A New Design Concept for Balanced-Type SAW Filters Using a Common-Mode Signal Suppression Circuit

Hiroyuki NAKAMURA
Toshio ISHIZAKI
Toshifumi NAKATANI
Shigeru TSUZUKI

Publication
IEICE TRANSACTIONS on Electronics   Vol.E88-C    No.1    pp.28-33
Publication Date: 2005/01/01
Online ISSN: 
DOI: 10.1093/ietele/e88-c.1.28
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Trends of Microwave and Millimeter-Wave Passive Circuit Components and Technologies for Improvement of Characteristics)
Category: 
Keyword: 
SAW filter,  balanced-type,  common-mode,  differential-mode,  balance characteristics,  

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Summary: 
A new design concept for a common-mode signal suppression circuit for a balanced-type filter has been investigated. The degradation mechanism of the balance characteristics was studied. The degradation is caused by the common-mode signals combined with the differential-mode signals in the balanced terminals. The concept employed is the reduction of the common-mode signal using a common-mode signal suppression circuit, connected to the balanced terminals. A serial resonance circuit is formed, in which the common-mode signals are shorted to ground. The circuit was applied to the balanced-type Surface Acoustic Wave (SAW) filter. The improvement in balance characteristics, without increasing in the insertion loss, was confirmed by experiments for Global System Mobile (GSM) applications.