ML6421

9

LAYOUT CONSIDERATIONS

In order to obtain full performance from these triple filters,

layout is very important. Good high frequency decoupling

is required between each power supply and ground.

Otherwise, oscillations and/or excessive crosstalk may

occur. A ground plane is recommended.

Each filter has its own supply and ground pins. In the test

circuit, 0.1µF capacitors are connected in parallel with

maximum noise rejection (Figure 9).

Further noise reduction is achieved by using series ferrite

beads. In typical applications, this degree of bypassing

may not be necessary.

Since there are three filters in one package, space the

signal leads away from each other as much as possible.

Power Considerations

The ML6421 power dissipation follows the formula:

PI

V

V

RL

DCC

CC

OUT

=×

×











!

"

$##

2

3

(1)

This is a measure of the amount of current the part sinks

(current in – current out to the load).

Under worst case conditions:

PmW

×











!

"

$##

=

0 175 5 5

15

75

3

872 5

2

.. –

.

.

05

ML6421 VIDEO LOW PASS FILTER

Filter Selection: The ML6421 provides several choices in

filter cut-off frequencies depending on the application.

RGB: When the BW of each signal is the same, then the

ML6421-1 (5.5MHz) or ML6421-3 (8MHz) are appropriate

depending on the sampling rate.

YUV: When the luminance bandwidth is different from the

color bandwidth, the ML6421-4 with the 8.0, and two

3.0MHz filters are most appropriate.

S-Video: For Y/C (S-video) and Y/C + CV (Composite

Video) systems the 5.5MHz or 8MHz filters are

appropriate. In NTSC the C signal occupies the bandwidth

from about 2.6MHz to about 4.6MHz, while in PAL the C

signal occupies the bandwidth from about 3.4MHz to

about 5.4MHz. In both cases, a 5.5MHz low pass filter

provides adequate rejection for both sampling and

reconstruction. In addition, using the same filter for both

Y/C and CV maintains identical signal timing without

adjustments.

Composite: When one or more composite signals need to

be filtered, then the 5.5MHz and 8MHz filters permit

filtering of one, two or three composite signals.

NTSC/PAL: A 5.5MHz cut-off frequency provides good

filtering for 4.2MHz, 5.0MHz and 5.5MHz signals without

the need to change filters on a production basis.

Sinx/x: For digital video system with output D/A

converters, there is a fall-off in response with frequency

4

2

0

–2

–4

FREQUENCY (MHz)

01234567

THEORETICAL SINX/X

CORRECTION FOR

13.5MHz SAMPLING

SINX/X ERROR FOR

TYPICAL DAC AT 13.5MHz

Figure 10. Sinx/x Frequency Response

R

8

DIGITAL

INPUTS

RED DAC

(CURRENT SOURCING

G

8

GREEN DAC

(CURRENT SOURCING

B

R

ANALOG

OUTPUTS

G

B

8

BLUE DAC

(CURRENT SOURCING

ML6421

DAC LOAD

ADJUSTED FOR

75

Ω

75

Ω

75

Ω

+5V

Figure 11. Typical ML6421 Reconstruction Application