An Ultra-Low-Power Memory With a Subthreshold Power Supply Voltage

A 512times13 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 muW power consumption, of which 0.366 muW is due to leakage and 0.831 muW 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