TELEVISION DISPLAY APPARATUS

摘要

1307547 Cathode-ray tube circuits PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 26 May 1970 [29 May 1969] 25213/70 Heading H4T In a television display system in which a correction current comprising a line frequency sawtooth current amplitude modulated by a field frequency sawtooth wave is combined with the line frequency scanning current for scan distortion correction (particularly distortion due to anisotropic astigmatism of the deflection coils), the correction current is produced by means of a modulator comprising switching diodes 15, 16 (Fig. 1) rendered non- conducting by line fly-back pulses derived from a winding 14 on the line transformer 13 and supplied with the modulating field frequency waveform 1 via a transistor amplifier 5, 6 the operating D.C. voltages for which, - V b1 + V b1 , are produced by the rectification action of the switching diodes on the line flyback pulses. Due to the modulation action sawtooth voltages of field frequency are superimposed on these D.C. voltages as shown in Fig. 2. The amplitude modulated line frequency component (Fig. 3) is developed across a high imdedance 19 and supplied, via a circuit 21 which introduces a further correction factor proportional to the third power of the line deflection current, to the line deflection circuit such that the correction current i k flows in opposite directions in the two halves 261, 2611 of the line deflection windings. The correction currents for the upper and lower portions of the display may be adjusted by respective potentiometers 3 and 4 and potentiometer 9 acts as a symmetry control. Capacitor 20 together with the line deflections circuit forms a resonant circuit having a period equal to twice the line fly-back period, capacitor 231 provides for "S"-correction and circuit 24 provides an adjustable D.C. current for centring. By modifying the circuit as shown in Fig. 4, the voltages + V b1 - V b1 become "pure direct voltages" and may be employed in other parts of the apparatus. Amplitude and symmetry adjustments may be provided for the modulating field frequency sawtooth waveform 1 (Fig. 5, not shown) and pre-amplification of the latter waveforms may be effected (Fig. 6) not shown.