SANDCASTLE PULSE
The decoder ICs shown in Figs 7.7 and 7.9 both use a sandcastle pulse for timing and gating purposes. It is generated in the line output stage or the line oscillator section, and takes the form shown in Fig.
7.10. The lower section of the pulse, used mainly for picture blanking during line flyback, is 12 μs wide and embraces the entire line blanking period. The narrow superimposed pulse on its top is used for gating during the period of the colour burst, and is about 3 μs wide; these line-rate pulses are separated by slicers within the chip. In some TV designs the sandcastle pulse has a component at field rate too, used for picture blanking and for extinguishing the scanning beams in the event of a loss of vertical deflection: it prevents burning of the screen phosphors.