Comparison of Millimeter Wave Power Amplifiers with Different Power Combining Techniques

Abstract Four-millimetre wave power amplifiers, three-stage differential cascode with inductively coupled impedance transformers, were designed and fabricated in a 130 nm SiGe HBT BiCMOS process with f MAX = 330 GHz. The PAs, where the signal splitting/combining, number of differential pairs and transistor size in the final stage differ, are used in power/efficiency benchmarking. Balun as output impedance transformer was used in two of PAs with different transistor sizes in their third stage, 120 µm respective 160 µm. The power combiners in two other PA embodiments were realized by Parallel Combining Transformer, PCT, and Series Combining Transformer, SCT. The PAs with balun combiner achieve a PSAT of 19.3 dBm with 10.5% third stage PAE at 8.5 dB backoff from P SAT , PAE 3rd BO . For the PA with SCT combiner, P SAT was 18.3 dBm with 7% PAE 3rd BO , and the PA using PCT achieved a P SAT of 18 dBm and 6.5% PAE 3rd BO , measured at 39 GHz. The fractional bandwidths exceeded 36% for balun and SCT and 32% for PCT, respectively. The implemented SCT and PCT with their lower input impedance show lower voltage swing at collector of final stage for equivalent output power level compared with one-way combiner (balun). Also the PAs with PCT and SCT show a lower sensitivity to load impedance variations.