Reviewing 4to2 Adders for MultiOperand Addition Recently there has been quite a number of papers discussing the use of redundant 4to2 adders for the accumulation of partial products in multipliers, claiming one type to be superior to other types. This paper analyses a recent proposal of various 3 and 4element redundant digit sets for radix 2, signed and unsigned, and compare their implementations using various encodings of the digits and carries. It is shown that theoretically they are equivalent, and differences in their implementations need only be very marginal. Another recent proposal for the use of the digitset 0,1,2,3, with a special 3bit encoding of digits, is analyzed and some optimizations are shown, including the possibility of using a 2bit encoding, with a quite significant saving in the wiring of a multiplier tree. All these proposed designs are shown to be equivalent to a standard 4to2, carrysave adder, except possibly for a few signal inversions.

Approximate Multiplier Using Reordered 4xe2x80x932 Compressor with ORbased Error Compensation Today, the approximate circuits have become an efficient solution for low power design on human related errortolerant applications, such as multimedia, recognition and several signal processing. Approximate multipliers are believed to be an important key to make approximate arithmetic systems, and more area efficient multiplier is expected. The paper proposes a new areaefficient 4xe2x80x932 compressor based on input reordering and ORbased error compensation. By the reordering, we can focus on just 2 of 4 inputs, and the compressor becomes very simple and less gates. Two multipliers are proposed with different accuracy based on reordered compressors with ORbased error compensation. The experimental results show that the proposed multipliers achieve high accuracy (98.7% and 97.39%) while reduce power consumption (by 44.72% and 45.95%) and area (by 31.72% and 34.85%). The proposed approximate multipliers are applied on image sharpening process and show high PSNR and SSIM.