AD8061/AD8062/AD8063

Rev. D | Page 17 of 20

APPLICATIONS

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.

75

Ω

VIDEO OUT

75

Ω

1k

Ω

75

Ω

1k

Ω

10

μF

3V

AD8061

0.1

μF

3

2

4

6

7

VIDEO IN

PIN NUMBERS ARE

FOR 8-LEAD PACKAGE

Figure 53. Single 3 V Sync Stripper Using AD8061

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.

500mV

INPUT

OUTPUT

1

2

10

μs

Figure 54. 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

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

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.

75

Ω

10

μF

0.1

μF

3V

3

2

4

6

7

75

Ω

MONITOR

#1

75

Ω

75

Ω

75

Ω

1k

Ω

1k

Ω

1k

Ω

1k

Ω

3V

1k

Ω

3

2

5

6

7

8

1

4

MONITOR

#2

GREEN

DAC

RED

GREEN

BLUE

RED

DAC

BLUE

DAC

75

Ω

75

Ω

75

Ω

75

Ω

AD8061

75

Ω

10

μF

0.1

μF

1k

Ω

AD8062

75

Ω

AD8062

75

Ω

Figure 55. 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 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.

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.