參數(shù)資料
型號: TMC22053AKHC
廠商: FAIRCHILD SEMICONDUCTOR CORP
元件分類: 顏色信號轉(zhuǎn)換
英文描述: Multistandard Digital Video Decoder Three-Line Adaptive Comb Decoder Family, 8 & 10 bit
中文描述: COLOR SIGNAL DECODER, PQFP100
封裝: MQFP-100
文件頁數(shù): 55/84頁
文件大小: 417K
代理商: TMC22053AKHC
PRODUCT SPECIFICATION
TMC22x5yA
REV. 1.0.0 2/4/03
55
Output Processor
Figure 24. Output Processor Block Diagram
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.
Table 11. Blanking Level Selection
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.
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.
Clamp Generator
The TMC22x5yA has the unique option to output a negative
going clamp pulse that is 0.5
μ
sec 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
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.
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.
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-
mable threshold is selected by the ANT
1-0
register bits as
shown in Table 12.
Table 12. Adaptive Notch Threshold Control
Mixed Sync
65-22x5y-65
SGx[9:0]
X
X
X
X
X
X
YGx[9:0]
YOFF[8:0]
Adaptive Luma
Notch Filter
ANT[1:0]
CLMP[1:0]
Clamp
Circuit
+
+
VCLPEN
PED[7:0]
Y Data
VIDEOB
LPF
U Data
V Data
256
240
YSEL ANEN
Fixed (B-Y)
Gain Stage
Fixed (R-Y)
Gain Stage
UGx[10:0]
VGx[10:0]
G/Y Data
B/Cb Data
R/Cr Data
Output
Formatter
CLMP[1:0]
00
01
10
11
Blanking Selection
Internal 240 level
Internal 256 level
External VIDEOB Input
Internal LPF Output
ANT
1-0
00
01
10
11
Magnitude difference
less than 16
less than 12
less than 8
less than 4
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