1. Clock Routing CLOCK H-Tree Network Observe: Only Relative Skew is Important CLOCK Main clock driver Secondary clock drivers Reduces absolute delay. Makes Power-Down easier Sensitive to variations in Buffer Delay Local Area module Comb-Tree Network [©Prentice Hall]

2. DEC Alpha 21164 [©Prentice Hall]

3. DEC Alpha 21164: Clock Skew [©Prentice Hall]

24. System Level Synchronization [©Prentice Hall] Reference clock  PC board Chip 1Chip 2 Logic I/O Data  1 ’  2 ’  1 “  2 “ Crystal-based clock-generator C l o c k G e n e r a t o r C l o c k G e n e r a t o r

25. Skew of Local Clocks vs Reference [©Prentice Hall]

26. Phase-Locked Loop Based Clock Generator [©Prentice Hall] Phase detector Charge pump Up Down Loop filter VCO Clock decode & buffer Divide by N Reference clock Local clock  1  2... V contr Acts also as Clock Multiplier Up Down