Trilevel sandcastle pulse encoding/decoding system

Abstract

A color TV receiver is provided with an encoding/decoding system for a trilevel sandcastle pulse train, exhibiting a middle pulse level during recurring kinescope bias control intervals, and comprising excursions between a base level, a low pulse level, and a high pulse level during periods outside said kinescope bias control intervals. The system's decoder includes a trio of voltage comparators for comparing incoming sandcastle pulses with respective reference voltages derived from three different intermediate points on a common voltage divider connected across the terminals of a DC supply. The system's encoder includes keyed means for determining the middle pulse level of the trilevel sandcastle pulse train in accordance with the output of a second voltage divider connected across the same DC supply as the first voltage divider. An output of a third, selectively enabled, voltage divider, connected across the same DC supply as the first and second voltage dividers, is determinative of said low pulse level. The third divider is subject to modification during base level appearances, with the base level determined by the third divider's modified output during the periods of divider modification. During high pulse level appearances, the third voltage divider is disabled to establish the high pulse level at or near the full output potential of the DC supply.