Independent electron gun bias control

Claim 2

Apparatus for controlling electron beam current in a color picture tube having a plurality of electron guns, each gun having a separate cathode, the combination comprising: a plurality of amplifier circuits each having an output electrode direct current coupled to a respective one of said cathodes and first and second input electrodes for application thereto of chrominance and luminance signals, respectively; a plurality of voltage clamping circuits each coupled to an associated output electrode; a single source of repetitive pulses of variable amplitude and predetermined duty cycle; a plurality of adjustable voltage dividing circuits each associated with a separate one of said amplifier circuits for coupling controllable amplitude pulses from said source to an associated clamping circuit; a plurality of current supplying means each coupled to an input electrode of an associated amplifier circuit and to an associated clamping circuit and responsive to a difference between the quiescent voltage at the associated amplifier circuit output electrode and the peak-to-average voltage difference of the repetitive pulse waveform applied to the associated clamping circuit for substantially maintaining a predetermined direct voltage at said associated output electrode and cathode.

Claim 3

Apparatus according to claim 1 wherein: each said amplifier circuit comprises a first transistor having base, emitter and collector electrodes; each said current supplying means comprises a second transistor having base, emitter and collector electrodes; each said clamping circuit comprises a unidirectional current conducting device and a first cpacitor, each said current conducting device having first and second terminals, each said first terminal being coupled to the collector of an associated first transistor and each said second terminal being coupled to the base of an associated second transistor and an associated first capacitor; each said first capacitor being coupled between a second terminal of an associated current conducting device and said source of pulses; the collector electrode of each said second transistor being coupled to the emitter electrode of an associated first transistor for supplying current thereto in response to direct voltage developed at the second terminal of an associated current conducting device to thereby maintain the associated output electrode substantially at a predetermined direct voltage.

Claim 4

Apparatus as described in claim 2 wherein a separate voltage dividing circuit is associated with each of said amplifier circuits, said voltage dividing circuits including: a common clipping circuit for limiting the amplitude of said repetitive pulses applied thereto; a potentiometer having an input coupled to said clipping circuit and an adjustable output coupled to an associated clamping circuit; and impedance means coupled between said clipping circuit and said potentiometers for de-coupling said associated clamping circuits from said clipping circuit.

Claim 5

Apparatus for controlling electron beam current in a color picture tube having a plurality of cathodes, a single screen grid and a single control grid, each said cathode being associated with a different color-representative signal, the combination comprising: a plurality of amplifier circuits equal in number to said cathodes, each amplifier circuit having an output electrode direct current coupled to one of said cathodes and first and second input electrodes for application thereto of chrominance and luminance signals; a separate clamping circuit coupled to each of said output electrodes; a single source of repetitive pulses of predetermined duty cycle; a plurality of adjustable voltage dividing circuits, one associated with each of said amplifying circuits, for coupling a controllable portion of said pulses to each said clamping circuit; current supplying means associated with each said amplifier circuit and coupled to an associated clamping circuit for supplying current to the associated amplifier circuit in response to differences between the quiescent voltage at the associated output electrode and the peak-to-average voltage difference of the pulses applied to the associated clamping circuit; and switching means operative for supplying chrominance and luminance inputs representative of black images to said first and second input electrodes of said amplifier circuits to facilitate adjustment of said voltage dividing circuits.

Claim 6

Apparatus for controlling electron beam current in a color picture tube having a plurality of cathodes, a single screen grid and a single control grid, each said cathode being associated with a different color-representative signal, the combination comprising: a plurality of amplifier circuits equal in number to said cathodes, each amplifier circuit having an output electrode direct current coupled to one of said cathodes and first and second input electrodes for application thereto of chrominance and luminance signals; a separate clamping circuit coupled to each of said output electrodes; a single source of repetitive pulses of predetermined duty cycle; a plurality of adjustable voltage dividing circuits, one associated with each of said amplifying circuits, for coupling a controllable portion of said pulses to each said clamping circuit; current supplying means associated with each said amplifier circuit and coupled to an associated clamping circuit for supplying current to the associated amplifier circuit in response to differences between the quiescent voltage at the associated output electrode and the peak-to-average voltage difference of the pulses applied to the associated clamping circuit; and switching means operative for supplying chrominance and luminance inputs representative of black images to said first and second input electrodes of said amplifier circuits to facilitate adjustment of said voltage dividing circuits.