A General Sign Bit Error Correction Scheme for Approximate Adders

Approximate computing is an emerging design technique for error-tolerant applications. As adders are the key building blocks in many applications, approximate adders have been widely studied recently. However, existing approximate adders may introduce sign bit error when doing two's complement signed addition, which is not tolerable for some applications. In this work, we propose a scheme that can correct sign bit error with low area and delay overhead. It is a general design applicable to many block-based approximate adders. This design not only can correct the sign bit error when it occurs, but also can fix some errors in the most significant bits even if there is no sign bit error. Experimental results on a real application, namely edge detection, showed that the approximate adders with our sign bit error correction module were up to 5.5 times better in peak signal-to-noise ratio than the original approximate adders, while the area and delay overhead is small.