Design and Application of an Optimizing XROM Silicon Compiler

It is demonstrated that optimization techniques incorporated within a silicon compiler for read-only memories (ROMs) can achieve significant yield, power, and speed improvements by minimizing the number of transistors, drains, and metal interconnections in the ROM. Transistor minimization adopts a heuristic solution to the NP-complete graph partitioning problem with a powerful technique applicable to various ROM design styles and technologies. If diffusion mask personalization is permitted, the design can be further improved by solving the traveling salesman problem to minimize transistor source/drain regions. In table look-up ROMs compiled for 3- and 1.2- mu m CMOS with diffusion mask programming, the compiler eliminated over 45% of the transistors and drains. Test results show that 3- mu m CMOS ROMs have access times between 50 and 70 ns. ROMs with 1.2- mu m features achieve simulated access times below 20 ns. A simple interface allows the optimizing compiler to work easily with other CAD tools such as microcode assemblers