| 摘要 |
A color television receiver having a circuitry for automatically adjusting the cut-off points of the electron guns, i.e. for adjusting the bias of each electron gun to make the guns responsive to video signals in a constant manner, wherein the bias and the video signal are both applied to the cathode of each gun through a switch. In permanent connection with the cathode is mounted an integrator operable to adopt and substantially maintain the bias voltage upon said switch being switched off, and in series with the integrator is arranged a current amplifier for detecting the cathode current in said series connection upon the other end thereof being connected to ground simultaneously with the switching off of said switch. The output of the current amplifier is fed through a further switch to the input terminal of a variable bias source so as to cause the same to maintain its output voltage if the current amplifier output has a value corresponding to a cathode current of a predetermined low intensity, but cause the bias voltage to increase or decrease if the amplifier output increases or decreases from said value, whereby the bias in the following period of display operation will be adjusted to stabilize the cut-off point of the electron gun. In a preparation phase defined by the vertical flyback control pulse the input of the video amplifier is connected to a constant voltage source providing a constant reference bias voltage applied to the cathode superimposed by the adjusted bias voltage from said variable bias source such that the combined bias sensed by said integrator is a well defined function of the adjusted bias voltage and therewith is usable for in a following detecting and adjusting phase to control the variable bias voltage in the relevant manner.
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