ADA4412-3

Rev. 0 | Page 9 of 16

THEORY OF OPERATION

The ADA4412-3 is an integrated video filtering and driving

solution that offers variable bandwidth to meet the needs of a

number of different video resolutions. There are three filters

targeted for use with component video signals. The filters

have selectable bandwidths that correspond to the popular

component video standards. Each filter has a sixth-order

Butterworth response that includes group delay optimization.

The group delay variation from 1 MHz to 36 MHz in the

36 MHz section is 7 ns, which produces a fast settling pulse

response.

The ADA4412-3 is designed to operate in many video environ-

ments. The supply range is 5 V to 12 V, single supply or dual

supply, and requires a relatively low nominal quiescent current

of 15 mA per channel. In single-supply applications, the PSRR

is greater than 60 dB, providing excellent rejection in systems

with supplies that are noisy or under-regulated. In applications

where power consumption is critical, the part can be powered

down to draw typically 10 μA by pulling the DISABLE pin to

the most positive rail. The ADA4412-3 is also well-suited for

high encoding frequency applications because it maintains a

stop-band attenuation of over 40 dB to 400 MHz.

The ADA4412-3 is intended to take dc-coupled inputs

from an encoder or other ground referenced video signals.

The ADA4412-3 input is high impedance. No minimum or

maximum input termination is required, though input

terminations above 1 kΩ can degrade crosstalk performance

at high frequencies. No clamping is provided internally. For

applications where dc restoration is required, dual supplies

work best. Using a termination resistance of less than a few

hundred ohms to ground on the inputs and suitably adjusting

the level-shifting circuitry provides precise placement of the

output voltage.

range extends from 100 mV below ground to within 2.0 V of

the most positive supply. Each filter input includes level-shifting

circuitry. The level-shifting circuitry adds a dc component to

ground-referenced input signals so that they can be reproduced

accurately without the output buffers hitting the negative rail.

Because the filters have negative rail input and rail-to-rail

output, dc level shifting is generally not necessary, unless

accuracy greater than that of the saturated output of the driver

is required at the most negative edge. This varies with load but

is typically 100 mV in a dc-coupled, single-supply application. If

ac coupling is used, the saturated output level is higher because

the drivers have to sink more current on the low side. If dual

dual-supply applications, the level-shifting circuitry can be used

to take a ground referenced signal and put the blanking level at

ground while the sync level is below ground.

The output drivers on the ADA4412-3 have rail-to-rail output

capabilities with 6 dB gain. Each output is capable of driving

two ac- or dc-coupled, 75 Ω source-terminated loads. If a large

dc output level is required while driving two loads, ac coupling

should be used to limit the power dissipation.