Efficient design approaches to CMOS full adder circuits

In the field of high-performance chip designs, many applications have the ability to tolerate small errors through the use of approximate full adders. By appropriately reducing the corresponding precision, the performance of hardware implementation can be greatly improved. The adders are commonly applied in digital signal processors (DSP), communication systems, image processing, etc., to quickly complete addition estimation operations. This paper proposes the designs of 8 approximate adders and compares their performance with existing circuit structures. Simulation results demonstrate that the approximate adders proposed in the first group (i.e., LCAFA1-LCAFA3) achieve an average area reduction of 21.44 % and an average delay reduction of 42.85 %. In the second group, the proposed approximate adders LCAFA4-LCAFA8 achieve an average power reduction of 28.35 %, an average area reduction of 17.39 %, an average delay reduction of 84.25 %, and an average decrease in the power-area-delay product (PADP) of 68.26 %.