Automatic white control circuit for color television receiver

Claim 1

An automatic white control circuit for a color CRT provided with red, green and blue cathodes, comprising: color signal source means for providing red, green and blue color signals; amplitude/level controller means for controlling the amplitude of each of said red, green and blue color signals in accordance with given red, green and blue amplitude control signals, and for controlling the DC level of each of said red, green and blue color signals in accordance with given red, green and blue level control signals, thereby generating red, green and blue amplitude and level-controlled signals; a CRT drive circuit for driving each of the red, green and blue cathodes of said color CRT in accordance with said red, green and blue amplitude and level-controlled signals; current detector means for detecting a current of each of said red, green and blue cathodes, and for providing red, green and blue cathode current indicative signals; pulse generator means for generating: (1) a first reference pulse having a first amplitude, (2) a second reference pulse having a second amplitude which differs from said first amplitude, (3) a first gate pulse generated in synchronism with said first reference pulse, and (4) a second gate pulse generated in synchronism with said second reference pulse; a pulse insertion means for inserting said first and second reference pulses into each of said red, green and blue color signals; means for sampling, in accordance with said first gate pulse, each signal level of said red, green and blue cathode current signals to provide red, green and blue DC level control potentials, and for sampling, in accordance with said second gate pulse, each signal level of said red, green and blue cathode current signals to provide red, green and blue amplitude control potentials; first comparator means for comparing each of said red, green and blue level control potentials with a first given reference potential, and for providing said given red, green and blue level control signals, thereby forming DC negative feedback control loops for controlling each bias of the red, green and blue cathodes of said color CRT; and second comparator means for comparing each of said red, green and blue amplitude control potentials with a second given reference potential, and for providing said given red, green and blue amplitude control signals, thereby forming AC negative feedback control loops for controlling each amplitude of the red, green and blue cathode currents of said color CRT, wherein the automatic white control for said color CRT is effected by the operation of said DC negative feedback control loops, whose control targets are defined by said first given reference potential, and by the operation of said AC negative feedback control loops whose control targets are defined by said second given reference potential.