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Abstract

A digital FIR filter for producing an L phase interpolation of a input sample ##STR1## based on L filter banks and n tap coefficients P.sub.1 (i) in each 1.sup.th one of the filter banks is disclosed, where 1.ltoreq.1.ltoreq.L and where 0.ltoreq.i.ltoreq.(n-1). The digital filter includes a first circuit for producing, for each time t, bank filter terms of a merged bank filter having an output value which changes between a previous time t-1 and the time t. The produced bank filter terms include at least one combination of two cross-symmetric bank filter terms: for the in phase condition: ##STR2## and for the out of phase condition: the same as the in phase condition except that the parameter i in the product terms, ##STR3## are replaced by i-1, of the L filter banks on which the digital filter is based, where 1.ltoreq.k.ltoreq.L and for any non-negative integer w=0,1,2, . . . , t=w.multidot.L+k. The digital filter also includes a second circuit for adding together, for each time t, the bank filter terms produced in the first circuit to produce the merged bank filter output value which changes between the previous time t-1 and the time t. A third circuit may be provided for adding together .left brkt-top.L/2.right brkt-top. merged bank filter output values to produce an interpolated value g(t) of the inputted sample ##STR4##

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