Low-power digital processor for wireless sensor networks

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 69-72).In order to make sensor networks cost-effective and practical, the electronic components of a wireless sensor node need to run for months to years on the same battery. This thesis explores the design of a low-power digital processor for these sensor nodes, employing techniques such as hardwired algorithms, lowered supply voltages, clock gating and subsystem shutdown. Prototypes were built on both a FPGA and ASIC platform, in order to verify functionality and characterize power consumption. The resulting 0.18[micro]m silicon fabricated in National Semiconductor Corporation's process was operational for supply voltages ranging from 0.5V to 1.8V. At the lowest operating voltage of 0.5V and a frequency of 100KHz, the chip performs 8 full-accuracy FFT computations per second and draws 1.2nJ of total energy per cycle. Although this energy/cycle metric does not surpass existing low-energy processors demonstrated in literature or commercial products, several low-power techniques are suggested that could drastically improve the energy metrics of a future implementation.by Daniel Frederic Finchelstein.S.M

Low-power techniques for video decoding

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 149-156).The H.264 video coding standard can deliver high compression efficiency at a cost of large complexity and power. The increasing popularity of video capture and playback on portable devices requires that the energy of the video processing be kept to a minimum. This work implements several architecture optimizations that reduce the system power of a high-definition video decoder. In order to decode high resolutions at low voltages and low frequencies, we employ techniques such as pipelining, unit parallelism, multiple cores, and multiple voltage/frequency domains. For example, a 3-core decoder can reduce the required clock frequency by 2.91 x, which enables a power reduction of 61% relative to a full-voltage single-core decoder. To reduce the total memory system power, several caching techniques are demonstrated that can dramatically reduce the off-chip memory bandwidth and power at the cost of increased chip area. A 123 kB data-forwarding cache can reduce the read bandwidth from external memory by 53%, which leads to 44% power savings in the memory reads. To demonstrate these low-power ideas, a H.264/AVC Baseline Level 3.2 decoder ASIC was fabricated in 65 nm CMOS and verified. It operates down to 0.7 V and has a measured power down to 1.8 mW when decoding a high definition 720p video at 30 frames per second, which is over an order of magnitude lower than previously published results.by Daniel Frederic Finchelstein.Ph.D

Multicore Processing and Efficient On-Chip Caching for H.264 and Future Video Decoders

Performance requirements for video decoding will continue to rise in the future due to the adoption of higher resolutions and faster frame rates. Multicore processing is an effective way to handle the resulting increase in computation. For power-constrained applications such as mobile devices, extra performance can be traded-off for lower power consumption via voltage scaling. As memory power is a significant part of system power, it is also important to reduce unnecessary on-chip and off-chip memory accesses. This paper proposes several techniques that enable multiple parallel decoders to process a single video sequence; the paper also demonstrates several on-chip caching schemes. First, we describe techniques that can be applied to the existing H.264 standard, such as multiframe processing. Second, with an eye toward future video standards, we propose replacing the traditional raster-scan processing with an interleaved macroblock ordering; this can increase parallelism with minimal impact on coding efficiency and latency. The proposed architectures allow N parallel hardware decoders to achieve a speedup of up to a factor of N. For example, if N=3, the proposed multiple frame and interleaved entropy slice multicore processing techniques can achieve performance improvements of 2.64times and 2.91times, respectively. This extra hardware performance can be used to decode higher definition videos. Alternatively, it can be traded-off for dynamic power savings of 60% relative to a single nominal-voltage decoder. Finally, on-chip caching methods are presented that significantly reduce off-chip memory bandwidth, leading to a further increase in performance and energy efficiency. Data-forwarding caches can reduce off-chip memory reads by 53%, while using a last-frame cache can eliminate 80% of the off-chip reads. The proposed techniques were validated and benchmarked using full-system Verilog hardware simulations based on an existing decoder; they should- also be applicable to most other decoder architectures. The metrics used to evaluate the ideas in this paper are performance, power, area, memory efficiency, coding efficiency, and input latency.Texas Instruments IncorporatedNokia CorporationIEEE Circuits and Systems Societ

A 0.7-V 1.8-mW H.264/AVC 720p Video Decoder

The H.264/AVC video coding standard can deliver high compression efficiency at a cost of increased complexity and power. The increasing popularity of video capture and playback on portable devices requires that the power of the video codec be kept to a minimum. This work implements several architecture optimizations such as increased parallelism, pipelining with FIFOs, multiple voltage/frequency domains, and custom voltage-scalable SRAMs that enable low voltage operation to reduce the power of a high-definition decoder. Dynamic voltage and frequency scaling can efficiently adapt to the varying workloads by leveraging the low voltage capabilities and domain partitioning of the decoder. An H.264/AVC Baseline Level 3.2 decoder ASIC was fabricated in 65-nm CMOS and verified. For high definition 720p video decoding at 30 frames per second (fps), it operates down to 0.7 V with a measured power of 1.8 mW, which is significantly lower than previously published results. The highly scalable decoder is capable of operating down to 0.5 V for decoding QCIF at 15 fps with a measured power of 29 muW.Texas Instruments IncorporatedNokia Corporatio

Technologies for Ultradynamic Voltage Scaling

Energy efficiency of electronic circuits is a critical concern in a wide range of applications from mobile multi-media to biomedical monitoring. An added challenge is that many of these applications have dynamic workloads. To reduce the energy consumption under these variable computation requirements, the underlying circuits must function efficiently over a wide range of supply voltages. This paper presents voltage-scalable circuits such as logic cells, SRAMs, ADCs, and dc-dc converters. Using these circuits as building blocks, two different applications are highlighted. First, we describe an H.264/AVC video decoder that efficiently scales between QCIF and 1080p resolutions, using a supply voltage varying from 0.5 V to 0.85 V. Second, we describe a 0.3 V 16-bit micro-controller with on-chip SRAM, where the supply voltage is generated efficiently by an integrated dc-dc converter.Natural Sciences and Engineering Research Council of Canada (NSERC)Texas Instruments Incorporated (Texas Instruments Graduate Women’s Fellowship for Leadership in Microelectronics)Intel Corporation (Intel Ph.D. Fellowship Program)Texas Instruments IncorporatedNokia CorporationSemiconductor Research Corporation . Focus Center for Circuit and System Solutions (C2S2)United States. Defense Advanced Research Projects Agenc