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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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ADVANCE INFORMATION  
VCT 38xxA  
2.10.4.Digital Brightness Adjustment  
Part 1 includes adjustable tilt point and gain. The gain  
before the tilt value is 1. Above the tilt value, a part  
(0...15/16) of the input signal is subtracted from the  
input signal itself. Therefore, the gain is adjustable  
from 16/16 to 1/16, when the slope value varies from  
0 to 15. The tilt value can be adjusted from 0 to 511.  
The DC-level of the luminance signal can be adjusted  
by adding an 8-bit number in the luminance signal path  
in front of the softlimiter.  
With a contrast adjustment of 32 (gain+1) the signal  
can be shifted by 100 %. After the brightness addition,  
the negative going signals are limited to zero. It is  
desirable to keep a small positive offset with the signal  
to prevent undershoots produced by the peaking from  
being cut. The digital brightness adjustment works  
separately for main and side picture.  
Part 2 has the same characteristics as part 1. The sub-  
tracting part is also relative to the input signal, so the  
total differential gain will become negative if the sum of  
slope 1 and slope 2 is greater than 16 and the input  
signal is above the both tilt values (see characteris-  
tics).  
Finally, the output signal of the soft limiter will be  
clipped by a hard limiter adjustable from 256 to 511.  
2.10.5.Soft Limiter  
The dynamic range of the processed luma signal must  
be limited to prevent the CRT from overload. An appro-  
priate headroom for contrast, peaking and brightness  
can be adjusted by the TV manufacturer according to  
the CRT characteristics. All signals above this limit will  
be ‘soft’-clipped. A characteristic diagram of the soft  
limiter is shown in Fig. 2–15. The total limiter consists  
of three parts:  
2.10.6.Chroma Interpolation  
A linear phase interpolator is used to convert the  
chroma sampling rate from 10.125 MHz (4:2:2) to  
20.25 MHz (4:4:4). All further processing is carried out  
at the full sampling rate.  
Output  
511  
Part 1  
Part 2  
Hard limiter  
Calculation Example for the  
0
Softlimiter Input Amplitude.  
(The real signal processing in  
the limiter is 2 bit more than  
described here)  
slope 1  
[0...15]  
2
4
6
0
2
4
400  
300  
200  
100  
0
8
10  
12  
Y Input  
16...235 (ITUR)  
range=  
256...511  
Black Level  
Contrast  
Dig. Brightness  
BLE  
16 (constant)  
6
8
10  
63  
20  
off  
off  
14  
slope 2  
[0...15]  
12  
14  
Peaking  
Limiter input signal:  
(Yin-Black Level) Contr./32 + Brightn.  
(235-16) 63/32 + 20 = 451  
tilt 1 [ 0...511]  
tilt 2 [ 0...511]  
Limiter Input  
0
100  
200  
300  
400  
500  
600  
700  
800  
900  
1023  
Fig. 2–15: Characteristic of soft limiter A and B and hard limiter  
2.10.7.Chroma Transient Improvement  
sharpened chroma signals are limited to a proper  
value automatically.  
The intention of this block is to enhance the chroma  
resolution. A correction signal is calculated by differen-  
tiation of the color difference signals. The differentia-  
tion can be selected according to the signal bandwidth,  
e.g. for PAL/NTSC/SECAM or digital component sig-  
nals, respectively. The amplitude of the correction sig-  
nal is adjustable. Small noise amplitudes in the correc-  
tion signal are suppressed by an adjustable coring  
circuit. To eliminate ‘wrong colors’, which are caused  
by over and undershoots at the chroma transition, the  
Micronas  
21  
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