Patent ID: 6023133
Filing Date: 2000-02-08
Classification: H04N

Abstract:
A parabolic signal generator for use in a cathode ray tube (CRT) display circuit, comprising:programmable delay means for receiving a CRT horizontal flyback signal and for producing an output which is delayed relative to the horizontal flyback signal by a programmable predetermined time;ramp generating means coupled to receive the output from the programmable delay means, the ramp generating means for producing a ramp signal in response to the output produced by the programmable delay means, wherein the ramp generating means comprises:capacitor means having a first terminal for connection to a first reference potential and having a second terminal;first switch means for connecting a charging current to the second terminal of the capacitor means during the second portion of the ramp signal;second switch means for connecting a discharging current to the second terminal of the capacitor means during the third portion of the ramp signal; andclamping means for clamping the second terminal of the capacitor means to a predetermined potential during the first portion of the ramp signal wherein the clamping means comprises:a resistive divider for connection between a first and a second reference potential and having an intermediate point for producing a potential between the first and second reference potentials; andthird switch means for connecting the intermediate point of the resistive divider to the second terminal of the capacitor means during the first portion of the ramp signal; anda timing counter responsive to the output produced by the programmable delay means, the timing counter for controlling:the duration of a first portion of the ramp signal during which the signal's amplitude remains substantially constant,the duration of a second portion of the ramp signal during which the signal's amplitude increases, andthe duration of a third portion of the ramp signal during which the signal's amplitude decreases;wherein the duration of the second portion of the ramp signal and the duration of the third portion of the ramp signal are substantially equal, and the rates of change of the ramp signal's magnitude during the second and third portions are substantially equal, whereby the ramp generating means produces a substantially symmetric ramp signal;parabola generating means coupled to receive the ramp signal from the ramp generating means for producing a parabolic signal.