Title :
A Transformer-Less Load-Modulated (TLLM) Architecture for Efficient Wideband Power Amplifiers
Author :
Akbarpour, Mohammadhassan ; Helaoui, Mohamed ; Ghannouchi, Fadhel M.
Author_Institution :
Dept. of Electr. & Comput. Eng., Univ. of Calgary, Calgary, AB, Canada
Abstract :
An architecture and design procedure for transformer-less load-modulated power amplifiers (PAs) having high efficiency at power back-off is presented. This architecture utilizes a comparable load modulation concept as in the Doherty PA; however, contrary to the Doherty PA, it neither requires an output impedance transformer, nor offset lines, which are the main limiting factors in designing wideband Doherty amplifiers. In this architecture, the proper load modulation at the transistor drain levels is directly dependant on the design of the main and peaking amplifiers´ matching networks. It is shown that the design of the output impedance of the peaking amplifier as a frequency-varying susceptance rather than as a quasi-open circuit impedance (as in Doherty amplifiers) helps in achieving better wideband performance. Based on the analytical results, a step-by-step procedure is proposed for designing wideband load-modulated PAs having high efficiency over a wide power back-off region. Based on the proposed architecture and its design procedure, a 10-W PA is designed and prototyped in the 1.96-2.46-GHz band exhibiting a power-added efficiency of more than 40% at a 6-dB power back-off. In comparison with a symmetrical Doherty amplifier design using the same device, the proposed architecture exhibits a 250% enhancement in its fractional bandwidth.
Keywords :
UHF power amplifiers; impedance convertors; wideband amplifiers; frequency 1.96 GHz to 2.46 GHz; frequency-varying susceptance; limiting factors; load modulation; matching networks; offset lines; output impedance transformer; power 10 W; power back-off; power-added efficiency; quasi-open circuit impedance; symmetrical Doherty amplifier design; transformer-less load-modulated architecture; transistor drain levels; wideband Doherty amplifiers; wideband load-modulated PA; wideband performance; wideband power amplifiers; Impedance; Impedance matching; Modulation; Power generation; Transistors; Wideband; Doherty amplifier; peak-to-average power ratio (PAPR); power back-off; power-added efficiency (PAE); software-defined radio (SDR); two-point matching; two-sided matching; wideband power amplifiers (PAs);
Journal_Title :
Microwave Theory and Techniques, IEEE Transactions on
DOI :
10.1109/TMTT.2012.2206050