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Forward and Backward Guarding in Early Output Logic

C. Brej and D.A. Edwards


Quasi Delay Insensitive asynchronous logic is a very robust system allowing safe implementations while requiring minimal timing assumptions. Unfortunately the design methodologies using this system have always yielded very slow designs. Early output logic is a method which aims to improve the performance of QDI circuits without decreasing their robustness. In order to force QDI restrictions on early output circuits a form of guarding is necessary. This paper presents a new form of guarding which allows partial stage completion allowing desynchronisation of inputs. This is shown to be highly advantageous in cases where the previous style performed poorly. Because the two styles can be mixed, the designs no longer suffer from very poor performance of some QDI constructions.

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