Abstract: A digital staircase search is provided for the automatic fine tuning (AFT) control of a television receiver to extend the range of fine tuning. The staircase search generator is of digital construction to provide the capability of holding the level of search voltage obtained when the picture carrier is detected and to realize discrete steps of tuning voltage change, each step being within the pull-in range of the AFT. The search signal generated has each step of the staircase of opposite polarity so that sweep of the tuning voltage is bi-directional. The absence of a picture carrier activates operation of the search mode and disables the automatic fine tuning control. Upon detection of the picture carrier a harmonic of the horizontal sync pulses in the detected carrier is converted to a control signal which disables the search process and enables operation of the automatic fine tuning control. The automatic fine tuning control operates from the step of the staircase held upon search termination.

Abstract: A chroma level control circuit for a television receiver is responsive to the average of selected portions of color difference signals to reduce deviations from a viewer-selected chroma level. The preferred chromal level is selected by the viewer and the automatic control circuit responds to amplitude variations in selected portions of the color difference signals to stabilize chroma level about the preferred level. A gating circuit is responsive to the demodulated color difference signals and selective of portions thereof, e.g. the positive portion of the R-Y signal, so that only selected hues are used to automatically control the chroma level by adjustment of the receiver's chroma gain controlled amplifier. The circuit is also responsive to low brightness levels in the scene to temporize chroma level control during low brightness scenes. In addition, the chroma level control circuit is frequency selective, i.e.

Abstract: An automatic saturation control system for a color television receiver using color information extracted from a vertical interval reference (VIR) signal to establish the saturation setting of the receiver. The saturation setting is governed by the ratio of an AC coupled luminance signal and one AC coupled color difference signal during a single interrogation of the VIR signal.

Abstract: An automatic hue control system for a color television receiver using a single sampling of a vertical interval reference (VIR) signal to establish the hue setting of the receiver. A VIR signal periodically appears during a pre-selected line in the vertical blanking interval of a broadcast video signal and includes a chrominance reference portion of such phase that one color difference signal as detected should be zero and another portion having no chroma content. Sampling of the VIR signal during at least a portion of the chrominance reference portion and AC coupling in the control loop enables the loop to respond to any transition in the one color difference signal between chroma reference times and no chroma times. Any such transitions are used to correct the hue setting of the receiver.