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BrightEye 72 - Page 32
3G/HD/SD SDI to HDMI Converter User Guide
TM
BrightEye 72
HDMI
The High Definition Multimedia Interface comes to us from the consumer marketplace where it is
becoming the de facto standard for the digital interconnect of display devices to audio and video
sources. It is an uncompressed, all-digital interface that transmits digital video and eight channels of
digital audio. HDMI is a bit-serial interface that carries the video content in digital component form
over multiple twisted-pairs. HDMI is closely related to the DVI interface for desktop computers and
their displays.
IEC
The International Electrotechnical Commission provides a wide range of worldwide standards. They
have provided standardization of the AC power connection to products by means of an IEC line cord.
The connection point uses three flat contact blades in a triangular arrangement, set in a rectangular
connector. The IEC specification does not dictate line voltage or frequency. Therefore, the user must
take care to verify that a device either has a universal input (capable of 90 to 230 volts, either 50 or 60
Hz), or that a line voltage switch, if present, is set correctly.
Interlace
Human vision can be fooled to see motion by presenting a series of images, each with a small change
relative to the previous image. In order to eliminate the flicker, our eyes need to see more than 30
images per second. This is accomplished in television systems by dividing the lines that make up
each video frame (which run at 25 or 30 frames per second) into two fields. All of the odd-numbered
lines are transmitted in the first field, the even-numbered lines 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, but
it introduces other temporal artifacts. Motion pictures use a slightly different technique to raise the
repetition rate from the original 24 frames that occur each second—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 of 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).
