AD8061/AD8062/AD8063
APPLICATIONS
The circuit can be modified to provide the sync stripping
function for such a waveform. Instead of connecting RG to
ground, connect it to a dc voltage that is two times the black
level of the input signal. The gain from the +input to the output
is two, which means the black level will be amplified by two to
the output. However, the gain through RG is –unity to the
output. It takes a dc level of twice the input black level to shift
the black level to ground at the output. When this occurs, the
sync will be stripped, and the active video will be passed as in
the ground-referenced case.
SINGLE-SUPPLY SYNC STRIPPER
When a video signal contains synchronization pulses, it is
sometimes desirable to remove them prior to performing
certain operations. In the case of A-to-D conversion, the sync
pulses consume some of the dynamic range, so removing them
increases the converter’s available dynamic range for the video
information.
Figure 53 shows a basic circuit for creating a sync stripper using
the AD8061 powered by a single supply. When the negative
supply is at ground potential, the lowest potential to which the
output can go is ground. This feature is exploited to create a
waveform whose lowest amplitude is the black level of the video
and does not include the sync level.
RED
DAC
75Ω
75Ω
75Ω
75Ω
75Ω
75Ω
MONITOR
#1
GREEN
DAC
BLUE
DAC
3V
0.1μF
10μF
75Ω
7
3
2
1kΩ
VIDEO IN
VIDEO OUT
6
75Ω
AD8061
3V
75Ω
R
1kΩ
4
F
0.1μF
10μF
7
1kΩ
2
3
R
1kΩ
G
PIN NUMBERS ARE
FOR 8-LEAD PACKAGE
75Ω
RED
75Ω
6
AD8061
4
Figure 53. Single 3 V Sync Stripper Using AD8061
1kΩ
In this case, the input video signal has its black level at ground, so
it comes out at ground at the input. Since the sync level is below
the black level, it will not show up at the output. However, all of
the active video portion of the waveform will be amplified by a
gain of two and then be normalized to unity gain by the back-
terminated transmission line. Figure 54 is an oscilloscope plot
of the input and output waveforms.
3V
8
MONITOR
#2
0.1μF
10μF
1kΩ
1kΩ
2
75Ω
75Ω
GREEN
1
AD8062
3
5
75Ω
BLUE
7
AD8062
75Ω
6
1
4
1kΩ
INPUT
Figure 55. RGB Cable Driver Using AD8061 and AD8062
RGB AMPLIFIER
2
Most RGB graphics signals are created by video DAC outputs
that drive a current through a resistor to ground. At the video
black level, the current goes to zero, and the voltage of the video
is also zero. Before the availability of high speed rail-to rail op
amps, it was essential that an amplifier have a negative supply
to amplify such a signal. Such an amplifier is necessary if one
wants to drive a second monitor from the same DAC outputs.
OUTPUT
10μs
500mV
Figure 54. Input and Output Waveforms for a Single-Supply
Video Sync Stripper Using an AD8061
However, high speed, rail-to-rail output amplifiers like the
AD8061 and AD8062 accept ground level input signals and
output ground level signals. They are used as RGB signal
amplifiers. A combination of the AD8061 (single) and the
AD8062 (dual) amplifies the three video channels of an RGB
system. Figure 55 shows a circuit that performs this function.
Some video signals with sync are derived from single-supply
devices, such as video DACs. These signals can contain sync,
but the whole waveform is positive, and the black level is not
at ground but at some positive voltage.
Rev. D | Page 17 of 20
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