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)
filtering for 4.2MHz, 5.0MHz.
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.
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 27MHzY/C and CV sampling and 6.75MHz or
13.5MHz U/V sampling. The ML6421 has the same pin-out
as the ML6420.
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
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
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.
RANGE input = 0V, 0.5V
V
1.5V; with RANGE input
IN
= 5V, 0.0 1.0V.) and the ADC. Figure 8 is typically
V
IN
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.
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.
USING VIDEO FILTERS
NTSC/PAL: A 5.50MHz cut-off frequency provides good
The ML6420 are monolithic, triple/dual lowpass filters
intended for input anti-aliasing prior to analog to digital
conversion in video systems.
8
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
