AD8061ART Просмотр технического описания (PDF) - Analog Devices

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AD8061ART

Low-Cost, 300 MHz Rail-to-Rail Amplifiers

Analog Devices 

AD8061/AD8062/AD8063

1

INPUT

2

OUTPUT

500mV

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.

RED

DAC

GREEN

DAC

BLUE

DAC

75⍀

75⍀

75⍀

75⍀

MONITOR

#1

75⍀

75⍀

1k⍀

3V

7

1k⍀ 2

0.1␮F

AD8061 6

3

4

1k⍀

3V

10␮F

75⍀

0.1␮F

8

1k⍀ 2

3 AD8062

10␮F

1

75⍀

5

1k⍀

6

7

AD8062

4

1k⍀

75⍀

RED

75⍀

MONITOR

#2

GREEN

75⍀

BLUE

75⍀

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.

+4V

0.1␮F 10␮F

1V P-P

3MHz

TIME

BASE

OUT

49.9⍀ AD8063 1

0.1␮F 10␮F

1k⍀

–4V

1k⍀

+4V

49.9⍀

VOUT

49.9⍀

0.1␮F 10␮F

2V P-P

1MHz

49.9⍀ AD8063 1

TIME

BASE

IN

0.1␮F 10␮F

–4V

1k⍀

1k⍀

SELECT

HCO4

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

REV. C

–15–

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