A Ka-Band Transformer-Based Doherty Power Amplifier for Multi-Gb/s Application in 90-nm CMOS

A Ka-band transformer (TF)-based Doherty power amplifier (DPA) is designed and fabricated in 90-nm CMOS process. Symmetrical Doherty structure is used to improve the 6-dB power backoff efficiency. The high turn ratio (N = 2) current-type TF is adopted for the load modulation in a DPA to avoid from leakage power. The measured small signal gain is 19.8 dB with 3-dB bandwidth from 28.7 to 41.9 GHz. The proposed PA achieves 20.7-dBm saturated output power with above 32% power added efficiency (PAE) at 34 GHz. In the 6-dB power backoff region, the PAE of the proposed PA is about 1.7× of that in a class-A PA.