Datasheet

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SB0S296C − MARCH 2004 − REVISED FEBRUARY 2005
www.ti.com
10
The output voltage swing for the circuit with sag correction
(see Figure 7b) is a function of the coupling capacitor
value. The value of the sag correction capacitor has only
a minor influence. The smaller the coupling capacitor, the
greater the output swing. Therefore, to accommodate the
large signal swing with very small coupling capacitors
(22µF and 33µF), a higher supply voltage might be
needed.
DC-COUPLED OUTPUT
Due to the excellent swing to ground, the OPA358 can also
be DC- coupled to a video load. As shown in Figure 8, this
eliminates the need for AC-coupling capacitors at the
output. This is especially important in portable video
applications where board space is restricted.
The DC-coupled output configuration also shows the best
video performance. There is no line or field tilt—allowing
use of the lowest power supply. In this mode, the OPA358
will safely operate down to 2.5V with no clipping of the
signal.
The disadvantage with DC-coupled output is that it uses
somewhat higher supply current.
WIDEBAND VIDEO MULTIPLEXING
One common application for video amplifiers which
include an enable pin is to wire multiple amplifier outputs
together, then select which one of several possible video
inputs to source onto a single line. This simple Wired-OR
Video Multiplexer can be easily implemented using the
OPA358, as shown in Figure 9.
R
OUT
75
Ω
V+ = 2.7V to 3.3V
Enable
(1)
Video
DAC
NOTE: (1) Optional 200
Ω
for use with TI’s digital media processors,
and 500
Ω
for OMAP2420 and OMAP2430 processors.
75
Ω
R
2
Television
or VCR
OPA358
R
1
GND
G=1+
R
1
R
2
Figure 8. DC-Coupled Input/DC-Coupled Output
1k
Ω
OPA358
+3.3
1
µ
F 10nF
75
Ω
V
OUT
75
Ω
Signal #1
75
Ω
1k
Ω
+
1k
Ω
HCO4
OPA358
+3.3V
1
µ
F 10nF
75
Ω
Signal #2
Select
1k
Ω
+
B
ON
A
ON
Figure 9. Multiplexed Output