A 66-MHz DSP-augmented RAMDAC for smooth-shaded graphic applications

A fundamentally new type of RAMDAC is described in which a custom digital signal processor (DSP) is interposed between the RAM and the DAC. The device provides pseudoincreased resolution and increased color range by means of real-time mixing of any two colors contained in the color palette. This feature allows color images to be displayed without the familiar jagged edges; the ability to represent continuous edges yields the name continuous edge graphics (CEG) RAMDAC. Instead of all pixel values representing pointers to colors, 32 now represent a ratio between colors. The device allows mixing between any of the remaining 223 colors in amounts that depend on which ratio is used. This drastically increases the number of colors that an 8-b frame buffer can represent from 256 to over 700000. The device, containing 60000 devices, is fabricated in a 1.2-μm CMOS process supporting a 15-ns cycle operation