Texas Instruments THS7374EVM Evaluation Module THS7374EVM THS7374EVM 데이터 시트
제품 코드
THS7374EVM
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
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
0.1 F
m
(1)
0.1 F
m
(1)
0.1 F
m
(1)
0.1 F
m
(1)
R
PU
+3.3 V
R
PU
330 F
m
(2)
+
75 W
CVBS Out 1
75 W
330 F
m
(2)
+
75 W
Y' Out 1
75 W
330 F
m
(2)
+
75 W
P' Out 1
B
75 W
330 F
m
(2)
+
75 W
P' Out 1
R
75 W
330 F
m
(2)
+
330 F
m
(2)
+
330 F
m
(2)
+
330 F
m
(2)
+
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SLOS590B – JULY 2008 – REVISED JANUARY 2011
OUTPUT MODE OF OPERATION: AC
This
configuration
helps
ensure
line-to-line
dc
COUPLED
isolation and avoids the potential problems discussed
above. Using a single 1000-
above. Using a single 1000-
m
F capacitor for two lines
A very common method of coupling the video signal
can be done, but there is a chance for ground loops
to the line is the use of a large capacitor. This
and interference to be created between the two
capacitor is typically between 220
m
F and 1000
m
F,
receivers.
although 470
m
F is very common. The value of this
capacitor must be large enough to minimize the line
Lastly, because of the edge rates and frequencies of
tilt (droop) and/or field tilt associated with ac coupling
operation, it is recommended (but not required) to
as
described
previously
in
this
document.
AC
place a 0.1-
m
F to 0.01-
m
F capacitor in parallel with
coupling is done for several reasons, but most often
the large 220-
m
F to 1000-
m
F capacitor. These
to ensure full interoperability with the receiving video
large-value
capacitors
are
generally
aluminum
system. AC coupling also ensures adherence to video
electrolytic. It is well-known that these capacitors
standard specifications. It ensures that regardless of
have significantly large equivalent series resistance
the reference dc voltage used on the transmit side,
(ESR), and the impedance at high frequencies is
the receive side re-establishes the dc reference
rather large because of the associated inductances
voltage to its own requirements.
involved with the leads and construction. The small
0.1-
0.1-
m
F
to
0.01-
m
F
capacitors
help
pass
these
As with the dc output mode of operation discussed
high-frequency (> 1-MHz) signals with much lower
previously, each line should have a 75-
Ω
source
impedance than the large capacitors.
termination resistor in series with the ac coupling
capacitor. If two lines are to be driven, it is best to
capacitor. If two lines are to be driven, it is best to
Although it is common to use the same capacitor
have each line use its own capacitor and resistor
values for all the video lines, the frequency bandwidth
rather than sharing these components, as shown in
of the chroma signal in a s-video system are not
.
required to go as low (or as high of a frequency) as
the luma channels. Thus, the capacitor values of the
chroma line(s) can be smaller, such as 0.1
the luma channels. Thus, the capacitor values of the
chroma line(s) can be smaller, such as 0.1
m
F.
(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 THS7374. To dc-couple, remove the 0.1
linear input and output voltage range of the THS7374. To dc-couple, remove the 0.1
m
F 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 62. Typical SDTV AC-Input System Driving Two AC-Coupled Video Lines
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25
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