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本刊1979年第1期刊登的“PAL制超声延迟线”一文介绍了PAL制延迟线,正确地分析了PAL制延迟线的相延迟时间以及其对PAL制色度信号分离的影响。本文继续对PAL制延迟线的群延迟时间及其影响进行分析。若PAL制延迟线的相延时或群延时不符合要求,就会出现爬行。一般说来,相延时不准引起大面积爬行,群延时不准引起小面积爬行。小面积爬行又叫边缘爬行,如图1所示。图1(a)为减法器输出的有用信号U,(b)为U路在V路中的边缘串色量,(c)为V路在U路的串色量,(d)为加法器输出的有用信号V。图1示出的是一般PAL制接收机中的色信号分离情况。由于相延时易调整,彩条信号的平坦部份分离比较高,可达几十比一;而一般接收机中不对群延时
The paper “PAL Ultrasound Delay Line”, published in 1979 in the first issue, introduced the PAL delay line and correctly analyzed the phase delay time of the PAL delay line and its influence on the separation of the PAL system chrominance signal. This article continues to analyze the group delay of PAL delay line and its impact. If PAL delay line phase delay or group delay does not meet the requirements, there will be crawling. In general, the phase delay may not cause large-scale crawling, group delay allowed to cause small area crawling. Small area creeping is also called edge creep, as shown in Figure 1. Figure 1 (a) shows the useful signal U output by the subtracter, (b) shows the amount of edge crosstalk of U-way in V-path, (c) shows the amount of crosstalk of V-way in U-path, The output of the useful signal V. Figure 1 shows the general PAL receiver color signal separation. Due to the phase delay easy to adjust, the flat part of the color bar signal separation is relatively high, up to dozens of one; and the general receiver is not on the group delay