Crt display unit

Abstract

A comparator detects a set-up voltage superimposed on a video signal. The detected set-up voltage is input to a timing information detection circuit to detect the display start timings and display end timings of a video signal or a single line and a single picture, respectively. Then, the detected timing information is input to an arithmetic operation means to determine the display period of the video signal for the single line and single picture and further determine the ratios thereof with respect to predetermined reference values. Further, the amounts of dislocation of the timing relationship between the display periods for the single line and single screen and a horizontal synchronizing signal and vertical synchronizing signal from predetermined reference relative relationships are determined, respectively. A picture display area adjustment means corrects the amplitudes of a horizontal deflection current and vertical deflection current corresponding to each other in accordance with the ratios determined by the arithmetic operation means, respectively and the level or phase of the horizontal deflection current and the level of the vertical deflection current corresponding to each other in accordance with the dislocations of the relative timing relationships of the determined display periods, respectively. As a result, even if an input video signal has a different timing specification, the size and position of a picture display area can be automatically adjusted to predetermined references.