Black compensation circuit for a video display system

Details Black compensation circuit for a video display system Black compensation circuit for a video display system

1993-02-05

1995-09-26

Groody, James J.

Television

Image signal processing circuitry specific to television

Dc insertion

348691, H04N 972

Patent

active

054537983

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.

REFERENCES:
patent: 3947631 (1976-03-01), Rhee
patent: 4118731 (1978-10-01), Hinn
patent: 4691235 (1987-09-01), Okui
patent: 4811101 (1989-03-01), Yagi
patent: 5083198 (1992-01-01), Haferl et al.
patent: 5162902 (1992-11-01), Bell
patent: 5223927 (1993-06-01), Kagayama
patent: 5339114 (1994-08-01), Lagoni et al.

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