Design Techniques for Fully Integrated Switched-Capacitor Voltage Regulators


Book Description

As parallelism increases the number of cores integrated onto a chip, there is a clear need for fully integrated DC-DC converters to enable efficient on-die power management. Due to the availability of high density and low series resistance capacitors in existing CMOS processes, switched-capacitor DC-DC converters have recently gained significant interest as a cost-effective means of enabling such power management functionality. In this thesis, described are design techniques to implement fully integrated switched-capacitor DC-DC converters with high power density and efficiency. The area required by a fully integrated switched-capacitor DC-DC converter in order to deliver a certain level of power to the load has direct implications on both cost and efficiency, and hence in Chapter 2 a methodology is presented to predict and minimize the losses of such a converter operating at a given power density. Chapter 3 further introduces gate driver and level shifter circuit design strategies to enable topology reconfiguration and hence efficient generation of a wider range of output voltages. In order to demonstrate the possibility of replacing all off-chip PMICs, Chapter 4 presents a battery-connected switched-capacitor DC-DC converter that is able to convert the wide input voltage range from Li-ion battery to an output regulated at ~1V using cascode switches and intermediate voltage rails. The SC converter in Chapter 4 also employs a fast control loop to regulate the output with sub-ns response times. Measured results from the converters presented in Chapters 3 and 4 match with the analytical prediction and, thus, confirm the design methodology presented in Chapter 2. The 32nm SOI prototype presented in Chapter 3 achieves ~80% efficiency at a power density of ~0.5-1W/mm2 for a 2:1 step-down converter operating from a 2V input and utilizing only standard MOS capacitors. Reconfiguration of the converter's topology enables it to maintain greater than 70% efficiency for most of the output voltage range from 0.7V to ~1.15V. The 65nm Bulk CMOS prototype discussed in Chapter 4 also utilizes only standard MOS capacitors to regulate the output voltage at ~1V from a ~2.9V-4V input. It achieves ~73% efficiency at 0.19 W/mm2 output power density and maintain efficiency above 72% over the whole range of target power density. The sub-ns response control loop maintains




Contribution to the Design of Switched-capacitor Voltage Regulators in 28nm FDSOI CMOS


Book Description

Mobile and multimedia devices offer more innovations and enhancements to satisfy user requirements. Chip manufacturers thus propose high performances SoC to address these needs. Unfortunately the growth in digital resources inevitably increases the power consumption while battery life-time does not rise as fast. Aggressive power management techniques such as dynamic voltage and frequency scaling have been introduced in order to keep competitive and relevant solutions. Nonetheless continuing in this direction involves more disruptive solutions to meet space and cost constraints. Fully integrated power supply is a promising solution. Switched-capacitor DC-DC converters seem to be a suitable candidate to keep compatibility with the manufacturing process of digital SoCs. This thesis focuses on the design of an embedded power supply architecture using switched-capacitor DC-DC converters.Addressing a large range of output power with significant efficiency leads to consider a multi-ratio power stage. With respect to the typical digital SoC, the input voltage is 1.8 V and the converter is specified to deliver an output voltage in the 0.3-1.2 V range. The reference voltage is varying according to typical DVFS requirements. A modular architecture accommodates the digital design flow where the flying capacitors are situated above the digital block to supply and the power switches are located as an external ring. Such an architecture offers high flexibility. Interleaving strategy is considered to mitigate the output voltage ripple. Such a converter admits the switching frequency as a control variable and linear regulation and hysteretic control are analyzed. A prototype has been fabricated in 28nm FDSOI technology by STMicroelectronics. A power density of 310 mW/mm2 is achieved at 72.5% peak efficiency with a silicon area penalty of 11.5% of the digital block area. The successful design methodology has been also applied to the design of a negative SC converter for body-biasing purpose in FDSOI. Simulation results demonstrate a strong interest for low power application.




Analytical Modeling and Design of High Efficiency Fully-integrated Switched-capacitor DC-DC Converters and a High-voltage Current Regulator


Book Description

A high-voltage micro-ampere current regulator is introduced that ensures a constant ion current in order to stabilize measurements in analytical ion instruments. The current regulator is placed in series with a high-voltage power supply and a corona discharge ionization source. The proposed current regulator stabilizes the current in the corona without requiring a portion of the corona ion current sampled. The current regulator includes a first feedback circuit to provide rapidly-adapting current regulation, and an optional secondary feedback which provide slowly-adapting current regulation. The secondary feedback circuit senses the voltage across the high-voltage current regulator and slowly varies a high-voltage power supply to improve the long-term stability. Measured results demonstrate 10 kV of isolation and an adjustable current range from 1 to 50 [mu]A.




Reconfigurable Switched-Capacitor Power Converters


Book Description

This book provides readers specializing in ultra-low power supply design for self-powered applications an invaluable reference on reconfigurable switched capacitor power converters. Readers will benefit from a comprehensive introduction to the design of robust power supplies for energy harvesting and self-power applications, focusing on the use of reconfigurable switched capacitor based DC-DC converters, which is ideal for such applications. Coverage includes all aspects of switched capacitor power supply designs, from fundamentals, to reconfigurable power stages, and sophisticated controller designs.




On-chip Buck-boost Switched-capacitor DC-DC Converter


Book Description

The increasing integration level of CMOS integrated circuits (ICs) poses significant challenges for the power delivery network. Multiple independent power domains, each of them individually adjustable, are desirable for complex ICs to optimize the tradeoff between performance and energy consumption. A two-stage power management system, in which a first-stage global converter with a large down conversion ratio is followed by multiple second-stage local regulators for different power domains, fits well in modern power delivery networks. The first stage can be built with conventional, fully optimized DC-DC converters, while the second stage requires flexible, high-density, and high-efficiency on-chip DC-DC converters. With the enhanced fabrication capability of high-density on-chip capacitors, the switched-capacitor (SC) DC-DC converter becomes a perfect candidate for these second-stage on-chip regulators. This dissertation presents the architecture, modeling and design techniques for the development of fully integrated on-chip SC DC-DC converters for the purpose of local regulation. The proposed converter can step up or down the voltage based on the output requirement and circuit performance. Using the unit cell array approach, conversion ratios of n/(n+1) with buck configurations and (n+1)/n with boost configurations are achievable when n cells are grouped as a single converter. Thus, adequate topologies exist to provide a large range of output voltage with high efficiency. A prototype chip with 204 unit cells and nine different finely spaced buck and boost topologies was designed and fabricated in a 45nm bulk CMOS technology. The input is 1V, and the output ranges from 0.58V to 1.3V. The SC converter achieves a peak efficiency of 82.2% at a maximum power density of 0.16W/mm2. Furthermore, the efficiency varies by only 4.2% over the output voltage range. A digital algorithm for closed loop control was implemented in a field-programmable gate array (FPGA) to demonstrate that performance regulation using this type of converter can match circuit performance requirements and compensate for operating conditions or process variations. This dissertation also projects the potential improvements in SC converters with more advanced technology nodes as well as capacitor density scaling, such as using special on-chip capacitor processes like Metal-Insulator-Metal (MIM) capacitors and deep trench capacitors.




IC Design Insights - from Selected Presentations at CICC 2017


Book Description

This book contains a selection of tutorial and invited presentations that were given at the IEEE CICC 2017 in Austin, Texas. The selection of the talks was made to provide a comprehensive coverage of key topics, including Circuits Techniques for mm-wave front-ends, RF and mm-wave receivers and frequency synthesis, data and DC-DC converters, and techniques for IoT security.The book is organized into five parts, namely:I: Millimeter-wave Transmitter CircuitsII: Millimeter-wave and RF Receiver Circuits III: Data ConvertersIV: DC-DC Converters and Voltage RegulatorsV: IoT Security Circuits and Techniques The book is part of an educational initiative of the IEEE Solid-State Circuits Society to offer its members state of the art educational material.




Advanced Multiphasing Switched-Capacitor DC-DC Converters


Book Description

This book gives a detailed analysis of switched-capacitor DC-DC converters that are entirely integrated on a single chip and establishes that these converters are mainly limited by the large parasitic coupling, the low capacitor energy density, and the fact that switched-capacitor converter topologies only have a fixed voltage conversion ratio. The authors introduce the concept of Advanced Multiphasing as a way to circumvent these limitations by having multiple out-of-phase parallel converter cores interact with each other to minimize capacitor charging losses, leading to several techniques that demonstrate record efficiency and power-density, and even a fundamentally new type of switched-capacitor topology that has a continuously-scalable conversion ratio. Provides single-source reference to the recently-developed Advanced Multiphasing concept; Enables greatly improved performance and capabilities in fully integrated switched-capacitor converters; Enables readers to design DC-DC converters, where multiple converter cores are put in parallel and actively interact with each other over several phases to improve their capabilities.




On-chip Voltage Regulator – Circuit Design and Automation


Book Description

With the increase of density and complexity of high-performance integrated circuits and systems, including many-core chips and system-on-chip (SoC), it is becoming difficult to meet the power delivery and regulation requirements with off-chip regulators. The off-chip regulators become a less attractive choice because of the higher overheads and complexity imposed by the additional wires, pins, and pads. The increased I2R loss makes it challenging to maintain the integrity of different voltage domains under a lower supply voltage environment in the smaller technology nodes. Fully integrated on-chip voltage regulators have proven to be an effective solution to mitigate power delivery and integrity issues. Two types of regulators are considered as most promising for on-chip implementation: (i) the low-drop-out (LDO) regulator and (ii) the switched-capacitor (SC)regulator. The first part of our research mainly focused on the LDO regulator. Inspired by the recent surge of interest for cap-less voltage regulators, we presented two fully on-chip external capacitor-less low-dropout voltage regulator design. The second part of this proposal explores the complexity of designing each block of the regulator/analog circuit and proposed a design methodology for analog circuit synthesis using simulation and learning-based approach. As the complexity is increasing day-by-day in an analog circuit, hierarchical flow mostly uses for design automation. In this work, we focused mainly on Circuit-level, one of the significant steps in the flow. We presented a novel, efficient circuit synthesis flow based on simulation and learning-based optimization methods. The proposed methodology has two phases: the learning phase and the evaluation phase. Random forest, a supervised learning is used to reduce the sample points in the design space and iteration number during the learning phase. Additionally, symmetric constraints are used further to reduce the iteration number during the sizing process. We introduced a three-step circuit synthesis flow to automate the analog circuit design. We used H-spice as a simulation tool during the evaluation phase of the proposed methodology. The three most common analog circuits are chosen: single-stage differential amplifier, operational transconductance amplifier, and two-stage differential amplifier to verify the algorithm. The tool is developed in Python, and the technology we used is 0.6um. We also verified the optimized result in Cadence Virtuoso.




Next-Generation ADCs, High-Performance Power Management, and Technology Considerations for Advanced Integrated Circuits


Book Description

This book is based on the 18 tutorials presented during the 28th workshop on Advances in Analog Circuit Design. Expert designers present readers with information about a variety of topics at the frontier of analog circuit design, including next-generation analog-to-digital converters , high-performance power management systems and technology considerations for advanced IC design. For anyone involved in analog circuit research and development, this book will be a valuable summary of the state-of-the-art in these areas. Provides a summary of the state-of-the-art in analog circuit design, written by experts from industry and academia; Presents material in a tutorial-based format; Includes coverage of next-generation analog-to-digital converters, high-performance power management systems, and technology considerations for advanced IC design.




Demystifying Switched Capacitor Circuits


Book Description

This book helps engineers to grasp fundamental theories and design principles by presenting physical and intuitive explanations of switched-capacitor circuits. Numerous circuit examples are discussed and the author emphasizes the most important and fundamental principles involved in implementing state-of-the-art switched-capacitor circuits for analog signal processing and power management applications. Throughout the book, the author presents numerous step-by-step tutorials and gives practical design examples.While some quantitative analysis is necessary to understand underlying concepts, tedious mathematical equations and formal proofs are avoided. An intuitive appreciation for switched-capacitor circuits is achieved.Much of the existing information on contemporary switched-capacitor circuit applications is in the form of applications notes and data sheets for various switched-capacitor ICs. This book compiles such information in a single volume and coherently organizes and structures it.The author has his own website at www.mingliangliu.com * Step-by-step tutorials which emphasize the most fundamental principals of switched-capacitor circuits * Few tedious mathematical equations * The first easy-to-understand compilation on this subject--most information available is not very cohesive