GB679725A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

679,725. Cathode-ray tubes. WESTERN ELECTRIC CO., Inc. June 29, 1949 [July 3, 1948], No. 17204/49. Class 39 (i). [Also in Group XL (c)] The pulse code modulation apparatus described in Specification 637,820, in which code groups of pulses are produced from samples of a complex input wave, is modified by forming the beam into a narrow sheet and using the input signal to deflect the beam to the code position on the target representative of the magnitude of the signal so that each complete group of pulses is produced simultaneously in separate output leads connected to targets 21 ... 25. Beam forming and focusing electrodes 12, which may alternatively be electromagnetic means or a combination of electrostatic and electromagnetic means, form the electrons into a thin sheet. The D.C. potentials applied to deflecting plates 13, 14 may also assist in the focusing of the beam. The electrodes may have slit-like apertures to give a cylindrical lens effect to assist in this focusing action. The coding electrode 17 has five rows of apertures 31 ... 35 arranged so that the code groups of pulses are formed in accordance with the binary system. The beam is deflected over the coding electrode 17 by means of deflecting plates 13, 14 to which the complex wave samples are applied. The plates may be replaced by coils, or a combination of plates and coils may be used. The lower end of plate 17, corresponding to minimum amplitude of signal, may be extended downwards so that no output results for any signal whose amplitude is less than a predetermined minimum value. Some of the apertures may be elongated in the direction of deflection, e.g. at the centre of the plate, Fig. 2 (not shown), to suppress noise or at any other intermediate position for limiting, clipping, compression or expansion of the output. As shown in Fig. 1, the end apertures may be elongated so that the same code pulse group results from abnormally large signal samples as for maximum signal samples within the normal amplitude range. The apertures may become progressively larger or smaller as the signal amplitude increases to give " compression " or " expansion " of the output. The apertured plate and collecting electrode structure could be replaced by a suitably shaped group of collecting electrodes. It is stated that any number of " signalling conditions " may be provided, i.e. a number other than two corresponding to pulse and no pulse, and any number of rows of apertures other than five may be employed. The collector electrodes 21 ... 25 may or may not be secondary emissive. In order to prevent the beam striking the coding plate between two rows of apertures an additional set of apertures 36 is provided between the other rows of apertures and is associated with a collector 26 connected by a feedback path to an auxiliary pair of deflecting plates 15, 16. The feedback path may include amplifying and centring devices. Specifications 651,520, [Group XXXIX], and 653,298 also are referred to.