VLSI, Lecture 3 Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut MOS INVERTERS

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Basic Properties

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Basic Properties Require Large “R” for limitation in current

VLSI, 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

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut NMOS Transistor (Depletion & Enhance) NMOS Depletion V = 0 but still has I ds

VLSI, 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

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Inverter transistor nMOS (depletion) => pull-up nMOS (enhance) => pull-down

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Relation between V out & V in Slope = V out V in

VLSI, 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

VLSI, 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

VLSI, 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

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Use R to pull-up

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Use nMOS(depletion) to pull-up Lose power while V in =1

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Use nMOS to pull-up Lose power when V GG = V DD

VLSI, Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut Use pMOS to pull-up I = 0 pmos < nmos

VLSI, 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

VLSI, 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

VLSI, 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

VLSI, 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 

VLSI, 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 )

VLSI, 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