Michael D. Seeman

Analysis and Optimization of Switched-Capacitor DC–DC Converters

Analysis methods are developed that fully determine a switched-capacitor (SC) dc-dc converters steady-state performance through evaluation of its output impedance. This analysis method has been verified through simulation and experimentation. The simple formulation developed permits optimization of the capacitor sizes to meet a constraint such as a total capacitance or total energy storage limit, and also permits optimization of the switch sizes subject to constraints on total switch conductances or total switch volt-ampere (V-A) products. These optimizations then permit comparison among several switched-capacitor topologies, and comparisons of SC converters with conventional magnetic-based dc-dc converter circuits, in the context of various application settings. Significantly, the performance (based on conduction loss) of a ladder-type converter is found to be superior to that of a conventional magnetic-based converter for medium to high conversion ratios.

Resonant Switched-Capacitor Converters for Sub-module Distributed Photovoltaic Power Management

This paper discusses the theory and implementation of a class of distributed power converters for photovoltaic (PV) energy optimization. Resonant switched-capacitor converters are configured in parallel with strings of PV cells at the sub-module level to improve energy capture in the event of shading or mismatch. The converters operate in a parallel-ladder architecture, enforcing voltage ratios among strings of cells at terminals normally connected to bypass diodes. The balancing function extends from the sub-module level to the entire series string through a dual-core cable and connector. The parallel configuration allows converters to handle only mismatch power and turn off if there is no mismatch in the array. Measurement results demonstrate insertion loss below 0.1% and effective conversion efficiency above 99% for short-circuit current mismatch gradients up to 40%. The circuit implementation eliminates large power magnetic components, achieving a vertical footprint less than 6 mm. The merits of a resonant topology are compared to a switched-capacitor topology.

Analysis and Optimization of Switched-Capacitor DC-DC Converters

Analysis methods are developed that fully determine a switched-capacitor (SC) dc-dc converters steady-state performance through evaluation of its output impedance. This analysis method has been verified through simulation and experimentation. The simple formulation developed permits optimization of the capacitor sizes to meet a constraint such as a total capacitance or total energy storage limit, and also permits optimization of the switch sizes subject to constraints on total switch conductances or total switch volt-ampere (V-A) products. These optimizations then permit comparison among several switched-capacitor topologies, and comparisons of SC converters with conventional magnetic-based dc-dc converter circuits, in the context of various application settings. Significantly, the performance (based on conduction loss) of a ladder-type converter is found to be superior to that of a conventional magnetic-based converter for medium to high conversion ratios.

A 32nm fully integrated reconfigurable switched-capacitor DC-DC converter delivering 0.55W/mm 2 at 81% efficiency

With the rising integration levels used to increase digital processing performance, there is a clear need for multiple independent on-chip supplies in order to support per-IP or block power management. Simply adding multiple off-chip DCDC converters is not only difficult due to supply impedance concerns, but also adds cost to the platform by increasing motherboard size and package complexity. There is therefore a strong motivation to integrate voltage conversion blocks on the silicon chip.

The Road to Fully Integrated DC–DC Conversion via the Switched-Capacitor Approach

This paper provides a perspective on progress toward realization of efficient, fully integrated dc-dc conversion and regulation functionality in CMOS platforms. In providing a comparative assessment between the inductor-based and switched-capacitor approaches, the presentation reviews the salient features in effectiveness in utilization of switch technology and in use and implementation of passives. The analytical conclusions point toward the strong advantages of the switched-capacitor (SC) approach with respect to both switch utilization and much higher energy densities of capacitors versus inductors. The analysis is substantiated with a review of recently developed and published integrated dc-dc converters of both the inductor-based and SC types.

Power Electronics Design Choice for Piezoelectric Microrobots

Piezoelectric actuators are advantageous for microrobots due to their light weight, high bandwidth, high force production, low power consumption, and simplicity of integration. However, the main disadvantage of either stack or cantilever piezoelectric actuators are the high drive voltages required for adequate force and displacement. This especially limits the ability for such actuators to be used in autonomous microrobots because of the weight and complexity of necessary power electronics. This paper approaches the design of all the component parts of an autonomous piezoelectric robot as a linear constraint on the weight and efficiency of those components. It then focuses on the choice and optimization of the power electronics section of the robot, specifically exploring three different high voltage generation methods. Finally, one of these power electronics designs is implemented and its behavior is experimentally explored

A comparative analysis of Switched-Capacitor and inductor-based DC-DC conversion technologies

This paper compares the performance of Switched-Capacitor (SC) and inductor-based DC-DC conversion technologies. A metric to compare between the two topologies is discussed, and is used to compare switch utilization. Fundamental limits on utilization of reactive elements developed in the literature for all DC-DC converters are also reviewed and discussed, and this analysis shows that popular SC and inductor-based converters achieve the limits of utilization for reactive components. These limits are stated in terms of the ratio of output power to required stored energy in reactive elements. A detailed analysis of available surface mount discrete components and on-die devices reveals that capacitors have substantially higher energy and power density than their magnetic counterparts. The challenging regulation task for SC converters is also discussed, with a promising strategy outlined. The SC converter is evidently a promising candidate for future high power density integrated DC-DC converters.

An ultra-low-power power management IC for energy-scavenged Wireless Sensor Nodes

A power interface IC is designed and demonstrated to convert and manage power for a wireless tire pressure sensor node. The IC includes two switched-capacitor DC-DC converters to supply power to the various components of the sensor at their appropriate voltages. The design of the two integrated converters is discussed, including the optimization of capacitors and power transistors. The losses due to parasitic capacitances are analyzed. Two gate drive techniques are used to drive the gates of the floating triple-well transistors. A synchronous rectifier efficiently harvests energy from an electromagnetic shaker and control circuitry regulates the output voltage while minimizing power consumption. The two converters achieve efficiencies of approximately 84% while the synchronous rectifier achieves an efficiency of 88%.

Design, fabrication and initial results of a 2g autonomous glider

Utilizing the core technologies of emerging microrobotic structures, the rapid design and prototyping of a passive micro air vehicle with the final goal of locating an audio source while avoiding hazardous obstacles is presented. The airfoil and control surfaces are optimized empirically to maximize lift and maneuverability while minimizing drag. Bimorph piezoelectric bending cantilevers actuate the control surfaces. Since such actuators require high voltages, an efficient boost circuit is presented along with appropriate high voltage electronics. To locate audio sources, a pair of acoustic sensors is designed and prototyped using a phase detection algorithm while a custom optic flow sensor is developed to avoid obstacles and give estimates of object distances and velocities. Finally, each subsystem is demonstrated and the complete glider is integrated to demonstrate initial open loop control performance.

An Ultra-Low-Power Power Management IC for Wireless Sensor Nodes

A power interface IC is designed and demonstrated to convert and manage power for a wireless tire pressure sensor node. Power conversion is performed using on-chip switched-capacitor converters with size-optimized devices and level-shifting gate drivers. A synchronous rectifier efficiently harvests energy from an electromagnetic shaker and control circuitry regulates the output voltage while minimizing power consumption. The converters achieve efficiencies approaching 80%.