ADA4410-6

Rev. B | Page 14 of 16

As previously discussed, the composite video output is

developed by passively summing the Y and C outputs that have

passed through their respective output gain stages, then multiplying

this sum by a factor of two to obtain the output (see Figure 1).

The offset of this output is equal to 2× that of the other outputs.

Because of this, in many cases, it is necessary to ac-couple the

CV output or ensure that it is connected to an input that is ac-

coupled. This is generally not an issue because it is common

practice to employ ac coupling on composite video inputs.

The maximum differential voltage that can be applied across the

LEVEL1 and LEVEL2 inputs is ±500 mV. From a single-ended

standpoint, the LEVEL1 and LEVEL2 inputs have the same

range as the filter inputs. See the Specifications tables for the

limits. The LEVEL1 and LEVEL2 inputs must each be bypassed

to GND with a 0.1 μF ceramic capacitor.

In single-supply applications, a positive output offset must be

applied to keep the negative-most excursions of the output

signals above the specified minimum output swing limit.

Figure 23 and Figure 24 illustrate several ways to use the

LEVEL1 and LEVEL2 inputs. Figure 23 shows an example of

how to generate fully adjustable LEVEL1 and LEVEL2 voltages

from ±5 V and single +5 V supplies. These circuits show a

general case, but a more practical approach is to fix one voltage

and vary the other. Figure 24 illustrates an effective way to

produce a 600 mV output offset voltage in a single-supply

application. Although the LEVEL2 input could simply be

connected to GND, Figure 24 includes bypassed resistive

voltage dividers for each input so that the input levels can be

changed, if necessary. Additionally, many in-circuit testers

require that I/O signals not be tied directly to the supplies or

GND. DNP indicates do not populate.

DUAL SUPPLY

0.1µF

LEVEL1

9.53kΩ

1kΩ

9.53kΩ

+5V

–5V

0.1µF

LEVEL2

9.53kΩ

1kΩ

9.53kΩ

+5V

–5V

SINGLE SUPPLY

0.1µF

LEVEL1

1kΩ

9.09kΩ

+5V

0.1µF

LEVEL2

1kΩ

9.09kΩ

+5V

Figure 23. Generating Fully Adjustable Output Offsets

0.1

μF

LEVEL1

634

Ω

10k

Ω

+5V

DNP

LEVEL2

0

Ω

DNP

+5V

Figure 24. Flexible Circuits to Set the LEVEL1 and LEVEL2 Inputs to Obtain

a 600 mV Output Offset on a Single Supply (G = ×2)

INPUT AND OUTPUT COUPLING

Inputs to the ADA4410-6 are normally dc-coupled. Ac coupling

the inputs is not recommended; however, if ac coupling is

necessary, suitable circuitry must be provided following the ac

coupling element to provide proper dc level and bias currents at

the ADA4410-6 input stages.

The ADA4410-6 outputs can be either ac- or dc-coupled. As

discussed in the Output DC Offset Control section, the CV

output offset is different from the other outputs, and the CV

output is generally ac-coupled.

When driving single ac-coupled loads in standard 75 Ω video

distribution systems, 220 μF coupling capacitors are recommended

for use on all but the chrominance signal output. Because the

chrominance signal is a narrow-band modulated carrier, it has

no low frequency content and can therefore be coupled with a

0.1 μF capacitor.

There are two ac coupling options when driving two loads from

one output. One is to simply use the same value capacitor on

the second load, while the other is to use a common coupling

capacitor that is at least twice the value used for the single load

(see Figure 25 and Figure 26).

75Ω

75Ω

75Ω

CABLE

75Ω

CABLE

220µF

220µF

75Ω

75Ω

Figure 25. Driving Two AC-Coupled Loads with Two Coupling Capacitors

75Ω

CABLE

75Ω

CABLE

75Ω

75Ω

75Ω

75Ω

470µF

Figure 26. Driving Two AC-Coupled Loads with One Common Coupling Capacitor