High-Speed FPGA 10's Complement Adders-Subtractors

Abstract EN

This paper first presents a study on the classical BCD adders from which a carry-chain type adder is redesigned to fit within the Xilinx FPGA's platforms.

Some new concepts are presented to compute the P and G functions for carry-chain optimization purposes.

Several alternative designs are presented.

Then, attention is given to FPGA implementations of add/subtract algorithms for 10's complement BCD numbers.

Carry-chain type circuits have been designed on 4-input LUTs (Virtex-4, Spartan-3) and 6-input LUTs (Virtex-5) Xilinx FPGA platforms.

All designs are presented with the corresponding time performance and area consumption figures.

Results have been compared to straight implementations of a decimal ripple-carry adder and an FPGA 2's complement binary adder-subtractor using the dedicated carry logic, both carried out on the same platform.

Better time delays have been registered for decimal numbers within the same range of operands.