數位電路最大頻率的計算 .

數位電路最大頻率的計算 (MAX FREQUENCY CALCULATION EXAMPLE)

Hint: to find the max frequency of the whole circuit, first find all the max frequencies between
FlipFlops and select the mininum one.
From DFFA to DFFB: total delayAB = tpINV + tpAND = 4 + 5 = 9ns
from DFFA to DFFC: total delayAC = tpOR + tpAND = 5 + 4 = 9 ns
from DFFB to DFFC: total delayBC = tpINV + tpOR + tpAND = 5 + 5 + 4 = 14 ns <====
So the critical delay path is between DFFB and DFFC.
Max Frequency = 1 / (tco + tdBC + td-setup + tskew) = 1 / (1+14 + 10+2) = 1/31 = 32.2MHz.

Note that tdBC >> td-hold. If the longest path somehow has less delay then hold time requirement, make sure that the hold time is satisfied.