AUTOMATIC CIRCUIT FOR CONTROLLING ASPECT RATIO OF A SCREEN

摘要

A circuit which can automatically control an aspect ratio based on the number of horizontal sync signals inputted for the period of vertical sync signal. The circuit includes a horizontal sync signal detecting part(10) for detecting a horizontal sync signal from an inputted video signal; a horizontal sync amplifying part(20) for amplifying the horizontal sync signal from the horizontal sync signal detecting part at a rate; a differentiator(30) for differentiating an amplified horizontal sync signal from the horizontal sync amplifying part; a horizontal AFC part(40) for automatically controlling a frequency of differentiated horizontal sync signal from the differentiator; a horizontal oscillating part(50) for synchronizing an automatically controlled frequence signal from the horizontal AFC part with a reference frequence; a horizontal filtering part(60) for filtering a noise from a signal from the horizontal oscillating part; a horizontal frequence detecting part(70) for detecting the frequence of a horizontal sync signal inputted from the horizontal sync signal detecting part; a detected signal output part(80) for integrating the horizontal sync signal from the horizontal frequence detecting part; a switching part(90) for comparing a voltage of integrated signal with a reference voltage; a horizontal deflection coil(100) for outputting a horizontal deflection current according to a switching operation of the switching part; and a horizontal output part for controlling an aspect ratio based on the signal from the horizontal filtering part and the horizontal deflection current from the horizontal deflection coil.