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Estimate power saving by clock slowdown for s5378 in 180nm and 32nm CMOS
Chao Han ELEC 6270
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Objective Understand the influence of frequency in power and energy saving for certain CMOS technology (180nm and 32nm) Understand the influence of frequency in power and energy saving between 180nm and 32nm CMOS technology
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Theory Ptotal = Ptran + Psc + Pstat Ptran = α fck CVDD2/2
Pstat = Isub VDD
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Theory Short-Circuit Energy
Increases with rise and fall times of input. Decreases for larger output load capacitance. Decreases and eventually becomes zero when VDD is scaled down but the threshold voltages are not scaled down.
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Circuit information S5378 Number of inputs: 35 Number of outputs: 49
Number of DFFs: 179 Number of gates: 2958 (counted in Powersim, one DFF counted as one gate) Number of vectors: 10
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Simulation Procedure Use Matlab to convert Benchmark netliest into rugster netlist Generate some random vectors as input signals Set conditions and do the simulation
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Simulation result 180nm Technology at 1.8V Clock rate
short circuit power leakage power transition power Total power Energy per cycle 40MHz 4.368uW 46.177uW 50.545uW 1263.6uWns 20Mhz 4.418uW 23.089uW 27.507uW 1375.4uWns 10Mhz 4.443uW 11.544uW 15.987uW 1598.7uWns 5Mhz 4.456uW 5.772uW 10.228uW 2045.6uWns 2.5Mhz 4.462uW 2.886uW 7.348uW 2939.2uwns
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Simulation result 32nm technology at 0.9V Clock rate
short circuit power leakage power transition power Total power Energy / cycle 40MHz 4.368uW 11.544uW 15.912uW 397.8uWns 20Mhz 4.418uW 5.772uW 10.190uW 509.5uWns 10Mhz 4.443uW 2.886uW 7.329uW 732.9uWns 5Mhz 4.456uW 1.443uW 5.899uW 1179.8uWns 2.5Mhz 4.462uW 0.722uW 5.184uW 2073.6uWns Ptran(180nm)/Ptran(32nm)=4
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Conclusion Clock slowdown has impact in power saving not energy saving, and it is not significant when frequency becomes very slow because the leakage power becomes more important. For 32nm CMOS technology, leakage power become extremely significant in proportion of the total power.
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Future Work Need to find other simulation tools to do the gate level power simulation Try to use Hspice to do the transistor level power simulation based on some small circuit
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Thanks! question?
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