A 130 nm Sub-VT Power-Gated Processor for Body Sensor Network Applications
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Transcript of A 130 nm Sub-VT Power-Gated Processor for Body Sensor Network Applications
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A 130 nm Sub-VT Power-Gated Processor for Body Sensor Network Applications
Yanqing ZhangYousef Shakhsheer
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MotivationTo reduce energy while idling without
degrading performance, especially in battery constrained applications
i.e. ECG algorithm – Sampling rate is 1 kHzAverage time to process one sample is 20
µs 980 µs of idle timeOpportunity for savings!
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Methodology• RTL• CPF • Place files in RTL
Compiler • Load Encounter• Commit CPF in Encounter
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Methodology• Move power domain
macro modules• Encounter leaves a row
and column between different domains
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Methodology• Add power switches in
respective power domain
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Methodology• Specify switch topology
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Methodology• Specify Global Net
Connections• Verilog has no concept of
VDD and GNDs, let alone different power domains
• Use “Override prior connection” button to your convenience
• Important step in flow
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Methodology• A successfully
floorplanned design that is power-gate ready
• Rest of flow is same as SOC place and route flow
• Yay! So CPF retains the convenience synthesis flow brings us, with powerful flexibility for low power design
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Our design
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Header Topologies – Lumped vs Distributed
Metric Best ChoiceIR Drop Lumped
Delay degradation DistributedPower gating savings Distributed
Recovery time LumpedBreakeven cycles DistributedEase of Design Lumped
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What we learned• Required to break the
VDD connection on the standard cell libraries
• Inherent VDD makes our life harder
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What we learned • Our set of tools will not
automatically characterize headers and decide on sizing
• Header sizing is hard• Trade offs in metrics
8.4 um 16.8 um 33.6 um 67.2 um 134.4 um0.95
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Switching Time Overhead
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Header Sizing
8.4 um 16.8 um 33.6 um 67.2 um 134.4 um0.920.930.940.950.960.970.980.99
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Vrail Min
8.4 um 16.8 um 33.6 um 67.2 um 134.4 um0
0.0050.01
0.0150.02
0.0250.03
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Energy During Power Gat-ing
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Header Sizing
8.4 um 16.8 um 33.6 um 67.2 um 134.4 um0
0.020.040.060.080.1
0.120.140.160.180.2
Recovery Time
8.4 um 16.8 um 33.6 um 67.2 um 134.4 um0.00
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Break Even Cycles
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Class Specific Action & Future Work• Using CPF to do header
insertion• Making tutorial
• Script based flow• Tool for analyzing header
sizing