A 30–60 GHz SiGe transformer balun with offset radii coils for low amplitude and phase imbalance

Characterization of a wide-band transformer balun with low magnitude and phase imbalance is presented in this paper. Excellent balance over a large bandwidth is achieved by adopting two new techniques for the transformer balun design, resulting in a very low magnitude imbalance of 0.12 dB and phase imbalance of less than 1° over 30 to 60 GHz. The tradeoff between the insertion loss and the balance of the balun is investigated. First, the appropriate width of the primary and the secondary coils is selected for a reasonable insertion loss. Secondly, the radii of the primary and secondary coils were offset to reduce the parasitic coupling capacitance, thereby improving the balance of the differential signal. The balun is fabricated in 0.13 μιη SiGe technology. The balun is very compact with chip size of 0.2 mm × 0.145 mm.