In telecommunications, eye line, also known as eye diagram.
Eye chart is formed by overlapping each code element waveform obtained by scanning due to the afterglow effect of oscilloscope. It refers to a pattern observed on an oscilloscope when an experimental method is used to estimate and improve (by tuning) the performance of a transmission system. The way to observe eye graph is to use an oscilloscope to span the output end of the receiving filter, and then adjust the oscilloscope scanning period so that the oscilloscope horizontal scanning period is synchronized with the period of the receiving code element. At this time, the graph seen on the oscilloscope screen looks like human eyes, so it is called "eye graph".
The eye chart is a common indicator of the quality of the signal in high-speed digital transmission. The eye chart usually includes some time samples of the voltage required for the sample rate below the data rate. A perfect eye diagram contains an enormous amount of parametric information about the signal, as if derived from physics, regardless of the frequency of the effects.
The influence of inter-code crosstalk and noise can be observed from the eye diagram, which reflects the overall characteristics of digital signal, so as to estimate the degree of advantages and disadvantages of the system. Therefore, the eye diagram analysis is the core of signal integrity analysis of high-speed interconnection system. In addition, this graph can be used to adjust the characteristics of the receiving filter to reduce inter-code crosstalk and improve the transmission performance of the system. Engineers can use it to check the signal integrity of the design and find problems early in the design process. Used in combination with other measurements such as bit error rates, eye diagrams can help designers predict performance and identify possible sources of problems.
There is a close relationship between eye chart and quality in testing. If the eye diagram is good and stable, that means the quality of the module is good.
There are many kinds of eye shapes, and so are eye charts. We can quickly judge the quality of the signal from the shape features of the eye diagram.
1. The eye chart below has a "double eyelid", which indicates that the signal may be crosstalk or pre-aggravation.
2. The eye chart below "bloodshot eyes" indicates poor signal quality, possibly due to faulty test methods or obvious PCB wiring errors.
3. A complete eye diagram should contain all the states from "000" to "111", with eight states forming one eye diagram.
