| 摘要 |
1. An electronic circuit conceived to ensure the control of the scanning circuit of the luminous spot on a TV-screen in accordance with a received video signal (SV), and to ensure the establishment of several signals related to the scanning, this circuit receiving the video signal (SV) and a pulse (RL) indication the flyback of the luminous spot to the start of a line and furnishing particularly a square signal (CC) at the line scan frequency and at a variable phase in order to control a switch (22) for attacking a horizontal spot deflection coil (12), this circuit comprising - an oscillator (52) with adjustable frequency, this frequency being very much higher than the line frequency and being a multiple of said frequency, - frequency dividers (58) establishing logic signals of frequencies which are submultiples of the oscillator frequency, especially a base signal which is constituted by a periodical square signal at the line frequency (FLA), - a logic circuit (60) receiving these signals of different frequencies and producing several logic signals at the line frequency, the durations and phases of these signals being perfectly defined with respect to the basic signal, - a saw-tooth signal generator (70) receiving one of the signals (EF) coming from the logic circuit, and elaborating from this signal a periodic saw-tooth (DSC) at the line frequency and perfectly phase-locked with respect to the basic signal, - a synchro-separator (50) for separating the line synchro and frame synchro signals from the video signals, - a first phase coincidence detector (62) receiving the line synchro signal and the basic signal and controlling the adjustable oscillator as to lock an original transition of this basic signal to the line synchro signal, - and a second coincidence detector (72) receiving the line flyback pulse (RL) and a logic signal at the line frequency (FLB) and furnishing a voltage which is function of the phase difference between the two incoming signals, characterized in that the saw-tooth signal (DSC) generator (70) creates a ramp which ends slightly before said original transition of the basic signal synchronized to the line synchro signal, and that ist further includes a comparator (74) which receives on the one hand the output of the second detector (72) and on the other hand the output of the saw-tooth signal generator and which delivers square pulses at the line frequency starting at a variable instant with respect to the output voltage of the second detector, in order to control the current flow in the horizontal deflection coil at such an instant that the periodical line flyback pulse which results therefrom is synchronized with respect to the logic signal coming from the second detector. |
