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.