GB889841A - Improvements in or relating to correction systems for colour cathode ray tubes - Google Patents

Abstract

889,841. Cathode-ray tube circuits. FERNSEH G.m.b.H. June 22, 1959 [June 20, 1958], No. 21315/59. Class 40(7). In a three-beam shadow-mask cathode ray colour reproducing tube the deflection correction magnets 13, 14 (Fig. 7) for the two beams which are not in the vertical plane of symmetry have supplied thereto, in addition to the normal correction currents from generators G, R, further correction currents derived from voltages produced by modulating in circuits 5, 6 respectively, a frame frequency sawtooth voltage 7 by a parabolic, line frequency, voltage 8 and a line frequency sawtooth voltage 9. The output of modulator 5 comprising the waveform 10 is supplied, via amplifier 11 and transformer 12, in anti-phase to the generators G, R resulting in currents, additional to the normal correction currents, of the form shown in Fig. 4. By adjusting the normal correction currents so that, instead of having errorfree positions along vertical and horizontal central lines as shown in Fig. 1. (the lines 1, 1<SP>1</SP>, 2, 2<SP>1</SP> and 3, 3<SP>1</SP> of which show the green, blue and red raster lines respectively), such positions occur at the upper margin, as shown in Fig. 2, the additional correction currents (Fig. 4) reduce the registration errors at the lower edge to the same small amount present at the centre. The remaining errors (parallelogram errors), i.e. at the side edges where, as shown in Fig. 5, the ends of the lines of the green raster (broken lines) are skewed in relation to those of the red raster (full lines) are compensated by the output of modulator 6 (waveform 22) which is supplied to the generators G, R, via amplifier 15 and transformer 16 and gives rise to currents of the form shown in Fig. 6c. Suitable circuits for the modulators 5 and 6 are described in connection with Fig. 8 (not shown).