Design and Characterization of a Compact and Broadband On-Chip Modified Three-Conductor Transmission Line Balun at G-Band

This paper studies the design and characterization of a millimeter-wave passive planar balun, which is implemented in the back end of line of a high-speed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$130-\text{nm}$</tex> SiGe BiCMOS technology. A modified three-conductor sub-quarter-wavelength transmission line based balun with an additional compensated transmission line is proposed to obtain a broad bandwidth, a compact area and reduced port imbalances. By means of a short termination approach and a deembedding method for reciprocal three-port component, measurement results show a 3-dB bandwidth from 140 GHz to 220 GHz with a minimum insertion loss of 0.7 dB. The amplitude imbalance is less than 0.8 dB and the phase error of differential output signals remains below 4° across the entire bandwidth. To the best knowledge of the authors, this proposed balun consumes the smallest area of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.0038 ~\text{mm}^{2}$</tex> (excluding the pads) with the best phase balance at the G-band.