An Efficient Light-weight Configurable Approximate Adder Design

Approximate computing is extensively used in fault-tolerant applications as an efficient technique of energy saving. To meet the demand of dynamic trade-off between accuracy loss and power saving, more and more configurable approximate architectures have been proposed. However, most of these designs have to introduce large power and area overheads due to the complex circuits for the mode configuration. In this paper, we present a Light-weight Configurable Approximate Adder (LCAA) based on the traditional accurate mirror adder with only 2 extra transistors. This more efficient design can dynamically switch between the accurate and approximate mode at runtime with better trade-off of the power and accuracy, owing to our proposed novel approximation strategy of the calculation. The simulation results show that compared with the traditional Ripple Carry Adder (RCA), the proposed 16 bits LCAA-based RCA provides up to 43.61% energy savings and 85.01% shorter critical path delay, at the cost of up to 11.96% accuracy degradation in the approximate mode, with only 1.88% more power consumption in the accurate mode. Furthermore, the advantages of our designs are confirmed by the real image addition application.