EECS 141 S02 Lecture 8 Power Dissipation CMOS Scaling Last Lecture CMOS Inverter loading Switching Performance Evaluation Design optimization Inverter Sizing 1
Today CMOS Inverter power dissipation» Dynamic» Short-Circuit» Leakage Scaling CMOS into the future Power Dissipation 2
Where Does Power Go in CMOS? Dynamic Power Consumption Charging and Discharging Capacitors Short Circuit Currents Short Circuit Path between Supply Rails during Switching Leakage Leaking diodes and transistors Dynamic Power Dissipation Vdd Vin Vout C L Energy/transition = C L * V dd 2 Power = Energy/transition * f = C L * V dd 2 * f Not a function of transistor sizes! Need to reduce C L, V dd, and f to reduce power. 3
Modification for Circuits with Reduced Swing V dd V dd V dd -V t C L E 0 1 = C L V dd ( V dd V t ) Can exploit reduced swing to lower power (e.g., reduced bit-line swing in memory) Adiabatic Charging 2 2 2 4
Adiabatic Charging Node Transition Activity and Power Consider switching a CMOS gate for N clock cycles E N = C L V 2 dd nn ( ) E N : the energy consumed for N clock cycles n(n): the number of 0->1 transition in N clock cycles P avg = lim N E N -------- f N clk = nn ( ) lim ------------ 2 C V N N dd fclk L α 0 1 = nn ( ) lim ------------ N N P avg = α 0 1 C L V 2 fclk dd 5
Transistor Sizing for Minimum Energy In Out C g1 1 f C ext Goal: Minimize Energy of whole circuit» Design parameters: f and V DD» tp tpref of circuit with f=1 and V DD =V ref t t p p0 f = t p0 1 + + 1 + γ VDD V V DD TE F fγ Transistor Sizing (2) Performance Constraint (γ=1) t t p pref t = t p0 p0ref 2 + f + F f V = ( 3+ F ) V V V ( 3+ F ) Energy for single Transition E = V E E ref 2 DD C V = V g1 DD ref V 2 + f + = 1 DD ref V ref DD TE TE [( 1+ γ )( 1+ f ) + F ] 2 2 + 2 f + F 4 + F F f 6
Transistor Sizing (3) V DD =f(f) E/E ref =f(f) 4 1.5 vdd (V) 3.5 3 2.5 2 1.5 1 F=1 2 5 10 normalized energy 1 0.5 0.5 20 0 1 2 3 4 5 6 7 f 0 1 2 3 4 5 6 7 f Short Circuit Currents Vdd Vin Vout C L 0.15 IVDD (ma) 0.10 0.05 0.0 1.0 2.0 3.0 V in (V) 4.0 5.0 7
How to keep Short-Circuit Currents Down? Short circuit current goes to zero if t fall >> t rise, but can t do this for cascade logic, so... Minimizing Short-Circuit Power 8 7 6 Vdd =3.3 P norm 5 4 Vdd =2.5 3 2 1 Vdd =1.5 0 0 1 2 3 4 5 t sin /t sout 8
Leakage Vdd Vout Drain Junction Leakage Sub-Threshold Current Sub-threshold current one of most compelling issues in low-energy circuit design! Reverse-Biased Diode Leakage GATE p + p+ N + - V dd Reverse Leakage Current I DL = J S A JS = 10-100 pa/µm2 at 25 deg C for 0.25µm CMOS JS doubles for every 9 deg C! 9
Subthreshold Leakage Component Static Power Consumption Vdd I stat V out V in =5V C L P stat = P (In=1).V dd. I stat Wasted energy Should be avoided in most cases, but could help reducing energy in others (e.g. sense amps) 10
Principles for Power Reduction Prime choice: Reduce voltage!» Recent years have seen an acceleration in supply voltage reduction» Design at very low voltages still open question (0.6 0.9 V by 2010!) Reduce switching activity Reduce physical capacitance» Device Sizing: for F=20 f opt (energy)=3.53, f opt (performance)=4.47 Impact of Technology Scaling 11
Goals of Technology Scaling Make things cheaper:» Want to sell more functions (transistors) per chip for the same money» Build same products cheaper, sell the same part for less money» Price of a transistor has to be reduced But also want to be faster, smaller, lower power Technology Scaling Goals of scaling the dimensions by 30%:» Reduce gate delay by 30% (increase operating frequency by 43%)» Double transistor density» Reduce energy per transition by 65% (50% power savings @ 43% increase in frequency Die size used to increase by 14% per generation Technology generation spans 2-3 years 12
Technology Evolution (2000 data) International Technology Roadmap for Semiconductors Year of Introduction 1999 2000 2001 2004 2008 2011 2014 Technology node [nm] 180 130 90 60 40 30 Supply [V] 1.5-1.8 1.5-1.8 1.2-1.5 0.9-1.2 0.6-0.9 0.5-0.6 0.3-0.6 Wiring levels Max frequency [GHz],Local-Global Max µp power [W] Bat. power [W] 6-7 1.2 90 1.4 6-7 1.6-1.4 106 1.7 7 2.1-1.6 130 2.0 8 3.5-2 160 2.4 9 7.1-2.5 171 2.1 9-10 11-3 177 2.3 10 14.9-3.6 186 2.5 Node years: 2007/65nm, 2010/45nm, 2013/33nm, 2016/23nm Technology Evolution (1999) 13
ITRS Technology Roadmap Acceleration Continues Technology Scaling (1) 10 2 10 1 Minimum Feature Size (micron) 10 0 10-1 10-2 1960 1970 1980 1990 2000 2010 Year Minimum Feature Size 14
Technology Scaling (2) Number of components per chip Technology Scaling (3) t p decreases by 13%/year 50% every 5 years! Propagation Delay 15
Technology Scaling (4) 100 x1.4 / 3 years 1000 κ 0.7 Power Dissipation (W) 10 1 0.1 0.01 80 x4 / 3 years 85 (a) Power dissipation vs. year. 90 Year MPU DSP 95 Power Density (mw/mm 2 ) 100 10 κ 3 1 1 Scaling Factor κ i normalized by 4µm design rule j (b) Power density vs. scaling factor. 10 From Kuroda Technology Scaling Models Full Scaling (Constant Electrical Field) ideal model dimensions and voltage scale together by the same factor S Fixed Voltage Scaling most common model until recently only dimensions scale, voltages remain constant General Scaling most realistic for todays situation voltages and dimensions scale with different factors 16
Scaling Relationships for Long Channel Devices Transistor Scaling (velocity-saturated devices) 17
µprocessor Scaling P.Gelsinger: µprocessors for the New Millenium, ISSCC 2001 µprocessor Power P.Gelsinger: µprocessors for the New Millenium, ISSCC 2001 18
µprocessor Performance P.Gelsinger: µprocessors for the New Millenium, ISSCC 2001 2010 Outlook Performance 2X/16 months» 1 TIP (terra instructions/s)» 30 GHz clock Size» No of transistors: 2 Billion» Die: 40*40 mm Power» 10kW!!» Leakage: 1/3 active Power P.Gelsinger: µprocessors for the New Millenium, ISSCC 2001 19
Some interesting questions What will cause this model to break? When will it break? Will the model gradually slow down?» Power and power density» Leakage» Process Variation 20