Cache Design for Low Power and High Yield

Baker Mohammad1,  Martin Saint Laurent1,  Paul Bassett2,  Jacob Abraham2
1Qualcomm, 2The University of Texas at Austin


A novel circuit approach to increase SRAM Static Noise Margin (SNM) and enable lower operating voltage is described. Increasing process variability [1] [2] for new technologies coupled with increased reliability effects like Negative Bias Temperature Instability (NBTI) [3] all contribute to raising the minimum voltage required for stable SRAM. Our strategy is to improve the noise margin of the 6T SRAM cell by reducing the effect of parametric variation of the cell [4], especially in the low voltage operation mode. This is done using a novel circuit that selectively reduces the voltage swing on the world line and reduces the memory supply voltage during write operation. The proposed design increases the SRAM Static Noise Margin (SNM) and write margin using a single voltage supply and with minimum impact to chip area, complexity, and timing. The technique supports both on-chip corner identification to adapt the SRAM behavior to silicon, and software controllability to tradeoff yield, power, and performance.