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 1 = C EFF V DD 2 f 1 = switching activity rate...
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EEL6323-S11-HLec09-Power-dissipation-2spp - 1 Lecture 9:...

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