Datasheet

75 W
Y'/G'Out
CVBS/Sync
CVBS
+3.3V
R
DAC/Encoder
SDTV
CVBS
S-Video
Y'P' P'
R'G'B'
B R
Y'/G'
R
P’ /B'
B
R
P’ /R'
R
R
1
2
3
4
5
6
7
14
13
12
11
10
9
8
CH1OUT
CH2OUT
CH3OUT
CH4OUT
V
S+
BYPASS
NC
CH1IN
CH2IN
CH3IN
CH4IN
GND
DISABLE
NC
THS7374
ToGPIOController
orGND
75 W
75 W
P' /B'Out
B
75 W
75 W
P' /R'Out
R
75 W
75 W
75 W
+3Vto+5V
THS7374
SLOS590B –JULY 2008–REVISED JANUARY 2011 www.ti.com
TYPICAL CONFIGURATION AND VIDEO This rationale is also used for the chroma (C') term.
TERMINOLOGY Chroma is derived from the non-linear R'G'B' terms
and thus it is nonlinear. Chominance (C) is derived
A typical application circuit that uses the THS7374 as
from linear RGB, giving the difference between
a video buffer is shown in Figure 57. It shows a DAC
chroma (C') and chrominance (C). The color
or encoder driving the input channels of the
difference signals (P'
B
/P'
R
/U'/V') are also referenced
THS7374. One channel is a composite video (CVBS)
in this way to denote the nonlinear (gamma
channel of a standard definition (SD) video system.
corrected) signals.
The other channels are the component video Y'P'
B
P'
R
(sometimes labeled Y'U'V' or incorrectly labeled R'G'B' (commonly mislabeled RGB) is also called
Y'C'
B
C'
R
) signals of a 480i or 576i system. These G'B'R' (again commonly mislabeled as GBR) in
channels could easily be the s-video Y'/C' channels professional video systems. The SMPTE component
or the R'G'B' channels of a SCART system. standard stipulates that the luma information is
placed on the first channel, the blue color difference
Note that the Y' term is used for the luma channels
is placed on the second channel, and the red color
throughout this document rather than the more
difference signal is placed on the third channel. This
common luminance (Y) term. The reason for this
configuration is consistent with the Y'P'
B
P'
R
usage is to account for the definition of luminance as
nomenclature. Because the luma channel (Y') carries
stipulated by the CIE (International Commission on
the sync information and the green channel (G') also
Illumination). Video departs from true luminance
carries the sync information, it makes logical sense
because a nonlinear term, gamma, is added to the
that G' be placed first in the system. Furthermore,
true RGB signals to form R'G'B' signals. These R'G'B'
because the blue color difference channel (P'
B
) is
signals are then used to mathematically create luma
next and the red color difference channel (P'
R
) is last,
(Y'). Thus, luminance (Y) is not maintained, providing
then it also makes logical sense to place the B' signal
a difference in terminology.
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 may not always be the
case in all systems.
Figure 57. Typical SDTV CVBS/Y'P'
B
P'
R
Inputs from DC-Coupled Encoder/DAC
with DC-Coupled Line Driving
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