眼图剖析入门手册.pdf.pdf

Abstract This paper describes what an eye diagram is, how it is constructed, mon methods of triggering used to generate one. It then describes different ways that information from an eye diagram can be sliced to gain more insight. It also discusses some basic ways that transmitters, channels, and receivers are tested. It is designed to give an engineer new to this field a basic grasp of the monly used. Anatomy of an Eye Diagram Application Note Application Note tscope 2 Eye Measurements Basics Eye diagrams are a very essful way of quickly and intuitively assessing the quality of a digital signal. A properly constructed eye should contain every possible bit sequence from simple 101’s and 010’s, through to isolated ones after long runs of consecutive zeros and other problem sequences that often show up weaknesses present in system design. What does it show? Eye diagrams show parametric information about the signal – effects deriving from physics such as system bandwidth health, etc. It will not show protocol or logical problems – if a logic 1 is healthy on the eye, this does not reveal the fact that the system meant to send a zero. However, if the physics of the system mean that a logic one es so distorted while passing through the system that the receiver at the far end mistakes it for a zero, this should be shown in a good eye diagram. Common ways of characterizing an eye are to measure the rise times, fall times, jitter at the middle of the crossing point of the eye, the overshoot present and many other numerical descriptions of eye behavior in order pare devices being measured. Instruments usually offer automated measurements that simplify and speed up the taking of such measurements. Figure 1. Overlaying of bit sequences to form an eye diagram. tscope 3 Anatomy of an Eye Diagram The Effects of Triggering on Eye Diagrams Many eye diagrams are constructed on test equipment that uses test patterns that repeat, such as PRBS patterns gene