ADA4410-6

Rev. B | Page 12 of 16

THEORY OF OPERATION

The ADA4410-6 is an integrated video filtering and driving

solution that offers variable bandwidth to meet the needs of

several different video formats. There are a total of five filter

sections, three for component video and two for Y/C and

composite video. The component video filters have switchable

bandwidths for standard definition interlaced, progressive, and

high definition systems. The Y/C channels have fixed 9 MHz,

3 dB cutoff frequencies and include a summing circuit that

feeds an additional buffer for a composite video output. Each

filter section has a sixth-order Butterworth response that

includes group delay optimization. The group delay variation

from 100 kHz to 36 MHz in the 36 MHz section is 8 ns, which

produces a fast settling pulse response.

The ADA4410-6 is designed to operate in many different video

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

dual supply, and requires a relatively low quiescent current of

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

greater than 70 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 15 μA by pulling the DISABLE pin to the most

positive rail. The ADA4410-6 is also well suited for high

encoding frequency applications because it maintains a stop-

band attenuation of 50 dB beyond 200 MHz.

The ADA4410-6 is intended to take dc-coupled inputs from an

encoder or other ground-referenced video signals. The ADA4410-6

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 shift

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 section has a 2:1 input

multiplexer that 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 supplies are used

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 ADA4410-6 have rail-to-rail output

capabilities. They provide either 6 dB or 12 dB of gain with

respect to the ground pins. Gain is controlled by the external

gain select pin. 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.

Input mux isolation is primarily a function of the source

resistance driving into the ADA4410-6. Higher resistances

result in lower isolation over frequency, while a low source

resistance, such as 75 Ω, has the best isolation performance. In

the SD channels, the isolation variation is most pronounced due

to the stray capacitance that exists between the adjacent input

pins. The HD input pins are not adjacent; therefore, this effect is

less pronounced on the HD channels. See Figure 15 for a

performance comparison of the different source resistances

feeding the SD inputs.