Joint optimization of the power-added efficiency and the error-vector measurement of 20-GHz pHEMT amplifier through a new dynamic bias-control method

This paper presents a method for the optimization of the power-added efficiency (PAE), as well as the error-vector measurement (EVM) of a 20-GHz power amplifier (PA) applied in this case to the M quadrature and amplitude modulations. A first key point lies in that both input and output biasing voltages of the solid-state power amplifiers (SSPAs) are dynamically controlled according to the RF power level associated with the symbol to be transmitted. The leading idea is that the dynamic biasing control is designed and implemented to keep fixed amplitude (AM/AM) and phase (AM/PM) conversion values, while the RF input power level changes. The power gain of the PAs can then be dynamically tuned to a fixed power gain corresponding to the compression gain behavior for which the PAE is optimum at low-, medium-, and high-input RF power levels. As a main consequence, PAE performances can be drastically improved as compared to classical backoff solutions and optimized while keeping a very good EVM. A Ka-band hybrid amplifier has been realized using an 8×75 μm power pseudomorphic high electron-mobility transistor. The proposed linearization technique is validated by comparisons between measured PAE and EVM on the SSPA when a fixed and controlled bias are used.