Current-Tracking Technique Improves RF Amplifier Efficiency in Lower HF Frequency Band

Over the past decade, a prominent trend in mobile radio communications has been the increasing adoption of envelope-tracking techniques to enhance the efficiency of radio frequency (RF) power amplifiers. An envelope-tracking amplifier is a hybrid linear/non-linear circuit where the supply voltage to the linear amplifier is dynamically adjusted by a nonlinear (switched-mode) power supply circuit to match the instantaneous amplitude (envelope) of the input signal. Inspired by this principle of operation, the presented research investigates a more straightforward approach: feeding the antenna directly with current generated by a highly efficient switched-mode source. The viability of the principle has been verified by simulations and measurement results on a demonstrator in the lower HF frequency range. The results have confirmed the substantial efficiency increase, in the operating frequency range of non-linear circuit.