Node voltage dependent subthreshold leakage current characteristics of dynamic circuits

Abstract

The subthreshold leakage current characteristics of domino logic circuits is evaluated in this paper. The strong dependence of the subthreshold leakage current on the node voltages is discussed. In a standard low threshold voltage domino logic circuit with stacked pulldown devices, a charged state rather than a discharge state of the dynamic node is preferred for lower leakage current. Alternatively, the subthreshold leakage current of a dual threshold voltage domino logic circuit is significantly reduced provided that the dynamic node is discharged. A dual threshold voltage circuit has degraded noise immunity characteristics as compared to a standard low threshold voltage circuit. Both keeper and output inverter sizing are necessary to compensate for this degradation in noise immunity. An alternative dual threshold voltage domino circuit technique employing a low threshold voltage keeper for enhanced noise immunity is also considered in this paper. Under similar noise immunity conditions as compared to a standard low threshold voltage domino logic circuit, the savings in subthreshold leakage current offered by a dual threshold voltage circuit technique with a high threshold voltage keeper is significantly higher than the savings offered by a dual threshold voltage circuit technique with a low threshold voltage keeper.