SGM9117_15 Datasheet, PDF (6/10 Pages) SG Micro Corp – 6dB Video Driver

SGM9117
APPLICATION INFORMATION
Functional Description
SGM9117 operates from a single 2.5V to 5V supply. In
application, SGM9117 is a fully integrated solution for
buffering RGB or HDTV component signals in front of
video decoder or behind video encoder. For example,
SGM9117 can replace three amplifier drivers at R\G\B
and Y\Pb\Pr output side in set-top box, Monitor and LCD
TV. This solution can help reduce PCB size and
production cost, and it also improves video signal
performance comparing with traditional design using
discrete components. SGM9117 features a DC-coupled
input buffer, 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
SGM9117 also can be DC-coupled or AC-coupled.
Input Considerations
Besides AC coupling, the SGM9117 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 SGM9117 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
SGM9117 is driven by an unknown external source or a
SCART switch which has its own clamping circuit, AC
coupling is needed.
200MHz, Triple, 6dB Video Driver
Output Considerations
The SGM9117 outputs can be DC-coupled or
AC-coupled. When input is 0V, the SGM9117 output
voltage is 260mV typically. In DC coupling design, one
75Ω resistor is used to connect SGM9117’s output pin
with external load directly, and this serial back-termination
resistor is used to match the impedance of the
transmission line between SGM9117 and external load to
cancel the signal reflection. The SGM9117 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 cancel 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 SGM9117. Place these two capacitors as close to the
SGM9117 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 SGM9117 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 SGM9117 as short as
possible to minimize the parasitic stray capacitance and
noise pickup. Designer needs to cavern out the ground
layer under input and output trace in order to reduce stray
capacitance and avoid signal peaking.
SG Micro Corp
6
www.sg-micro.com