K- and Ka-band miniature CMOS balun with a single spiral coupled structure

Abstract

This paper presents a CMOS wideband miniature balun operating over the full K- and Ka-bands. The balun is based on a single spiral coupled structure where two symmetric spiral lines are stacked vertically (i.e. broadside-coupled) in an antipodal manner. The proposed structure provides ultra-wideband balun performance while occupying a minimal chip area compared with conventional spiral baluns. In order to offset residual inductance of the spirals, a compensation capacitor is shunted at the end of an unbalanced input line, which further improves the bandwidth. The proposed balun is implemented in a bulk 0.13-μm CMOS process. The measured insertion loss is less than 6.5 dB from 14 to 40 GHz. The amplitude and phase imbalances are less than 1 dB and 10°, respectively, over the entire bandwidth. The balun occupies an area of only 0.0095 mm², which, to the authors’ knowledge, is significantly smaller than any previously reported CMOS baluns at similar frequency bands.

Keywords:

• balun
• CMOS
• RFIC
• spiral structure
• wideband

Acknowledgement

This research was supported by Basic Science Research Programme through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2010-0025551). The authors also thank IDEC for chip fabrication.