PAL/NTSC兼容梳状滤波器Y/C分离电路

Y/C separation circuit using PAL/NTSC compatible comb filter

为满足人们对彩电画质及色彩日益增长的要求，对ＮＴＳＣ制彩色信号均已采用梳状滤波器进行Ｙ／Ｃ分离。由于ＰＡＬ制彩色逐行倒相，亮度信号与色度信号采用１／４行频间置，因此ＰＡＬ制Ｙ／Ｃ分离梳状滤波器必须用延迟两行的信号与直通信号加减才能实现Ｙ／Ｃ分离，这对彩色信号相关性提出了更高的要求。最新实用的ＳＡＡ４９６１，ＮＴＳＣ／ＰＡＬ制兼容梳状滤波器（ＩＣ），采用三行数字式自适应电路，对其中彩色相关性强的两行信号加、减，以保证彩色轮廓边缘处的垂直分辨率。文中有原理分析及最新实用电路的介绍。该电路已成功地使用在康佳Ｔ３４７７大屏幕彩电的电路中。

Comb filter for Y/C separation is already used in NTSC colour system.Due to that in PAL system the phase of chrominance signals alternates in successive lines and 1/4 line frequency offset is used for luminance and chrominance signals,the sum of the signal delayed by 2 lines and the signal in the direct through pass must be used in a comb filter for Y/C separation.This put tighter requirements to the correlation of colour signals.The new NTSC/PAL compatible IC chip SAA4961 uses 3line adaptive digital delay circuit to add the signals in the most correlated 2 of them so as to ensure vertical resolution at the edge of the contour.This article provides a theoretical analysis and practical circuits that are already used in KONKA Model T3477.