GB525680A - Improvements in or relating to circuits for generating deflecting waveforms for cathode ray tubes - Google Patents

Abstract

525,680. Television valve generating circuits. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. Jan. 25, 1939, No. 2529. Convention date, Jan. 26, 1938. Addition to 483,999. [Classes 40 (iii) and 40 (v)] The parent Specification relates to a saw-tooth line-frequency current generator comprising an inductance 3, Fig. 8, associated with a capacity, preferably its distributed capacity 4, to which is applied a saw-tooth voltage at frame frequency so as to produce the required lengthening or shortening of the lines for a trapezoidal scanned area. The saw-tooth voltage of frame frequency may be produced by a condenser 6, associated with a rectifier 2 across the oscillatory circuit 3, 4. According to the present invention-(1) the linearity of the voltage across the condenser 6 is improved by connecting it in the anodecathode circuit of a valve 7 which is controlled by the voltage generated across condenser 6 and by a further voltage of saw-tooth wave form applied e.g. to its grid; (2) to remove the distortion from symmetry of the keystone scanning field due to a direct-current component which varies in a saw-tooth manner at frame frequency, current passed by the valve 7, or a current derived therefrom, is superimposed on the current in the deflecting coil. The current derived from the valve 7 may be fed to the coil 3 through a transformer, Figs. 14, 15, 16, 17 (not shown). To prevent displacement of the scanning field during the frame return stroke, the condenser 6 may be shunted by an additional valve controlled by impulses in such a way that the discharge of the condenser during the short flank of the saw-tooth wave form passes through the valve and not through the coil, Figs. 11, 14, 15 (not shown). The coil may also be connected to the charging valve 1 through a transformer Figs. 12, 13, 14 (not shown).