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Very Low Voltage Operation Very Low Voltage Operation of Benchmark Circuit c6288of Benchmark Circuit c6288

Presented By: -Presented By: -Murali DharanMurali Dharan

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ObjectivesObjectivesReduce the power and power delay Reduce the power and power delay

product of c6288 benchmark circuitproduct of c6288 benchmark circuit

To study the effect of voltage reduction on To study the effect of voltage reduction on the power dissipation and delaythe power dissipation and delay

To operate the circuit at subthreshold To operate the circuit at subthreshold voltage region and study its effectvoltage region and study its effect

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Need for Voltage ReductionNeed for Voltage ReductionPPtotaltotal = P = Pstaticstatic + P + Pdynamicdynamic

Power dissipation with technology Power dissipation with technology scalingscaling

High PHigh Pstaticstatic dissipation from 65nm dissipation from 65nm onwardsonwards

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Circuit OperationCircuit Operation Above threshold voltage, Above threshold voltage,

transition due to channel transition due to channel currentcurrent

Scaling down supply Scaling down supply voltage reduces Short voltage reduces Short circuit powercircuit power

VVdddd ≤ |V≤ |Vtptp| + V| + Vtntn

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Why Subthreshold operation?Why Subthreshold operation? Below threshold Below threshold

voltage, transition voltage, transition due to subthreshold due to subthreshold currentcurrent

Isub= μ0 Cox(W/L)Vt2 exp {(VGS –VTH + ηVDS)/nVt}

VDS = drain to source voltageη: a proportionality factorn = sub threshold slope factor (1 + Cd/Cox)

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c6288 Circuit Designc6288 Circuit DesignThe circuit was designed in VerilogThe circuit was designed in Verilog It was synthesized in 0.18 micron It was synthesized in 0.18 micron

technology using LeonardoSpectrumtechnology using LeonardoSpectrumThe synthesized netlist was imported into The synthesized netlist was imported into

Design ArchitectDesign ArchitectTiming and power analysis was done Timing and power analysis was done

using ELDOusing ELDO

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Model of 16 Bit Multiplier (c6288)Model of 16 Bit Multiplier (c6288)

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Simulation ResultsSimulation ResultsVoltageVoltage

(V)(V)Power (Power (μμW)W) DelayDelay

(ns)(ns)Power x Power x

Delay (fJ)Delay (fJ)

33 304.9304.9 0.1220.122 37.29637.296

22 92.392.3 0.1290.129 11.8311.83

1.51.5 32.832.8 0.1480.148 4.83994.8399

1.11.1 14.714.7 0.2900.290 4.2444.244

0.850.85 8.348.34 0.5270.527 4.3924.392

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Subthreshold OperationSubthreshold OperationVoltageVoltage

(V)(V)Power Power ((μμW)W)

DelayDelay(ns)(ns)

Power x Power x Delay (fJ)Delay (fJ)

0.60.6 1.501.50 1.501.50 2.2392.239

0.40.4 4.06 x 104.06 x 10-3-3 49.549.5 0.20060.2006

0.30.3 2.78 x 102.78 x 10-3-3 461.3461.3 1.28241.2824

0.20.2 1.41 x 101.41 x 10-3-3 4017 4017 5.635.63

0.10.1 0.64 x 100.64 x 10-3-3 3345033450 21.3921.39

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Timing PlotTiming Plot

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Power Delay Product GraphsPower Delay Product GraphsPower Delay Plots

0

5

10

15

20

25

30

35

40

0 0.5 1 1.5 2 2.5 3 3.5

Voltage (V)

Pow

er D

elay

Pro

duct

(fJ)

Normal Operation

Subthreshold Operation

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ConclusionConclusion From the graphs, we can infer that the optimum From the graphs, we can infer that the optimum

low voltage operating point is 0.4V which is just low voltage operating point is 0.4V which is just above the threshold voltage.above the threshold voltage.

Circuit still functions properly in subthreshold Circuit still functions properly in subthreshold region and gives comparable energy savings to region and gives comparable energy savings to normal operation mode.normal operation mode.

More circuits need to be tested to check for More circuits need to be tested to check for subthreshold voltage operations.subthreshold voltage operations.

Check circuits in high leakage technologies like Check circuits in high leakage technologies like 65nm and below.65nm and below.

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Future Research WorkFuture Research Work Testing subthreshold operations of sequential Testing subthreshold operations of sequential

circuits to check if operations like feedback circuits to check if operations like feedback causes circuits to malfunction.causes circuits to malfunction.

Testing subthreshold operation of benchmark Testing subthreshold operation of benchmark circuits at high leakage technologies as more circuits at high leakage technologies as more leakage current can lead to faster switching with leakage current can lead to faster switching with less power overhead leading to more energy less power overhead leading to more energy savings.savings.

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ReferencesReferences Spring 2009 slides: ELEC6270 Low Power Spring 2009 slides: ELEC6270 Low Power

Design of Electronic CircuitsDesign of Electronic Circuits Dr. Vishwani D. AgrawalDr. Vishwani D. Agrawal

““Modeling and sizing for Minimum Energy Modeling and sizing for Minimum Energy Operation in Subthreshold Circuits”Operation in Subthreshold Circuits”IEEE Journal of Solid-State Circuits, Vol.40, No. IEEE Journal of Solid-State Circuits, Vol.40, No. 9, September 20059, September 2005 Benton H. Calhoun, Benton H. Calhoun, Student memberStudent member, IEEE, Alice , IEEE, Alice

Wang, Wang, MemberMember, IEEE, and Anantha Chandrakasan, , IEEE, and Anantha Chandrakasan, FellowFellow, IEEE, IEEE