User`s guide

12 Di

ital Worst-Case Timin

Analysis

Glitch Suppression Due

to Inertial Dela

Signal propagation through digital primitives is performed by

the simulator subject to constraints such as the primitive’s

function, delay parameter values, and the frequency of the

applied stimulus. These constraints are applied both in the

context of a normal, well-behaved stimulus, and a stimulus that

represents timing hazards.

There are certain situations in which timing hazards may not

result in the prediction of an X or glitch output from a primitive.

These are due to the delay characteristics of the primitive, which

the simulator models using the concept of inertial delay.

A device presented with a combination of rising and falling

input transitions (assuming no other dominant inputs) produces

a glitch due to the uncertainty of the arrival times of the

transitions (see Figure 16-13).

ure 16-13

Glitch Suppression Example 1

However, when the duration of the conflicting input stimulus is

less than the inertial delay of the device, the X result is

automatically suppressed by the simulator because it would be

overly pessimistic (see Figure 16-14).

In the analysis of reconvergent fanout cases (where common

ambiguity is recognized), it is possible that conflicting signal

ambiguities may still overlap at the inputs to a primitive, even

after factoring out the commonality. In such cases, where the

n ≥ TPLHMX-TPLHMN

n < TPLHMX-TPLHMN

ure 16-14

Glitch Suppression Example 2