Contamination delay

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In digital circuits, the contamination delay is the minimum time for a change at the input of a combinational circuit to affect the output. If there is insufficient delay from the output of one flip-flop to the input of the next, the input may change before the hold time has passed. Because the second flip-flop is still unstable, its data would then be "contaminated." Every path from an input to an output can be characterized with a particular contamination delay.

Well-balanced circuits will have similar speeds for all paths through a combinational stage, so the minimum propagation time is close to the maximum. This corresponding maximum time is the propagation delay. The condition of data being contaminated is called a race.