Sum-of-products multiplier

Claim 1

A sum-of-products multiplier, for forming the sum of a number of independent multiplications, as defined by the equation where v is the sum of products, u j are the inpute and a. are the coefficients to be used for the multiplications, M is the number of inputs to the multiplier involved in a sum-of-products multiplications. N is the number of binary weights used in the determination of said coefficients and W k is the k'th of said binary weights, wherein for each value of k the inner summation of said equation can take any one of 2 M possible values which are usable for all values of k, said values corresponding to the 2 M possible combinations of the binary variables u O,k, u 1,k, .... u M-1,k , and wherein memory means is provided in which said set of combinations to be used for the multiplications is stored, characterised in this, that the memory means includes a plurality of sub-memories each of which can contain a selection of the coefficient combinations to be used, that selection means controlled by the respective bits [u j,k ] of the input numbers select the coefficient combinations to be read-out for those bits, aaid read-outs being effected for different ones of said bits from different ones of the sub-memories, that the outputs from said sub-memories are applied to an adder, that the result of the summation in said adder is applied to an accumulator /shifter with the accumulations being shifted according to the bits [u j,k ,] and that an add/subtract control is provided for the accumulator/shister whereby the coefficient combination associated with a positive weight of the input bits. [u j,k ] is added to the contents of the accumulator and the coefficient combination associated with a negative weight of the input bits u j,k is subtracted from the contents of the accumulator, so that the required sum of products is derived from the output of the multiplier/shifter.