SGM9116_15 Datasheet, PDF (6/10 Pages) SG Micro Corp – HDTV Video Filter Driver

SGM9116
APPLICATION INFORMATION
Functional Description
SGM9116 operates from a single 3.3V to 5.5V supply. In
application, SGM9116 is a fully integrated solution for
filtering and buffering HDTV signals in front of video
decoder or behind video encoder. For example,
SGM9116 can replace three passive LC filters and three
amplifier drivers at R\G\B and Y\Pb\Pr output side in
set-top box and DVD player. This solution can help
reduce PCB size and production cost, and it also
improves video signal performance comparing with
traditional design using discrete components. SGM9116
features a DC-coupled input buffer, a 6th-order low-pass
filter to eliminate out-of-band noise of video encoder, and
a gain of 6dB in the output amplifier to drive 75Ω load.
The AC- or DC-coupled input buffer eliminates sync
crush, droop, and field tilt. The output of SGM9116 also
can be DC-coupled or AC-coupled.
Input Considerations
Besides AC coupling, the SGM9116 inputs also can be
DC-coupled. In DC coupling application, no input
coupling capacitors are needed because the amplitude of
input video signal from DAC includes ground and
extends up to 1.4V, and SGM9116 can be directly
connected to the output of a single-supply, current-output
DAC without any external bias network. In applications
where DAC’s output level exceeds the range from 0V to
1.4V, or SGM9116 is driven by an unknown external
source or a SCART switch which has its own clamping
circuit, AC coupling is needed.
Triple, 35MHz, 6th-Order
HDTV Video Filter Driver
Output Considerations
The SGM9116 outputs can be DC-coupled or
AC-coupled. When input is 0V, the SGM9116 output
voltage is 494mV typically. In DC coupling design, one
75Ω resistor is used to connect SGM9116’s output pin
with external load directly, and this serial back-termination
resistor is used to match the impedance of the
transmission line between SGM9116 and external load to
cancel the signal reflection. The SGM9116 outputs can
sink and source current allowing the device to be
AC-coupled with external load. In AC coupling, at least
220µF capacitor will be used in order to eliminate field tilt.
Power-Supply Bypassing and Layout
Correct power supply bypassing is very important for
optimizing video performance in design. One 0.1µF and
one 10µF capacitors are always used to bypass +V_S pin
of SGM9116. Place these two capacitors as close to the
SGM9116 supply pin as possible. A large ground plane is
also needed to ensure optimum performance. The input
and output termination resistors should be placed as
close to the related pins of SGM9116 as possible to avoid
performance degradation. The PCB traces at the output
side should have 75Ω characteristic impedance in order
to match the 75Ω characteristic impedance of the cable
connecting external load. In design, keep the board trace
at the inputs and outputs of the SGM9116 as short as
possible to minimize the parasitic stray capacitance and
noise pickup.
SG Micro Corp
6
www.sg-micro.com