FMS6363_08 Datasheet, PDF (5/9 Pages) Fairchild Semiconductor – Low-Cost, Three-Channel, 6th-Order, High-Definition, Video Filter Driver

Applications Information
Functional Description
The FMS6363 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 Figure 8.
1.02V
0.32V
0.02V
V_IN
2.28V
0.88V
0.28V
V_OUT
Driven by:
DC-Coupled DAC Outputs o r
AC-Coupled and Clamped
Y, R, G, B, CV
There will be a 280mV offset from the DC input level to
the DC output level.
Vout = 2 * Vin + 280mV
0.85V
0.5V
0.15V
V_IN
1.98V
1.28V
0.58V
V_OUT
Driven by:
DC-Coupled DAC Outputs
AC-Coupled and Biased
U, V, Pb, Pr, C
Figure 8. Typical Voltage Levels
The FMS6363 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
FMS6363 without an AC coupling capacitor. The worst-
case sync tip compression due to the clamp does not
exceed 7mV. The input level set by the clamp,
combined with the internal DC offset, keeps the output
within its acceptable range. When the input is AC-
coupled, the diode clamp sets the sync tip (or lowest
voltage) just below ground.
For symmetric signals like C, U, V, Cb, Cr, Pb and Pr;
the average DC bias is fairly constant and the inputs can
be AC-coupled with the addition of a pull-up resistor to
set the DC input voltage. 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 9.
0.65 V
YIN
Driver
YOUT
800kΩ
Figure 9. Input Clamp Circuit
I/O Configurations
For DC-coupled DAC drive with DC-coupled outputs,
use the configuration in Figure 10.
DVD or
STB
SoC
DAC
Output
0V - 1.4V
LCVF
75 Ω
Clamp
Inactive
Figure 10. 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 shown in Figure 11.
DVD or
STB
SoC
DAC
Output
0V - 1.4V
0.1 µ
LCVF
75 Ω
Clamp
Active
Figure 11. AC-coupled Inputs, DC-coupled Outputs
When the FMS6363 is driven by an unknown external
source or a SCART with its own clamping circuitry the
inputs should be AC-coupled, shown in Figure 12.
External Video
source must
be AC-coupled.
0V - 1.4V
0.1µ
LCVF
75Ω
Clamp
Active
75Ω
Figure 12. SCART with DC-coupled Outputs
© 2005 Fairchild Semiconductor Corporation
FMS6363 • Rev. 1.0.3
5
www.fairchildsemi.com