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Linearity Improvement of Doherty Amplifier Using Analog Predistorter with Phase-Controlled Error Generator  

Lee, Yong-Sub (Pohang University of Science and Technology)
Jeong, Yoon-Ha (Pohang University of Science and Technology)
Publication Information
Journal of the Institute of Electronics Engineers of Korea SC / v.44, no.2, 2007 , pp. 32-38 More about this Journal
Abstract
This paper represents a Doherty amplifier (DPA) with analog predistorter (PD) to improve the linearity of the DPA while preserving the high efficiency. A third-order PD cancels fifth-order intermodulation (IM5) as well as third-order intermodulation (IM3) components by their same phase difference in the PD and DPA. This is accomplished by independently controlling their phase by using the phase-controlled error generator in the PD. Also, we confirm the phase-control ability of the error generator experimentally with a simple and accurate phase measurement setup. For experimental verification, a third-order PD has been implemented and tested in a 180-W DPA at the wide-band code division multiple access (WCDMA) band of 2.11-2.17 GHz. Two-tone test results show that significant cancellation of IM3 and IM5 components can be obtained. For four-carrier WCDMA applications, significant adjacent channel leakage ratio (ACLR) improvement is achieved over a wide range of output power levels. This technique is cost-effective and convenient due to its simple structure, compact size, and three control parameters.
Keywords
Adjacent channel leakage ratio; Doherty amplifier; error generator; phase; predistorter;
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