SGM9346 Datasheet, PDF (10/14 Pages) SG Micro Corp – 6-Channel, 6th-Order Video Filter Driver

SGM9346
APPLICATION INFORMATION
Functional Description
The SGM9346 video filter provides 6dB gain from input to
output, and the input will be slightly offset to optimize the output
driver performance. The offset is held to the minimum required
value to decrease the standing DC current into the load.
The SGM9346 provides an internal clamp to support
AC-coupled input signals. If the input signal does not go below
ground, the input clamp will not operate. This allows DAC
outputs to directly drive the SGM9346 without an AC coupling
capacitor. The worst-case sync tip compression due to the
clamp will not exceed 7mV. The input level set by the clamp
combined with the internal DC offset will keep the output within
its acceptable range. When the input is AC-coupled, the clamp
will set the sync tip (or lowest voltage) just below ground.
I/O Configuration
The Figure1 and Figure 2 can be used with AC-coupled outputs
if desired.
DVD or
STB
SoC
DAC
Output
0V - 1.4V
LCVF
Clamp
Inactive
75Ω 220μF
Figure 1. DC-coupled Inputs, AC-coupled Outputs
6-Channel, 6th-Order
Video Filter Driver for SD/HD
DVD or
STB
SoC
DAC
Output
0V - 1.4V
0.1μF
LCVF
Clamp
Active
75Ω ^220μF
Figure 2. AC-coupled Inputs, AC-coupled Outputs
NOTE: The video tilt or line time distortion will be dominated by
the AC coupling capacitor. The value may need to be increased
beyond 220μF in order to obtain satisfactory operation in some
applications.
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 SGM9346.
Place these two capacitors as close to the SGM9346 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
SGM9346 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 SGM9346 as short as
possible to minimize the parasitic stray capacitance and noise
pickup.
SG Micro Corp
10
www.sg-micro.com