Applications Information
Functional Description
Typical Application Diagram
The following schematic in Figure 2 is normally used for AC
coupled output and DC-coupled input with DAC which has an
output voltage range of 0V to 1.4V. AC coupled output offer
slightly lower power dissipation and high ESD protection ability.
The schematics in Figure 1 is are also popular in design.
SGM9116 operates from a single +2.5V to +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 you save PCB size and production cost, it
also improves video signal performance comparing with
traditional design using discrete components. SGM9116
features a DC-coupled input buffer, 3-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 SGM9116 also can be DC-coupled or
AC-coupled.
Figure 3 is a kind of special application in STB.
+5V
0.1µF
or 0.01µF
10µF
4
+VS
OUT1
SGM9116
1
8
IN1
R/Pr
G/Y
R/Pr
G/Y
75Ω
75Ω
75Ω
75Ω
2
3
7
6
IN2
OUT2
75Ω
75Ω
IN3
OUT3
B/Pb
B/Pb
Input Considerations
GND
5
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, then
SGM9116 can be directly connected to the output of a
single-supply, current-output DAC without any external bias
network. Some time, if DAC’s output level exceeds the range of
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 in such application.
Figure 1. DC Coupling Application Schematic
+5V
0.1µF
or 0.01µF
10µF
4
+VS
OUT1
SGM9116
1
8
IN1
R/Pr
G/Y
R/Pr
G/Y
75Ω
220µF
75Ω
75Ω
75Ω
Output Considerations
2
3
7
6
IN2
OUT2
75Ω
75Ω
220µF
220µF
The SGM9116 outputs can be DC-coupled or AC-coupled.
While 0V is input, the SGM9116 output voltage is 260mV
typically. In DC coupling design, one 75Ω resistor is used to
Connect SGM9116’s output pin with external load directly, 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
IN3
OUT3
B/Pb
B/Pb
GND
5
Figure 2. Input DC Coupling and Output AC
Coupling Application Schematic
AC-coupled with external load, in AC coupling, 220µF at least
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 VCC pin of
SGM9116, please place these two capacitors as close to the
SGM9116 output 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
pin 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 cable connecting external load. In
design, please 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.
６
SGM9116
SGMICRO [ Shengbang Microelectronics Co, Ltd ]
