Transfer Function Preserving Transformations on Equal-Ripple RC Polyphase Filters for Reducing Design Efforts

Hiroaki TANABE
Hiroshi TANIMOTO

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E90-A    No.2    pp.333-338
Publication Date: 2007/02/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e90-a.2.333
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit Techniques and Related Topics)
Category: 
Keyword: 
RC polyphase filter,  equal ripple,  transfer function preserving transformation,  element value spread,  

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Summary: 
Element value spread of an equal-ripple RC polyphase filter depends heavily on the order of zero assignment. To find the optimum design, we must conduct exhaustive design for all the possible zero assignments. This paper describes two circuit transformations on equal-ripple RC polyphase filters, which preserve their transfer functions, for reducing circuit design efforts. Proposed Method I exchanges (R,C) values to (1/C,1/R) for each stage. This gives a new circuit with different zero assignment for each stage of its original circuit. Method II flips over the original circuit and exchanges the resulting (Ri,Ci) values for (Cn-i+1,Rn-i+1) for each i-th stage. Those circuit transformations can reduce a number of circuit designs down to 1/4 of the straight-forward method. This considerably reduces a burden for exhaustive design for searching the minimum element value spread condition. Some design examples are given to illustrate the proposed methods.


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