Adiabatic SRAM with a large margin of VT variation by controlling the cell-power-line and word-line voltage

Abstract

An adiabatic 1-kb SRAM circuit was designed, which enables gradual charging during writing and reading while maintaining a large VDD so that the problems of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> variation and electromigration in the nanocircuit can be resolved. In the writing mode, the voltage of the memory cell power line is reduced to ground gradually using a high-resistivity nMOSFET, and we turn off the nMOSFET so that the memory cell power line is set in a high-impedance state. Then, we can write data easily by inputting adiabatic signal from one bit line, while the other bit line is set to ground. For reading, a verifying operation is proposed for resolving the electromigration problem. The word line voltage is changed stepwise while the voltages of the bit lines are verified. The reading method enables a gradual current flow in the memory cell. We designed the cell layout and found that there is no area penalty. In addition, a new charge recycle circuit with tank capacitors is proposed.