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在PAL彩色电视接收中,超声延迟线的群延时误差是造成图象彩色水平过渡边缘串色及爬行的重要根源。本文讨论了减少群延时误差的理论根据,并给出了实际调试中减少群延时误差的措施。由于超声延迟线的相位频率特性不过原点,在一定条件下,PAL制对延迟线群延时、相延时提出的不同要求,可以以很小的误差同时得到满足。
In PAL color television reception, the group delay error of the ultrasonic delay line is an important source of color and creeping caused by the transition of color level in the image. This paper discusses the theoretical basis for reducing the group delay error and gives the measures to reduce the group delay error in practical debugging. Due to the fact that the phase and frequency characteristics of the ultrasonic delay line are not the origin, under certain conditions, the different requirements of the PAL system for the delay line group delay and the phase delay can be satisfied with a small error at the same time.