Vir-controlled hue correction circuit

Abstract

A hue correction circuit for use in video display apparatus which is responsive to a composite color video signal including luminance, chrominance, burst and VIR signals. A controllable local oscillator circuit generates a reference oscillating signal of controllable phase for use in demodulating the chrominance signal. A first phase control circuit is responsive to the burst signal for deriving a first phase control signal as a function of the phase error between the burst signal and the reference oscillating signal, this first phase control signal being applied to the local oscillator circuit to vary the phase thereof for minimizing the phase error. A gain controlled amplifier is connected to receive the luminance signal and has a controllable gain for deriving a second phase control signal as a function of the luminance signal, this second phase control signal being applied to the local oscillator circuit to vary the phase thereof. The gain of the gain controlled amplifier is varied as a function of the phase error between the chrominance reference component included in the VIR signal and the reference oscillating signal. In one embodiment, the local oscillator circuit comprises a voltage-controlled oscillator which receives the first phase control signal as the control voltage therefor, the output of this voltage-controlled oscillator being coupled to a controllable phase shifter which receives the second phase control signal. In another embodiment, the local oscillator circuit is a voltage-controlled oscillator whose phase is controlled by the output of a matrix circuit, the latter receiving both the first and second phase control signals. In this embodiment, a differentiated version of the luminance signal is amplified by the gain controlled amplifier to produce the second phase control signal.