# 3.3 Eye Diagrams

## Generation of eye diagrams

#### The eye diagram is a convenient visual method of diagnosing problems with data systems. An eye diagram is generated conventionally using an oscilloscope connected to the demodulated, filtered symbol stream, prior to conversion of the symbols to binary digits. The oscilloscope is re-triggered at every symbol period or fixed multiple of symbol periods using a symbol timing signal derived from the received waveform. By relying on the persistence of a typical oscilloscope display, the result is an overlaying of consecutive received symbol samples which form an ‘eye’ pattern on the screen. (This effect is re-created using modern digital storage scopes or computer displays in test equipment.) |

#### The eye diagram is used throughout the remainder of this book to illustrate the effect of differing channel responses and source of degradation on the data receiver performance.

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