Stacking SRAM Banks for Ultra Low Power Standby Mode Operation

On-chip SRAM caches have come to dominate the total chip area and leakage power consumed in state-of-the-art microprocessor designs. Such large memories are necessary to attain high performance, however it is critical to minimize the idle currents drawn while these SRAM banks are inactive. This work proposes a novel voltage reduction technique to reduce SRAM leakage power during the standby mode. The design employs an implicit voltage reduction method that "stacks" SRAM banks in series while these blocks are inactive. No explicit DC/DC converters are required to achieve the reduced voltages, which leads to large area reductions over techniques requiring on-chip regulation circuits. This stacking technique reduces the voltage on each block close to the absolute data retention voltage (DRV) of each cell, and achieves a maximum leakage power reduction of 93% from the active power mode. Simulation results show the stability of the scheme around corners, process variations, and on-chip noise.