Method for controlling cut-off point and gain in video reproduction device means of three measured currents

在垂直帧消隐期间向各彩色通道注入用于阴极电流的截止和驱动控制的测量行。由于物理相关的指数型束流特性曲线是阴极控制电压V#-[K]的函数，所以利用特性曲线的指数γ及两阴极电流I#-[K1]和I#-[K2]之比来形成截止和驱动控制的控制基准值。控制过程从固定指数值γ或两阴极电流I#-[K1]和I#-[K2]之比开始。然而已发现，即使假定指数值γ或两阴极电流I#-[K1]和I#-[K2]之比为固定值，也不能得到单色图像显示最佳结果。于是，本发明将指数γ定义为彩色显像管1的函数，目的在于将依赖γ的DC电压偏置u#-[0f]减小为零。 Recent circuit concepts inject measurement lines, for cutoff and drive control of the cathode current, into each colour channel during the vertical frame blanking period. Owing to the physically dependent exponential beam current characteristic profile as a function of the cathode control voltage VK, the exponent gamma of the characteristic profile and the ratio of two cathode components IK1 and IK2 are in this case used to form control reference values for cutoff and drive control, this process being started in each case from a fixed value of the exponent gamma or of the ratio of the two cathode currents IK1 and IK2. However, it has been found that, if a fixed value is assumed for the exponent gamma or for the ratio of the two cathode currents IK1 and IK2, it is not possible to achieve an optimum result for displaying monochrome pictures. Thus, according to the invention, the exponent gamma is defined as a function of the colour tube 1. The aim in this case is to reduce a gamma -dependent DC voltage offset u0f to zero.