System Linearity-Based Characterization of High-Frequency Multilevel DC-DC Converters for S-Band EER Transmitters

Resumen

In modern telecommunications systems, the requirements for the amount and speed of transmitted data are increasing rapidly. For better spectral efficiency complex type modulations (QAM, OFDM) are used, resulting in high PAPR signals. As a consequence, when conventional linear amplifiers (classes A, AB) are used in transmitters, both prominent linearity and poor efficiency are assured. The efficiency of the transmitters can be significantly improved using some of the popular techniques: Kahn EER principle, ET technique, Doherty amplifier, and Chireix’s amplifier. In this paper, two different approaches in supplying a 2.4 GHz class-E power amplifier (S-band) based on the EER technique are analyzed and compared. The consistent part of the EER transmitters is a switched-capacitor based voltage divider combined with a switching structure -analog multiplexer, in the envelope amplifiers and a class-E power amplifier. The analog multiplexer is assisted with a series linear regulator in the first system and a fourth order LC filter in the second system, providing supply modulation for the power amplifier. The systems are compared in terms of efficiency and system linearity using the standard metrics (EVM, ACPR). Special consideration is devoted to characterization of how the envelope amplifiers affect the quality of the RF output signal. It is shown that the tested EER transmitters can reproduce 16–QAM and 64–QAM signals up to 2.5 MHz, manifesting an average efficiency of about 32% with the first transmitter, and 16–QAM signals up to 660 kHz RF bandwidth and an average efficiency of 44% with the second transmitter. A software tool that accurately estimates the EA linearity is utilized and successfully tested on both EER transmitters.