Compact Transformer Power Combiners for Millimeter-wave Wireless Applications

Two current-summing transformer combiners for 60GHz-band power amplification in millimeter-wave wireless applications are characterized. The parasitic-compensated balun and fully-differential combiners mitigate imbalances caused by interwinding capacitance, while self-shielded output windings inhibit substrate coupling. Excellent agreement is seen between measurement and electromagnetic simulation. Power loss for both prototypes at 60GHz is <1.0dB and chip area is <0.015mm(2). Reflected impedance uniformity between ports at 60GHz for the balun and fully-differential combiners is better than 2.4% and 4.5%, respectively. A lumped-element model for large-signal circuit design with <5.0% error in power loss and reflected port impedance across the 55-65GHz band is also described.