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EEL6323-S11-HLec09-Power-dissipation-2spp

EEL6323-S11-HLec09-Power-dissipation-2spp - 1 Lecture 9...

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Unformatted text preview: 1 Lecture 9: Power Dissipation • Power and Energy • Dynamic and Static Power • Leakage • Reading: Ch. 4 Power Trends • Trend in CMOS power dissipation – Proportional to chip area and frequency [M. Horowitz, EE246, Stanford Univ] 2 Power Issues • Three reasons why power is important • 1. Hard to get large current into chip (Amps of current) – 100W at 1V is 100 Amps • 2. Cheap device – Use plastic package in low cost box – No fans, so thermal resistance is high (ex: 35 o C/Watt) – Limits power • 3. For a portable system – Need to carry the energy (power x time) you use – Energy is heavy (20 Whr/lb) – Low power means less battery weight [M. Horowitz, EE246, Stanford Univ] Power • Power is current times voltage – iV • There are tow types of current that need to be considered • Static – Current due to resistive path between supply and ground – Leakage currents • Dynamic – Current used to charge and discharge capacitors – Current depends on how often the capacitor changes state – Dominant current in CMOS chips 3 Power and Energy • Power is drawn from a voltage source attached to the V DD pin(s) of a chip. • Instantaneous Power: • Energy: • Average Power: ( ) ( ) D D D D P t i t V ( ) ( ) T T DD DD E P t d t i t V d t avg 1 ( ) T DD DD E P i t V d t T T Dynamic Power • One half of the power from the supply is consumed in the pull-up network and one half is stored on CL • Charge from CL is dumped during the 1 → 0 transition 2 ) ( DD L VDD out DD L out L DD DD VDD VDD V C dv V C dt dt dv C V dt V t i E 2 ) ( 2 DD L VDD out out L out out L DD out VDD C V C dv v C dt v dt dv C V dt v t i E 4 Dynamic Power Consumption • Power = Energy/transition x transition rate = C L V DD 2 f 1 = C L V DD 2 f α 1 = C EFF V DD 2 f – α 1 = switching activity rate...
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EEL6323-S11-HLec09-Power-dissipation-2spp - 1 Lecture 9...

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