Line Time Base Circuits

Abstract

Horizontal scanning of the screen is under the control of an oscillator which is synchronised with the action of the electron beam of the camera tube at the transmitter. In the 625-line system the line repetition frequency is 15 625 Hz, and each line period of 64 μs consists of 52 μs of actual picture information (active picture line) and 12 μs line blanking. During the latter period there is a line synchronising pulse which lasts 4.7 μs. These timings are important, because they explain the different design of line time base circuits when compared with their field counterparts described in chapter 9. The common factor between them is the requirement to provide an approximately sawtooth deflection current waveform in the scan coils.