Data Sheet

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FMS6363A • Rev. 2.0.2 6
FMS6363A —Three-Channel 7
th
-Order High-Definition VoltagePlus™ Video Filter Driver
Application Information
Application Circuits
The FMS6363A VoltagePlus™ video filter 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 Figure 4:

T
here is a 280mV offset from the DC input level to the
DC output level. V
OUT
= 2 * V
IN
+ 280mV.
0
.0 -> 0.02V
0
.3 -> 0.32V
0
.65 -> 0.67V
1.0 -> 1.02V
V
IN
0
.28V
0
.88V
1.58V
2
.28V
Driven by:
DC-Coupled DAC Outputs
AC-Coupled and Clamped
Y, CV, R, G, B
V
OUT
0
.15V
0
.5V
0
.85V
V
IN
0
.58V
1.28V
1.98V
Driven by:
AC-Coupled and Biased
U, V, Pb, Pr, C
V
OUT
Figure 4. Typical Voltage Levels
The FMS6363A 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
FMS6363A 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 can not 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 5.
Y
OUT
Video Cables
Video Cables
75
75
75
75
Driver
Y
IN
LOAD1
LOAD2
(optional)
0.65V
Figure 5. Input Clamp Circuit
I/O Configurations
For a DC-coupled DAC drive with DC-coupled outputs,
use this configuration:
DVD or
STB
SoC
DAC
Output
75W
LCVF
Clamp
Inactive
0V - 1.4V
Figure 6. DC-Coupled Inputs and Outputs
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 follows:
DVD or
STB
SoC
DAC
Output
LCVF
Clamp
Active
0.1
0V - 1.4V
75
Figure 7. AC-Coupled Inputs, DC-Coupled Outputs
When the FMS6363A is driven by an unknown external
source or a SCART switch with its own clamping circuitry,
the inputs should be AC-coupled like this:
75
LCVF
Clamp
Active
0.1
External video
source must
be AC coupled
0V - 1.4V
75
Figure 8. SCART with DC-Coupled Outputs