US 4,387,405 AGranted

Automatic kinescope bias control system with digital signal processing

AssigneeRCA Corporation

InventorWerner Hinn

Life of this patent

Estimating the term…

Loading patent…

Abstract

Apparatus is disclosed in a video signal processing system for automatically monitoring and controlling the blanking (black) current level of an image reproducing kinescope. A kinescope cathode output signal proportional to the level of cathode black level current conduction is induced during periodic monitoring intervals during which image signals are absent. The cathode signal is induced in response to a grid drive pulse applied during the monitoring intervals. The induced cathode signal is processed by a digital signal processing network to produce incremental bias control voltage steps for modifying the cathode bias, if necessary, in a direction to produce a desired cathode black current level. In addition, there is disclosed a special form of grid drive pulse which serves to prevent system "hunting" in the vicinity of the correct cathode bias.

Claims23

Dependent claims

In a system for processing an image representative video signal having periodically recurring image display intervals and image blanking intervals during which image information to be displayed is absent, said system including an image display kinescope having an electron gun with cathode and grid intensity control electrodes;

and means for coupling video signals to said kinescope electron gun;
apparatus for automatically controlling the level of cathode blanking current conducted by said kinescope, comprising:
means for providing a reference bias voltage to said cathode electrode during a monitoring interval within said blanking interval when said blanking current conduction of said kinescope is to be monitored;
means operative during said monitoring interval for deriving a signal proportional to the level of cathode current conducted during said blanking interval;
and
signal processing means responsive to said derived signal, comprising
digital signal processing means for sensing the condition of the level of a sequence of N derived signals, where N is an integer greater than 1, to develop a first signal when a sensed sequence of derived signals corresponds to a condition of desired cathode blanking current level, and a second signal when a sensed sequence of derived signals corresponds to a deviation of said cathode blanking current level from said desired level;
and
bias control voltage generator means responsive to said second signal for supplying a bias control voltage to said video signal coupling means with a sense for modifying the bias of said kinescope cathode in a direction to adjust said cathode blanking current level toward said desired level.

6 more elements

and means for coupling video signals to said cathode electrode;
apparatus for automatically controlling the level of cathode blanking current conducted by said kinescope, comprising:
means for providing a reference bias voltage to said cathode electrode during a monitoring interval within said blanking interval when said blanking current conduction of said kinescope is to be monitored;
means for providing an auxiliary signal to said grid electrode with a sense for forward biasing said grid electrode during said monitoring interval;
means operative during said monitoring interval for deriving a signal proportional to the level of cathode current conducted during said blanking interval in response to said auxiliary signal;
and
signal processing means responsive to said derived signal, comprising
digital signal processing means for sensing the condition of the level of a sequence of N derived signals, where N is an integer greater than 1, to develop a first signal when a sensed sequence of derived signals corresponds to a condition of desired cathode blanking current level, and a second signal when a sensed sequence of derived signals corresponds to a deviation of said cathode blanking current level from said desired level;
and
bias control voltage generator means responsive to said second signal for supplying a bias control voltage to said video signal coupling means with a sense for modifying the bias of said kinescope cathode in a direction to adjust said cathode blanking current level toward said desired level.

7 more elements

In a system for processing color image representative video signals having periodically recurring image display intervals and image blanking intervals during which image information to be displayed is absent, said system including a color image display kinescope having plural electron guns each with a cathode elctrode, and an associated grid electrode energized in common with said cathode electrodes;

and means for respectively coupling video signals to said cathode electrodes;
apparatus separately associated with each of said cathode electrodes for automatically controlling the level of respective cathode blanking currents conducted by said kinescope, each of said apparatus comprising:
means for providing a reference bias voltage to said cathode electrode during a monitoring interval within said blanking interval when said blanking current conduction of said kinescope is to be monitored;
means for providing an auxiliary signal to said grid electrode with a sense for forward biasing said grid electrode during said monitoring interval;
means operative during said monitoring interval for deriving a signal proportional to the level of cathode current conducted during said blanking interval;
and
signal processing means responsive to said derived signal, comprising
digital signal processing means for sensing the condition of the level of a sequence of N derived signals, where N is an integer greater than 1, to develop a first signal when a sensed sequence of derived signals corresponds to a condition of desired cathode blanking current level, and a second signal when a sensed sequence of derived signal corresponds to a deviation of said cathode blanking current level from said desired level;
and
bias control voltage generator means responsive to said second signal for supplying a bias control voltage to said video signal coupling means with a sense for modifying the bias of said kinescope cathode in a direction to adjust said cathode blanking current level toward said desired level.

7 more elements

Dependencies are inferred from the claim text.