Design of a High-Linearity Power Amplifier Using Feedback Structures at High Frequencies

Eliyas Niknamy¹ Arash Azizpor² Rashin farhadi³ Pourya Ahmadi Amirabadi⁴

Abstract :
Radio-frequency (RF) power amplifiers (PAs) are among the most critical components of wireless transmitters. However, their operation near the compression and saturation regions is characterized by nonlinear gain and phase behavior. When handling multicarrier signals or signals with a high peak-to-average power ratio (PAPR), these nonlinearities result in in-band distortion, an increase in Error Vector Magnitude (EVM), and spectral regrowth outside the desired band. Consequently, to meet linearity requirements, the power amplifier is often forced to operate at a level below its maximum output power, which generally leads to reduced power efficiency [1]–[3]. Various methods have been developed for the linearization of power amplifiers, including digital pre-distortion (DPD), feedforward linearization, and feedback-based architectures. DPD has emerged as one of the most widely used techniques due to its adaptive implementation capability and ability to compensate for memory effects. However, in wideband applications, algorithmic complexity, sampling rate requirements, and data converter limitations can pose significant challenges [4], [5]. Negative feedback is a classic technique in both control theory and amplifier design for reducing gain sensitivity and nonlinear behavior. Although direct feedback at radio frequencies faces limitations such as phase delay, parasitic coupling, gain reduction, and stability constraints, hybrid architectures combining feedback with digital pre-distortion can mitigate some of these issues. In Digital Feedback Pre-Distortion (DFBPD), feedback information is used to generate a correction signal, while a look-up table (LUT) implements the required pre-distortion. This architecture can alleviate bandwidth limitations associated with loop delay and reduce the tendency toward oscillation [6]. GaN HEMT technology is considered another key technology for microwave and high-frequency power amplifiers due to its wide bandgap, high breakdown voltage, high power density, and high-frequency operation capability. However, self-heating and charge-trapping phenomena in GaN devices can give rise to memory effects and impact the linearity of the power amplifier [7]–[10]. This paper first presents mathematical models for nonlinear power amplifiers (PAs) and the generation of third-order intermodulation distortion (IMD3). It then analyzes the impact of negative feedback on linear gain and nonlinear coefficients, followed by an examination of stability constraints at high frequencies. Finally, various feedback structures—including direct RF feedback, active feedback, envelope feedback, and digital feedback—are investigated. Finally, the performance of the DFBPD is discussed based on reported simulation and measurement results. Specifically, a 180 W Doherty power amplifier (PA) operating at 2.14 GHz is considered, for which an ACLR of -58 dB at a frequency offset of 2.5 MHz and an improvement of approximately 15 dB have been reported [6].

Keywords : power amplifier linearization feedback pre distortion dfbpd dpd imd3 gan hemt aclr doherty power amplifier

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زبان مقاله : انگلیسی
محور مقاله : مهندسی برق
محل انتشار : چهارمین کنگره بین المللی علوم، مهندسی و فن آوری های نو
آدرس وب سایت کنفرانس : secongress.com
کد IOI مقاله : ACCA-ACZCBA
لینک مستقیم مقاله : https://isnac.ir/ACCA-ACZCBA
نمایش چکیده فارسی : https://isnac.ir/SA/ACCA-ACZCBA

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