The need for high speed digital circuits became more prominent as portable multimedia and communication applications incorporating information processing and computing. The drawback of modern computers lead to the deterioration in performance of arithmetic operations such as addition, subtraction, division, multiplication on the aspects of carry propagation time delay, high power consumption and large circuit complexity. This system explores the carry free n digits addition/subtraction as the carry propagation delay is most important factor regarding the speed of any digital system. In this paper ,we are giving the review of papers for the QSD Adder / Subtractor .

Keywords : Carry free addition, Fast computing, FPGA, Quaternary Signed Digit, VHDL, VLSI.