A 170 MHz CMOS pixel processor for windowing graphics

A pixel-processing RAMDAC chip, in 1.5-μm CMOS, has been designed and tested and will operate at a clock rate of up to 170 MHz, under worst-case conditions. The authors describe the pixel-processing block of about 38000 transistors and the pipelined architecture and delay-matched circuitry used to achieve this performance. This block provides the ability to assign different visual types and color maps to each window in a graphics systems of one million or more pixels per frame. Previous RAMDACs have provided only one color mapping for an entire screen, causing inactive windows to be corrupted. Pixel processing at full pixel clock rate required full-custom circuit forms and layout and careful simulation to ensure matched propagation delays through each logic pipeline. First silicon of this part has been installed successfully in a windowing color workstation, as well as 24-plane windowing add-in cards