A signed digit adder with error correction and graceful degradation capabilities

This paper proposes a methodology to obtain fault localization and graceful degradation of a self-checking adder based on signed digit representation. The main idea underlying the paper is to exploit the fact that in signed digit arithmetic the carry operation is confined to neighbor digits. The usage of a "carry free" adder implies some advantages in terms of error detection, fault localization and repair For the detection standpoint, a parity checker can be easily applied to detect errors caused by faults belonging to the considered stuck-at fault set. Regarding the fault localization, the "carry free" property of the adder ensures the confinement of the error due to a permanent fault only to a few digits. Finally, if a fault is correctly localized, the faulty digit can be excluded and the logic which computes the other digits can be used to perform the adder operation with a reduced dynamic range.