| 摘要 |
1,272,996. Cathode-ray tube circuits. R.C.A. CORPORATION. 19 May, 1969 [22 May, 1968], No. 25375/69. Heading H4T. In a dynamic vertical convergence correction system for a colour television display cathoderay tube the convergence coils are supplied with separate, individually adjustable, correction waveforms derived from respective circuits during alternate halves of the vertical scanning waveforms. Referring to Fig. 1, a (partially integrated) vertical scanning sawtooth derived from the vertical deflection circuits 11 is supplied via capacitor 13 and wave-shaping arrangement of resistor 15 and diode 17 to one end of the red and green convergence coils 23, 25 and is also differentiated by means of capacitor 31 and resistances 33, 35 to produce a substantially sawtooth voltage across 35. During the positive portion of the scanning sawtooth (i.e. the portion corresponding to the top half of the picture) diode 17 is non-conducting whilst diode conducts and brings the common end of the convergence coils to earth potential so that current flow therethrough due to the scanning sawtooth is prevented. However, because of the low impedance to earth of the common end of the coils the sawtooth across potentiometer 35 provides an adjustable correction current waveform which may be differentially adjusted by potentiometer 29 and which is terminated during the negative portion of the scanning sawtooth corresponding to the bottom half of the picture when diode 21 becomes non-conducting. At this point diode 17 conducts and the scanning sawtooth suitably shaped by diode 17 and resistor 15 provides a current flow through the coils, potentiometer 19 providing a master control and potentiometer 27 a differential control. Thus the (different) corrections required during the two halves of the scan may be independently controlled for the red and green convergence coils. The blue convergence coils 49 are supplied from potentiometer 47 which controls correction in the top half of the raster and by potentiometer 45 which controls correction in the bottom half of the raster. |
