High-Performance Low-Power Carry Speculative Addition With Variable Latency

Adders are one of the most critical arithmetic circuits in a system and their throughput affects the overall performance of the system. Traditional n-bit adders provide accurate results, but the lower bound of their critical path delay is Ω(log n). To achieve a critical path delay lower than Ω(log n), many approximate adders have been proposed. These approximate adders decrease the critical path delay and improve the speed by sacrificing computation accuracy or predicting the computation results. This paper proposes a high-performance low-power carry speculative adder (CSPA). This adder separates the carry generator and sum generator. Only one sum generator is used in a block adder to reduce the critical path delay and area overhead. In addition, to generate 100% accurate results, error detection and recovery circuits are added to the proposed CSPA to construct a variable-latency carry speculative adder (VLCSPA). Instead of recalculating all results, the error detection and recovery circuits find and correct the block adder that generates incorrect partial sum bits, reducing power consumption. The experimental results show that the proposed CSPA achieves a 26.59% delay reduction, a 14.06% area reduction, and a 19.03% power consumption reduction compared to the corresponding values for an existing speculative carry-select adder. The experimental results also show the proposed CSPA can be used to improve image denoising results as well.