NCS2566
http://onsemi.com
11
APPLICATIONS INFORMATION
The NCS2566 6−channel video filter driver has been
optimized for Standard and High Definition video
applications covering the requirements of the standards
Composite video (CVBS), S−Video, Component Video
(480i/525i, 576i/625i, 720p/1080i) and related (RGB). The
first 3−channels (SD1, SD2, SD3) are dedicated for
Standard Definition, CVBS and S−Video applications for
which the frequency bandwidth required does not exceed 8
MHz. The 3 other channels (SD/HD1, SD/HD2, SD/HD3)
have selectable filters (8 MHz and 34 MHz) for covering
either standard−definition−like video applications or High
Definition video applications. These frequencies are
selectable using the pin SD
/HD. If the application requires,
the video driver outputs may also be disabled using the
SD EN
or SD/HD EN required by the application the pins
SD EN
or SD/HD EN.
In the regular mode of operation each channel provides an
internal voltage−to−voltage gain of 2 from input to output.
This effectively reduces the number of external components
required as compared to discrete approaches implemented
with stand−alone op amps. An internal level shifter is
employed shifting up the output voltage by adding an offset
of 200 mV. This prevents sync pulse clipping and allows
DC−coupled output to the 150 W video load. In addition the
NCS2566 integrates a 6
th
−order Butterworth filter for each
channel. This allows rejection of aliases or unwanted
over−sampling effects produced by the video DAC.
Similary for DVD recorders which uses an ADC, this
anti−aliasing filter (reconstruction filter) will avoid picture
quality issues and will aide filtration of parasitic signals
caused by EMI interference.
A built−in diode−like clamp is used in the chip for each
channel to support the AC−coupled mode of operation. The
clamp is active when the input signal goes below 0 V.
The built−in clamp and level shifter allow the device to
operate in different configuration modes depending on the
DAC output signal level and the input common mode
voltage of the video driver. When the configuration is
DC−Coupled at the Inputs and Outputs the 0.1 mF and
220 mF coupling capacitors are no longer used and the
clamps are in that case inactive; this configuration provides
a low cost solution which can be implemented with few
external components.
The input is AC−coupled when either the input−signal
amplitude goes over the range 0 V to 1.4 V or if the video
source requires such a coupling. In some circumstances it
may be necessary to auto−bias signals with the addition of
a pull−up and pull−down resistors or only pull−up resistor
(Typical 7.5 MW combined with the internal 800 kW
pulldown) making the clamp inactive.
The output AC−coupling configuration is advantageous
for eliminating DC ground loop, but may have the drawback
of increasing sensitivity to video line or field tilt issues if the
output coupling capacitor is too small. DC ground loop with
the drawback of making the device more sensitive to video
line or field tilt issues in the case of a too low output coupling
capacitor. In some cases it may be necessary to increase the
nominal 220 mF capacitor value.
All the device pins are protected against electrostatic
discharge at a level of 4 kV HBM and 8 kV according to
IEC61000−4−2. This feature has been considered with a
particular attention with ESD structure able to sustain the
typical values requested by the systems like Set Top Boxes
or Blue-Ray players. This parameter is particularly
important for video driver which usually constitutes the last
stage in the video chain before the video output connector.
The IEC61000-4-2 standard has been used to test our
devices in the real application environment. Test
methodology can be provided on request.
