CMOS Power Amplifier With Novel Transformer Power Combiner

A novel transformer combiner structure for watt-level CMOS power amplifier design is presented in this brief. The proposed active skewered transformer (AST) utilizes the slab inductor as the secondary winding and overcomes the quality factor degradation issue when input cells are increased. Slab inductor has been previously used in the distributed active transformer (DAT) as the primary winding and achieved superior passive efficiency for the transformer combined CMOS power amplifier. However, we find that the slab inductor could be more beneficial as the secondary winding when we are aiming for higher output power from the CMOS power amplifier. The full-wave EM simulation has been performed and shows the advantage of AST over the conventional series-combining transformers (SCTs). Finally, a 2.4GHz CMOS power amplifier is designed based on the AST structure and fabricated in 0.18um CMOS process. The measured output power and power-added efficiency of the proposed power amplifier satisfying LTE specification with 5/20MHz bandwidth are recorded as 26.0/25.0dBm and 24.0/20.9%, respectively.