161_pdfsam_VLSI - static hazard refers to the transient pulse on a signal line whose static value does not change Depending on what the signal’s

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
130 VLSI Test Principles and Architectures 3.3.4 Hazards Because of the difference in delays along reconvergent signal paths, input transi- tions may cause unwanted transient pulses or glitches, called hazards , to appear at internal signals or primary outputs. We will use circuit N to illustrate the cause of hazards. In this example, the inverter has a nominal delay of 3 ns, and the other gates have nominal delays of 2 ns. At first, the input vector to circuit N is ABC = 110 and the output value is K = 0. After circuit N stabilizes, the second input vector ABC = 100 is applied. Without considering the gate delays, the simulator will report that K remains unchanged; however, as shown in Figure 3.20, a delay-aware simu- lator will reveal the existence of a spurious one pulse at K , called a static 0-hazard. Hazards are divided into two categories: static and dynamic. A
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: static hazard refers to the transient pulse on a signal line whose static value does not change. Depending on what the signal’s static value is, a static hazard may be a static 1-hazard or a static 0-hazard . A dynamic hazard , on the other hand, refers to the transient pulse during a 0-to-1 or 1-to-0 transition. Figure 3.21 illustrates the possible outputs of a network with hazards. In the figures, only one hazard pulse is shown, but in general there can be multiple pulses. The presence of hazards may cause a sequential network to malfunction. Following the above example, if the A B C E H J K 1 2 3 4 5 6 7 8 ± FIGURE 3.20 Static 0-hazard. static 1-hazard static 0-hazard dynamic 1-hazard dynamic 0-hazard ± FIGURE 3.21 Types of hazards....
View Full Document

This note was uploaded on 05/16/2011 for the course ENGINEERIN mp108 taught by Professor Elbarki during the Spring '08 term at Alexandria University.

Ask a homework question - tutors are online