DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Figure 34.7
BNC connector
Figure 34.8
RCA phono connector
Analog electrical interface
Analog video is usually conveyed in the studio as
a voltage on an unbalanced coaxial cable into a pureresistive
impedance of 75 Ω. At equipment output,
video is DC-coupled. Reference blanking level (zero in
the equations used in Chapters 41 through 44) corresponds
to a level of 0 VDC. Reference black is also at
0 VDC, except in 480i systems with 7.5% setup, where
it is at 3 ⁄ 56 V, or about 54 mV. Reference white (unity in
the equations in Part 4) corresponds to 700 mV, except
for “NTSC-related” signals having 10:4 picture-to-sync
ratio, where white is 5 ⁄7 V, or about 714 mV.
Analog video is ordinarily AC-coupled at equipment
input; DC level is blocked by capacitive coupling.
A clamp or DC restoration circuit is used to establish
blanking level within the equipment. Clamping or DC
restoration is accomplished by introducing an offset
which forces the back-porch level of each component
to zero (or some other fixed level). Once the signal
containing sync is DC-restored, accurate sync can be
obtained, and this fine sync can be used to improve the
accuracy of DC restoration.
Analog mechanical interface
It is standard for studio analog video to use a BNC
connector, depicted in Figure 34.7, that conforms to
IEC 169-8. That standard defines a 50 Ω connector, but
video systems use an impedance of 75 Ω, and video
standards encourage the use of connectors whose
impedance is 75 Ω. A set of three connectors is used for
R’G’B’ interface. In video, sync is usually inserted on the
green component (sync on green, “RGSB”), or on the
luma component. In computing, separate sync is
common (“RGBS”).
Industrial and consumer equipment interfaces
composite video at baseband, directly as a voltage from
DC to about 5 MHz, using an RCA phono connector,
called Cinch in Europe, depicted in Figure 34.8. An
accompanying audio signal uses a separate phono
connector; accompanying stereo audio uses a separate
pair of phono connectors.
408 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES