Ensemble Designs 9400 3G Test Signal and Sync Pulse Generator - Manual (Page 81)

www.ensembledesigns.com Avenue 7400 and 9400 - Page 81
Model 7400 HD/SD and Model 9400 3G/HD/SD Sync Pulse Generator and Test Signal Generator
Tri-Level Sync
For many, many years, television systems used composite black as a genlock reference source. This
was a natural evolution from analog systems to digital implementations. With the advent of High
Definition television, with even higher data rates and tighter jitter requirements, problems with this
legacy genlock signal surfaced. Further, a reference signal with a 50 or 60 Hz frame rate was useless
with 24 Hz HD systems running at film rates. Today we can think of composite black as a bi-level sync
signal – it has two levels, one at sync tip and one at blanking. For HD systems, Tri-Level Sync, which has
the same blanking level (at ground) of bi-level sync, but the sync pulse now has both a negative and
a positive element. This keeps the signal symmetrically balanced so that its DC content is zero. And it
also means that the timing pickoff point is now at the point where the signal crosses blanking and is
no longer subject to variation with amplitude. This makes Tri-Level Sync a much more robust signal
and one which can be delivered with less jitter.
USB
The Universal Serial Bus, developed in the computer industry to replace the previously ubiquitous
RS-232 serial interface, now appears in many different forms and with many different uses. It actually
forms a small local area network, allowing multiple devices to coexist on a single bus where they can
be individually addressed and accessed.
VGA
Video Graphics Array. Traditional 15-pin, analog interface between a PC and monitor.
Word Clock
Use of Word Clock to genlock digital audio devices developed in the audio recording industry. Early
digital audio products were interconnected with a massive parallel connector carrying a twisted pair
for every bit in the digital audio word. A clock signal, which is a square wave at the audio sampling
frequency, is carried on a 75 ohm coaxial cable. Early systems would daisychain this 44.1 or 48 kilohertz
clock from one device to another with coax cable and Tee connectors. On the rising edge of this Work
Clock these twisted pairs would carry the left channel, while on the falling edge, they would carry the
right channel. In most television systems using digital audio, the audio sample clock frequency (and
hence the ‘genlock’ between the audio and video worlds) is derived from the video genlock signal. But
products that are purely audio, with no video reference capability, may still require Word Clock.
WSS
Wide Screen Signaling is used in the PAL/625 video standards, both in analog and digital form, to
convey information about the aspect ratio and format of the transmitted signal. Carried in the vertical
interval, much like closed captioning, it can be used to signal a television receiver to adjust its vertical
or horizontal sizing to reflect incoming material. Although an NTSC specification for WSS exists, it
never achieved any traction in the marketplace.
YUV
Strictly speaking, YUV does not apply to component video. The letters refer to the Luminance (Y), and
the U and V encoding axes using in the PAL composite system. Since the U axis is very close to the B-Y
axis, and the V axis is very close to the R-Y axis, YUV is often used as a sort of shorthand for the more
long-winded “Y/R-Y/B-Y”.