GB1323154A - Colour television display arrangement - Google Patents

Abstract

1323154 Electron beam magnetic deflecting apparatus PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 6 July 1970 [9 July 1969] 32716/70 Heading H1D [Also in Division H4] In a colour television tube isotropic astigmatism is corrected by providing four toroidal correction coils 20-23, Fig. 3, which are arranged to produce a quadrupole field and which are fed with currents proportional to the squares of the deflection currents. As shown in Fig. 3 the coils 20-23 may be wound in the gaps between the deflection coils 25 and 26 on a common core ; coils 20 and 23 are wound in the opposite sense to coils 21 and 22 so that when the coils are energized in series a quadruple field is produced (Fig. 4, not shown). As an alternative the coils 20-23 may be located on the neck of the tube underneath the deflection coils. When the tube uses three electron guns in delta formation the usual dynamic convergence unit is provided, and the correction coils are fed with currents of the form ax<SP>2</SP>-by<SP>2</SP>; adjustable currents proportional to Œx or Œy may be added to correct for asymmetry between the coil halves or for gun alignment errors (Fig. 11, not shown). When the tube uses three co-planar beams, or if the tube is of the single beam index type, the coils are supplied with currents of the form ax<SP>2</SP> + by<SP>2</SP>, and a separate convergence unit is not necessary.