doubt

Question

A 4bit carry lookahead adder which add two 4bit number is designed using AND,OR,NOT,NAND,NOR gates only.Assuming that all the inputs are available in both complemented and uncomplemented form and the delay of each gate is one time unit ,what is over all propagation delay of the adder?assume that carry network has been implemented using two level AND-Or logic .

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For reference : https://www.youtube.com/watch?v=EmJA-eEy-b0&index=13&list=PLsFENPUZBqiprGoEWrpexJPlPjmfPCtzM

 

Answer 1

Its 4 unit time.....

C i+1= ai bi+bi ci + ci ai

As we can write carry in terms of C0 that is initial carry....in this carry will not propogate.......

Since Ci+1 is a sop expression it will take only 2 unit time....once all carries  are available  sum will also take 2 unit time so overall time is 4 unit time

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Priyanka Agarwal and bhavnakumrawat5 please have a look at this link.. it is a gate question and the best answer chosen says that 6 is the correct one..

https://gateoverflow.in/1057/gate2004-62

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Priyanka Agarwal can you please explain a bit how the Sum can be implemented using 2 level gate?

Edit: I got it :)

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https://www.google.co.in/amp/s/www.geeksforgeeks.org/gate-gate-cs-2004-question-62/amp/

Please Refer this...