This paper proposes a fully integrated broadband power amplifier for LTE-A application using GaAs HBT process. To improve the linearity and broadband performance, RC feedback structures and dynamic bias circuits are employed and designed through optimization. With careful design of the broadband matching networks in the proposed 3-stage power amplifier topology, a power gain above 21.6 dB is achieved from 1.8 GHz to 2.8 GHz. Driven by an 80 MHz wideband LTE-A signal with PAPR of 7.5 dB, the designed RF power amplifier achieves an average output power about 22 dBm at ACLR = −30 dBc over the entire 1 GHz frequency band. Considering the broad bandwidth of the driven signal and wide frequency coverage bandwidth, the performance merits of the proposed design compare favorably with the state-of-the-art. 1. INTRODUCTION LTE-advanced (LTE-A) has fulfilled the requirements of the 4G standards made by ITU with the help of Carrier Aggregation (CA) and high modulation density up to 64QAM. CA is one of the most important features of LTE-A, enabling an overall bandwidth of 100 MHz and a high data rate up to 1 GBit/s by aggregating up to five LTE carriers, each of 20 MHz bandwidth [1]. A power amplifier is one of the most important components, for its performance directly influences the overall system bandwidth, linearity, output power and efficiency. The increase of the signal bandwidth and peak-to-average power ratio (PAPR) in LTE-A demands a higher linearity in power amplifiers design. In base stations, the final stage output power amplifier often employs GaN transistors together with a digital pre-distortion (DPD) system to achieve enough output power and linearity. Along with CA, the broad bandwidth and high PAPR of the modulated signals will force the components of the base-station to work in a back-off state to get enough linearity. Therefore an extra drive stage is often needed to pre-amplify the RF signals before sending them to the final output stage. For the drive stage power amplifier, a broadband and linear fully integrated chip is a good solution that offers enough power gain with low cost. Different from the final stage power amplifiers, the bandwidth and linearity requirements of the drive stage PA are more important than efficiency. Recently, many fully integrated PA chips have been designed for the LTE-A application. CMOS process has a high level of integration and low cost, and some CMOS-based PAs have been reported for LTE-A [2-4]. However, CMOS suffers from low breakdown voltage and substrate loss, resulting into relatively low output power and poor linearity. So far, GaAs is still the most mature process for medium-power PAs with good linearity. Doherty structure is suitable for the back-off power application, and a broadband MMIC Doherty PA has been designed, covering the 1.6∼2.1 GHz frequency range [5]. Another MMIC PA is proposed in [6] which is designed in GaAs pHEMT process and operates from 2 to 6.5 GHz. In [7], a class-J PA is realized using GaAs HBTs and optimized for the LTE application
Abstract-In this paper, a broadband power amplifier with high efficiency and output power based on GaN HEMT is presented. The design of broadband matching network and transistor package modeling is presented, and a simulation strategy is proposed to increase the simulation accuracy. According to measured results, the PA module shows a linear gain of 10∼13 dB during 1.9-4 GHz. The efficiency can reach 74.5%, and the maximum output power reaches 33.2 Watt. For a 5-MHz WCDMA signal, the designed power amplifier achieves an average output power above 20 W when ACLR = −30 dBc over the entire working band.
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