Eye pattern
Encyclopedia
In telecommunication
, an eye pattern, also known as an eye diagram, is an oscilloscope
display in which a digital data signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep. It is so called because, for several types of coding, the pattern looks like a series of eyes between a pair of rails.
Several system
performance measures can be derived by analyzing the display. If the signals are too long, too short, poorly synchronized with the system clock, too high, too low, too noisy, or too slow to change, or have too much undershoot or overshoot
, this can be observed from the eye diagram. An open eye pattern corresponds to minimal signal distortion
. Distortion of the signal waveform
due to intersymbol interference
and noise appears as closure of the eye pattern.
Amplitude Measurements
Time Measurements
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
, an eye pattern, also known as an eye diagram, is an oscilloscope
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...
display in which a digital data signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep. It is so called because, for several types of coding, the pattern looks like a series of eyes between a pair of rails.
Several system
System
System is a set of interacting or interdependent components forming an integrated whole....
performance measures can be derived by analyzing the display. If the signals are too long, too short, poorly synchronized with the system clock, too high, too low, too noisy, or too slow to change, or have too much undershoot or overshoot
Overshoot (signal)
In signal processing, control theory, electronics, and mathematics, overshoot is when a signal or function exceeds its target. It arises especially in the step response of bandlimited systems such as low-pass filters...
, this can be observed from the eye diagram. An open eye pattern corresponds to minimal signal distortion
Distortion
A distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...
. Distortion of the signal waveform
Waveform
Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph...
due to intersymbol interference
Intersymbol interference
In telecommunication, intersymbol interference is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable...
and noise appears as closure of the eye pattern.
Measurements
There are many measurements that can be obtained from an Eye Diagram:Amplitude Measurements
- Eye Amplitude
- Eye Crossing Amplitude
- Eye Crossing Percentage
- Eye Height
- Eye Level
- Eye SNR
- Quality Factor
- Vertical Eye Opening
Time Measurements
- Deterministic Jitter
- Eye Crossing Time
- Eye Delay
- Eye Fall Time
- Eye Rise Time
- Eye Width
- Horizontal Eye Opening
- Peak-to-Peak Jitter
- Random Jitter
- RMS Jitter
- Total Jitter
Interpreting Measurements
| Eye-diagram feature | What it measures |
|---|---|
| Eye opening (height, peak to peak) | Additive noise Noise In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise... in the signal |
| Eye overshoot/undershoot | Peak distortion Distortion A distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice... due to interruptions in the signal path |
| Eye width | Timing synchronization & jitter Jitter Jitter is the undesired deviation from true periodicity of an assumed periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of... effects |