An ultra-low-power memory with a subthreshold power supply voltage

A 512 × 13 bit ultra-low-power subthreshold memory is fabricated on a 130-nm process technology. The fabricated memory is fully functional for read operation with a 190-mV power supply at 28 kHz, and 216 mV for write operation. Single bits are measured to read and write properly with V _DD as low as 103 mV and 129 mV, respectively. The memory operates at a 1-MHz clock rate with a 310-mV power supply. This operating point has 1.197 _μW power consumption, of which 0.366 _μW is due to leakage and 0.831 _μW is due to dynamic power dissipation. Analysis of the available fan-out or fan-in that can be supported at a given voltage is summarized. A number of circuit techniques are presented to overcome the substantially reduced on-to-off current ratios and the poor drive strength of transistors operating in subthreshold. These include a gated feedback memory cell, and hierarchical read and decode circuits. The memory is dynamic, with pseudo-static operation provided via self-timed control of the keeper transistors to mitigate increased variability manifested in subthreshold operation.