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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  
2.11.3.Average Beam Current Limiter  
2.11.4.Analog RGB Insertion  
The average beam current limiter (BCL) uses the  
SENSE input for the beam current measurement. The  
BCL uses a different filter to average the beam current  
during the active picture. The filter bandwidth is  
approx. 2 kHz. The beam current limiter has an auto-  
matic offset adjustment that is active two lines before  
the first cutoff measurement line.  
The VCT 38xxA allows insertion of external analog  
RGB signals. The RGB signal is key-clamped and  
inserted into the main RGB by the Fast-Blank switch.  
The external RGB input can be overlaid or underlaid to  
the digital picture. The external RGB signals can be  
adjusted independently as regards DC level (bright-  
ness) and magnitude (contrast).  
The beam current limiter function is located in the  
front-end. The data exchange between the front-end  
and the back-end is done via a single-wire serial inter-  
face.  
All signals for analog RGB insertion (RIN, GIN, BIN,  
FBLIN) must be synchronized to the horizontal flyback,  
otherwise a horizontal jitter will be visible. The  
VCT 38xxA has no means for timing correction of the  
analog RGB input signals.  
The beam current limiter allows the setting of a thresh-  
old current. If the beam current is above the threshold,  
the excess current is low-pass filtered and used to  
attenuate the RGB outputs by adjusting the white-drive  
multipliers for the internal (digital) RGB signals, and  
the analog contrast multipliers for the analog RGB  
inputs, respectively. The lower limit of the attenuator is  
programmable, thus a minimum contrast can always  
be set. During the tube measurement, the ABL attenu-  
ation is switched off. After the white-drive measure-  
ment line it takes 3 lines to switch back to BCL limited  
drives and brightness.  
2.11.5.Fast-Blank Monitor  
The presence of external analog RGB sources can be  
detected by means of a Fast-Blank monitor. The status  
of the Fast-Blank input can be monitored via an I2C  
bus register. There is a 2 bit information, giving static  
and dynamic indication of a Fast-Blank signal. The  
static bit is directly reading the Fast-Blank input line,  
whereas the dynamic bit is reading the status of a  
flip-flop triggered by the negative edge of the Fast-  
Blank signal.  
Typical characteristics of the ABL for different loop  
gains are shown in Fig. 2–22; for this example the tube  
has been assumed to have square law characteristics.  
With this monitor logic it is possible to detect if there is  
an external RGB source active and if it is a full screen  
insertion or only a box. The monitor logic is connected  
directly to the FBLIN pin.  
Fig. 2–22: Beam current limiter characteristics:  
beam current output vs. drive  
BCL threshold: 1  
Micronas  
27  
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