AD8061-EB Analog Devices, AD8061-EB Datasheet - Page 15

• Manufacturer Part Number: AD8061-EB
• Description: Low-Cost/ 300 MHz Rail-to-Rail Amplifiers
• Manufacturer: Analog Devices

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. The circuit can be modified to
provide the sync stripping function for such a waveform. Instead
of connecting RG to ground, it should be connected 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 that
the black level will be amplified by two to the output. However,
the gain through RG is –unity to the output. It will take 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.
REV. A
GREEN
Figure 51. RGB Cable Driver Using AD8061 and AD8062
BLUE
RED
DAC
DAC
DAC
Figure 50. Input and Output Waveforms for a Single
Supply Video Sync Stripper Using an AD8061
1
2
75
75
75
500mV
1k
1k
1k
2
3
3
5
2
6
AD8061
+3V
8
+3V
7
4
1k
AD8062
AD8062
0.1 F
0.1 F
1k
1k
75
75
6
75
MONITOR
4
10 s
10 F
1
10 F
7
#1
75
75
75
INPUT
OUTPUT
MONITOR
RED
GREEN
BLUE
75
#2
75
75
–15–
RGB Amplifier
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 thus 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 with from the same
DAC outputs.
However, high speed, rail-to-rail output amplifiers like the AD8061
and AD8062 can accept ground level input signals and output
ground level signals, and thus be used as RGB signal amplifiers.
A combination of the AD8061 (single) and AD8062 (dual) can
amplify the three video channels of an RGB system. Figure 51
shows a circuit that performs this function.
Multiplexer
The AD8063 has a disable pin that can be used to power-down
the amplifier to save power, or can be used to create a mux circuit.
If two (or more) AD8063 outputs are connected together and
only one is enabled, then only the signal of the enabled amplifier
will appear at the output. This configuration can be used to select
from various input-signal sources. Additionally, the same input
signal can be applied to different gain stages or differently
tuned filters to make a gain-step amplifier or a selectable-
frequency amplifier.
Figure 52 shows a schematic of two AD8063s used to create a
mux that selects between two inputs. One of these is a 1 V p-p,
3 MHz sine wave and the other is a 2 V p-p, 1 MHz sine wave.
1V
2V
Figure 52. Two-to-One Multiplexer Using Two AD8063s
3MHz
1MHz
P-P
P-P
BASE
SELECT
TIME
OUT
BASE
TIME
IN
1k
1k
49.9
49.9
AD8061/AD8062/AD8063
AD8063
AD8063
+4V
–4V
+4V
–4V
0.1 F
0.1 F
0.1 F
0.1 F
HCO4
1
1
1k
1k
10 F
10 F
10 F
10 F
49.9
49.9
V
OUT