A C-testable carry-free divider

摘要

In this paper, the design of a C-testable, high-performancencarry-free array divider is presented. A radix-2 redundant number basedncarry-free divider is considered and is modified to make it C-testable,ni.e., it can be exhaustively tested using a constant number of testnvectors irrespective of its word-length. Previous C-testable designsnconsidered dividers which used carry-propagate adders/subtractors. Thesendividers are slow because of their O(W2) computation timen(where W is the word-length of the divider). High-performance carry-freendividers use carry-free redundant arithmetic adders/subtractors. Due tonthis feature, they have O(W) computation time. The on-the-fly converternused by carry-free dividers to convert the redundant quotient tontwo's-complement form is shown to be not C-testable. It is modified tonbe linear-testable (in word-length) instead of exponential time requirednfor exhaustive testing of all possible combinations at its inputs. Wenconclude that the number of test vectors needed is 99 for C-testing ofnthe divider array and (3W+10) for linear testing of the converter. Thenhardware overhead required to make the divider C-testable and thenon-the-fly converter linear testable is also shown to be nominal