资 源 简 介
This design note describes why the SMPTE serial digital interface (SDI) form of digital video isdifficult to transmit over fiber opTIc links, and howthe MAX3656 laser driver can be used tosuccessfully overcome this problem.Early digital fiber-opTIc transmission systems weredesigned to deliver digiTIzed audio (voice) over largetelecommunicaTIon networks. For example,Synchronous Optical Network (SONET) is anoptical transmission standard that uses scrambling tomake clock and data recovery easier. Scrambling canhelp randomize the data to make it easier for thereceiver to recover the clock without increasingoverhead data.Uncompressed digital video also uses scrambling tohelp randomize the data being transmitted. However,the problem with digital video is that it can becreated artificially by color generators, and digitalcolor generators can create video with no noise. Inparticular, two colors do not always get adequatelyrandomized by the scrambler and can result inrepeating patterns that have either a large DC offsetor a low transition density. These difficult-totransmitpatterns are called “pathological patterns.”The pathological pattern containing the large DCoffset is very troublesome for fiber optictransmitters. Overcoming problems withpathological patterns is the focus of this application note.
