Design of a Wideband CMOS Balun and Its Application in a Wideband RF Front-End

This paper presents a 1:2 wideband CMOS balun, and its application for sub-6 GHz wideband front-end. In order to eliminate the amplitude/phase mismatch, the primary and secondary windings are shorted by a transmission line (T-line) for a common ground. The float metal in the primary winding is used for artificial dielectric compensation which further reduce the amplitude imbalance by up to about 0.5 dB. A 2.0-to-3.7 GHz wideband RF front-end is also designed by using the proposed CMOS balun. The balun and RF front-end are fabricated in a 0.13- $\mu \text{m}$ bulk CMOS technology. The bandwidth of the balun with $\vert \text {S}11\vert < {-}10$ dB is 2.2-to-5.1 GHz. The fractional bandwidth is large than 79.5%. The corresponding maximum amplitude and phase mismatch is 1.5 dB and 2°, respectively. The measured insertion loss is 4.8-to-5.6 dB from 2.2 to 5.1 GHz.