THS7319 Datasheet, PDF (17/34 Pages) Texas Instruments – 3-Channel, Very Low Power Video Amplifiers with EDTV Filters and 6-dB Gain

THS7319
www.ti.com.............................................................................................................................................................. SBOS468A – JUNE 2009 – REVISED JULY 2009
TYPICAL CONFIGURATION AND VIDEO
TERMINOLOGY
A typical application circuit using the THS7319 as a
video buffer is shown in Figure 50. It shows a DAC or
encoder dc-coupled to the input channels of the
THS7319 and the output of the THS7319 dc-coupled
to the video line. These signals can be NTSC, PAL,
or SECAM signals including composite video
baseband signal (CVBS), S-Video Y'C', component
Y'P'_BP'_R video, broadcast G'B'R' video, or computer
R'G'B' video signals.
Note that the Y’ term is used for the luma channels
throughout this document rather than the more
common luminance (Y) term. This usage accounts for
the definition of luminance as stipulated by the
International Commission on Illumination (CIE). Video
departs from true luminance because a nonlinear
term, gamma, is added to the true RGB signals to
form R’G’B’ signals. These R’G’B’ signals are then
used to mathematically create luma (Y’). Thus,
luminance (Y) is not maintained, providing a
difference in terminology.
This rationale is also used for the chroma (C’) term.
Chroma is derived from the nonlinear R’G’B’ terms
and, thus, it is nonlinear. Chominance (C) is derived
from linear RGB, giving the difference between
chroma (C’) and chrominance (C). The color
difference signals (P’_B/P’_R/U’/V’) are also referenced
in this manner to denote the nonlinear (gamma
corrected) signals.
R’G’B’ (commonly mislabeled RGB) is also called
G’B’R’ (again commonly mislabeled as GBR) in
professional video systems. The Society of Motion
Picture and Television Engineers (SMPTE)
component standard stipulates that the luma
information is placed on the first channel, the blue
color difference is placed on the second channel, and
the red color difference signal is placed on the third
channel. This practice is consistent with the Y'P'_BP'_R
nomenclature. Because the luma channel (Y') carries
the sync information and the green channel (G') also
carries the sync information, it makes logical sense
that G' be placed first in the system. Because the
blue color difference channel (P'_B) is next and the red
color difference channel (P'_R) is last, then it also
makes logical sense to place the B' signal on the
second channel and the R' signal on the third
channel, respectfully. Thus, hardware compatibility is
better achieved when using G'B'R' rather than R'G'B'.
Note that for many G'B'R' systems, sync is embedded
on all three channels, but this configuration may not
always be the case in all systems.
Channel 1
Channel 2
Channel 3
x1
R
x1
R
x1
R
Level
Shift
Level
Shift
Level
Shift
3-Pole
20-MHz
LPF
3-Pole
20-MHz
LPF
3-Pole
20-MHz
LPF
6 dB
6 dB
6 dB
75 W ^{Out 1}
75 W ^{Out 2}
75 W ^{Out 3}
75 W
75 W
75 W
+2.6 V to +5 V Enable
Figure 50. Typical THS7319 System with DC-Coupled Encoder/DAC and DC-Coupled Line Driving
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