PRODUCT SPECIFICATION
TMC22x5yA
Output Processor
Mixed Sync
+
X
SGx[9:0]
Adaptive Luma
Notch Filter
Y Data
+
–
–
X
G/Y Data
YOFF[8:0]
YGx[9:0]
YSEL ANEN
ANT[1:0]
VIDEOB
PED[7:0]
Output
Formatter
Clamp
Circuit
LPF
256
240
X
B/Cb Data
R/Cr Data
CLMP[1:0]
VCLPEN
Fixed (B-Y)
Gain Stage
U Data
V Data
X
UGx[10:0]
X
Fixed (R-Y)
Gain Stage
X
65-22x5y-65
VGx[10:0]
Figure 24. Output Processor Block Diagram
clamp pulse can be used to control where an analog clamp
circuit grabs the analog reference to establish the correct
voltage level into the A/D. Usually the clamp pulse is gener-
ated on the back porch or duing the sync tip of a video line.
Clamp Circuit
A clamp pulse generated by the Burst Gate signal is used to
grab either a sample of the low-pass-filtered luma during the
video back porch, the signal on VIDEOB, or one of two
internally generated levels. The selection is made by the
CLMP[1:0] register bits.
Adaptive Notch Filter
The PAL line-locked comb decoder can never provide
perfect subcarrier cancellation due to the 25Hz offset in the
subcarrier frequency. This 25Hz offset causes residual and
phase modified subcarrier to be left on the luminance signal
which can produce a visible dot crawl on flat areas of color.
However, for all comb filter structures, the quality of the
comb depends on the quality of the sampling clock, as line to
line clock jitter will also cause small phase changes between
the inputs to the comb filter. It is therefore possible that
NTSC comb decoders may also require some coring of the
luma output. To meet the wide range of sample frequencies
that the decoder must deal with two separate coring filters
are selectable.
Table 11. Blanking Level Selection
CLMP[1:0]
Blanking Selection
Internal 240 level
00
01
10
11
Internal 256 level
External VIDEOB Input
Internal LPF Output
The blanking level is subtracted from the decoded luma.
If the sign is negative, the result is assumed to be mixed sync
and is passed through a delay and into the sync gain stage
within the output matrix. If the sign is positive, the result is
assumed to be pure luma (blanking to peak white) and is fed
to the pedestal removal circuit.
The luma signal from the pedestal stripper is compared
against the preceding pixel to detect the magnitude change
between pixels. This magnitude difference will be almost
zero for flat areas of picture, and large for high frequency
changes in the picture. The magnitude difference is com-
pared to one of four programmable thresholds. The program-
Pedestal Removal
The 8 bit programmable pedestal is subtracted from the pure
luma signal. The negative super black signals are clipped to
zero when register 0Ah bit 4 is set LOW, or the super black
signals are passed through the luma scalar when register 0Ah
bit 4 is HIGH.
mable threshold is selected by the ANT register bits as
1-0
shown in Table 12.
Table 12. Adaptive Notch Threshold Control
ANT
1-0
Magnitude difference
less than 16
Clamp Generator
00
01
10
11
The TMC22x5yA has the unique option to output a negative
going clamp pulse that is 0.5 µsec wide. This pulse can be
output on the AVOUT pin by placing a HIGH on register 24
bit 7. The pulse’s position relative to HSYNC can be varied
by register 25. This value is the number of PCK clock cycles
after an HSYNC that the pulse will be output to the pin. The
less than 12
less than 8
less than 4
REV. 1.0.0 2/4/03
55
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
