ML6440
FUNCTIONAL DESCRIPTION
The ML6440 is an adaptive digital comb filter that offers
automatic self-adjusting or manual thresholds to handle
vertical and horizontal contouring during Y/C separation.
The ML6440 implements a SmartComb algorithm where
full bandwidth video and artifact suppression techniques
are used to automatically select suppression thresholds for
all video content. Video artifacts such as hanging dots, dot
crawl, and cross luminance are dramatically reduced. The
algorithm functionally performs a statistical analysis of the
video content of over 60 lines. It then calculates and
selects the best threshold for artifact reduction at 12-bit
resolution.
The ML6440 is a comb for NTSC (525 lines) and PAL (625
lines) with the ability to handle CCIR601 and square pixel
sampling rates.
CCIR601 is the existing standard for digitized video of
either NTSC or PAL at a 13.5MHz rate, and is used by
MPEG encoders and decoders for image compression. The
comb algorithms in the comb filter substantially reduce
rainbow and dot-crawl artifacts which interfere with
efficient image compression.
Square pixel is video digitized at 12.27MHz for NTSC,
and 14.75MHz for PAL, so that each sample corresponds
to a single pixel in computer displays without the effort or
expense of a multi-phase image resizing filter done in
hardware or software.
Using the ML6440 comb filter requires no external
components for operation. The comb filter can be
bypassed to accommodate selection of external S-video
signals. The comb filter is controllable via parallel pin or
serial interface.
SMARTCOMB OPERATION
The user supplies 8-bit video as either digital Y/C or digital
composite video inputs and receives delayed and combed
data at the Y/C digital outputs. Use of Y/C input assumes
that combing is unnecessary and sends the data through
the same delay as the composite video path to prevent
shifting of the video position on the screen. This makes the
ML6440 useful in source selection such as S-video inputs
and composite video. Composite video (CV), applied to
the ML6440 with comb operation enabled, permits the
separation of luminance and chrominance with minimal
artifacts.
The SmartComb controls the application of the comb filter
and bandsplit-notch filters on a pixel-by-pixel basis. The
digital video image is sampled, and an analysis is
performed. SmartComb step 1: looks for differences in the
low frequency spectra (vertical detail). SmartComb step 2:
searches for changes in phase angle/saturation of the
chroma sub-carrier, which represents changes in color in
the vertical direction. Finally, SmartComb step 3: an
averaging circuit is used as "smoothing function" to
eliminate dithering in the horizontal dimension caused by
excessive filter switching.
Figure 1 provides a simplified block diagram of the
SmartComb architecture. This architecture implements
several complex computations to determine the amount of
notch vs. comb filtering. Three 8-Bit detectors are used to
examine vertical and horizontal detail for luma and
chroma signals on a pixel-by-pixel basis for 3-line
analysis. These data are then fed into a weighting function
to determine the best filtering approach over the existing
3-lines of video. Furthermore, this data is then compared
CV
IN
1H
1H
VIDEO
SIGNALS
HI-BAND
LOW BAND
AUTOMATIC
THRESHOLD
SELECT
HI-BAND
LOW BAND
HI-BAND
LOW BAND
LUMA VERTICAL
DETAIL DETECTOR
8-BIT
LUMA HORIZONTAL
DETAIL DETECTOR
8-BIT
CHROMA VERTICAL
DETAIL DETECTOR
8-BIT
COMB/NOTCH
CONTROL FUNCTION
24-BIT, 3-LINE
COMB/NOTCH
THRESHOLD SELECT
MANUAL
THRESHOLD
SELECT
COMP
FADER
COMB/NOTCH
CONTROL FUNCTION
12-BIT, FRAME, 60-LINE
MIXER
8-BIT
Y
OUT
C
OUT
Figure 1. SmartComb Architecture: Simplified Block Diagram
7
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
