GB722146A - Improvements in signal translating apparatus correction systems - Google Patents

Abstract

722,146. Copying telegraphy. RADIO CORPORATION OF AMERICA. July 23, 1952 [July 31, 1951], No. 18671/52. Class 40 (3). In apparatus for controlling an image reproducing cathode-ray tube so as to obtain a linear or predetermined shape of transfer characteristic, the beam current is switched on and off by a source of pulses of sufficiently high frequency to prevent resolution of the dot structure on the screen and the image signals are applied to control the duration of the pulses. By employing linear saw-tooth pulses which are clipped to obtain square waves at a level determined by the image signals a linear transfer characteristic is obtained. By employing a wave shape others than saw-tooth, other arbitrary transfer characteristics may be obtained. In the Figure sawtooth waves are generated across condenser 38 by valve circuit 10, 20 and applied to the grid of triode 40. The peak position level of the saw-tooth is set to the stabilized potential at the junction of resistors 70, 72 by the righthand diode 60. Triode 40 functions as a cathode follower to apply the saw-tooth wave to the triode 50 by virtue of the common cathode resistor 48. Image signals obtained from a source of signals 80, such as a flying spot scanner, are applied through amplifier 84 to the grid of triode 50. The signals control the level at which the valve cuts off under the action of the cathode saw-tooth wave and are applied in such sense as to increase the level of the sawtooth at which cut off takes place with increase of signal. By this means there is obtained from across anode load 56 a substantially rectangular wave, the width of which is controlled by the image signals. Potentiometer 86 permits the bias to be set such that no output of rectangular wave is obtained with zero image signal. The output from load 56 is applied to the grid of cathode-ray tube 90 and the upper level of the wave is set to the potential at the junction of resistors 75, 76 by the left-hand diode 60. The bias 96 for the cathode-ray tube is set so that the rectangular pulses switch the beam on and off. A photographic film or plate is placed in front of the screen of the tube to develop the image thereon.