Carry-Skip Adders

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## Carry-Skip Adders

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**Carry-Skip Adders**• Generalization of Manchester Adders • With CMOS Implementation – Carry Skip speed Comparable to CLA • Less Area/Power • Based on Observation that Carry Process Can “Skip” Stage for Which xi yi (that is pi = xiyi = 1) • Adder of n stages Divided into Stages of Selected Lengths • With Simple Ripple Carry • Each Group Generates “Group Carry-Propagate”=1 if all pi=1 in Each Group • This Signal Allows Incoming Carry to “Skip” Stages within Group and Generate Carry-out**Carry-Skip Adder-Group Carry**GCin cin cin GCout P1 P0 P2 GCin•P[2:0]