ADA4410-6 Analog Devices, ADA4410-6 Datasheet - Page 12

• Manufacturer Part Number: ADA4410-6
• Manufacturer: Analog Devices

ADA4410-6
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 underregulated. In applications where
power consumption is critical, the part can be powered down to
draw less than 10 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, although, 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.
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For single-supply applications (V
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 (V
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
perform-ance comparison of the different source resistances
feeding the SD inputs.
S−
< GND), no level shifting is required. In dual-supply
S−
= GND), the input voltage