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Recursive-type digital filter with reduced round-off noise

  • US 4,337,518 A
  • Filed: 07/28/1980
  • Issued: 06/29/1982
  • Est. Priority Date: 02/15/1978
  • Status: Expired due to Term
First Claim
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1. In a recursive-type digital filter having a calculating means for calculating an output signal yn, and a first means for supplying said calculating means with at least an m-bit input signal xn of ##EQU14## one bit by one bit;

  • and second means including a data conversion means which cooperates with said calculating means to delay by one sample period said output signal yn, and a feedback means for feeding back one bit by one bit to said calculating means at least an m-bit output signal yn-1 of ##EQU15## wherein M and N are positive integers which represent a delay of the signal transmission and wherein the respective signals received by said calculating means from said first and said feedback means are multiplied by corresponding weighting coefficients ak and bk in order to produce at every sampling period a (m+l)-bit data yn satisfying, ##EQU16## and ak and bk represent coefficients with aM, bN

    0 with the upper m-bits of said data yn being serially outputted as an output signal corresponding to said input signal xn from said filter, wherein the improvements comprises;

    third means including a second data conversion means which cooperates with said calculating means to delay by one sampling period at least one of the lower l bits of said data yn and outputting a y'"'"'n-1 signal, andfourth means receiving said y'"'"'n-1 signal and outputting one bit by one bit to said calculating means a y'"'"'n-k signal so that said calculating means supplements said yn data by adding the product of said bk coefficient and the signal received from said fourth means, whereby said y'"'"'n-k signal, which is delayed by k sampling periods from said input signal xn, reduces round off errors.

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