THS7375 Datasheet, PDF (18/36 Pages) Texas Instruments – 4-Channel SDTV Video Amplifier with 6th-Order Filters and 5.6-V/V Gain

THS7375
SBOS449 – SEPTEMBER 2008......................................................................................................................................................................................... www.ti.com
TYPICAL CONFIGURATION AND VIDEO
TERMINOLOGY
A typical application circuit that uses the THS7375 as
a video buffer is shown in Figure 46. It shows a DAC
or encoder driving the input channels of the
THS7375. One channel is a composite video (CVBS)
channel of a standard definition (SD) video system.
The other channels are the component video Y'P'_BP'_R
(sometimes labeled Y'U'V' or incorrectly labeled
Y'C'_BC'_R) signals of a 480i or 576i system. These
channels could easily be the S-Video Y'/C' channels
or the R'G'B' channels of a SCART system.
Note that the Y' term is used for the luma channels
throughout this document rather than the more
common luminance (Y) term. The reason for this
usage is to account 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 also 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 way 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 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
configuration 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. Furthermore,
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.
+3.3 V
CVBS
R
DaVinci
DAC/Encoder
Y'/G'
SDTV
R
CVBS
S-Video
Y'P'_BP'_R
R'G'B'
P’_B/B'
R
P’_R/R'
R
THS7375
1 CH1 IN CH1 OUT 14
2 CH2 IN CH2 OUT 13
3 CH3 IN CH3 OUT 12
4 CH4 IN CH4 OUT 11
5 GND
V_S+ 10
6 DISABLE BYPASS 9
7 NC
NC 8
CVBS/Sync
75 W ^{330 mF}
Y'/G' Out
75 W ^{330 mF}
P'_B/B' Out
75 W ^{330 mF}
To GPIO Controller
or GND
+3 V to +5 V
P'_R/R' Out
75 W ^{330 mF}
75 W
75 W
75 W
75 W
Figure 46. Typical SDTV CVBS/Y'P'_BP'_R Inputs from DC-Coupled Encoder/DAC
with AC-Coupled Line Driving
18
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