ML6420CS-4 datasheet(8/20 Pages) MICRO-LINEAR

8 / 20 page

ML6420

RGB: When the bandwidth of each signal is the same,

then the 5.5MHz or 8.0MHz/9.3MHz are appropriate

depending on the sampling rate. (13.5MHz vs 27MHz)

YUV: When the luminance bandwidth is different from the

color bandwidth, the ML6420-4 with the 8.0, 3.0 and

3.0MHz filters are more appropriate.

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

Video) systems the ML6420 with 5.5MHz or 8.0MHz

filters or ML6422 with 5.5MHZ and 9.3MHz 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 5.50MHz, 8.0MHz, or 9.3MHz filters

permit filtering of one, two or three composite signals.

4X Over sampling: While the ML6420 filters can eliminate

the need for over sampling combined with digital filtering,

there are times when over sampling is needed. For these

situations, 8.0MHz or 9.3MHz is used in place of

5.5MHz, and 3.0MHz is used in place

of 1.8MHz.

NTSC/PAL: A 5.50MHz cut-off frequency provides good

filtering for 4.2MHz, 5.0MHz.

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

there is a fall-off in response with frequency due to discrete

sampling. The fall-off follows a sinx/x response. The ML6421

and ML6423 filters have a complementary boost to provide

a flatter overall response. The boost is designed for 13.5MHz

and 27MHz Y/C and CV sampling and 6.75MHz or

13.5MHz U/V sampling. The ML6421 has the same pin-out

as the ML6420.

TYPICAL CLAMPING SCHEMES

Figures 8 and 9 show two typical applications of the

ML6420 for anti-aliasing prior to A-to-D conversion. In

Figure 8, a single precision digital feedback clamp circuit

includes both the ADC and the ML6420. This establishes

the proper DC operating point for the ML6420 (with

RANGE input = 0V, 0.5V

£ VIN £ 1.5V; with RANGE input

= 5V, 0.0

£ VIN £ 1.0V.) and the ADC. Figure 8 is typically

used with ADC’s that require external clamp circuitry.

Figure 9 shows AC coupled application for ADC’s with

built-in clamps. In this case, the clamp is internal to the

ADC and the ML6420 uses a simple coarse clamp at its

input to establish the proper operating point.

USING VIDEO FILTERS

The ML6420 are monolithic, triple/dual lowpass filters

intended for input anti-aliasing prior to analog to digital

conversion in video systems.

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