Reversible adder-subtractor circuit with carry and borrow propagate facility

Dissipation of energy is major issue in VLSI circuit. Although present day VLSI technology is performing in good way but better technology is always a target of engineering designs. Reversible computation does not erase any information bit because number of inputs and outputs are same in such kind of devices. Since information bits are safe so they can be used further. In this way, energy dissipation in bit erase operations can be avoided. In this paper two designs of reversible circuit are proposed. These circuits can be used as an Adder as well as a Subtractor. These circuit also generate carry and borrow propagate signal to predict carry and borrow for faster add and subtract operations. At input these circuits contains one control signal and three input bit signals. There are three output signals namely sum or difference signal, carry or borrow signal and carry propagate or borrow propagate signal. Constant inputs and Garbage outputs are also present to maintain reversibility but they are minimized up to possible extent. However proposed designs can be implemented in carry skip Adders and borrow skip subtractor. As a result proposed designs are faster than some existing designs.