fmax for sequential ckts

VISIT BLOG FOR MORE TUTORIALS LIKE THIS on timing;
AUTHOR : ARUN KATHIRU (HARDWARE DESIGN ENGINEER).
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timing tutorial 1 (Fmax calculation...)
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tco(source flip flop) = 3ns , tcombo = 0ns(assuming no wire delay), tsu(destination flip flop) = 3ns.....
------ ------
-----|d1 Q|------|d2 q2|-----
| | | |
| | | |
|-| clk | |-| clk |
| ------ | ------
| |
|----------------- clk

fmax <= 1/(3 + 0 + 3)ns. if clock frequency exceeds the calculated value set-up violations will happen at the destination flip-flop(second flip-flop).
tco = delay for the o/p of a flip flop to change after receiving the positive edge of clock.
tcombo = delay of the combinational gates which comes in between two flops.
tsu: setup time requirement of destination flip-flop...