Design a cmos circuit producing the function fabcd a

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DESIGN A CMOS CIRCUIT PRODUCING THE  FUNCTION   F(A,B,C,D) = !A + (!B +!C) !D.     !F(A,B,C,D) = A(BC + D)         PULL-UP NETWORK    PULL-DOWN NETWORK
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Copyright  ©  2004 by M   21 POSITIVE & NEGATIVE LOGIC THE BEHAVIOR OF A SWITCHING DEVICE, LIKE A CMOS GATE, IS  GIVEN IN TERMS OF  HIGH AND LOW VOLTAGES. FOR A GIVEN  DEVICE, THIS BEHAVIOR IS UNIQUE. HOWEVER, ITS LOGIC BEHAVIOR CAN BE DEFINED EITHER WITH  POSITIVE LOGIC CONVENCTION : HIGH FOR  1  ;  LOW FOR  0 OR WITH   NEGATIVE LOGIC CONVENCTION : HIGH FOR  0;  LOW  FOR  1. IN GENERAL THE LOGIC BEHAVIOR OF A SWITCHING DEVICE  MAY BE DIFFERENT IN POSITIVE AND NEGATIVE LOGICS. FOR  EXAMPLE, THE CMOS DEVICE ON NEXT SLIDE REPRESENTS  THE NAND GATE IN POSITIVE LOGIC AND THE NOR GATE IN  NEGATIVE LOGIC    
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Copyright  ©  2004 by M   22 POSITIVE & NEGATIVE LOGIC EXAMPLE OF POSITIVE AND NEGATIVE LOGICS a1 1 a2 2 b1 5
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Copyright  ©  2004 by M   23 PHYSICAL CHARACTERISTICS TRANSISTOR AS A SWITCH STATIC CURRENT NOISE MARGIN DYNAMIC OPERATION PROPAGATION DELAY POWER DISSIPATION FAN-IN/FAN-OUT
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Copyright  ©  2004 by M   24 PHYSICAL CHARACTERISTICS TRANSISTOR AS A SWITCH: STATIC CURRENT; THE NOT  GATE WHEN THE TRASISTOR IS CUT-OFF, IT CAN CONDUCT A  VERY LOW CURRENT, CALLED  LEAKAGE CURRENT R R R DD f DS DS V V + = mA K V R V I DS f SAT 2 . 0 1 2 . 0 = = = V DD V X V f PULL-UP DEVICE V f = V OL R R DS I SAT V X = HIGH VOLTAGE
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Copyright  ©  2004 by M   25 PHYSICAL CHARACTERISTICS VOLTAGE TRANSFER CHARACTERISTIC V T  is the threshold voltage ~  0.2 V DD V OH   is the output high voltage  = V DD V OL   is the output low voltage = 0.2 volts The plot of V f  versus V x  shows the voltage transfer characteristic  
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Copyright  ©  2004 by M   26 PHYSICAL CHARACTERISTICS NOISE MARGIN TWO MARGINS:  NM , NM H BY DEFINITION: NM = V IL  - V OL  ;  NM H  = V OH  – V IL EXAMPLE: FOR CMOS SWITCHING CIRCUITS LET V OH  = V DD  AND V OL = 0 v. Finding the two points where SLOPE = -1 V IL ~  1/8 (3 V DD  + 2 V T ), V IH ~  1/8 (5 V DD  - 2 V T ) IF V T  = 0.2 V DD  THEN NM = NM = 0.425 V DD For  V DD  = 5 v. NM = NM = 2.1 v. For  V DD  = 3.3 v. NM = NM = 1.4 v.
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Copyright  ©  2004 by M   27 PHYSICAL CHARACTERISTICS DYNAMIC OPERATION LET US CONSIDER TWO INVERTERS CONNECTED IN  CASCADE CAPACITIVE LOAD AT NODE   A  IS DUE TO SILICON  CONSTRUCTION OF TRANSISTOR. IT IS CALLED  PARASITIC OR  STRAY CAPACITANCE V F V DD T 1 T 2 V X V DD T 1 T 2 A
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Copyright  ©  2004 by M   28 PHYSICAL CHARACTERISTICS DYNAMIC OPERATION (Continues) Each transistor contributes a  GATE CAPACITANCE C = W . L . C
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