On Bifunctional Polymorphic Gates Controlled by a Special Signal

hardware engineering, digital circuits, CMOS logic gates, polymorphic electronics, VLSI, reconfigurable digital circuits

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.