DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Trilevel sync comprises a negative portion asserted to
-300±6 mV during the 44 reference clock intervals
preceding 0 H, and a positive portion asserted to
+300±6 mV during the 44 reference clock intervals after
0 H. The risetime of each transition is 4±1.5 reference
clock intervals.
Details of horizontal timing are shown in Figure 47.1
overleaf.
Vertical sync is signaled by broad pulses, whose structure
differs between progressive and interlaced systems.
A progressive system has five broad pulses per frame,
one each on lines 1 through 5. Each broad pulse is
asserted to -300±6 mV, 132 reference clock intervals
after 0 H , and deasserted 2112 reference clock intervals
after 0 H . (Deassertion coincides with the end of active
video – that is, with the right-hand edge of the production
aperture.) The risetime of each transition is
4±1.5 reference clock intervals. Line 1 is defined by the
first broad pulse of a frame – that is, by a line with
a broad pulse preceded by a line without one. Line 6
has a second trilevel pulse whose zerocrossing is S TL /2
reference clock intervals after 0 H. This pulse is reminiscent
of an equalization pulse in analog SDTV.
In an interlaced system, several lines in the vertical
interval have a second trilevel sync pulse whose zerocrossing
is at S TL / 2 reference clock intervals after 0 H .
An interlaced system has ten broad pulses per field, in
the arrangement indicated in Table 47.2. Each broad
pulse is asserted to -300±6 mV, 132 reference clock
intervals after the zerocrossing of the immediately
preceding trilevel sync, and is deasserted 880 reference
clock intervals later. The risetime at each transition is
4±1.5 reference clock intervals. Line 1 can be decoded
as the first broad pulse in a left-hand halfline – that is,
by detecting a normal line (with no broad pulse and no
mid-line trilevel sync) followed by a broad pulse immediately
after 0 H. Each broad pulse is preceded by
a trilevel pulse whose zerocrossing is either at 0 H or
delayed S TL / 2 reference clock intervals from 0 H .
CHAPTER 47 1920 × 1080 HDTV 561