In this lecture, we are going to earn about the Eye diagram. We will clarify the concept of eye pattern in digital communication. So let’s start with the basic concept of the eye diagram.
Concept of Eye Pattern
- An eye pattern is a pattern displayed on the screen of a cathode ray oscilloscope (C.R.O.). The shape of this pattern resembles the shape of the human eye. therefore, it is called an eye pattern.
- The eye pattern is a practical way to study intersymbol interference (ISI) and its effects on a PCM or data communication system.
- The eye pattern is obtained on the C.R.O. by applying the received signal to vertical deflection plates (Y-Plates) of the C.R.O. and a sawtooth wave at the transmission symbol rate i.e., (1/Tb) to the horizontal deflection plates (X-plates) as shown in figure(b) below.
- The received digital signal and the corresponding oscilloscope display are shown in figure(a) and figure (c) below respectively.
- The resulting oscilloscope display shown in figure (3) is called the eye pattern. This is due to its resemblance to the human eye.
- The interior region of the eye pattern is called the eye-opening. The eye pattern provides a great deal of information about the performance of the system. The information obtainable is in the last figure.
Information obtained from Eye pattern
- The width of the eye-opening defines the time interval over which the received wave can be sampled, without an error due to ISI. the best time for sampling is when the eye is open widest.
- The sensitivity of the system to the timing error is determined by the rate of closure of the eye as the sampling rate is varied.
- The height of eye-opening at a specified sampling time defines the margin over the noise.
- When the effect of ISI is severe, the eye is completely closed and it is impossible to avoid error due to the combined presence of ISI and noise in the system.
Frequently Asked Questions on Eye Diagram
What is the use of an eye diagram in digital communication?
Ans: The eye diagram takes its name from the fact that it has the appearance of a human eye. It is created simply by superimposing successive waveforms to form a composite image. The eye diagram is used primarily to look at digital signals for the purpose of recognizing the effects of distortion and finding its source
What is ISI in communication?
Ans: Intersymbol interference (ISI) occurs when a pulse spreads out in such a way that it interferes with adjacent at the sampling instant.
How does the eye diagram give information about ISI?
Ans: An eye pattern provides the following information about a particular system. Actual eye patterns are used to estimate the bit error rate and the signal-to-noise ratio. The width of the eye-opening defines the time interval over which the received wave can be sampled without error from ISI.
What are eye pattern properties?
Ans: The eye pattern is a composite signal that reflects the channel bandwidth, attenuation, jitter, and rise/fall time variations. As the signal frequency increases for a given bandwidth and the signal is attenuated and interfered with, the eye begins to close.