PRODUCT SPECIFICATION
TMC22x5yA
ADAPT[1:0]
YCSEL
FAST
UYE
LYE
2:1
MUX
CFSEL[3:0]
Filter
UPE
LPE
Comb
Fail
Logic
YERR
PERR
MERR
UME
LME
STA[3:0]
CAT[1:0]
65-22x5y-60
Figure 19. Comb Filter Selection
mix signal, K. For 3-line Y/C comb filters, an external 1H
delay is required in the uncombed channel to compensate for
the comb filter delay.
Table 5. Adaption Modes
ADAPT[1:0]
Function
00
Adapts to the best of 3 types of line
based comb filters in NTSC only.
This principle is equally true for NTSC frame and field based
comb decoders. The feature is not available for any of the
PAL comb filter architectures.
01
3 line (tap) comb always adapts to
lower 2 line (tap) comb, when the 3 line
(tap) comb fails. Normally used with
NTSC field and frame based comb
filters.
The Comb filter Adaption Threshold register bits CAT[1:0]
determine if 5%, 15%, 25%, or 50% errors in picture correla-
tion is required to adapt the NTSC comb filter. In NTSC, due
to the 180 degree advance in subcarrier phase per line, it is
possible to switch between the 3 line comb and the choice of
either the upper two line comb or the lower two line comb. If
this switching occurs on a pixel by pixel basis the picture
will contain vertical alias components. This artifact can be
reduced by either setting the FAST register bit LOW, which
filters the comb filter selection, and/ or setting the CAT[1:0]
register bits to a higher percentage threshold.
10
11
3 line (tap) comb only. Never adapts to
a 2 line(tap) filter. The higher set of
comb filter error signals are sent to the
XLUT. NTSC or PAL comb filter.
Adapts to best of two 3 line comb filters
in PAL only.
XLUT
The comb filter adaption is further controlled by the
ADAPT[1:0] register bit selection, when the COMB[3:0]
register bits select a 3 line comb. These bits control if the
comb filter adapts from a 3 line comb to the best of the upper
or lower 2 line combs, from a 3 line comb to just the lower 2
line comb, performs a fixed 3 line comb, or implements a
best of two 3 line combs in PAL. If the COMB[3:0] register
bits select one of the 2 line comb filters, the ADAPT[1:0]
register bits are ignored, and no adaption is implemented.
The CFSEL[1:0] signal, shown in Figure 19, controls which
comb filter is selected on a pixel by pixel basis, and can be
externally monitored by reading CFSTAT[1:0] in register
4Bh.
The comb fail signals control both the comb filter adaption
and the cross fade between the adaptive comb filter output
YCOMB and the SIMPLE bandsplit signal. Which of the fail
signals is fed to the XLUT is determined by which comb
filter is selected in NTSC. When a 3 line comb filter is
selected, the larger set of error signals are sent to the XLUT,
when a upper 2 line comb is selected UYE, UME, and UPE
error signals are selected, and when a lower two line comb
filter is selected the LYE, LME, and LPE error signals are
selected.
REV. 1.0.0 2/4/03
51
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
