4.9 A 60GHz CMOS Power Amplifier with Cascaded Asymmetric Distributed-Active-Transformer Achieving Watt-Level Peak Output Power with 20.8% PAE and Supporting 2Gsym/s 64-QAM Modulation

Since its invention in early 2000s, Distributed Active Transformer (DAT) has been a popular power-combiner technique for high-power high-efficiency Power Amplifiers (PAs) in voltage-limited Silicon processes at GHz frequencies [1, 2]. However, successful DAT implementations at high mm-wave frequencies still remain elusive. Substantial inter-winding capacitance causes asymmetry in impedance transformation among the DAT sections, resulting in mismatched and non-optimum loads for high-frequency mm-wave DAT PAs, including those using transformer-based DAT combiners [3]. Moreover, the DAT physical size at mm-wave frequencies is comparable to a mm-wave signal wavelength, which leads to significant physical phase delays between DAT sections. As a result, the combined vectoral signal at the DAT output is substantially mismatched, causing appreciable degradation in the DAT output power and efficiency [4].