An adiabatic 64-kb SRAM circuit with shared reading and writing ports was designed, which enables gradual charging and discharging while maintaining a large VDD so that the problems of V T variation and electromigration in the nanocircuit can be solved. In the writing mode, the voltage of the memory cell ground line is increased to VDD/2 gradually, and the nMOSFET is turned off so that the memory cell ground line is set in a high-impedance state. Data can then be written easily by decreasing the voltage of one bit line adiabatically, while the voltage of the other bit line remains high. For reading, using the shared reading port, the voltage swing of the global bit-line can be decreased to VDD/4 so that the problems of electromigration can be solved. The reading method enables a gradual current flow in the memory cell. We designed the cell layout and confirmed that the number of transistors in the cell is quasi-six. In addition, two types of new step voltage circuits with tank capacitors are proposed. One is for producing the memory cell ground line voltage and the other for charging the word line voltage adiabatically. Spontaneous step voltage formation is confirmed experimentally.
The stability of a stepwise waveform of an adiabatic charge recycling circuit with tank capacitors is investigated. We propose a new tank capacitor circuit with two-string capacitor arrays. We experimentally confirmed the stability of the five-step waveform from the tank capacitors. The voltage changes of tank capacitors in the experiment are consistent with the simulation. The power consumption is reduced to one-fifth due to the five-step waveform. We analyze the stability using matrix theory. The results prove that the step waveform is stable for any circuit topology. Moreover, we consider the effects of conductors fixed at a certain voltage and floating conductors and confirm the system is stable using matrix theory.
This paper describes characteristics of stepwise adiabatic charging with an inductor current by controlling switching transistors. An exact analytical resolution is obtained by using a vector comprising a voltage and a current. From a matrix calculation, the voltage and current can be written with solutions of the characteristic equation, power supply voltage, the switching ratio in the switching transistor circuit, and the number of switchings. Using the expression, the voltage and current in the stepwise adiabatic charging method can be derived clearly. As a result, it is clarified analytically that, in N-step charging, the current is reduced to 1/N so that the energy dissipation is reduced to 1/N. Next, the experimental switching transistor circuit with the controller is described, which is composed of discrete ICs. The experimental inductor current in the circuit is investigated. The measured current is reduced to 1/N in N-step charging, which is consistent with the simulated one from the theory. It is also confirmed experimentally from the average power supply current that power consumption is reduced to 1/N.
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