Wideband Dynamic Drain Current Measurements with a Galvanically Isolated Probe Targeting Supply-Modulated RF Power Amplifiers for 5G Infrastructure

Supply modulation of RF power amplifiers (PA) is a powerful efficiency enhancement technique. For optimization of the RF PA and the supply modulator the dynamic low frequency drain current is of high interest but measurements are difficult due to the large voltage variations at the PA drain bias supply terminal and non 50 Ω, low impedance interface. A non-invasive technique is preferred to the use of bulky directional couplers. A sensor based on a shunt resistor is a favorable choice but the extremely large common-mode voltage complicates the situation. In this paper a measurement technique based on reflection measurements of an active reflector element using an interferometer based on a Doppler radar is investigated. The system allows for very wideband current measurements with high common-mode rejection and low parasitic loading of the shunt resistor. Thereby, the method has the potential to meet the requirements for the extreme wide bandwidth signals used in the future telecommunication infrastructure for 5G.