VLSI implementation of fast addition using quaternary Signed Digit number system

Abstract

With the binary number system, the computation speed is limited by formation and propagation of carry especially as the number of bits increases. Using a quaternary Signed Digit number system one may perform carry free addition, borrow free subtraction and multiplication. However the QSD number system requires a different set of prime modulo based logic elements for each arithmetic operation. A carry free arithmetic operation can be achieved using a higher radix number system such as Quaternary Signed Digit (QSD). In QSD, each digit can be represented by a number from -3 to 3. Carry free addition and other operations on a large number of digits such as 64, 128, or more can be implemented with constant delay and less complexity. Design is simulated & synthesized using Modelsim6.0, Microwind and Leonardo Spectrum.