DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

FRONT
PORCH
0 H
SYNCTIP BACK PORCH
Figure 34.5 Sync features
BREEZEWAY
BURST
SETUP (optional in 480i,
absent in 576i)
Genlock
Different pieces of video processing and recording
equipment have their sync structures (and so, their
video timing) brought into synchronism by having their
sync generators locked – genlock. This requires that
each piece of equipment contain a voltage-controlled
crystal oscillator (VCXO), a kind of phase-locked loop
(PLL). The frequency swing of a VCXO is typically about
100 parts per million, or perhaps 1.5 kHz at
14.318 MHz. This is ten times better than the tolerance
of typical PC video, and several times better than the
tolerance of typical workstation video. Studio equipment
cannot usually genlock to a PC or workstation.
Studio video equipment SDI inputs are typically
equipped with digital delays, of a line time or so, to
accommodate timing differences between inputs.
Analog horizontal blanking interval
Features of the analog horizontal blanking interval are
shown in Figure 34.5 above, using as an example the
blackburst signal that is the ubiquitous timing reference
for both analog and digital equipment in the
studio. Blackburst is used not only in analog systems,
but also in digital video. This example indicates, with
a dashed line, the 7.5% setup that is optional in 480i
systems; setup is not required for use of this signal as
a timing reference. I show with a dashed line the sync
pulse of the next line, following its 0H .
CHAPTER 34 ANALOG SDTV SYNC, GENLOCK, AND INTERFACE 405