GaN HEMT Based High Power and High Efficiency Doherty Amplifiers with Digital Pre-Distortion Correction for WiBro Applications

Abstract

This paper presents high power and high efficiency Doherty amplifiers for 2.345 GHz wireless broadband (WiBro) applications that use a Nitronex 125-W (<TEX>$P_{3dB}$</TEX>) GaN high electron mobility transistor (HEMT). Two- and three-way Doherty amplifiers and a saturated Doherty amplifier using Class-F circuitry are implemented. The measured result for a center frequency of 2.345 GHz shows that the two-way Doherty amplifier attains a high <TEX>$P_{3dB}$</TEX> of 51.5 dBm, a gain of 12.5 dB, and a power-added efficiency (PAE) improvement of about 16 % compared to a single class AB amplifier at 6-dB back-off power region from <TEX>$P_{3dB}$</TEX>. For a WiBro OFDMA signal, the Doherty amplifier provides an adjacent channel leakage ratio (ACLR) at 4.77 MHz offset that is -33 dBc at an output power of 42 dBm, which is a 9.5 dB back-off power region from <TEX>$P_{3dB}$</TEX>. By employing a digital pre-distortion (DPD) technique, the ACLR of the Doherty amplifier is improved from -33 dBc to -48 dBc. The measured result for the same frequency shows that the three-way Doherty amplifier, which has a <TEX>$P_{3dB}$</TEX> of 53.16 dBm and a gain of 10.3 dB, and the saturated Doherty amplifier, which has a <TEX>$P_{3dB}$</TEX> of 51.1 dBm and a gain of 10.3 dB, provide a PAE improvement of 11 % at the 9-dB back-off power region and 7.5 % at the 6-dB back-off region, respectively, compared to the two-way Doherty amplifier.