This letter presents a V-band buffer-less, high-power frequency quadrupler realized in 0.13-μm SiGe heterojunction bipolar transistor (HBT) technology. A compact, stacked transformer-based differential quadrature hybrid is proposed, not only for direct power combining at fourth harmonic but also obtaining a built-in harmonic rejection. For output power ( POUT) and conversion gain (CG) boosting, a common-centroid SiGe HBT cascode with a negative Miller capacitance at a common base (CB) SiGe HBT is devised. A prototype attains measured peak POUT, efficiency ŋ, and CG of 8.8 dBm, 3.8%, and 4.0 dB at 56 GHz, respectively, with its 3-dB bandwidth (BW) from 52 to 60 GHz and harmonic rejection ratio (HRR) higher than 30 dBc without any lossy output filter.
