FMS6364A Fairchild Semiconductor, FMS6364A Datasheet - Page 8

• Manufacturer Part Number: FMS6364A
• Description: Low-cost Four-channel Standard Definition Sd & High Hd Definition Video Filter Driver
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FMS6364A • Rev. 3.0.1
Application Information
Application Circuits
The FMS6364A Low-Cost Video Filter (LCVF) provides
6dB gain from input to output. In addition, the input is
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. Typical
voltage levels are shown in the diagram below:
The FMS6364A provides an internal diode clamp to
support AC-coupled input signals. If the input signal
does not go below ground, the input clamp does not
operate. This allows DAC outputs to directly drive the
FMS6364A without an AC-coupling capacitor. When the
input is AC-coupled, the diode clamp sets the sync tip
(or lowest voltage) just below ground. The worst-case
sync tip compression due to the clamp cannot exceed
7mV. The input level set by the clamp, combined with
the internal DC offset, keeps the output within its
acceptable range.
For symmetric signals like Chroma, U, V, Pb, and Pr;
the average DC bias is fairly constant and the inputs
can be AC coupled. DAC outputs can also drive these
same signals without the AC-coupling capacitor. A
conceptual illustration of the input clamp circuit is shown
in Figure 13:
1.0 -> 1.02V
0.65 -> 0.67V
0.3 -> 0.32V
0.0 -> 0.02V
2.28V
1.58V
0.88V
0.28V
There is a 280mV offset from the DC input level to the
DC output level. V
0.85V
0.5V
0.15V
1.98V
1.28V
0.58V
Figure 12. Typical Voltage Levels
V
V
V
OUT
OUT
OUT
IN
= 2 * V
V
IN
IN
+ 280mV.
Driven by:
DC-Coupled DAC Outputs
AC-Coupled and Clamped
Y, CV, R, G, B
Driven by:
AC-Coupled and Biased
U, V, Pb, Pr, C

8
I/O Configurations
For a DC-coupled DAC drive with DC-coupled outputs,
use the configuration in Figure 14.
Alternatively, if the DAC’s average DC output level
causes the signal to exceed the range of 0V to 1.4V, it
can be AC coupled as shown in Figure 15.
When the FMS6364A is driven by an unknown external
source or a SCART switch with its own clamping
circuitry, the inputs should be AC coupled as shown in
Figure 16.
External video
source must
be AC coupled
0.65 V
Figure 15. AC-Coupled Inputs, DC-Coupled Outputs
Y IN
DVD or
DVD or
Output
Output
DAC
STB
SoC
DAC
STB
SoC
Figure 16.
Figure 14.
Figure 13.
Driver
0V - 1.4V
SCART with DC-Coupled Outputs
DC-Coupled Inputs and Outputs
75Ω
0.1μ
Y OUT
0.1μ
0V - 1.4V
75Ω
75Ω
Input Clamp Circuit
0V - 1.4V
Video Cables
Video Cables
Inactive
Clamp
LCVF
Clamp
Active
LCVF
Clamp
Active
LCVF
75Ω
75Ω
www.fairchildsemi.com
75W
75Ω
75Ω
LOAD1
LOAD2
(optional)