This paper proposes a novel approximate adder that exploits an error-reduced carry prediction and constant truncation with error reduction schemes. The proposed adder design techniques significantly improve overall computation accuracy while providing excellent hardware efficiency. Particularly, the proposed carry prediction technique can reduce a prediction error rate by up to 75% compared to existing approximate adders considered in this paper. Furthermore, the error reduction technique also enhances the overall computation accuracy by decreasing the error distance (ED). Our experimental results show that the proposed adder improves the normalized mean ED (NMED) and mean relative ED (MRED) by up to 91.4% and 98.9%, respectively, compared to the other approximate adders. Importantly, an excellent design tradeoff allows the proposed adder to be the most competitive of the adders under consideration. Specifically, the proposed adder achieves up to 95.7%, 91.1%, and 93.2% reductions of the power-NMED, energy-NMED, and area-delay product (ADP)-NMED products, respectively, compared to the other adders. Our adder enhances the power-, energy-, and ADP-MRED products by up to 99.4% compared to the others. In particular, the figure of merit (FoM) considering both hardware and accuracy of the proposed adder is up to 93.05% smaller than that of the other approximate adders considered herein. Furthermore, we confirm that the approximation errors caused by the proposed adder have very little impact on output quality when adopted in practical applications, such as digital image processing and machine learning.

This paper presents an energy-efficient approximate adder with a novel hybrid error reduction scheme to significantly improve the computation accuracy at the cost of extremely low additional power and area overheads. The proposed hybrid error reduction scheme utilizes only two input bits and adjusts the approximate outputs to reduce the error distance, which leads to an overall improvement in accuracy. The proposed design, when implemented in 65-nm CMOS technology, has 3, 2, and 2 times greater energy, power, and area efficiencies, respectively, than conventional accurate adders. In terms of the accuracy, the proposed hybrid error reduction scheme allows that the error rate of the proposed adder decreases to 50% whereas those of the lower-part OR adder and optimized lower-part OR constant adder reach 68% and 85%, respectively. Furthermore, the proposed adder has up to 2.24, 2.24, and 1.16 times better performance with respect to the mean error distance, normalized mean error distance (NMED), and mean relative error distance, respectively, than the other approximate adder considered in this paper. Importantly, because of an excellent design tradeoff among delay, power, energy, and accuracy, the proposed adder is found to be the most competitive approximate adder when jointly analyzed in terms of the hardware cost and computation accuracy. Specifically, our proposed adder achieves 51%, 49%, and 47% reductions of the power-, energy-, and error-delay-product-NMED products, respectively, compared to the other considered approximate adders.

This paper presents a novel dual sub-adder based approximate adder that splits a precise adder into two to significantly reduce the latency. The proposed error recovery and reduction technique effectively compensates for the catastrophic accuracy degradation incurred by the split. Implemented in a 65- $nm$ CMOS technology, our design reduces the delay and energy consumption by up to 68% and 78%, respectively, compared to a traditional adder, and outperforms other existing approximate adders in hardware and accuracy joint metrics. The proposed design's efficacy is shown through digital image processing applications where our design makes processed output images closest to the one using the accurate adder over other approximate adders. Furthermore, the proposed design is proven to be a general adder model that can be employed in existing approximate adders to enhance hardware resource and error characteristics considerably.

Electric vehicle (EV) demand is considerably increasing, aided by battery technology development and government policy support. Therefore, it is necessary to consider various charging infrastructures and secure sufficient power to support this. In several cities or countries, a large population lives in a small area, and the supply of large residential complexes such as apartments is common. Given that old apartments may not have sufficient power capacity, it is challenging to secure additional power for charging EVs. In particular, power shortages can intensify during high power usage, such as the summer season, and may become an obstacle to the spread of EVs. Therefore, an efficient charging strategy for residential complexes must be established under the condition of limited power supply. This study proposes two scheduling methods to optimally charge EVs in residential complexes considering limited power supply. The proposed scheduling algorithms are thoroughly examined through extensive simulations with parking data collected from real situations and are demonstrated to be effective for online EV charging systems.

This paper presents a delay- and energy-efficient approximate adder design exploiting an effective carry speculation scheme with error reduction. The proposed scheme reduces the delay and improves the energy efficiency without any significant accuracy degradation by effectively adding the predicted carry input using the OR operation. Additionally, the error reduction technique improves the overall computation accuracy at the expense of a few logic gates. As a result, the proposed adder achieves 3.84- and 7.79-times greater energy and energy-delay product (EDP) efficiencies than the traditional adder when implemented in 65-nm CMOS technology. In particular, when jointly analyzed with hardware accuracy, our design attains 69% and 70% reductions of the energy- and EDP-normalized mean error distance (NMED) products, respectively, compared to the other approximate adders under consideration. Furthermore, the proposed adder’s efficacy over the existing adders is demonstrated by adopting it in a machine learning application.