A Ka-Band Doherty-Like Non-Load Modulated Power Amplifier

This article describes a three-way power amplifier (PA) topology that achieves broadband power back-off (PBO) efficiency enhancement without using active load modulation on the Main PA or supply modulation. This allows the PA to avoid the classic trade-off between load modulation and bandwidth that is typical among Doherty PAs. Unlike Doherty PAs, the proposed PA has both its voltage and current drive profiles reach a maximum at PBO, which causes the impedance of the Main PA to be constant across the entire input drive. This is achieved with a novel parallel-series output matching network (OMN) that primarily utilizes coupled-line baluns. A prototype is fabricated in the GlobalFoundries 45 nm RFSOI and achieves a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {avg}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {PAE_{avg}}$ </tex-math></inline-formula> of 6.45–12.61 dBm and 5.9%–16.4% from 25 to 40 GHz, respectively. With a 200 MHz signal, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {avg}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {PAE_{avg}}$ </tex-math></inline-formula> are 5.58–11.1 dBm and 4.8%–13.3%, respectively.