自由采样下视频信号的时序提取与数字行锁相的研究  

Research of timing information extractions and digital line-locked sampling of video signal in free-running sampling system

作　　者：沈庆宏[1] 肖波[1] 柯翔[2] 

机构地区：[1]南京大学,电子科学与工程系,南京210093 [2]江苏交通控股有限公司,营运安全部,南京210002

出　　处：《南京大学学报（自然科学版）》2009年第3期424-431,共8页Journal of Nanjing University（Natural Science）

摘　　要：视频解码系统在电视机处于核心地位,负责将复合全电视信号解码成红绿蓝三色信号供显示器显示.其实现机理有多种方案,目前有全模拟型、数模混合型和全数字型等,其中全数字方案最有前景,符合数字电视的发展需要.本文提出了在全数字视频解码系统中,一种进行时序信息提取和全数字行锁的新方法.在视频信号数字化时,常规方法是使用模拟锁相环对采样率进行控制以达到同步采样,这增加了设计的复杂度和解码系统的成本.为简化采样系统的硬件架构,设计让产生采样时钟的晶振处于自由振荡模式,采样芯片使用50 MHz的固定频率对视频信号进行自由采样,采样点的行同步化过程在全数字域中通过信号处理算法实现.本方法省去了大量模拟器件的辅助,并且锁相精度比传统方法更高.首先需要提取数字视频流的时序信息,这里使用匹配滤波器法来寻找行、场同步信号的起始位置和进行奇偶场识别,与常规的电平切割法相比,实现方便,具有较好的噪声抑制性能.在此基础上,提出了使用改进的双向差分模型对视频行同步信号进行线性回归拟合求小数相位的方法,从而进一步提高了行同步起始位置的精度.同时,利用本系统采样率较高的特点,提出了带信号延时比较器的梳状滤波器的亮色分离方法,改善了亮色分离的效果;提出了一个实用的数字行锁相环,来滤除提取到的行同步起始位置的相位噪声,给出了详细设计并分析了相关性能.环路结合以辛克函数为内核的高阶插值滤波器对视频亮色信号进行重采样,实现了数字行锁相.实践证明,以上算法行之有效,取得了较好的效果,文章最后给出了使用从电视信号发生器中采集的数据进行解码的仿真结果.The video signal decoding system takes the core position in a TV set, whose duty is converting the composite video broadcast signals into RGB video signals in order to display on the monitor. At present, there are several mechanisms to realize a decoder, such as all-analog, mixed analog-digital and all-digital. The all digital scheme has a most prospective future, which also meets the need of the digital TV development. This paper presents new implementations of video signal timing information extractions and an all-digital line locked sampling loop used in the video signal digital decoding system. When the video signal is digitized, the traditional decoder uses an analog phase locked loop to control the sampling ratio for synchronous line locked sampling, which adds the complexity of design and the cost of the decoding system. To simplify the hardware architecture of the sampling system, the crystal which generates the sampling clock is designed to work in the free-running mode without any control and the sampling chip uses a fixed clock which is 50 MHz to sample the video signal. And then the realization of line-locked sampling can be done by signal processing algorithms in all digital domains. In contrast to the existing analog phase locked loop techniques, this method omits the assistance of a large number of analog parts and gets a higher precision locked phase. Firstly, the timing information should be extracted from digital video stream. Here, the matched filter method is used to identify horizontal sync and vertical sync starting point, and to recognize even or odd field and so on. Compared with the conventional sync slicer method, the mathched filter method has better performance in the suppression of phase noise, and it is easier to realize. On the basis of this, the improved bidirectional difference model which applies the linear regression algorithm to fit the video horizontal sync signal is used to calculate the fractional phase in order to elevate the precision of the horizontal sync starting point.

关 键 词：数字视频解码 匹配滤波器 双向差分 数字行锁 亮色分离 

分 类 号：TN911[电子电信—通信与信息系统]