Guest Editors' Introduction: Hot Chips 19

This special issue showcases articles written from five of the best presentations at the Hot Chips 19 conference, held in August 2007. The guest editors give highlights of the conference and introduce the articles, which cover the mobile-optimized northbridge of AMD's Griffin microprocessor family; the IBM z10 next-generation mainframe microprocessor; fault tolerance in IBM's Power6 microprocessor; NVIDIA's Tesla unified graphics and computing architecture; and SiBEAM's 4-Gbps 1080p-capable uncompressed HD A/V wireless 60-GHz transceiver chipset.     

A micropower programmable DSP using approximate signal processing based on distributed arithmetic

A recent trend in low-power design has been the employment of reduced precision processing methods for decreasing arithmetic activity and average power dissipation. Such designs can trade off power and arithmetic precision as system requirements change. This work explores the potential of distributed arithmetic (DA) computation structures for low-power precision-on-demand computation. We present an ultralow-power DSP which uses variable precision arithmetic, low-voltage circuits, and conditional clocks to implement a biomedical detection and classification algorithm using only 560 nW. Low energy consumption enables self-powered operation using ambient mechanical vibrations, converted to electric energy by a MEMS transducer and accompanying power electronics. The MEMS energy scavenging system is estimated to deliver 4.3 to 5.6 /spl mu/W of power to the DSP load.     

Vibration-to-electric energy conversion

A system is proposed to convert ambient mechanical vibration into electrical energy for use in powering autonomous low power electronic systems. The energy is transduced through the use of a variable capacitor. Using microelectromechanical systems (MEMS) technology, such a device has been designed for the system. A low-power controller IC has been fabricated in a 0.6-μm CMOS process and has been tested and measured for losses. Based on the tests, the system is expected to produce 8 μW of usable power. In addition to the fabricated programmable controller, an ultra low-power delay locked loop (DLL)-based system capable of autonomously achieving a steady-state lock to the vibration frequency is described     

Effect of Sediment pH on Resuspension of Kaolinite Sediments

The resuspension of contaminated cohesive sediments can impact water quality by mobilizing sediment particles and adsorbed contaminants. Changes in psysicochemical and electrochemical environments, around resuspended sediment particles, may cause some contaminants to desorb into the water column. The contribution of contaminated sediments to degradation of water quality depends on an estimate of sediment resuspension rates. In this study, the resuspension of Georgia kaolinite sediments under varying pH conditions was investigated in laboratory flume experiments. Because the edge charge of kaolinite particles is pH dependent, kaolinite particles exhibit different modes of particle associations under varying pH conditions. The paper characterizes these particle associations and relates them to the resuspension of kaolinite sediments for varying pH values. Variations in sediment water content, changes from a stratified to a uniform sediment bed, changes in rheological properties, and variations in the electrophoretic mobility of kaolinite particles were all indicative of the changes in particle associations that resulted from changes in sediment pH. The critical shear stress and the erosion rate coefficient were evaluated for varying pH values and explained by particle associations. A rheometer was used to measure rheological properties of the settled sediment bed; the measured yield stresses had a direct correlation with critical shear stresses.     

Integrated Solar Energy Harvesting and Storage

To explore integrated solar energy harvesting as a power source for low power systems, an array of energy scavenging photodiodes based on a passive-pixel architecture for CMOS imagers has been fabricated together with storage capacitors implemented using on-chip interconnect in a 0.35-mum bulk process. Integrated vertical plate capacitors enable dense energy storage without limiting optical efficiency. Tests were conducted with both a white light source and a green laser. Measurements indicate that 225 muW/mm² output power may be generated by white light with an intensity of 20 kLUX.     

Influence of Sediment Structure on Erosional Strength and Density of Kaolinite Sediment Beds

The role of sediment pore-water chemistry and the resulting particle structure in determining the erosional stability of settled cohesive sediment beds in rivers, lakes, and estuaries is examined. Kaolinite sediment is used as the surrogate sediment in this experimental investigation with the beds settled from concentrated suspensions. The bed stability with respect to erosion or resuspension is measured in a laboratory flume as a function of sediment pore-water chemistry. The chemical properties varied are sediment pH, ionic strength, and natural organic matter. The remolded bed sample is prepared from a sediment suspension having controlled chemical properties that is allowed to settle into the flume bed where its erosional strength and density are determined with depth in the sample. Different structures of settled beds are observed with changes in chemical parameters. Under low pH and low organic content conditions, the initial suspension before settling is flocculated. The resulting settled beds show strong stratification with respect to erosional strength but weak stratification of bulk density with depth. On the other hand, under high pH or high organic content conditions at low ionic strength, the initial suspension is dispersed. The resulting settled beds have lower erosional strength and weak stratification of erosional strength with depth but strong stratification of bulk density with depth. This research shows that the relationship between erosional strength and bulk density of a settled bed depends strongly on the structure of the sediment particle associations as determined by pore-water chemistry.     

Numerical Modeling of Helical Static Mixers for Water Treatment

To improve the understanding of how static mixers work and how to better utilize them in environmental engineering (or, specifically, drinking water treatment), a numerical model for simulating turbulent flows in helical static mixers is developed. The model solves the three-dimensional, Reynolds-averaged Navier-Stokes equations, closed with the k-ω turbulence model, using a second-order-accurate finite-volume numerical method. Numerical simulations are carried out for a two-element helical static mixer, and the computed results are analyzed to elucidate the complex, three-dimensional features of the flow. The results show that the flow field within the mixer is characterized by the presence of pockets of reversed flow and the growth and interaction of strong longitudinal vortices. As an example of the kind of practical insights that can be gained from such detailed three-dimensional computations, the simulated flow field is used to investigate two quantities that are often used to characterize mixing within a static mixer and to discuss the merits of these quantities for coagulant mixing in drinking water treatment.     

Recursive TMR: scaling fault tolerance in the nanoscale era

As process technologies decrease in feature size, designers face new reliability challenges. Feature sizes of less than 0.25 /spl mu/m increase the risk of noise-related faults that result from electrical disturbances in the logic values held in circuits and on wires. Such transient faults can cause single-bit upsets, which in turn can introduce a logical fault in the circuit. In this article, we classify the sources of noise that can be scalably corrected (where using RTMR is beneficial as device size scales) with recursive triple modular redundancy (RTMR) and those that cannot. In particular, we have found that single-event upsets caused by energetic particles can be effectively compensated with RTMR. Flicker noise in devices, however, is not competitively correctable. In other words, noise models show that an RTMR circuit composed of small, less reliable devices does not always compete in speed and area with an equivalent circuit composed of large more reliable devices. In light of this finding, we discuss microarchitectural design options for mixing large and small devices to trade off reliability, speed, and area.     

High-efficiency multiple-output DC-DC conversion for low-voltagesystems

This versatile power converter controller provides dual outputs at a fixed switching frequency and can regulate either output voltage or target system delay (using an external L-C filter). In the voltage regulation mode, the output voltage is monitored with an analog-digital (A/D) converter, and the feedback compensation network is implemented digitally. The generation of the pulsewidth modulation (PWM) signal is done with a hybrid delay line/counter approach, which saves power and area relative to previous implementations. Power devices are included on chip to create the two independently regulated output PWM signals. The key features of this design are its low-power dissipation, reconfigurability, use of either delay or voltage feedback, and multiple outputs     

Life Cycle Aware Computing: Reusing Silicon Technology

Despite the high costs associated with processor manufacturing, the typical chip is used for only a fraction of its expected lifetime. Reusing processors would create a "food chain" of electronic devices that amortizes the energy required to build chips over several computing generations.