Design of a 32 b monolithic microprocessor based on GaAs HMESFET technology

This paper examines the design of a 32-b GaAs Fast RISC microprocessor (F-RISC/I). F-RISC/I is a single chip GaAs HMESFET processor targeted for implementation on a multichip module (MCM) together with cache memories. The CPU architecture, circuit design, implementation, and testing are optimized for a seven-stage instruction pipeline implemented with GaAs super-buffered FET logic (SBFL). We have been able to verify novel GaAs SBFL standard cells and compare measured CPU performance with performance estimates based on circuit and device models. The prototype 32-b microprocessor has been implemented using an automated standard cell approach because of time constraints and fabricated using an experimental process by Rockwell International. The CPU chip integrates 92 340 transistors on a 7 7 mm2 die and dissipates 6.13 W at 180 MHz. Test results from a prototype fabrication run have demonstrated the operation of the ALU, the program counter, and the register file with delays below 6, 5, and 3.4 ns, respectively. The successful modeling and verification indicate that a 0.5 m HMESFET implementation of F-RISC/I could achieve a peak performance of 350 MHz. The wiring delays account for 42% of the critical path delay.