SGM9111_15 Datasheet, PDF (6/11 Pages) SG Micro Corp – Video Driver with 6dB Gain

SGM9111
APPLICATION INFORMATION
Functional Description
SGM9111 operates from a single 3.0V to 5.5V supply. In
application, SGM9111 is a fully integrated solution for
filtering and buffering SDTV signals in front of video
decoder or behind video encoder. For example,
SGM9111 can replace a passive LC filter and an
amplifier driver at CVBS 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. SGM9111 features a DC-coupled
input buffer, a 5-pole 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 SGM9111 also can be
DC-coupled or AC-coupled.
Input Considerations
Besides AC coupling, the SGM9111 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 SGM9111 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
SGM9111 is driven by an unknown external source or a
SCART switch which has its own clamping circuit, AC
coupling is needed.
8MHz Rail-to-Rail Composite
Video Driver with 6dB Gain
Output Considerations
The SGM9111 outputs can be DC-coupled or
AC-coupled. When input is 0V, the SGM9111 output
voltage is 340mV typically. In DC coupling design, one
75Ω resistor is used to connect SGM9111’s output pin
with external load directly, and this serial back-
termination resistor is used to match the impedance of
the transmission line between SGM9111 and external
load to cancel the signal reflection. The SGM9111
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_CC pin
of SGM9111. Place these two capacitors as close to the
SGM9111 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 SGM9111 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 SGM9111 as short as
possible to minimize the parasitic stray capacitance and
noise pickup.
SG Micro Corp
6
www.sg-micro.com