User`s guide

Propa

ation of Timin

Ambi

uity 16

-5

Propa

ation of Timin

Ambi

uit

As signals propagate through the circuit, ambiguity is

contributed by each primitive having a nonzero MIN/MAX

delay spread. Consider the following example that uses the

delay values of the previous BUF model.

ure 16-2

Timing Ambiguity Example 2

This accumulation of ambiguity may have adverse effects on

proper circuit operation. In the following example, consider

ambiguity on the data input to a flip-flop.

ure 16-3

Timing Ambiguity Example 3

The simulator must predict an X output, because it is not known

with any certainty when the data input actually made the 0-1

transition. If the cumulative ambiguity present in the data signal

had been less, the 1 state would be latched-up correctly.

Figure 16-4 illustrates the case of unambiguous data change

(settled before the clock could transition) being latched-up by a

clock signal with some ambiguity. Note that the Q output will

change, but the time of its transition is a function of both the

clock’s ambiguity and that contributed by the flip-flop MIN/

MAX delays.

ure 16-4

Timing Ambiguity Example 4

20 45

35 85