Combined Emitter and Base Excitation in Power Amplifiers for Efficient 6G-Communications at Millimetrewaves (CEBEPA)

• Applicant: Professor Dr.-Ing. Frank Ellinger
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538373584

For future 6G-communications, existing power amplifier (PA) concepts approach their physical limits. The high operation frequencies require aggressively scaled semiconductors providing only small breakdown voltages and swings. This leads to increasing relative losses regarding saturation voltages and therefore decreasing efficiencies. Hence, research to find, optimise and understand corresponding solutions for this key challenge is important. Due to its high efficiency, PAs are based on a common source/emitter stage where the source/emitter voltages are constant and/or on ground. Wang et. al. recently proposed a new concept called dual-drive. To avoid confusion with multi-drive-transistor-stacking, we call the new concept CEBE (combined emitter and base excitation). Here, the input signal drives not only the gate/base, but via a coupler, also the source/emitter, in a way that output voltage swing and efficiency increase. Up to now, a very efficient CEBE CMOS PA up to 35 GHz was published at ISSCC 21. Based on a student work, we simulated a first CEBE BiCMOS PA verifying the CEBE advantages. Since there are only a very few papers on CEBE PAs yet, there is lot of space for in-depth investigations and extensions. CEBEPA studies the CEBE approach in depth up to highest reasonable frequencies of around 220 GHz. The fastest available SiGe BiCMOS technology (IHP SG13G3) is applied for hardware implementations. Its low loss copper metal stack is excellently suited for the required low loss CEBE couplers. High linearity for quadrature amplitude modulation and large bandwidths are required for 6G. Hence, compared to the state of research, we investigate not only how the CEBE coupler can increase the swing and efficiency, but also, how, by reusing the inductive negative series feedback inherent in the CEBE coupler, at the same time, also the linearity (e.g. oP1dB closer to Psat) and bandwidth (since input becomes more resistive) can be improved. We study novel CEBE approaches e.g. based on tuneable phase shifters to relax the phase specs for the coupler and amplifier core. We propose and study the novel combination of CEBE with transistor stacking, where in addition to the base and emitter of the common emitter stage also the bases of the stacked transistors are modulated by derivatives of the input signal to enable higher swing at high efficiency. Various CEBE coupler approaches are modelled and compared, e.g. symmetric vs. asymmetric, edge vs. broadside, hybrid combinations incl. U-type, etc. Trade-offs, e.g. regarding CEBE coupling factor on improvements regarding output swing, efficiency, bandwidth, linearity, robustness on process variations on one hand and gain reductions on other hand are studied. The CEBE theory is extended, e.g. technology-overarching equations are derived, which reveal the impact of the coupler losses on the overall PA.

• DFG Programme: Research Grants