Datasheet

WIDEBAND VIDEO MULTIPLEXING
2kW
82.5W
75 CableW
RG-59
82.5W
75W
511W432W
Video1
+5V
+5V
-5V
1/2
OPA2695
1/2
OPA2695
2kW
75W
511W432W
Video2
-5V
+5V
V
DIS
DIS
DIS
Power-supply
decouplingnotshown.
OPA2695
SBOS354A – APRIL 2008 – REVISED AUGUST 2008 ...................................................................................................................................................... www.ti.com
transition between channels, the outputs are
(QFN-16 Package Only) combined through the output impedance matching
resistors (82.5 Ω in this case). When one channel is
One common application for video speed amplifiers
disabled, its feedback network forms part of the
that include a disable pin is to wire multiple amplifier
output impedance and slightly attenuates the signal in
outputs together, then select one of several possible
getting out onto the cable. The gain and output
video inputs to source onto a single line. This simple
matching resistors have been slightly increased to
wired-OR video multiplexer can be easily
achieve a signal gain of +1V/V at the matched load
implemented using the OPA2695IRGT, as Figure 72
and provide a 75 Ω output impedance to the cable.
shows.
The video multiplexer connection (as shown in
Figure 72 ) also ensures that the maximum differential
Typically, channel switching is performed either on
voltage across the inputs of the unselected channel
sync or retrace time in the video signal. The two
does not exceed the rated ± 1.2V maximum for
inputs are approximately equal at this time. The
standard video signal levels.
make-before-break disable characteristic of the
OPA2695 ensures that there is always one amplifier
controlling the line when using a wired-OR circuit
such as the one presented in Figure 72 . Because
both inputs may be on for a short period during the
Figure 72. Two-Channel Video Multiplexer
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