Experimental demonstration of a tunable Marchand balun at K band in Silicon Germanium (SiGe) technology

This paper demonstrates the operation of a Marchand balun prototype in a standard Silicon process that can switch its operation between 2 adjacent regions of the K band. Pass gate CMOS switches connect or disconnect additional lengths of line in the windings of the balun to change the balun´s frequency response while maintaining its mixed mode performance. Digital control of the balun is enabled by the CMOS switches. The balun is fabricated in a high performance SiGe BiCMOS process built on standard 180 nm CMOS technology and characterized in terms of mixed mode scattering parameters. A broad instantaneous bandwidth is demonstrated with relative long gate length MOS devices. The authors believe that this is the first experimental demonstration of a balun tunable by pass gate switches in the high region of the microwave range.