Practical Design Methodology of Mode-Conversion-Free Tightly Coupled Asymmetrically Tapered Bend for High-Density Differential Wiring

Chenyu WANG  Kengo IOKIBE  Yoshitaka TOYOTA  

Publication
IEICE TRANSACTIONS on Communications   Vol.E104-B   No.3   pp.304-311
Publication Date: 2021/03/01
Publicized: 2020/09/15
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2020EBP3056
Type of Manuscript: PAPER
Category: Electromagnetic Compatibility(EMC)
Keyword: 
differential transmission lines,  mode-conversion,  high-density wiring,  asymmetric tapers,  design methodology,  

Full Text: FreePDF(1.3MB)


Summary: 
The plain bend in a pair of differential transmission lines causes a path difference, which leads to differential-to-common mode conversion due to the phase difference. This conversion can cause serious common-mode noise issues. We previously proposed a tightly coupled asymmetrically tapered bend to suppress forward differential-to-common mode conversion and derived the constraint conditions for high-density wiring. To provide sufficient suppression of mode conversion, however, the additional correction was required to make the effective path difference vanish. This paper proposes a practical and straightforward design methodology by using a very tightly coupled bend (decreasing the line width and the line separation of the tightly coupled bend). Full-wave simulations below 20GHz demonstrated that sufficient suppression of the forward differential-to-common mode conversion is successfully achieved as designed. Measurements showed that our design methodology is effective.