Ensemble Designs BrightEye 46 3G/HD/SD/ASI Electrical to Optical Converter - Manual (Page 13)

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3G/HD/SD/ASI Electrical to Optical Converter User Guide TM
BrightEye 46
lines are transmitted in the first field, the even-numbered lines are in the second field. In this way, the
repetition rate is 50 or 60 Hz, without using more bandwidth. This trick has worked well for years, bit
it introduces other temporal artifacts. Motion pictures use a slightly different technique to raise the
repetition rate from the original 24 frames that make up each second of film—they just project each
one twice.
IRE
Video level is measured on the IRE scale, where 0 IRE is black, and 100 IRE is full white. The actual
voltages that these levels correspond to can vary between formats.
ITU-R 601
This is the principal standard for standard definition component digital video. It defines the luminance
and color difference coding system that is also referred to as 4:2:2. The standard applies to both PAL
and NTSC derived signals. They both will result in an image that contains 720 pixels horizontally, with
486 vertical pixels in NTSC, and 576 vertically in PAL. Both systems use a sample clock rate of 27 Mhz,
and are serialized at 270 Mb/s.
Jitter
Serial digital signals (either video or audio) are subject to the effects of jitter. This refers to the
instantaneous error that can occur from one bit to the next in the exact position each digital transition.
Although the signal may be at the correct frequency on average, in the interim it varies. Some bits
come slightly early, other come slightly late. The measurement of this jitter is given either as the
amount of time uncertainty or as the fraction of a bit width. For 270 Mb/s video, the allowable jitter is
740 picoseconds, or 0.2 UI (Unit Interval – one bit width).
Luminance
The “black & white” content of the image. Human vision had more acuity in luminance, so television
systems generally devote more bandwidth to the luminance content. In component systems, the
luminance is referred to as Y.
Multi-mode
Multi-mode fibers have a larger diameter core (either 50 or 62.5 microns), and a correspondingly larger
aperture. It is much easier to couple light energy into a multimode fiber, but internal reflections will
cause multiple “modes” of the signal to propagate down the fiber. This will degrade the ability of the
fiber to be used over long distances.
See also Single mode.
NTSC
The color television encoding system used in North America was originally defined by the National
Television Standards Committee. This American standard has also been adopted by Canada, Mexico,
Japan, Korea, and Taiwan. (This standard is referred to disparagingly as Never Twice Same Color.)