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

Volume

24

Issue

7

fYear

2014

fDate

Jul-14

Firstpage

505

Lastpage

507

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);

fLanguage

English

Journal_Title

Microwave and Wireless Components Letters, IEEE

Publisher

ieee

ISSN

1531-1309

Type

jour

DOI

10.1109/LMWC.2014.2316507

Filename

6810198