On Bifunctional Polymorphic Gates Controlled by a Special Signal

Polymorphic digital circuits are circuits composed of polymorphic (multifunctional) as well as ordinary gates. In addition to its standard logic function (such as NAND), a polymorphic gate exhibits another logic function which is activated under a specific condition, for example, when Vdd, temperature, illumination or a special signal reaches a certain level. This paper describes existing polymorphic gates and their features, benefits and limits and discusses special class of polymorphic gates - bifunctional polymorphic gates controlled by a special signal. These gates seem to be most flexible polymorphic gates. In the paper a new two-input bifunctional gate for polymorphic circuits is proposed. The gate produces NAND or XOR function according to a special signal. The proposed gate is effective in terms of area overhead - it consists of 9 transistors only, while corresponding circuit employing conventional gates consists of more than 10 transistors.