Title :
Effect of Load Modulation on Phase Distortion in Doherty Power Amplifiers
Author :
Piazzon, L. ; Giofre, R. ; Quaglia, R. ; Camarchia, Vittorio ; Pirola, Marco ; Colantonio, P. ; Giannini, F. ; Ghione, G.
Author_Institution :
Dept. of Electron. Eng., Univ. of Roma Tor Vergata, Rome, Italy
Abstract :
The mechanisms leading to higher phase distortion of Doherty power amplifiers in comparison to standard architectures are theoretically investigated and experimentally verified. The analysis focuses on the Main amplifier contribution to AM/PM due to the load modulation, a key feature of the Doherty, and is based on a simplified active device circuit approach. Experimental characterization is carried out by source/load-pull measurements on a 4 W die GaN-HEMT at 7 GHz. Measured results confirm the role of the load modulation on the AM/PM distortion, showing that, even if the device nonlinearities are minimized by properly selecting the bias point, a significant residual AM/PM distortion (10° in the present case) appears when the output load is modulated. The effect of this phase distortion on a 14 MHz-256 QAM signal has been evaluated by system level simulations.
Keywords :
III-V semiconductors; active networks; gallium compounds; high electron mobility transistors; microwave power amplifiers; quadrature amplitude modulation; wide band gap semiconductors; AM-PM distortion; Doherty power amplifiers; GaN; GaN-HEMT; QAM signal; active device circuit; frequency 14 MHz; frequency 7 GHz; load modulation; main amplifier contribution; phase distortion; power 4 W; source-load-pull measurements; system level simulations; Distortion measurement; Equivalent circuits; Integrated circuit modeling; Load modeling; Microwave circuits; Modulation; Power generation; AM/PM distortion; Doherty amplifier; efficiency; linearity; load modulation; power amplifier (PA);
Journal_Title :
Microwave and Wireless Components Letters, IEEE
DOI :
10.1109/LMWC.2014.2316507
