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US4908787A Interpolator/decimator filter structure and a notch filter therefor 失效
插值器/抽取器滤波器结构及其陷波滤波器

Interpolator/decimator filter structure and a notch filter therefor
摘要:
A filter structure including a notch filter is designed to have a transmission zero at a frequency slightly displaced from one half of the lower sampling rate of the interpolator/decimator, and thus providing increase in attenuation at the half-rate frequency. The notch filter is comprised of two like all-pass-network filters and has feed forward and feedback connections, the latter connection including a coefficient multiplier. The feedback connection is made between a tapped output of the second of the network filters and an input node. The tapped filter is characterized by throughput and a tapped output transform functions X(Z) and Y(Z) given by the following expressions:X(Z)=[Z.sup.-1 -K]/[1-KZ.sup.-1 ; and,Y(Z)=.alpha.Z.sup.-1 /[1-KZ.sup.-1 ;where Z.sup.-1 is the unit delay operator, K the multiplier coefficient and, .alpha., a structure dependant constant.
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