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240-451 VLSI, 2000 1 Lecture 3 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut MOS INVERTERS
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240-451 VLSI, 2000 2 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Basic Properties
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240-451 VLSI, 2000 3 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Basic Properties Require Large “R” for limitation in current
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240-451 VLSI, 2000 4 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Basic Properties Vin > Vth transistor ON V out = “0” pull down Vin < Vth transistor OFF V out = “1” pull up
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240-451 VLSI, 2000 5 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut NMOS Transistor (Depletion & Enhance) NMOS Depletion V = 0 but still has I ds
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240-451 VLSI, 2000 6 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Inverter transistor V DD = V ds(dep) + V ds(enh) V ds(enh) = V DD - V ds(dep) V out = V ds(enh) I ds(dep) = I ds(enh) V gs(dep) = 0 V gs(enh) = V in
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240-451 VLSI, 2000 7 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Inverter transistor nMOS (depletion) => pull-up nMOS (enhance) => pull-down
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240-451 VLSI, 2000 8 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Relation between V out & V in Slope = V out V in
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240-451 VLSI, 2000 9 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Z pu / Z pd in nMOS Inverter A V in V out * Steady state I ds = W (V gs - V th ) 2 2 LD I ds = W pu (- V thd ) 2 ; V gs = 0 2 DL pu I ds = W pd (V inv - V the ) 2 ; V gs = V inv 2 DL pd depletion enhance
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240-451 VLSI, 2000 10 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Z pu / Z pd in nMOS Inverter I ds (depletion) = I ds (enhance) W pd (V inv - V the ) 2 = W pu (- V thd ) 2 L pd L pu Let Z pd = L pd ; Z pu = L pu W pd W pu 1 (V inv - V the ) 2 = 1 (- V thd ) 2 Z pd Z pu
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240-451 VLSI, 2000 11 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Z pu / Z pd in nMOS Inverter V inv = V the - V thd (Z pu / Z pd ) 1/2 Vt = 0.2 V DD Vtd = -0.6 V DD V inv = 0.5 V DD Z pu / Z pd = 4 /1
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240-451 VLSI, 2000 12 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Use R to pull-up
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240-451 VLSI, 2000 13 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Use nMOS(depletion) to pull-up Lose power while V in =1
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240-451 VLSI, 2000 14 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Use nMOS to pull-up Lose power when V GG = V DD
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240-451 VLSI, 2000 15 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Use pMOS to pull-up I = 0 pmos < nmos
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240-451 VLSI, 2000 16 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut CMOS Inverter transistor I ds = W (V gs - V th ) 2 2 LD K = 2D = W L I ds = (V gs - V th ) 2 2
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240-451 VLSI, 2000 17 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut CMOS Inverter transistor = W n L n Steady state = W p L p I dsp = - I dsn = p (V in - V DD - V thp ) 2 2 I dsn = n (V in - V thn ) 2 2
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240-451 VLSI, 2000 18 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut CMOS Inverter transistor W p = 2.5 W n L p L n See the example in your book
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240-451 VLSI, 2000 19 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut How to calculate delay K = Z pu / Z pd See the example in your book Down delay = f Up delay = f K
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240-451 VLSI, 2000 20 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut How to calculate R & C VLSI technology defined diffusion and poly layer = 2 (2521 ; = 3 m )
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240-451 VLSI, 2000 21 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut How to calculate R & C R = L A A = tw R = L tw If L=W= 1 then R = t See the example in your book
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