On the Design of RNS Reverse Converters for the Four-Moduli Set ${\bf\{2^{\mmb n}+1, 2^{\mmb n}-1, 2^{\mmb n}, 2^{{\mmb n}+1}+1\}}$

In this brief, we propose a method to design efficient adder-based converters for the four-moduli set {2
ⁿ
+1, 2
ⁿ
-1, 2
ⁿ
, 2
ⁿ⁺¹
+1} with n odd, which provides a dynamic range of 4n+1 bits for the residue number system (RNS). This method hierarchically applies the mixed radix approach to balanced pairs of residues in two levels. With the proposed method, only simple binary and modulo 2
^k
-1 additions are required, fully avoiding the usage of modulo 2
^k
+1 arithmetic operations, which is a significant advantage over the currently available RNS reverse converters for this type of moduli set. Experimental results show that the delay of the proposed converters is significantly reduced when compared with the related state of the art; for example, for a 65-nm CMOS ASIC technology and a dynamic range of 21 bits, the conversion time and the circuit area are reduced by about 44% and 30%, respectively, while the conversion time is reduced by 34% for a dynamic range of 37 bits with the circuit area increasing only by 25%. Moreover, the proposed reverse converters outperform the related state of the art for any value of n by up to 70%, according to the figure-of-merit energy per conversion.