Stabilization network for a cathode ray tube

In a color television receiver which develops a video signal and which includes a cathode ray tube having a plurality of cathodes, a stabilization network which compensates for variable emission characteristics of a cathode, comprising:

• means for generating a reference current indicative of a desired level of cathode current when the video signal is set at a predetermined level;
• means for sampling cathode current in response to an enabling signal, for comparing cathode current to the reference current, and for generating a control signal indicative of the difference between cathode current and the reference current;
• first and second emitter-coupled transistors, the base of the first transistor receiving a bias voltage, the base of the second transistor receiving the control signal, and the collector of the second transistor being coupled to a load across which an output signal is developed for application to the cathode;
• transistor means receiving the video signal and coupled to the emitters of the first and second transistors for modulating the collector current of the second transistor in response to amplitude variations in the video signal;
• and
• a timing generator for developing and applying an enable signal to said sampling means during the receiver's vertical interval and for simultaneously injecting current to the emitters of said first and second transistors to simulate a condition representing said predetermined level of the video signal so that the control signal alters the conduction of said second transistor and the cathode current is set to said reference current level.

In a color television receiver which includes a cathode ray tube having three cathodes, which develops yoke current for vertically deflecting the beam of the cathode ray tube, and which develops a video signal having a blank level offset from its black level by a known voltage difference, a stabilization network which compensates for variable emission characteristics of a cathode, comprising:

• a variable gain amplifier receiving the video signal for driving the cathode with an amplified video signal and a D.C. bias, said amplifier being responsive to a variable control voltage for altering its gain and its D.C. bias output such that, for a given cathode current which is developed in response to the D.C. bias, a selected peak white cathode current is developed in response to peak white portions of the video signal;
• means for generating a reference current indicative of a desired black level cathode current;
• a comparator receiving the cathode current and the reference current and responsive to an enabling signal for comparing the cathode current to the reference current and for generating a control signal indicative of the difference between the cathode current and the reference current;
• means for coupling the control signal to the amplifier;
• and
• a timing generator receiving the yoke current for generating an enable signal during that portion of the yoke current which corresponds to uppermost beam deflection and for simultaneously offsetting the output of the amplifer by an amount corresponding to the voltage difference between the video signal's blank level and black level to simulate a black level output from said amplifier, whereby the control signal alters both the gain and the D.C. bias output of the amplifier such that the cathode current is set to the reference black level current, and video signals received subsequent to the vertical interval are amplified so that their peak white portions develop given peak white cathode currents.