Black compensation circuit for a video display system
US5453798A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 5, 1993 |
| Grant date | Sep 26, 1995 |
| Priority date | — |
| Expiry date | Feb 5, 2013 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N9/73
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A driver for a cathode ray tube includes a black level compensation circuit which generates an offset voltage which tracks the current flowing to the output of the driver and therefore the average picture level (APL). The offset voltage is added as a component of the output voltage so as to increasingly shift the output voltage toward black as the APL increases. This compensates for CRT gamma non-linearities and for light scattering effects which might otherwise cause the loss of perceived detail and sharpness in dark areas of a high APL image. In the disclosed embodiment, the driver comprises a cascode amplifier and the offset voltage generating element includes a capacitively bypassed resistor connected in a reference voltage network connected to the emitter circuit of the lower (common emitter configured) transistor of the cascode amplilfier.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.