Interference-free setting of background on TV receiver - using integrator in brightness signal operating at rear edge of dark signal

摘要

The application is to t.v. receivers with facility for receiving and displaying videotext information. If the incoming signal is weak and susceptible to noise this can give rise to a disconcerting striated background effect when videotext is being displayed. The relevant part of the video signal can be cleaned up by adding an integrator (13) to the brightness signal channel (Y) between the decoder (2) and the picture controller (3). This integrator, or filter, is controlled by a switch (14) activated by pulses (15) from the controller in synchronism with the received signals. The integrator ensures that during the relevant interval a steady voltage level exists to set the background luminance on the tube (4) to an undisturbed value.