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VCT3801A 参数 Datasheet PDF下载

VCT3801A图片预览
型号: VCT3801A
PDF下载: 下载PDF文件 查看货源
内容描述: 视频/控制/图文电视IC系列 [Video/Controller/Teletext IC Family]
分类和应用: 电视
文件页数/大小: 172 页 / 2219 K
品牌: MICRONAS [ MICRONAS ]
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VCT 38xxA  
ADVANCE INFORMATION  
2.9. Macrovision Detection  
2.10.2.Black-Level Expander  
Video signals from Macrovision encoded VCR tapes  
are decoded without loss of picture quality. However, it  
might be necessary in some applications to detect the  
presence of Macrovision encoded video signals. This  
is possible by reading the Macrovision status register  
(FP-RAM 0x170).  
The black-level expander enhances the contrast of the  
picture. Therefore the luminance signal is modified  
with an adjustable, non-linear function. Dark areas of  
the picture are changed to black, while bright areas  
remain unchanged. The advantage of this black-level  
expander is that the black expansion is performed only  
if it will be most noticeable to the viewer.  
Macrovision encoded video signals typically have AGC  
pulses and pseudo sync pulses added during VBI. The  
amplitude of the AGC pulses is modulated in time. The  
Macrovision detection logic measures the VBI lines  
and compares the signal against thresholds.  
The black-level expander works adaptively. Depending  
on the measured amplitudes ‘Lmin’ and ‘Lmax’ of the  
low-pass-filtered luminance and an adjustable coeffi-  
cient BTLT, a tilt point ‘Lt’ is established by  
The window wherein the video lines are checked for  
Macrovision pulses can be defined in terms of start  
and stop line (e.g. 6-15 for NTSC).  
Lt = Lmin + BTLT (Lmax - Lmin).  
Above this value there is no expansion, while all lumi-  
nance values below this point are expanded according  
to:  
2.10.Display Processing  
Lout = Lin + BAM (Lin - Lt)  
In the display processing the conversion from digital  
YCrCb to analog RGB is carried out. A block diagram is  
shown in Fig. 2–18 on page 24. In the luminance pro-  
cessing path, contrast and brightness adjustments and  
a variety of features, such as black-level expansion,  
dynamic peaking and soft limiting, are provided. In the  
chrominance path, the CrCb signals are converted to  
4:4:4 format and filtered by a color transient improve-  
ment circuit. The YCrCb signals are converted by a  
programmable matrix to RGB color space.  
A second threshold, Ltr, can be programmed, above  
which there is no expansion. The characteristics of the  
black-level expander are shown in Fig. 2–11and Fig.  
2–12.  
Lmax  
Ltr  
Lout  
The display processor provides separate control set-  
tings for two pictures, i.e. different coefficients for a  
‘main’ and a ‘side’ picture.  
Lt  
BAM  
BTLT  
Lmin  
The digital OSD insertion circuit allows the insertion of  
a 5-bit OSD signal. The color space for this signal is  
controlled by a partially programmable color look-up  
table (CLUT) and contrast adjustment.  
The OSD signals and the display clock are synchro-  
nized to the horizontal flyback. For the display clock, a  
gate delay phase shifter is used. In the analog back-  
end, three 10-bit digital-to-analog converters provide  
the analog output signals.  
Lin  
BTHR  
Ltr  
Fig. 2–11: Characteristics of the black-level expander  
The tilt point Lt is a function of the dynamic range of  
the video signal. Thus, the black-level expansion is  
only performed when the video signal has a large  
dynamic range. Otherwise, the expansion to black is  
zero. This allows the correction of the characteristics of  
the picture tube.  
2.10.1.Luma Contrast Adjustment  
The contrast of the luminance signal can be adjusted  
by multiplication with a 6-bit contrast value. The con-  
trast value corresponds to a gain factor from 0 to 2,  
where the value 32 is equivalent to a gain of 1. The  
contrast can be adjusted separately for main picture  
and side picture.  
18  
Micronas  
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