Paper presentation Ultra-Portable Devices Paper: Omer Can Akgun and - - PowerPoint PPT Presentation

Paper presentation – Ultra-Portable Devices

Paper: Presented by:

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Omer Can Akgun and Yusuf Leblebici. Energy Efficiency Comparison of Asynchronous and Synchronous Circuits Operating in the Sub-Threshold Regime, Journal of Low Power Electronics Vol.4, 1–17, Date: 2008.

• S. M. Yasser Sherazi

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Outline

• Introduction.
• Motivation and Background.
• Sub-threshold Energy Consumption Model.
• Architectural Improvements.
• Conclusion.

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” Introduction ”

• Power density and power consumption of digital sytems are a

major concern

• Any significant reduction in power consumption can only be

achieved by lowering the operting voltage

• The supply voltage is scaled such that the transistors operate

in sub-threshold mode (weak inversion)

• Sub-threshold operation of static CMOS logic was analyzed

using EKV model

• Static CMOS can be operated with supply voltage as low as

50mV at ambient temperature

• Circuit working at these extreme low voltages work at much

lower speeds.

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’’Motivation and Background’’

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µ is the mobility of carriers, Cox is the gate oxide capacitance per unit area, Ut is the thermal voltage whose value is 26 mV at 300 K W/L is the aspect ratio

• f the transistor.

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”Effects of Process Variation on Sub- Threshold Operation”

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”Asynchronous Operation”

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”Asynchronous Operation”

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”Asynchronous Operation”

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”Asynchronous Operation”

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”SUB-Threshold Energy Consumption Model”

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• Assumption-1: As soon as the asynchronous block finishes

processing the current data, a new data input can be applied, i.e., there is no idle time between data inputs to the asynchronous block.

• Assumption-2: The energy consumption and processing

delays of the circuit per computation are randomly distributed. This assumption is guaranteed by applying a randomly distributed data set to the input of the circuit.

• Assumption-3: Synchronous circuits work at their maximum

speed, i.e., clocked at a speed equal to their critical path delay.

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”SUB-Threshold Energy Consumption Model”

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’’Energy Model’’

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ei is a scaling parameter that defines the switching property of the circuit Ctot is the maximum possible switched capacitance of the circuit, µe is the mean Kcap-logic = Ctot/Cinv Kleak is average leaking factor

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’’Energy Model’’

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di is a scaling parameter that defines the delay properties of the circuit processing the current data, kcrit is a coefficient that defines the critical path delay of the circuit in terms of the inverter delay Tsw_inv is the delay of an Inverter µd is the switching mean kcomoh is a parameter defining the overhead caused by the asynchronous communication in terms of the critical path delay of the purely combinational logic block

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’’Energy Model’’

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Asynchronous Synchronous

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’’Energy Model’’

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’’Energy Model’’

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’’Energy Model’’

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’’Real-World Application Comparison ’’

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’’Real-World Application Comparison’’

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’’Real-World Application Comparison’’

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’’Real-World Application Comparison’’

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”Synthesis Results Based Model Accuracy”

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”Synthesis Results Based Model Accuracy”

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”Architectural Improvements”

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• Parallelism

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”Architectural Improvements”

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”Architectural Improvements”

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• Pipelining

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”Architectural Improvements”

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”Architectural Improvements”

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”Architectural Improvements”

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”Architectural Improvements”

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”Architectural Improvements”

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”Architectural Improvements”

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”Architectural Improvements”

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Conclusion

• The energy model presented is highly aqurate and efficient
• Pipeling helps is reducing the energy cost.
• Parallel processing in sub-threshold domain does not reduce

the energy dissipation.