| 摘要 |
PURPOSE:To prevent characteristic deterioration due to an error of quantization of an integer coefficient, by having a cascade connection between a filter having a quantized coefficient of a finite word length and a filter formed with the integer coefficient and having finite units of zero points at an attenuated band. CONSTITUTION:A digital input signal is fed to a cascade connection circuit of a delaying circut T of sampling period. The input signal and the output signal of the circuit T are multiplied by coefficients a0, a1- through a multipliers. The outputs of the multipliers are added through an adder and by a noncyclic digital filter DF1 of direct constitution. Then a cascade connection is given between the filter DF1 and a noncyclic digital filter DF2 formed with the integer coefficient and having finite units of zero points at an attenuated band. The filter DF1 has a transmission function F(Z)=a0+a1Z<-1>+a2Z<-2>+-(Z=epsilon<j> T), and the coefficients a0, a1- are obtained so as to minimize an error evaluation function epsilon. The filter DF2 has accuracy with the transmission function W(Z)=(1+2Z<-1>+ Z<-2>)(1+Z<-1>+Z<-2>) and has no error. In such way, the characteristic deterioration due to an error of quantization of the coefficient is prevented with a reduction attained for the coefficient word for a digital filter. |
