DIGITAL FILTERS WITH CONTROL OF LIMIT CYCLES

摘要

Lawrence-2 16. DIGITAL FILTERS WITH CONTROL OF LIMIT CYCLES Limit cycles are eliminated in digital filters driven by zero, d.c. and period 2 inputs, by adjusting the filter output in response to the state variables present within the filter. The filter includes a quantizer (201) adapted to provide a fixed length output word p in response to an input y, where p < y < p+k and k is the quantizer step size. The filter is further arranged to form the products a Xn and b Xn, where a and b are multiplier coefficients and Xn and Xn+1, the state variables, are once and twice delayed versions of the filter output Xn+1, and to combine the aforesaid products and the filter input Un to yield the value y. The quantizer output is adjusted to p + k, if Xn-1 > p + k or Xn-1 = p and ¦Xn + Sgn(a) Xn-1¦ ? T or Xn-1 = p + k and ¦Xn + Sgn(a) Sn-1¦ < T, where T is a fixed threshold value and Sgn(a) is the sign of the multiplier coefficient a.