Automatic hue control system

An automatic hue control circuit for a color television receiver responsive to a composite signal including at least a subcarrier signal, modulated in phase and amplitude to represent hue and saturation of a color image, and a burst component, said circuit providing a subcarrier reference signal at the frequency of the received subcarrier signal and including in combination:

• first means for supplying signals corresponding in frequency and phase to the received subcarrier signal;
• second means for supplying reference signals at the frequency of the received subcarrier signal and at a predetermined phase relative to the phase of the burst component;
• phase comparator circuit means having first and second inputs coupled with said first and second means for supplying signals. respectively, and having an output;
• means for supplying a reference voltage;
• amplitude comparator circuit means having first and second inputs, with said first input coupled with the output of said phase comparator circuit means and said second input coupled with said means for supplying said reference voltage, and having an output for supplying output signals thereon indicative of which of the two input signals applied thereto is of the greater amplitude;
• and
• switching circuit means having an output for providing the subcarrier reference signal for said hue control circuit, first and second signal inputs, and a control input, the control input coupled with the output of said amplitude comparator circuit means and the first and second inputs thereof coupled with said first and second means for supplying signals, respectively, said first input thereof being coupled with the output thereof in response to output signals from said amplitude comparator circuit means indicative of a first predetermined relationship of the amplitudes of the input signals applied to said amplitude comparator circuit means, and said switching circuit means coupling said second input thereof with the output thereof in response to output signals from said amplitude comparator circuit means indicative of a second predetermined relationship of the amplitudes of the signals applied to said amplitude comparator circuit means.

A hue control circuit for providing a chrominance demodulating signal responsive to a chrominance information signal modulated in phase and amplitude to represent hue and saturation of a color image and to a subcarrier reference signal, the hue control circuit including in combination:

• limiter means adapted to receive the chrominance information signal, said limiter means being responsive to the chrominance information signal to supply a first signal having a constant amplitude and corresponding in frequency and phase to the chrominance information signal;
• circuit means for supplying a second signal at a frequency controlled by the subcarrier reference signal;
• phase comparator circuit having inputs coupled with said limiter means and said circuit means, said phase comparator circuit means comparing said first and second signals and providing an output signal at an output terminal thereof;
• and
• switch means having a control terminal being coupled to said output terminal of said phase comparator, and input terminals coupled to said circuit means and to said limiter means, said switch means selectively combining said first signal and said second signal in response to the output signal of said phase detector to form the chrominance demodulating signal.

A method of providing hue control in a color television, including the steps of:

• providing first signals at the frequency and phase of the chrominance signal;
• providing second signals at a frequency and phase controlled by the reference subcarrier for the chrominance signal;
• phase detecting said first and second signals to provide a control signal having an amplitude responsive to the phase differential between said first and second signals;
• and
• combining said first and second signals to form a chrominance demodulating reference signal, the magnitude of said control signal being capable of controlling the magnitude of at least one of said first and second signals being combined so that said magnitude can have any value within a continuous operating range.

A hue control circuit for providing a chrominance demodulating signal responsive to a chrominance information signal modulated in phase and amplitude to represent hue and saturation of a color image and to a subcarrier reference signal, the hue control circuit including in combination:

• limiter means adapted to receive the chrominance information signal, said limiter means being responsive to the chrominance information signal to supply a first signal having a constant amplitude and corresponding in frequency and phase to the chrominance information signal;
• first circuit means for supplying a second signal at a frequency controlled by the subcarrier reference signal;
• a phase comparator circuit having inputs coupled with said limiter means and said first circuit means, said phase comparator circuit comparing said first and second signals and providing an output signal at an output terminal thereof;
• and
• second circuit means having a control terminal coupled to said output terminal of said phase comparator circuit for receiving a control signal which has a magnitude that is a function of the magnitude of said output signal of said phase comparator circuit, and input terminals coupled to said first circuit means and to said limiter means, said second circuit means having a variable conductance for selectively combining said first signal and said second signal in response to the magnitude of said control signal to form the chrominance demodulating signal, said variable conductance of said second circuit means being capable of continuously adjusting the magnitude of at least one of said first signal and said second signal to any value between upper and lower limits in response to said magnitude of said control signal so that said one of said first signal and said second signal has a continuous range of operating magnitudes.