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SGM9147 Datasheet(PDF) 6 Page - SG Micro Corp

Part No. SGM9147
Description  13MHz Rail-to-Rail Composite Video Driver
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Maker  SGMICRO [SG Micro Corp]
Homepage  http://www.sg-micro.com
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SGM9147 Datasheet(HTML) 6 Page - SG Micro Corp

   
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13MHz Rail-to-Rail Composite
SGM9147
Video Driver with 6dB Gain
SG Micro Corp
www.sg-micro.com
TYPICAL APPLICATION CIRCUIT
SGM9147
CVBS
75Ω
IN
GND
OUT
VCC
75Ω
0.1µF
or 0.01µF
10µF
+5V
CVBS
0.1µF
220µF
NOTE:
1. Power supply VCC must be sequenced on first before input video signals.
Figure 1. AC Coupling Application Schematic
APPLICATION INFORMATION
Output Considerations
 
Functional Description
SGM9147 operates from a single 3.0V to 5.5V supply.
In application, SGM9147 is a fully integrated solution
for filtering and buffering SDTV signals in front of video
decoder or behind video encoder. For example,
SGM9147 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. SGM9147 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 SGM9147 also can be
DC-coupled or AC-coupled.
The SGM9147 outputs can be DC-coupled or
AC-coupled. When input is 0V, the SGM9147 output
voltage is 290mV typically. In DC coupling design, one
75Ω resistor is used to connect SGM9147’s output pin
with external load directly, and this serial back-
termination resistor is used to match the impedance of
the transmission line between SGM9147 and external
load to cancel the signal reflection. The SGM9147
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 VCC pin
of SGM9147. Place these two capacitors as close to
the SGM9147 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 SGM9147 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 SGM9147 as short as possible to minimize the
parasitic stray capacitance and noise pickup.
Input Considerations
Besides AC coupling, the SGM9147 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 SGM9147 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 SGM9147 is driven by an
unknown external source or a SCART switch which has
its own clamping circuit, AC coupling is needed.
6


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