SEDAAF: FPGA Based Single Exact Dual Approximate Adders for Approximate Processors

Approximate circuits for ASICs have gained immense traction in recent years due to the benefits obtained in both energy and performance with little or no loss in output quality. Approximation in FPGAs remain a challenge due to the higher level of granularity at which logic is implemented on FPGAs. The smallest configurable blocks in FPGAs used for implementing logic consists of the look up tables (LUTs). In this paper, we exploit the inherent structures available in the FPGAs to implement SEDAAF. SEDAAF is a runtime configurable approximate adder that can perform a one-bit exact addition or two-bit approximate addition using the same hardware. SEDAAF also has a maximum bounded error, i.e. for an n-bit adder if m-bits are approximated the maximum error is 2^m − 1. SEDAAF consumes 25% lesser power and has a 17% lesser power delay product as compared to existing designs. SEDAAF outperforms the existing state of the art designs in terms of output quality for Sobel edge detection application and can be used in approximate processors for performing both exact and approximate additions.