A Novel Very Low Voltage Topology to implement MCML XOR Gates

Abstract

A new very low-voltage topology to implement MOS current mode logic (MCML) XOR gates is proposed in this paper. Instead of stacking several level oftransistors to implement a two inputs XOR gate, a p-type differential pair is used to steer the current in n-type differential pairs through current mirrors. The proposed topology allows to reduce the minimum supply voltage of MCML XOR gates while guaranteeing a fully current mode behavior as in the conventional XOR gate. The proposed topology has been compared against the conventional and triple tail MCML XOR gates. Simulation results referring to a $40\mathrm {n}\mathrm {m}$ CMOS technology for $V_{DD}=1\mathrm {V}$ confirm that the XOR gate presented in this work exhibits a lower propagation delay than the previously published low voltage MCML XOR gate. Furthermore both theoretical analysis and simulation results in a $40\mathrm {n}\mathrm {m}$ process show that the proposed topology is able to work with a VDD as low as $0.~65\mathrm {V}$ whereas state of the art topologies are not usable below $0.~8\mathrm {V}.$