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FMS6364A • Rev. 3.0.5

8

Application Information

Application Circuits

The FMS6364A

VoltagePlus™ video filter provides a

6 dB 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:

Figure 12. Typical Voltage Levels

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:

Figure 13.

Input Clamp Circuit

I/O Configurations

For a DC-coupled DAC drive with DC-coupled outputs,

use the configuration in Figure 14.

Figure 14.

DC-Coupled Inputs and Outputs

Alternatively, if the DAC’s average DC output level

causes the signal to exceed the range of 0 V to 1.4 V, it

can be AC coupled as shown in Figure 15.

Figure 15. AC-Coupled Inputs, DC-Coupled Outputs

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.

Figure 16.

SCART with DC-Coupled Outputs

There is a 280mV offset from the DC input level to the

0.0 -> 0.02V

0.3 -> 0.32V

0.65 -> 0.67V

1.0 -> 1.02V

0.28V

0.88V

1.58V

2.28V

Driven by:

DC-Coupled DAC Outputs

AC-Coupled and Clamped

Y, CV, R, G, B

0.15V

0.5V

0.85V

0.58V

1.28V

1.98V

Driven by:

AC-Coupled and Biased

U, V, Pb, Pr, C

DVD or

STB

SoC

DAC

Output

75W

LCVF

Clamp

Inactive

0V - 1.4V

DVD or

STB

SoC

DAC

Output

LCVF

Clamp

Active

0.1μ

0V - 1.4V

75Ω

75Ω

LCVF

Clamp

Active

0.1μ

External video

source must

be AC coupled

0V - 1.4V

75Ω