A Compact and Broadband Doherty Power Amplifier Without Post-Matching Network

Abstract

Post-matching network (PMN) dominates broadband Doherty power amplifier (DPA) design, but at the cost of large footprint. This brief presents a PMN-free, compact and broadband DPA based on dual-mode impedance transformer (IT) which can simultaneously realize a complex-to-real conversion at two frequencies. The conversion ratio of the IT is significantly increased while its fluctuation is reduced after collaborating a short drain bias. The dual-mode ITs are used as the output matching networks in the carrier and peaking paths. An out-of-phase <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2^{\mathrm{ nd}}$ </tex-math></inline-formula> harmonic injection path is constructed based on the inherent structure of the IT without additional bridge, resulting in enhanced saturated efficiency and output power at the upper band edge. A prototype circuit operating from 2.1 to 3.1 GHz is fabricated, and measured results show a 7-8.2 dB gain and 42.2-43.3 dBm output power at saturation. The 6-dB OBO and saturated efficiency is 42.3-52% and 60.4-67.7%, respectively. The area of the whole OMNs is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$19\mathbf {\times }$ </tex-math></inline-formula> 37 mm2, indicating a significant size reduction, while the DPA’s performance is comparable with the PMN types.