Video display control circuitry
AssigneeNixdorf Computer AG
InventorCharles Ranalli
Life of this patent
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Abstract
A multilevel video display control circuit. A plurality of current levels are developed in response to coded command signals (P1, P2, P3). The generated currents are summed together and converted to analog voltage signals (V25) to control the brightness of the pixels on the display. A contrast adjustment network (26) includes a first potentiometer (K1) for setting the magnitude of one of the currents at a desired level. A second potentiometer (K2) is provided for varying the magnitudes of the other current levels while maintaining the first current at the preset magnitude. Preferably, the magnitude of the first current is inversely varied with respect to other current levels.
Claims9
Multilevel video display circuitry comprising:
- first circuit means (10) for developing a first current in response to a first command signal (P1);
- second circuit means (12) for developing a second current in response to a second command signal (P2);
- third circuit means (14) for developing a third current in response to a third command signal (P3);
- summing means (28) coupled to the outputs of said first, second, and third circuits for summing the currents developed thereby;
- output means (22) for providing selected voltage levels to control the brightness of dots on the video display as a function of the output of the summing means;
- and
- contrast adjustment network means (26) including first means (K1) for setting the magnitude of the first current at a desired dim but visible level by varying the first current and simultaneously inversely varying said second and third currents, and second means (K2) for varying the magnitude of said second and third currents while maintaining said first current at said desired level.
A method of generating and adjusting the contrast of multilevels of video display signals, said method comprising:
- generating a first brightness level on a video display from a first current generating circuit;
- generating a second brightness level on the video display from a summation of currents from the first circuit and a second current generating circuit;
- initially setting the first brightness level to a dim but visible level on the display by varying the current from the first circuit and simultaneously inversely varying the current from the second circuit;
- and
- thereafter, adjusting the current from the second circuit to adjust the brightness of the second level while maintaining the current from the first circuit at the previously adjusted level.
Dependencies are inferred from the claim text.