Editing Eye pattern (section)

=== Emphasis ===

[[Emphasis (telecommunications)|Emphasis]] applied to a signal produces an additional level for each value of the signal which is higher (for pre-emphasis) or lower (for de-emphasis) than the nominal value.

The eye pattern for a signal with emphasis may be mistaken for that of a PAM signal at first glance, however closer inspection reveals some key differences. Most notably, an emphasized signal has a limited set of legal transitions:

* Strong state to corresponding weak state (1-1 or 0-0 bit pattern)
* Strong state to opposite strong state (second transition of a 1-0-1 or 0-1-0 bit pattern)
* Weak state to opposite strong state (second transition of a 1-1-0 or 0-0-1 bit pattern)

An emphasized signal will never transition from a weak state to the corresponding strong state, a weak state to another weak state, or remain in the same strong state for more than one UI. A PAM signal also normally has equally spaced levels while emphasized levels are normally closer to the nominal signal level.

[[File:Eye pattern emphasis.png|thumb|upright=1.5|none|Eye pattern of a 1.25&nbsp;Gbps NRZ signal with 6 dB of pre-emphasis]]