EEL6323-S10-HLec017-Adders-4spp

EEL6323-S10-HLec017-Adders-4spp - Lecture 17: Adders...

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1 Lecture 17: Adders Single-bit Addition Carry-Ripple Adder Carry-Skip Adder Carry-Select Adder Carry-Lookahead Adder Tree Adder Reading: Chapter 10, W&H Single-Bit Addition Half Adder Full Adder 1 1 0 1 1 0 0 0 S C out B A 1 1 1 0 1 1 1 0 1 0 0 1 1 1 0 0 1 0 1 0 0 0 0 0 S C out C B A AB S C out C S C out S = C out = S = A B C out = AB Full Adder Design I Brute force implementation from eqns out (,, ) SABC C MAJ ABC  A B C S C out MAJ A B C A BB B A C S C C C B AA C B B C A B C B A C out C A A B B Complimentary Static CMOS Full Adder B A C i C i A X V DD V DD A B C i B A B V DD A B C i C i A B A C i B C o V DD S
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2 A Better Structure: The Mirror Adder V DD C i A B B A B A A B Kill Generate "1"-Propagate "0"-Propagate V DD C i AB C i C i B A C i A B B A V DD S C o Mirror Adder Stick Diagram C i V DD GND B C o AC i C o C i S Layout Clever layout circumvents usual line of diffusion – Use wide transistors on critical path – Eliminate output inverters Carry Propagate Adders N-bit adder called CPA + B N...1 A N...1 S N...1 C in C out 1 1111 +0000 A 4...1 carries B 4...1 S 4...1 C in C out 0 1111 +0000 C in C out
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3 Carry-Ripple Adder Simplest design: cascade full adders C in C out B 1 A 1 B
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EEL6323-S10-HLec017-Adders-4spp - Lecture 17: Adders...

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