Day 18: October 21, 2011 Energy and Power Optimization ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 18: October 21, 2011 Energy and Power Optimization Penn ESE370 Fall2011 -- DeHon

Previously Three components of power Ptot = Pstatic + Psc + Pdyn Short circuit Capacitive switching Ptot = Pstatic + Psc + Pdyn Penn ESE370 Fall2011 -- DeHon

Today Power Sources Reducing Switching Energy Energy-Delay tradeoffs Static Short Circuit Capacitive Switching Reducing Switching Energy Energy-Delay tradeoffs Penn ESE370 Fall2011 -- DeHon

Short Circuit Power Penn ESE370 Fall2011 -- DeHon

Preclass 1 Vin vs. Ipwr,gnd? 140mV 400mV 500mV 600mV 840mV Penn ESE370 Fall2011 -- DeHon

Short Circuit Power Between VTN and Vdd-VTP Roughly: Both N and P devices conducting Roughly: Penn ESE370 Fall2011 -- DeHon

Peak Current Ipeak around Vdd/2 If |VTN|=|VTP| and sized equal rise/fall Penn ESE370 Fall2011 -- DeHon

Short-Circuit Energy Penn ESE370 Fall2011 -- DeHon

Short-Circuit Energy Penn ESE370 Fall2011 -- DeHon

Short Circuit Energy Looks like a capacitance Q=I×t Q=CV Penn ESE370 Fall2011 -- DeHon

Short Circuit Energy and Power Every time switch Also dissipate short-circuit energy: E = CV2 Different C = Csc Ccs “fake” capacitance (for accounting) Largely same dependence as charging Psc = aCscV2 f Penn ESE370 Fall2011 -- DeHon

Reduce Short-Circuit Power? Psc = aCscV2 f Penn ESE370 Fall2011 -- DeHon

Preclass 2 Vin vs. Ipwr,gnd vs. Vin @ Vdd=500mV? 140mV 400mV 500mV Penn ESE370 Fall2011 -- DeHon

Total Power Ptot = Pstatic + Psc + Pdyn Pdyn + Psc = a(½Cload+Csc)V2f Ptot ≈ a(½Cload+Csc)V2f+VI’s(W/L)e-Vt/(nkT/q) Penn ESE370 Fall2010 -- DeHon

Dynamic Power Penn ESE370 Fall2011 -- DeHon

Reduce Dynamic Power? Pdyn = a × ½CV2 f How do we reduce dynamic power? Penn ESE370 Fall2011 -- DeHon

Slow Down What happens to power contributions as reduce clock frequency? What suggest about Vth? Penn ESE370 Fall2011 -- DeHon

Reduce V What happens as reduce V? Delay? Energy? Static Switching Penn ESE370 Fall2011 -- DeHon

Old Reduce V (no vsat) tgd=Q/I=(CV)/I tgd impact? tgd α 1/V Id=(mCOX/2)(W/L)(Vgs-VTH)2 tgd impact? tgd α 1/V Penn ESE370 Fall 2010 -- DeHon

Saturation Observe Ignoring leakage Penn ESE370 Fall2011 -- DeHon

Reduce V (velocity saturation) tgd=Q/I=(CV)/I Ids=(nsatCOX)(W)(Vgs-VTH-VDSAT/2) Preclass 3 Vdd Tau/Tau(Vdd=1V) Esw/Esw(1V) 1V 1 700mV 1.75 0.5 500mV 3.5 0.25 350mV 14 0.13 250mV 1200 0.06 Penn ESE370 Fall2011 -- DeHon

Energy vs. Power? Which do we care about? Battery operated devices? Desktops? Pay for energy by kW-Hr? Penn ESE370 Fall2011 -- DeHon

Increase Vth? Recall increasing threshold voltage decreased leakage (9W vs. 4.5mW for 4BT chip) What is impact of increasing threshold on delay? Penn ESE370 Fall2011 -- DeHon

Increase Vth tgd=Q/I=(CV)/I Preclass 4 Ids=(nsatCOX)(W)(Vgs-VTH-VDSAT/2) Preclass 4 Vth=-Vthp Tau/tau(|Vth|=300mV) 300mV 1 500mV 1.4 700mV 2.3 Penn ESE370 Fall2011 -- DeHon

Admin Project 1 out Two weeks That means you need to be starting on it now…and working on it all next week Read assignment today Baseline design no later than Wed (10/26) Set of opt. ideas no later than Fri (10/28) Penn ESE370 Fall2011 -- DeHon

Idea Short circuit energy looks like more capacitance for switching energy Tradeoff Speed Switching energy Leakage energy Energy-Delay tradeoff: Et2 ? Et Penn ESE370 Fall2011 -- DeHon