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chap4_1

# chap4_1 - Principles of VLSI Design Performance Estimation...

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Unformatted text preview: Principles of VLSI Design Performance Estimation CMPE 413 1 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE COU NTY 1 9 6 6 Introduction Needsimplemodelstoestimatesystemperformanceintermsofsignaldelay and power dissipation. Issues include: • Resistance, capacitance and inductance calculations. • Delay estimations. • Determination of conductor size for power and clock distribution. • Power consumption. • Charge sharing mechanisms. • Design Margining. • Reliability. • Effects of scaling. Principles of VLSI Design Performance Estimation CMPE 413 2 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE COU NTY 1 9 6 6 Resistance Estimation The resistance of a uniform slab of conducting material may be expressed as For example, in a layout editor, such as magic or virtuoso: R ρ t-- l w--- Ohms = where ρ = resistivity t = thickness l/w = length/width Alternatively as R R S l w--- Ohms = where R S = sheet resistance in ohms/square. is equivalent to 2 λ λ 8 16 λ 4 λ Metal1/Metal2 0.07 material Ω /sq Metal 3 Poly Diffusion n-well 0.04 20 25 2K 0.5 μ to 1.0 μ processes Typical sheet resistances of contacts => 0.25 to 20 ohms. Irregular shapes require more elaborate calculation - see text for examples. Principles of VLSI Design Performance Estimation CMPE 413 3 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE COU NTY 1 9 6 6 Resistance Estimation Channel resistance can be estimated in the linear region as: A range of 1,000 to 30,000 ohms/square are possible for n-channel and p- channel devices. Typicalbetasforidenticallysizeddevices;n-dev:~90,p-dev:~30microA/V 2 . Temperature changes both mu (mobility) and V t (threshold voltage) and, therefore channel resistance. Channel resistance increases with temperature, approximately +0.25% per degree C above 25 degrees. Metal and poly resistance change about 0.3% and well diffusions about 1% per degree C. R c 1 μ C ox V gs V t – ( 29----------------------------------------- L W----- Ohms 1 β V gs V t – ( 29------------------------------ Ohms = = Principles of VLSI Design Performance Estimation CMPE 413 4 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T IM ORE COU NTY 1 9 6 6 Capacitance Estimation Switching speed of MOS systems strongly dependent: Parasitic capacitances associated with the MOS transistor. Interconnect capacitance of "wires". Resistance of transistors and wires. Total load capacitance on the output of a CMOS gate is sum of: Gate capacitance (of receiver logic gates downstream). Driver diffusion (source/drain) capacitance. Routing ( line ) capacitance of substrate and other wires. Let’s consider approximations of each of these capacitances and subsequent approximations of delay based on these expressions. Driver C s and C d Line capacitance Receivers C g Principles of VLSI Design Performance Estimation CMPE 413 5 UMBC U M B C U N IV E R S I T Y O F M A R Y L A N D B A L T...
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chap4_1 - Principles of VLSI Design Performance Estimation...

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