What is Eye Pattern?
Digital data is transmitted as sampled values. In sequential or serial data transmission when output sample placed one after another, then overlapping happens due to various facts like ISI. The overlapped pattern form a shape of human eye. That is why it is called eye pattern or diagram.
By the by the more easy presentation we have either a pulse of one or a pulse of zero in digital communications. If you superimpose these two pulses on each other for several times, you will get a pattern like an eye (take into consideration that a pulse is not a sharp react and has a rise and fall time) .
Eye patterns can be observed using an oscilloscope. The received wave is applied to the vertical deflection plates of an oscilloscope and the sawtooth wave at a rate equal to transmitted symbol rate is applied to the horizontal deflection plates, resulting display is eye pattern as it resembles human eye.
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| Simplified eye pattern |
This have some significance in digital data transmission. In the pattern there exists some information shown in figure whose can be used to observe the characteristics of the communication channel.
Information obtained from eye pattern:
- The width of the eye opening: It defines the time interval over which the received wave can be sampled, without an error due to ISI.
- The middle of the eye lid with maximum eye opening: It is the best sampling instant.
- The rate of closure of the eye: It defines the sensitivity of the system to the timing error.
- The eye is completely close: It signifies severe effect of ISI and it is impossible to overcome the combined effect of ISI and noise.
- Squinted (asymmetric) eye: It signifies non-linear transmission distortion.