A 0.5 V SIMOX-MTCMOS circuit with 200 ps logic gate

Abstract

Multi-threshold CMOS (MTCMOS) circuit technology combining low-Vth CMOS logic gates and high-Vth MOSFETs is suitable for 1 V LSIs for battery-operated portable equipment. Improvements in MTCMOS device technology promise to lead to higher operating frequencies. However, higher frequencies will increase power consumption even if the supply voltage is 1 V. To reduce the power consumption, it is necessary to lower the supply voltage below 1 V, without sacrificing speed. A circuit consisting of depletion-mode MOSFETs operates with 200 mV supply. However, it cannot be applied to an LSI with more than 1 k gates because active-mode leakage current is too large. In addition, the circuit needs backgate bias, which is much larger than the supply voltage, to increase the threshold voltage and to reduce the leakage current in the sleep mode. To generate the large back-gate bias, multiple supply voltages or a boost circuit are required. The proposed low supply-voltage MTCMOS circuit with SIMOX technology uses enhancement-mode MOSFFTs and contains no boost circuit. High-speed operation of this SIMOX-MTCMOS circuit at 0.5 V supply is obtained by use of low-Vth CMOS logic gates consisting of fully-depleted body-floating MOSFETs.