Automatic Brightness Control and Linearity Correction Circuits for Large Screen Color Oscilloscopes

In ordinary oscilloscopes, the brilliance of the trace depends strongly on the deflection speed of the beam. With the circuit described here, a uniform optimal brightness of the oscillograms is obtained independently of the shape of the curve and the frequency of repetition. Thus even steep slopes are well visible from a distance, and manual adjustment of the brightness becomes superfluous. This is especially important in lecture demonstrations. A protective circuit limits the cathode current so that a standing beam cannot burn out the screen. The circuits were designed for large color picture tubes, but they are also suitable, in a simplified form, for improving monochromatic oscilloscopes [1]. In lage picture tubes, the relation between the beam deflection and the deflection currents is not linear. The resulting distortions on the screen call for proper correction signals. These while depending on x- and y-beam positions, must not be influenced by the deflection frequency.