www.ensembledesigns.com
BrightEye 72 - Page 34
3G/HD/SD SDI to HDMI Converter User Guide
TM
BrightEye 72
television systems.
Return Loss
An idealized input or output circuit will exactly match its desired impedance (generally 75 ohms) as a
purely resistive element, with no reactive (capacitive or inductive) elements. In the real world we can
only approach the ideal. So our real inputs and outputs will have some capacitance and inductance.
This will create impedance matching errors, especially at higher frequencies. The Return Loss of
an input or output measures how much energy is returned (reflected back due to the impedance
mismatch). For digital circuits, a return loss of 15 dB is typical. This means that the energy returned is
15 dB less than the original signal. In analog circuits, a 40 dB figure is expected.
RGB
RGB systems carry the totality of the picture information as independent Red, Green, and Blue signals.
Television is an additive color system, where all three components add to produce white. Because the
luminance (or detail) information is carried partially in each of the RGB channels, all three must be
carried at full bandwidth in order to faithfully reproduce an image.
ScH Phase
Used in composite systems, ScH Phase measures the relative phase between the leading edge of sync
on line 1 of field 1 and a continuous subcarrier sine wave. Due to the arithmetic details of both PAL
and NTSC, this relationship is not the same at the beginning of each frame. In PAL, the pattern repeats
every 4 frames (8 fields), which is also known as the Bruch Blanking sequence. In NTSC, the repeat is
every 2 frames (4 fields). This creates enormous headaches in editing systems and the system timing of
analog composite facilities.
SDI
Serial Digital Interface. This term refers to inputs and outputs of devices that support serial digital
component video. This could refer to standard definition at 270 Mb/s, HD SDI or High Definition Serial
Digital video at 1.485 Gb/s, or to the newer 3G standard of High Definition video at 2.97 Gb/s.
SMPTE
The Society of Motion Picture and Television Engineers is a professional organization which has done
tremendous work in setting standards for both the film and television industries. The term “SMPTE’” is
also shorthand for one particular component video format—luminance and color difference.
Single mode
A Single mode (or monomode) optical fiber carries an optical signal on a very small diameter (9
micron) core surrounded with cladding. The small diameter means that no internally reflected
lightwaves will be propagated. Thus only the original “mode” of the signal passes down the fiber. A
single mode fiber used in an optical SDI system can carry a signal for up to 20 kilometers. Single mode
fibers require particular care in their installation due to the extremely small optical aperture that they
present at splice and connection points.
See also Multi-mode.
