AD8061ART datasheet(15/16 Pages) AD

15 / 16 page

AD8061/AD8062/AD8063

–15–

REV. C

500mV

INPUT

OUTPUT

10 s

Figure 12. Input and Output Waveforms for a Single

Supply Video Sync Stripper Using an AD8061

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.

10 F

0.1 F

MONITOR

GREEN

DAC

RED

GREEN

BLUE

RED

DAC

BLUE

DAC

AD8061

10 F

0.1 F

AD8062

Figure 13. RGB Cable Driver Using AD8061 and AD8062

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 13 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 14 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.

49.9

+4V

–4V

49.9

TIME

BASE

OUT

TIME

BASE

1V P-P

3MHz

2V P-P

1MHz

VOUT

49.9

SELECT

HCO4

10 F

0.1 F

10 F

0.1 F

AD8063

49.9

+4V

–4V

10 F

0.1 F

10 F

0.1 F

AD8063

Figure 14. Two-to-One Multiplexer Using Two AD8063s

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