User`s guide

8 Di

ital Worst-Case Timin

Analysis

Cumulative Ambi

uit

Hazard

In worst-case mode, simple signal propagation through the

network will result in a buildup of ambiguity along the paths

between synchronization points (see Glitch Suppression Due to

Inertial Delay on page 16-12). The cumulative ambiguity is

illustrated in Figure 16-8.

ure 16-8

Cumulative Ambiguity Hazard Example 1

The rising and falling transitions applied to the input of the

buffer have a 1 nsec ambiguity. The delay specifications of the

buffer indicate that an additional 2 nsec of ambiguity is added to

each edge as they propagate through the device. Notice that the

duration of the stable state 1 has diminished due to the

accumulation of ambiguity. Now, consider the effects of

additional cumulative ambiguity shown in Figure 16-9.

ure 16-9

Cumulative Ambiguity Hazard Example 2

The X result is predicted here because the ambiguity of the

rising edge propagating through the device has increased to the

point where it will overlap the later falling edge ambiguity.

Specifically, the rising edge should occur between 3 nsec and 12

nsec; but, the subsequent falling edge applied to the input

predicts the output starts to fall at 10 nsec. This situation is

called a cumulative ambiguity hazard.

12 89

TPxxMN=1

25912

TPxxMX=3

TPxxMN=1

25912

310

TPxxMX=7