GB1242465A - Convergence deflection system for a color picture tube - Google Patents

Abstract

1,242,465. Cathode-ray tube circuits. SONY CORP. 16 June, 1969 [15 June, 1968], No. 30388/69. Heading H4T. In a single-gun three beam colour television cathode-ray tube in which the beams are focused on the tube screen by means of an electron lens through the optical centre of which all of the beams pass with two of the beams emerging from the lens along paths which are divergent to the optical axis whilst the third beam travels along this axis, convergence of the three beams at the screen is effected by means of electrostatic deflecting means acting on the two divergent beams the deflecting means being supplied with a fraction of the EHT operating D.C. voltage to provide for static convergence and with a parabolic wave of line scanning frequency modulated by a sawtooth wave, also at line scanning frequency, to provide for dynamic convergence. As shown in Fig. 1 the divergent beams B B (Blue) and B R (Red) emerging from lens L are converged with the axial beam B G (Green) to pass through a common opening in an aperture grill (or shadow-mask) and then diverge to fall on respective colour dot or stripe elements S R (Red), S G (Green) and S B (Blue) on the colour screen S by the application of the static and dynamic deflecting voltages to pairs of electrostatic deflecting plates P, Q and P<SP>1</SP>, Q<SP>1</SP> acting on the beams B B and B R respectively. For static convergence a voltage V Q derived from a potential divider 30, 32 connected across the EHT supply V p is supplied to the plates Q, Q<SP>1</SP> whilst the full voltage V p (=V Q +200 to 300 V) is supplied to the plates P, P<SP>1</SP> (and also to the electrodes G3, G5 and to the screen S) the arrangement resulting in a static convergence voltage V c adjustable by means of resistor 32 appearing between the plates P, P<SP>1</SP> and Q, Q<SP>1</SP>. For dynamic convergence a parabolic wave derived from a capacitor 27 in series with the line deflection coil 26 is supplied via an amplitude adjusting inductor 43 to one end of the primary 31a of a transformer 31 in which it is combined with a sawtooth wave at line frequency derived by the integrating effect of an inductor 35 and the resistance of a potentiometer 36 on line frequency pulse in a secondary winding 25C on the line transformer 25. A portion of the parabolic wave from a capacitance divider 38, 39 is fed to the centre tap of potentiometer 36 and the output from the slider 42 is fed to the other end of primary 31a. The dynamic convergence wave thus derived, the tilt of which is adjustable by potentiometer 42 and the magnitude by inductor 43, is then combined via the transformer 31 (which serves to isolate the EHT circuitry) with the static convergence voltage V c to provide a composite convergence voltage V c + e c . In a modification the adjustable resistor 32 is connected to the junction of resistor 30 and capacitor 44 (Fig. 3, not shown).