it a description of carry skip adder.

1. 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 = xi⊕yi = 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

2. Fixed Block Width Carry-Skip
Adders

3. Carry-Skip Adder-Group Carry
GCout
GCin
P0 P1 P2
GCin•P[2:0]
2 1 0( )out in inGC c P P P GC= + × × ×
cin
cin

4. Fixed Block Width Carry-Skip
Propagation Delay

5. Variable Sized Blocks

6. Optimum Block Size

7. Optimum Block Size

8. Multilevel Carry-Skip Adders

9. Multilevel Carry-Skip Adders

10. Example Carry-Skip Adder

11. Example Carry-Skip Adder

12. Example Carry-Skip Adder

13. Example Carry-Skip Adder

14. Example Carry-Skip Adder

15. Skip Adder Delay Model

16. Example 2 Delays

17. Example 2 Delays