Ensemble Designs BrightEye 5 Analog Composite TBC and Frame Sync - Manual (Page 25)

www.ensembledesigns.com BrightEye 5 - Page 25
5 Analog Composite TBC and Frame Sync User Guide
Oversampling
A technique to perform digital sampling at a multiple of the required sample rate. This has the
advantage of raising the Nyquist Rate (the maximum frequency which can be reproduced by a given
sample rate) much higher than the desired passband. This allows more easily realized anti-aliasing
filters.
PAL
During the early days of color television in North America, European broadcasters developed a
competing system called Phase Alternation by Line. This slightly more complex system is better able
to withstand the differential gain and phase errors that appear in amplifiers and transmission systems.
Engineers at the BBC claim that it stands for Perfection At Last.
Pathological Test Pattern – see Checkfield
Progressive
An image scanning technique which progresses through all of the lines in a frame in a single pass.
Computer monitors all use progressive displays. This contrasts to the interlace technique common to
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 sinewave. 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 ever
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.