Keyed DC stabilization system with protection from error introduction during vertical sync interval.

摘要

DC stabilization system for a color TV receiver includes three control loops, each including a keyed comparator (35, 31, 33) for comparing a respectively different one of a set of blue, green, and red color signals with a common reference voltage (RV) during keying periods determined by line rate keying of «backporch» timing pulses (K). The output of the keyed comparator (35) responding to the blue signal adjusts the DC level of a luminance signal component used in color signal formation. The output of the keyed comparator (33) responding to the red signal adjusts the DC level of an I color-difference signal component used for color signal formation. The output of the keyed comparator (31) responding to the green signal adjusts the DC level of a Q color-difference signal used for color signal formation. The line rate keying pulse source (50) is subject to field-rate blanking to prevent comparator keying during significant portion of received signal's vertical sync interval.