, the flash quantizer, the amplifier, and the switched capacitor network of the MDAC. Complementing the theoretical analyses of the various techniques, a power efficient operational transconductance amplifier is implemented and experimentally characterized. Furthermore, a medium-low resolution reference-free high-speed time-interleaved pipeline ADC employing all mentioned design techniques and circuits is presented, implemented and experimentally characterized. This ADC is said to be reference-free because it precludes any reference voltage, therefore saving power and area, as reference circuits are not necessary. Experimental results demonstrate the potential of the techniques which enabled the implementation of area and power efficient circuits.

This book is a step-by-step tutorial on how to design a low-power, high-resolution (not less than 12 bit), and high-speed (not less than 200 MSps) integrated CMOS analog-to-digital (AD) converter, to respond to the challenge from the rapid growth of IoT. The discussion includes design techniques on both the system level and the circuit block level. In the architecture level, the power-efficient pipelined AD converter, the hybrid AD converter and the time-interleaved AD converter are described. In the circuit block level, the reference voltage buffer, the opamp, the comparator, and the calibration are presented. Readers designing low-power and high-performance AD converters won’t want to miss this invaluable reference. Provides an in-depth introduction to the newest design techniques for the power-efficient, high-resolution (not less than 12 bit), and high-speed (not less than 200 MSps) AD converter; Presents three types of power-efficient architectures of the high-resolution and high-speed AD converter; Discusses the relevant circuit blocks (i.e., the reference voltage buffer, the opamp, and the comparator) in two aspects, relaxing the requirements and improving the performance.

Analog-to-Digital Converters (ADCs) play an important role in most modern signal processing and wireless communication systems where extensive signal manipulation is necessary to be performed by complicated digital signal processing (DSP) circuitry. This trend also creates the possibility of fabricating all functional blocks of a system in a single chip (System On Chip - SoC), with great reductions in cost, chip area and power consumption. However, this tendency places an increasing challenge, in terms of speed, resolution, power consumption, and noise performance, in the design of the front-end ADC which is usually the bottleneck of the whole system, especially under the unavoidable low supply-voltage imposed by technology scaling, as well as the requirement of battery operated portable devices. Generalized Low-Voltage Circuit Techniques for Very High-Speed Time-Interleaved Analog-to-Digital Converters will present new techniques tailored for low-voltage and high-speed Switched-Capacitor (SC) ADC with various design-specific considerations.

Pipelined ADCs have seen phenomenal improvements in performance over the last few years. As such, when designing a pipelined ADC a clear understanding of the design tradeoffs, and state of the art techniques is required to implement today's high performance low power ADCs.

With the fast advancement of CMOS fabrication technology, more and more signal-processing functions are implemented in the digital domain for a lower cost, lower power consumption, higher yield, and higher re-configurability. This has recently generated a great demand for low-power, low-voltage A/D converters that can be realized in a mainstream deep-submicron CMOS technology. However, the discrepancies between lithography wavelengths and circuit feature sizes are increasing. Lower power supply voltages significantly reduce noise margins and increase variations in process, device and design parameters. Consequently, it is steadily more difficult to control the fabrication process precisely enough to maintain uniformity. The inherent randomness of materials used in fabrication at nanoscopic scales means that performance will be increasingly variable, not only from die-to-die but also within each individual die. Parametric variability will be compounded by degradation in nanoscale integrated circuits resulting in instability of parameters over time, eventually leading to the development of faults. Process variation cannot be solved by improving manufacturing tolerances; variability must be reduced by new device technology or managed by design in order for scaling to continue. Similarly, within-die performance variation also imposes new challenges for test methods. In an attempt to address these issues, Low-Power High-Resolution Analog-to-Digital Converters specifically focus on: i) improving the power efficiency for the high-speed, and low spurious spectral A/D conversion performance by exploring the potential of low-voltage analog design and calibration techniques, respectively, and ii) development of circuit techniques and algorithms to enhance testing and debugging potential to detect errors dynamically, to isolate and confine faults, and to recover errors continuously. The feasibility of the described methods has been verified by measurements from the silicon prototypes fabricated in standard 180nm, 90nm and 65nm CMOS technology.

This book discusses the theoretical foundations and design techniques needed to effectively design high-speed (multi-GS/s) and high-performance pipelined ADCs, which play a critical role in the signal chain of various systems. Readers will be walked through the design and analysis of pipelined ADCs and their topologies, and will learn both theoretical and practical design details that will enable them to explore and build these data converters. The author also presents details on various aspects of pipelined ADCs and their impact on the ADC speed and performance, with a focus on the input buffer and sampling network, the reference amplifier, comparators and their impact on ADC error rate and high-frequency performance, and mismatch estimation and correction.

This excellent reference proposes and develops new strategies, methodologies and tools for designing low-power and low-area CMOS pipelined A/D converters. The task is tackled by following a scientifically-consistent approach. The book may also be used as a text for advanced reading on the subject.

This useful monograph presents a total of seven prototypes: two double-sampled S/H circuits, a time-interleaved ADC, an IF-sampling self-calibrated pipelined ADC, a current steering DAC with a deglitcher, and two pipelined ADCs employing the SO techniques.