Delay-optimized floating point fused add-subtract unit

This paper presents a delay-optimized floating point fused add-subtract (FAS) unit. A FAS unit is very useful for FFT and DCT butterfly operations since it can perform addition and subtraction of two floating point numbers simultaneously. The latency of critical path is reduced by using injection-based rounding method and performing parallel exponent adjustment. The proposed FAS is modeled in Verilog-HDL and synthesized using TSMC 65 nm technology library. Synthesis results show that the proposed FAS requires roughly 60% area of two discrete adders. Comparison results show that our proposed FAS unit is 30% faster and 56% less area than the fastest FAS in previous work.