Many applications have an inherent tolerance for insignificant inaccuracies. Full adders are key arithmetic functions for many error-tolerant applications. Approximate full adders are considered an efficient technique to trade off energy relative to performance and accuracy. In this paper, we propose four approximate full adders with low overhead. The proposed and the existing approximate full adders are classified into two groups according to their error distances. Simulation results show that, compared with the existing approximate full adders, in the first group, the proposed ones can reduce power-area-delay product (PADP) by 61.83%, power by 54.15%, area by 44.67%, and delay by 22.78%on average; in the second group, the proposed ones can reduce PADP by 97.01%, power by 93.43%, area by 24.98%, and delay by 36.14% on average.

As CMOS processes continue to shrink, nano-scale CMOS latches have become increasingly sensitive to multiple-node upset (MNU) errors caused by radiation. To tolerate MNU, a novel quadruple-node-upset (QNU) self-recoverable latch is proposed in this paper. The proposed latch is mainly constructed from six blocks of three-level C-elements (TLCEs) and six inverters. With the mutual feedback of the various TLCEs, the proposed latch can recover from any QNU. Furthermore, due to the clock gating methodology and a high-speed transmission path, the proposed latch has lower overhead in terms of power dissipation and transmission delay. Simulation results show that the proposed latch achieves high reliability with moderate overhead compared to typical existing latches.

With the advancement of semiconductor technologies, nano-scale CMOS circuits have become more vulnerable to soft errors, such as single-node-upsets (SNUs) and double-node-upsets (DNUs). In order to effectively tolerate DNUs caused by radiation and reduce the delay and area consumption of latches, this paper proposes a DNU resilient latch in the nanoscale CMOS technology. The latch mainly comprises four input-split inverters and four 2-input C-elements. Since all internal nodes are interlocked, the latch can recover from all possible DNUs. Simulation results show that, compared with the state-of-the-art DNU self-recovery latch designs, the proposed latch can save 64.51% transmission delay and 56.88% delay-area-power-product (DAPP) on average, respectively.