Excellerator: custom CMOS leaf cell layout generator

A description is given of a program, Excellerator, which automatically generates full-custom symbolic CMOS cell layouts. The input is a transistor-level netlist with optimal constraints on layout shape and I/O port positions. The output is a high-quality virtual-grid-based layout suitable for use in a two-dimensional tiling methodology. I/O port locations can be optimized. Versatile support for different layout shapes and port locations makes this system ideal for use in a top-down, fully automatic physical design system. Transistor routing is provided by a novel, recursive version of the A-Star search procedure. This technique reduces the frequency and seriousness of routing blockages by finding near-optimal compromises between new connections and reroutes of previous connections. Routing occurs in two metal layers plus polysilicon and diffusion, and is easily extendable to any number of routing layers. Routing priority can be given to critical nodes