UWB Active Balun Design with Small Group Delay Variation and Improved Return Loss

Kyoung-Pyo AHN  Ryo ISHIKAWA  Kazuhiko HONJO  

IEICE TRANSACTIONS on Electronics   Vol.E94-C   No.5   pp.905-908
Publication Date: 2011/05/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E94.C.905
Print ISSN: 0916-8516
Type of Manuscript: BRIEF PAPER
Category: Microwaves, Millimeter-Waves
differential mode,  group delay,  negative group delay (NGD) circuit,  return loss,  ultra-wideband (UWB),  

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Different from distributed baluns, active baluns have group delay variations in the lower bands related to inherent internal capacitances and resistance in transistors. A negative group delay (NGD) circuit is employed as a compensator of group delay variation for an ultra-wideband (UWB) active balun. First, three-cell NGD circuit is inserted into a simple active balun circuit for realizing both group delay compensation and return loss improvement. The simulated results show a group delay variation of 4.8 ps and an input return loss of above 11.5 dB in the UWB band (3.1-10.6 GHz). Then, a pair of one-cell NGD circuits is added to reduce the remaining group delay variation (3.4 ps in simulation). The circuit with the NGD circuits was fabricated on an InGaP/GaAs HBT MMIC substrate. The measured results achieved a group delay variation of 7.7 ps, a gain variation of 0.5 dB, an input return loss of greater than 10 dB, and an output return loss of larger than 8.1 dB in the UWB band.