A novel planar type broadband CMOS on-chip balun with relative bandwidth of 158%

A novel planar type broadband balun having a symmetrical structure has been proposed. Considering a lossless and uniform material, balun operation is analyzed and impedance matching condition is formulated. Applying the proposed balun configuration, and using CMOS multi-layer structure, a CMOS on-chip balun has been fabricated. The fabricated balun has achieved ultra-broadband performance. Measured characteristics of the balun are return loss of more than 8dB, insertion loss of 1.5 similar to 6.3dB from the unbalanced to the balanced ports, and the amplitude difference and phase difference between the balanced ports of -0.2 similar to +1.5dB and 173.5 similar to 179deg, respectively, over the frequency range of 13 similar to 110GHz.