Digital filter

Claim 1

A digital filter for filtering successive binary coded input samples X(n) in the form: ##EQU13## in which n is the number of the sample, B is the number of bits, per sample, and furnishing a series of coded values Y(n) related to the said input samples by the relationship: ##EQU14## in which m is the order of the filter, αi and βi are weighting factors, comprising: first memory means furnishing a first value φ j (Y) from m+1 address bits; second memory means furnishing a second value φ j (W) from the same m+1 address bits; first means to combine the said successive first values φ j (Y) so as to obtain a final value: ##EQU15## second means to combine the said successive second value φ j (W) so as to obtain an intermediate value: ##EQU16## third means to apply serially to the said first and second memory means the B bits of the said input sample X(n); fourth means to apply serially to the said first and second memory means the B bits of each of the said intermediate values W(n-1) to W(n-m), the m j th bits of the said intermediate values constituting with the j th bit of the said input sample the m+1 address bits of the said memories; and in that the said first value φ j (Y) is related to the said m+1 address bits by the relationship: φ.sub.j (Y) = X.sub.i (n) + (α.sub.1 -β.sub.1).W.sub.j (n-1) + (α.sub.2 -β.sub.2).W.sub.j (n-2) . . . + (αm-βm).W.sub.j (n-m) and the second value φ j (W) is related to the said m+1 address bits by the relationship: φ.sub.j (W) = X.sub.j (n) - β.sub.1.W.sub.j (n-1) - β.sub.2.W.sub.j (n-2) . . . -βm.W.sub.j (n-m).