AD8063ARZ1 Просмотр технического описания (PDF) - Analog Devices

Номер в каталоге

Компоненты Описание

производитель

AD8063ARZ1

Low Cost, 300 MHz Rail-to-Rail Amplifiers

Analog Devices 

AD8061/AD8062/AD8063

APPLICATIONS INFORMATION

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 analog-to-digital 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.

3V

VIDEO IN

0.1µF

3

7

75Ω AD8061 6

2

4 RF

1kΩ

RG

1kΩ

10µF

75Ω

VIDEO OUT

75Ω

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. Because the sync level is

below the black level, it does not show up at the output. However,

all of the active video portion of the waveform is amplified by a

gain of 2 and then normalized to unity gain by the back-

terminated transmission line. Figure 54 is an oscilloscope plot

of the input and output waveforms.

1

INPUT

2

OUTPUT

500mV

10µs

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 a positive voltage.

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 noninverting input

to the output is 2, which means the black level is amplified by 2

to the output. However, the gain through RG is −1 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 is

stripped, and the active video is passed as in the ground-

referenced case.

RED

DAC

75Ω

GREEN

DAC

75Ω

BLUE

DAC

75Ω

75Ω

MONITOR

#1

75Ω

75Ω

1kΩ

3V

7

1kΩ 2

0.1µF

AD8061 6

3

4

1kΩ

3V

10µF

75Ω

0.1µF

8

1kΩ 2

3 AD8062

10µF

1

75Ω

RED

75Ω

MONITOR

#2

GREEN

75Ω

5

7

75Ω

1kΩ

AD8062

6

4

1kΩ

BLUE

75Ω

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.

Rev. E | Page 17 of 20

Share Link: