Performance Efficient and Fault Tolerant Approximate Adder

Fault tolerant adders are an important design paradigm to improve the robustness of the adder while at the same time improving the yield. The major downside of fault tolerant adders are the additional modules that are intrinsic to this design. On the other hand, approximate adders take the advantage of computing resilience and inherently improve the area, delay & power metrics. A combination of these two seemingly contradictory approaches are juxtaposed to put forth a design for robust fault tolerant approximate adders that mitigate the effects of redundancy and would help improve the yield. The fault tolerant schemes included are the Triple Modular Redundancy and Partial Triple Modular Redundancy. These are used in conjunction with the approximate Lower part-OR Adder (LOA). The designed fault tolerant approximate adder along with the fault intolerant precise and fault intolerant imprecise adder is used for image sharpening using the Gaussian filter. The results analyzed in the presence and absence of faults indicate that the visual quality of the image in the presence of a single stuck-at fault is almost as good as that obtained without a fault and maintains a PSNR of above 27 in case of fault tolerant approximate adder. There is a significant loss in the image quality if a fault occurs in a non-redundant precise or approximate adder. The deterioration in image quality is more significant if a stuck-at-one fault occurs, as the image becomes visually indecipherable.