GB1407223A - Deflection circuits for cathode-ray tubes - Google Patents

Abstract

1407223 Electron beam electrostatic focusing and deflecting systems PHILIPS ELECTROMC & ASSOCIATED INDUSTRIES Ltd 1 Sept 1972 [4 Sept 1971] 40578/72 Heading H1D [Also in Division H4] A combined focusing and deflecting system comprises an electrode divided into segments (such as S1-S8, Fig. 2) which are connected in a bridge circuit to two deflection signal generators and to a source of focusing potential; the electrode may be arranged between two cylindrical electrodes to form a lens in an image pick-up tube (Fig. 1, not shown). In the arrangement shown in Fig. 2 the horizontal and vertical deflection generators G H and G V supply voltages ŒU H #2 and #Uv#2 to opposite points of the bridge; resistances R1-R8 are equal whilst the ratio of R9 to R10 (and similar pairs) is such that the potential on S1 is U V which has a maximum value of 25 volts. Thus the potentials on the segments are as shown and correspond to the function U V cos #+U H sin # where is the mean angle of the segment with respect to the vertical axis. A focussing potential U F of 100 volts is supplied to the centre of the bridge. In a modification (Fig. 3, not shown), the focusing potential V F is connected to a potentiometer connected between point P5 (the junction of R10 and R11) and point P6 (the junction of R14 and R15), these points being connected through respective resistances to a common resistance leading to earth; this produces an adjustable quadrupole field between the four odd segments which can correct for astigmatism. By connecting the four even segments in a similar way to the focusing potential source the axes of the quadrupole field may be altered; the four resistances then provided to connect the even segments may be made less than resistances R10, R11, R14 and R15 in order to correct for pincushion distortion or greater in order to correct for barrel distortion. To provide for vertical shift a D.C. component may be added to the A.C. supplied across points P1 and P3, and a similar arrangement may be provided for horizontal shift. If the supply to the electrode segments is made via a cable having appreciable capacitance, resistances R2, R3 and R13 and the corresponding resistances near P4 should be shunted by capacitors; this would be unnecessary if the bridge were formed of a printed circuit near or on the tube envelope, either inside or outside. In a modification, Fig. 4 (not shown), the electrode comprises only six segments, segments S3 and S7 being omitted and the potential on S2 being and the electrode might even be reduced to four segments disposed between the deflection axes.