| 摘要 |
<p>Video signals to be displayed are applied via a video driver amplifier (50) to the cathode electrode (32, 34, 36) of a kinescope (30). A beam current sensor (56), also coupled to the cathode electrode (32, 34, 36), provides a beam current indicating signal (S6). An AKB regulator (60), responsive to the beam current indicating signal (S6), supplies a black level correction signal (Ia) to the driver amplifier (50) for regulating the black level of images displayed by the kinescope (30). A screen grid supply system (70, 90) is provided for controlling the G-2 (screen grid) voltage of the kinescope (30) as a predetermined function of the black level correction signal (Ia) thereby forming with the AKB regulator (60) a dual feedback loop for providing black level regulation by both the driver amplifier (50) and the screen grid (G2) thereby maximizing or extending the overall black level control range. Consequently, the high voltage screen control potentiometer (97) normally required for setting screen grid bias may be completely eliminated if desired, or, in applications where it is retained, no adjustments are required subsequent to an initial adjustement.</p> |
