Question

a) Two different dynamic logic gates are shown below each having four inputs. If all transistors in both of these two logic gates have the same size, which logic gate is faster the one with the A, B, C, D inputs or the one with the In1, In2, In3, In4 inputs AND WHY? ANSWER: VDD A-(3-(0-[04C Out Out JJ 1114 b) If in the above two different logic gates all transistors are properly sized so both gates have the same speed which gate will occupy LESS AREA, i.e. have smaller physical size, the one with the A, B, C, D inputs or the one with the In1, In2, In3. In4 inputs AND WHY? ANSWER:

Answer 1

The transistor sizing I have mentioned above in the diagram for the first Logic with inputs A, B, C and D the four nMos are in parallel so the resultant size doesn't change (So size =2)

Given en was Circuit:- Pseudo Amos clrcuit ) voo I size) El out VDD N[2size] N [2 (size) Lout A HEBT He ot/2 (size) In 153 Inz C & C size) of Transistor Ing 108 Iny [8 1 let € Circuit 2. let circuit 1 a) one Here the logic gate with inputs A, B, C, D is the faster logic gate .. Wathy because 4 nMOS Transistors are in parallel to pull the "out" Coutput) LOW (0) when either input is HIGH. If any x nmos in Circuit i on the output goes to 'o', But in Circuitz the output goes to zero (o) only when all the NMOS are On in Dircuit 2 . So Cirovit 1 is taster than circuit z. b) Area is based on the sizes of Transistors . Let us assume for nmos the reference size is (W = 2 yem). Based on that if transistors are in series then resultant size of transistor is number of transistor x multiplied with reference size . [dor Circuit 2, there are 4 tran in series i. Size = 4x2 = fum]. And for parallel transistors the size is same as reference clum) Circuit 1 (inputs A,B,C,D) i Occupies less area compared to Circuit 2 C inputs in,,ing, inz, ina). .

But in logic with inputs In1 In2 In3 and In4 the four nNos are in series the resultant size is 4 *2 = 8 because 4 nMos are in series. So the logic with inputs A, B, C, and D is occupies less area than Logic circuit 2