Patent GB-483999-A (GB)
Title: Improvements in or relating to circuits for generating deflecting waveforms for cathode ray tubes
IPC: H04N3/233
Filed: 1936-10-28
Abstract: 483,999. Valve generating circuits. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. Oct. 28, 1936, No. 29332. Convention date, Oct. 28, 1935. [Classes 40 (iii) and 40 (v)] A saw-tooth line frequency oscillator, particularly for television, comprises an in ductance associated with a capacity, preferably its distributed capacity, 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 action of the line frequency oscillator, before the frame frequency oscillation is applied, is described with reference to Figs. 1, 2. The screen grid valve 10, Fig. 1, is rendered conducting and its anode current flows over (1) inductance 11 and (2) diode 12. The current i1, Fig. 2, through inductance 11 increases linearly while the current i0 through the diode 12 decreases. When i1 reaches a valve i2 the valve 10 is rendered non- conducting and current ceases to flow in the diode while the interruption in the inductance circuit causes the inductance to oscillate. In one half-cycle of oscillation, the current through the inductance goes to i3 (=-i2) and the voltage across the inductance is zero. In the next half-cycle, the voltage across the inductance quickly becomes greater than that of source 13, so that the diode 12 becomes conducting, and the current through the inductance slowly decreases to zero. Before it reaches zero, valve 10 is rendered conducting and the current in the inductance then rises from zero to i2 when the valve 10 is again rendered nonconducting. The wave form shown in Fig. 2 is thus produced and it is stated that the slope from t3 to t4 is dependent on the value of the source 13. To produce a trapezoidal scanned area, the source 13 is augmented by a saw-tooth voltage at frame frequency. This may be produced by a transformer 17, Fig. 3, whose primary is energized with a parabolic current to give a saw-tooth voltage in the secondary. Alternatively, a condenser 18, Fig. 7, and resistance 19 may be employed. The condenser 18 charged over the diode and is partially discharged over the resistance 19 when the valve 10 is rendered nonconducting for an appreciable time, as by a frame synchronizing signal. The time constant of 18, 19 is such that condenser 18 is not discharged when the valve 10 is rendered nonconducting at the end of each line. The resistance 19 may be replaced by a screen grid valve, Fig. 9 (not shown), which may be rendered conducting by the framing signals, Fig. 10 (not shown), and may also be partially conducting at other times, Fig. 12 (not shown). The condenser 18, Fig. 14, may be rapidly discharged by a valve 24 rendered conducting by the framing signals, and slowly charged through a valve 21 during the scanning. Alternatively, the condenser 18 may be slowly discharged by valve 21 during the scanning and rapidly charged by valve 24 rendered conducting by the framing signals, Fig. 16 (not shown). In order to maintain the current i0, Fig. 2, constant during the scanning, the screen grid of valvo 10 may be energized with a frame frequency saw-tooth voltage, Fig. 19 (not shown). Specification 412,813 is referred to.