Slide 1Low-Power Design Rules – Anno 1997Adding Leakage to the EquationLow-Power Design Rules – Anno 2007Some Concepts Worth WatchingNovel Switching DevicesExample: Nano-Mechanical RelaysRelay Circuit Design and ComparisonAdiabatic Logic and Energy RecoverySelf-Timed and Asynchronous LogicExploring the Unknown – Alternative Computational ModelsExample: Collaborative NetworksLearning from Sensor Network Concept“Sensor Networks on a Chip”Example: PN code acquisition for CDMABook SummaryInteresting References for Further ContemplationJan M. RabaeyLow Power Design Essentials ©2008Chapter 13SummaryandPerspectivesLow Power Design Essentials ©200813.2 Low-Power Design Rules – Anno 1997Minimize waste (or reduce switching capacitance)–Match computation and architecture–Preserve locality inherent in algorithm–Exploit signal statistics–Energy (performance) on demandVoltage as a design variable–Match voltage and frequency to required performanceMore easily accomplished in application-specific than programmable devices[Ref: J. Rabaey, Intel’97]Low Power Design Essentials ©200813.3 Adding Leakage to the EquationThe emergence of power domainsLeakage not necessarily a bad thing–Optimal designs have high leakage (ELk/ESw ≈ 0.5)Leakage management requires runtime optimization–Activity sets dynamic/static power ratioMemories dominate standby power–Logic blocks should not consume power in standby[Emerged in late 1990s]Low Power Design Essentials ©200813.4 Low-Power Design Rules – Anno 2007Concurrency Galore–Many simple things are way better than one complex oneAlways-Optimal Design–Aware of operational, manufacture and environmental variationsBetter-than-worst-case Design–Go beyond the acceptable and recoupThe Continuation of Voltage Scaling–Descending into ultra-low voltages–How close can we get to the limits?Explore the Unknown[Ref: J. Rabaey, SOC’07]Low Power Design Essentials ©200813.5 Some Concepts Worth WatchingNovel switching devicesAdiabatic logic and energy-recoverySelf-timed and asynchronous designEmbracing non-conventional computational paradigms–Towards massive parallelism?Low Power Design Essentials ©200813.6 Novel Switching DevicesNanotechnology brings promise of broad range of novel devices–Carbon-nanotube transistors, NEMS, spintronics, molecular, quantum, etc–Potential is there – long-term impact unclear–Will most probably need revisiting of logic design technologyOut-of-the-box thinking essentialLow Power Design Essentials ©200813.7 Example: Nano-Mechanical RelaysMinimum energy in CMOS limited by leakage–Even if had a perfect (zero leakage) power gateHow about a nano-scale mechanical switch?–Infinite Roff, low Ron[Ref: H. Kam, UCB’08] SourceDrainLow Power Design Essentials ©200813.8 Relay Circuit Design and Comparison90nm CMOSRelay FA Cell[Ref: E. Alon, UCB’08]Low Power Design Essentials ©200813.9 Adiabatic Logic and Energy Recovery Concept explored in the 1990’s-Proven to be ineffective at that time With voltage scaling getting harder, may become attractive again Example: Resonant AdiabaticMixed-Signal Processor Array forCharge-Based Pattern Recognition [Ref: R. Karakiewicz, JSSC’07] Adiabatic mixed-signal multiply-accumulation (MAC). Charge-coupled MOS pair represents variable capacitive load.Adiabatic logic modeled as transmission gate driving capacitive load from resonant clock© IEEE 2007Low Power Design Essentials ©200813.10 Self-Timed and Asynchronous LogicSynchronicity performs best under deterministic conditions and when duty cycle is highHowever, worst-case model does not fair well when variability is highIn ideal case, self-timed logic operates at “average conditions”delaynumberDelay distribution as a function of variabilityProtocol and signaling overhead of self-timed made it unattractive when delay distributions where narrowThis is not longer the case, especially under ultra low-voltage conditionsEffective “synchronous island” size is shrinkingThe “design flow” argument does not really hold either−Example: Handshake Solutions [Ref: Handshake]Low Power Design Essentials ©200813.11 Exploring the Unknown –Alternative Computational Models•10-15% of terrestrial animal biomass109 Neurons/”node”Since 105 years agoHumans•10-15% of terrestrial animal biomass105 Neurons/”node”Since 108 years agoAntsEasier to make ants than humans“Small, simple, swarm”Easier to make ants than humans“Small, simple, swarm”[Courtesy: D. Petrovic, UCB]Low Power Design Essentials ©200813.12 Example: Collaborative Networks Networks are intrinsically robust → exploit it! Massive ensemble of cheap, unreliable components Network Properties:–Local information exchange → global resiliency–Randomized topology & functionality → fits nano properties–Distributed nature → lacks an “Achilles heel”Bio-inspiredMetcalfe’s Law to the rescue ofMoore’s Law!Low Power Design Essentials ©200813.13 Learning from Sensor Network Concept[Ref: J. Rabaey, I&C’04]Low Power Design Essentials ©200813.14 “Sensor Networks on a Chip” “Large” number of very simple unreliable components provide estimates of result Fusion block combines estimates exploiting the statistics Fusion block only “reliable” componentEstimators need to be independentfor this scheme to be effective[Ref: S. Narayanan, Asilomar’07]Sensor NOC© IEEE 2007Low Power Design Essentials ©200813.15 Example: PN code acquisition for CDMAStatistically similar decomposition of function for distributed sensor-based computation.Robust statistics framework for design of fusion block. Creates better result with power savings of up to 40% for 8 sensors in PN-code acquisition in CDMA systemsNew applications in filtering, ME, DCT, FFT and others[Ref: S. Narayanan, Asilomar’07]Prob (Detection)© IEEE 2007Low Power Design Essentials ©200813.16 Book SummaryEnergy-Efficient one of (if not the most) compelling issues in Integrated Circuit Design today and in the coming decadesThe field has matured substantially–From “getting rid of the fat” and reducing waste–To “truly energy-lean” design technologiesStill plenty of opportunities to move beyond what can be done todayThere is plenty of room at the bottomLow Power Design Essentials ©200813.17 Interesting References for Further