Process Variation Tolerant Register Files Based On Dynamic Memories

Transistor gate length and threshold voltage variability due to process variations will greatly impact the stability, leakage power, and performance of future microprocessors. These variations are especially detrimental to continued scaling of 6T SRAM (6-transistor static memory) structures. This paper proposes replacing traditional SRAM-based cells in mutliported register files with cells based on 3T1D DRAM (3-transistor, 1diode dynamic memory) cells, which can absorb the effects of device physical variations into a single parameter – the data retention time. By leveraging the transient data in the processor and dependency slack in the pipeline, retention time variation can be hidden into the existing processor architecture. Thus the proposed register file can effectively tolerate very large process variation with little or even no impact on performance, addresses stability concerns, and reduces power consumption, when compared with ideal SRAM-based designs. Detailed circuit and architectural simulations and analysis verify a 1% normalized performance loss even under very large process variations, and 22% average power savings.