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3. Logic Gate 3.1 Introduction static, fully complementary CMOS psudo-nMOS, domino logic 3.2 Combinational Logic Functions combinational logic ---- specification expression logic gate networks ---- implementation area, delay, power ---- costs
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literal [Completeness] Function {|}=NAND function: complete 1:a|(a|a) = a|a’ = 1 0:{a|(a|a}|{a|(a|a)} = 1|1 = 0. a’:a|a = a’. ab:(a|b)|(a|b) = ab a+b:(a|a)|(b|b) = a’|b’=a+b NOR function: complete AND and OR function: not complete [Irredundant] no literal can be removed. redundant Ab+ab’=a
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3.3 Static Complementary Gates 3.3.1 Gate Structure Pullup network (pMOS) output is connected to VDD Pulldown network (nMOS) Output is connected to VSS VDD VSS
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Pullup network (pMOS) output is connected to VDD when ab=0. Pulldown network (nMOS) Output is connected to VSS when ab=1. VDD VSS CMOS NAND
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Pullup network (pMOS) output is connected to VDD when a+b=0. Pulldown network (nMOS) Output is connected to VSS when a+b=1. VDD VSS CMOS NOR
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Static Complementary gate [a(b+c)]’ Dual graph
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And Or Inverter (AOI) gate (ab+c)’
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3.3.2 Basic Gate Layouts Layout of Inverter
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Layout of NAND gate
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Layout of NOR gate
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Layout of a wide transistor by split into two sections.
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3.3.3 Logic Levels VOH: minimum voltage output for logic 1. VOL: maximum voltage output for logic 0. VIH: minimum voltage input for logic 1. VIL: maximum voltage input for logic 0. VOL < VIL VOH > VIH
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Minimum size transistors VIL VIH VOL VOH Noise Margin NML = VIL-VOL NMH = VOH-VIH
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3.3.4 Delay
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3.3.5 Power Consumption
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Speed-power product = power-delay product SP=(1/f)P=CV 2 3.3.6 The Speed-Power Product
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3.3.7 Layout and Parasitics Resistance parastics
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3.3.8 Driving Large Loads Alpha=(Cbig/Cg)(1/n) Ttot = Nopt=
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Delta1=r1 x (C1+---+Cn) =n rc Delta2=r2 x (C2+----+Cn) =(n-1)rc DeltaN=rn x Cn =rc total=Delta1+ ----- + DeltaN =n(n+1)/2 x rc 3.4 Wires and Delay 3.4.1 Elmore Delay Model
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3.4.2 Wire Sizing Optimum-shaped wire
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3.4.3 RC Trees
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3.5 Switch Logic Logic 0 transfer Logic 1 transfer
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3.6 Alternative Gate Cirucits 3.6.1 Pseudo-nMOS Logic
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3.6.2 DCVS (Differential Cascaded voltages switch logic) Logic
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3.6.3 Domino Logic
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Successive evaluation in a domino logic network
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Charge sharing
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