Digitally compensated multiplying digital to analog converter

DETAILED DESCRIPTION Among the integrated circuit color graphics controllers presently available on the market, there appears a distinct lack of an integrated circuit controller which provides a chip-area efficient implementation for converting digital color (hue and saturation) and intensity data into analog signals suitable to control the red, green and blue guns of a video display while providing the ability to fade the colors, change the selectable group of colors, and provide overlay and flood colors, where all the color sets are alterable at frequencies compatible with the blanking cycle of the color video displays.
The present invention, in its various forms, satisfies these objectives by providing a dynamically variable set of pixel colors in digital format and grouped by intensity, red color, green color and blue color, which colors are intensity adjusted and converted into analog signals with a cascaded, multiple stage R-2R type D/A converter employing switches and resistive elements integrated into field effect transistors.
To attain video frequency operation of the function by which color data is multiplied equally by common intensity data in the context of R-2R ladders, compensation data is generated for each color and concurrently converted to analog form in such a way as to offset ladder impedance changes with color data content in the context of cascaded R-2R ladders.
In this way, color balance can be maintained during intensity fading.
Attention is now directed to FIG.
1 of the drawings, where one embodiment of the invention is set forth in the context of the functional architecture for an integrated circuit type color graphics control device, with the color generation circuitry generally designated at 1.
Though the focus of attention will be on the multiplying D/A converter with digital compensation, functional block 2, the composite color generation circuitry depicted in FIG.
1 provides a useful background for more fully appreciating the various beneficial aspects of the present invention