© 2005 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FMS6363 • Rev. 1.0.4

5

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.

There will be a 280mV offset from the DC input level to

the DC output level.

Vout = 2 * Vin + 280mV

0.02V

0.32V

1.02V

0.15V

0.5V

0.85V

0.28V

0.88V

2.28V

Driven by:

DC-Coupled DAC Outputs o r

AC-Coupled and Clamped

Y, R, G, B, CV

0.58V

1.28V

1.98V

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.

YOUT

800kΩ

Driver

YIN

0.65V

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

75

Ω

LCVF

Clamp

Inactive

0V- 1.4V

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

75

Ω

LCVF

Clamp

Active

0.1µ

0V- 1.4V

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.

75

Ω

LCVF

Clamp

Active

75

Ω

0.1µ

External Video

source must

be AC-coupled.

0V- 1.4V

Figure 12. SCART with DC-coupled Outputs