Datasheet

75 W
Y'/G'Out
CVBS/Sync
CVBS
+3.3V
+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
THS7375
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
0.1 Fm
(1)
0.1 Fm
(1)
0.1 Fm
(1)
0.1 Fm
(1)
R
PU
+3.3V
R
PU
330 Fm
(2)
+
75 W
CVBSOut1
75 W
330 Fm
(2)
+
75 W
Y'Out1
75 W
330 Fm
(2)
+
75 W
P' Out1
B
75 W
330 Fm
(2)
+
75 W
P' Out1
R
75 W
330 Fm
(2)
+
330 Fm
(2)
+
330 Fm
(2)
+
330 Fm
(2)
+
THS7375
www.ti.com SBOS449A –SEPTEMBER 2008–REVISED JANUARY 2011
OUTPUT MODE OF OPERATION: This configuration helps ensure line-to-line dc
AC-COUPLED isolation and avoids the potential problems discussed
above. Using a single 1000-mF capacitor for two lines
A very common method of coupling the video signal
can be done, but there is a chance for interference to
to the line is the use of a large capacitor. This
be created between the two receivers.
capacitor is typically between 220 mF and 1000 mF,
although 470 mF is very common. The value of this Lastly, because of the edge rates and frequencies of
capacitor must be large enough to minimize the line operation, it is recommended (but not required) to
tilt (droop) and/or field tilt associated with ac coupling place a 0.1-mF to 0.01-mF capacitor in parallel with
as described previously in this document. AC the large 220-mF to 1000-mF capacitor. These
coupling is done for several reasons, but most often large-value capacitors are generally aluminum
to ensure full interoperability with the receiving video electrolytic. It is well-known that these capacitors
system. AC coupling also ensures adherence to video have significantly large equivalent series resistance
standard specifications. It ensures that regardless of (ESR), and the impedance at high frequencies is
the reference dc voltage used on the transmit side, rather large because of the associated inductances
the receive side re-establishes the dc reference involved with the leads and construction. The small
voltage to its own requirements. 0.1-mF to 0.01-mF capacitors help pass these
high-frequency (> 1-MHz) signals with much lower
As with the dc output mode of operation discussed
impedance than the large capacitors.
previously, each line should have a 75-Ω source
termination resistor in series with the ac coupling Although it is common to use the same capacitor
capacitor. If two lines are to be driven, it is best to values for all the video lines, the frequency bandwidth
have each line use its own capacitor and resistor of the chroma signal in a S-Video system are not
rather than sharing these components, as shown in required to go as low (or as high of a frequency) as
Figure 53. the luma channels. Thus, the capacitor values of the
chroma line(s) can be smaller, such as 0.1 mF.
(1) An ac-coupled input is shown in this example. DC coupling is also allowed as long as the DAC output voltage is within the allowable
linear input and output voltage range of the THS7375. To dc-couple, remove the 0.1-mF input capacitors and R
PU
.
(2) An ac-coupled output is shown in this example. DC coupling is also allowed by simply removing these capacitors.
Figure 53. Typical SDTV AC-Input System Driving Two AC-Coupled Video Lines
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