Recovery system for a control loop

Abstract

Non-inverting amplifier, with bandpass filter in regenerative feedback path, forms color reference oscillator in a color TV receiver. Phase shift circuit, responsive to an oscillator output, supplies signals to a first phase shifted signal amplifier, which shares a load with the non-inverting amplifier, and is subject to control by complementary outputs of a phase comparator functioning to compare the phase of an oscillator output with the phase of incoming color synchronizing bursts. A voltage comparator, responsive to the respective phase comparator outputs, is periodically enabled by field rate keying pulses. The voltage comparator output controls the charging or discharging of a capacitor during the keying intervals. A second phase shifted signal amplifier, responsive to the output of the phase shift circuit, and delivering its output to the oscillator's feedback path, is subject to control in dependence upon a comparison of a control voltage derived from the voltage held by the capacitor with a reference DC voltage. A latching circuit, subject to disabling only when receiver's color killer circuit operates in a color unkilling mode, is switched into a first latched mode of operation if voltage held by capacitor reaches a first extreme of its variation range, said first latched mode of operation forcing an unbalance of a first sense upon the voltage comparator inputs. Latching circuit is switched into a second latched mode of operation, forcing an opposite sense unbalance upon the voltage comparator inputs, if voltage held by capacitor reaches opposite extreme of its variation range.