Delay Parameters
Every circuit output requires a nonzero amount of time to respond to changes on its input, as specified by delay parameters tPLH and tPHL .
Recall that tPLH designates the delay time between an input change and a corresponding low-to-high transition of an output.
tPHL is the delay between an input change and a corresponding high-to-low transition.
For a latch circuit the delay parameters represent the sum of the propagation delays through the gates between a given latch input and output, with separate delay parameters usually specified for each input/output pair.