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A frequency-scalable, three-stage, transformer-coupled millimeter-wave power amplifier (PA) is implemented in 130 nm SiGe-BiCMOS. Differential common-base gain stages extend collector-emitter breakdown voltage beyond 3 V, while collector-emitter neutralization increases reverse isolation and stability. Monolithic self-shielded transformers designed for low insertion loss and compact dimensions on-chip include: a 2:4 input power splitter, a 4:1 output balun combiner and inter-stage coupling transformers. The balun combiner and fully-differential splitter are compensated for imbalances caused by parasitic interwinding capacitance, and simulations predict better than 3% uniformity between reflected port-to-port impedances at 60 GHz. Simulated impedance uniformity is within 6% from 55-65 GHz, and insertion loss of the 0.015 mm2 combiner prototypes at 60 GHz is below 1 dB. The 0.72 mm2 60 GHz-band PA realizes a measured peak small-signal gain higher than 20 dB with over 10 GHz 3 dB bandwidth. Reverse isolation is better than 51 dB from 50-65 GHz and the PA is unconditionally stable. It consumes 353 mW (quiescent) from a 1.8 V supply and the active area is 0.25 mm2. Maximum output power and peak power-added efficiency (PAE) are 20.1 dBm and 18% at 62 GHz, respectively. An up-banded 79-87.5 GHz PA is also implemented to verify frequency scalability of the design. The 0.23 mm2 active area 79 GHz PA prototype produces 18 dBm saturated output power and 9% peak-PAE at 84 GHz from a 2.5 V supply.
Date of Publication: Sept. 2012