| 摘要 |
1,092,498. Colour television. HAZELTINE CORPORATION. Aug. 23, 1966 [Dec. 30, 1965], No. 37691/66. Heading H4F. In a colour television receiver in which three colour difference signals (R-Y), (B-Y) and (G-Y) are applied to a colour image reproducing device, e.g. to the grids of a three-gun tube, the D.C. component of a selected one, i.e. (G-Y), of the colour-difference signals is suppressed. In addition the D.C. components of the (R-Y) and (B-Y) may be partially attenuated by predetermined amounts. According to the Specification this elimination of full D.C. stabilization or D.C. restoration in all of the colour difference signal paths does not appreciably degrade the subjective quality of the reproduced colour image. In a first embodiment, Fig. 3, the D.C. component of (G-Y) is suppressed by A.C. coupling it to the green control grid of the tube by means of series coupling capacitor 18. Since this also blocks the D.C. operating bias which is normally supplied to the green grid along with the (G-Y) signal, a fixed D.C. operating bias is supplied by voltage divider 19, 20. This fixed bias must be selected to provide proper reproduction of the grey-scale during monochrome reproduction. In this embodiment the full D.C. and A.C. components of the (R-Y) and (B-Y) signals are coupled to their respective control grids, but in a second embodiment, Fig. 4, not shown, the D.C. components of the (R-Y) and (B-Y) signals are partially attenuated by means of partial D.C. coupling networks (22, 23, 24) and (21, 25, 26) placed in both the signal paths to the red and blue grids of the colour tube. In a third embodiment, Fig. 5, not shown, grey scale balance is ensured by developing a D.C. bias for the green grid directly from the output circuits of the (R-Y) and (B-Y) demodulators in the chrominance signal decoder since if in the arrangement of Fig. 4, not shown, variations of the D.C. operating conditions of the receiver occur the D.C. voltages applied to the red and blue grids would change, but the D.C. bias applied to the green grid would remain constant. |
