Baseband Termination Research Articles

High-Efficiency Moderate-Power Amplifier Using Packaged GaN Transistor With Improved Average PAE and Gain for Batteryless IoT Applications

One of the fundamental problems in power amplifier (PA) design is the mismatch between the optimum loads for maximum output power and maximum efficiency. This work demonstrates that a GaN transistor of choice can reduce such mismatch when operating at the minimum input RF power required ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {in}}$ </tex-math></inline-formula> ) to obtain its maximum output power. Furthermore, this work investigates the average power-added efficiency (PAE) degradation caused by the baseband terminations for high-efficient switch-mode class-E PAs. Our results show that the average PAE degradation mechanism of class-E PAs is similar to that of class-B ones, but some class-E solutions are more susceptible to the driving signal’s bandwidth. To clarify that, two class-E PAs were implemented using commercial package GaN transistors based on two different modes from the continuum of class-E solutions. Despite being driven by half of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {in}}$ </tex-math></inline-formula> typically employed by designers, the PAs have achieved a gain almost 3 dB higher than the state-of-the-art and excellent efficiency controlling only the second harmonic. Based on the obtained results, the proposed design strategy is believed to have a promising potential for developing high-efficiency simultaneous wireless information and power transmission (SWIPT) base stations for batteryless Internet of Things (IoT).

Wideband IMD3 suppression through negative baseband impedance synthesis

This article presents a power amplifier (PA) linearisation approach based on synthesising a negative impedance termination at the baseband frequency. Negative baseband termination has been previously shown to suppress intermodulation distortion (IMD) products in power amplifiers. Here, this effect is synthesised using a passive feedback network between the drain and gate bias paths of the PA, so that the IMD is suppressed without an increase in the system complexity. The design targets IMD3 suppression at the PA's 3-dB compression point (P3dB), enabling linear operation into compression, therefore, resulting in improved device utilisation and efficiency. Based on simulation of the feedback response over a 1-200 MHz frequency range, a network topology is designed that provides both the bias structure and the appropriate transfer function for IMD3 suppression, demonstrating the first reported practical structure to realize this behaviour over a wide range of baseband frequencies. Two different transfer functions are implemented and compared in performance to the nominal design case with standard baseband terminations. Due to the feedback nature of the approach, stability is also addressed. The 2.14-GHz proof-of-concept prototype with feedback exhibits up to 9.5 dB suppression of the two-tone IMD3 over 10-150 MHz tone spacing, without reducing the CW performance of the PA.

Impact of the Input Baseband Terminations on the Efficiency of Wideband Power Amplifiers Under Concurrent Band Operation

This article presents a theoretical explanation of the efficiency degradation in wideband radio frequency power amplifiers (RFPAs) under concurrent dual-band operation that is still visible after eliminating all known causes related to the output matching network (OMN). First, the origin of this degradation, identified by the reduction of the PA’s efficiency and linearity, is traced to the input baseband impedance terminations. Then, a theoretical model that describes the phenomenon and qualitatively predicts the efficiency variation under concurrent dual-band operation is presented using a simple model based on two-tone excitation. Finally, the proposed explanation is confirmed by comparing the efficiency performance of two 30-W GaN RFPAs of distinct instantaneous bandwidth determined by different input video-bandwidth terminations, under two-tone and concurrent dual-band operation. This article shows that, in addition to the adequate OMN design, an optimal input baseband impedance profile is also an important design constraint needed to keep the efficiency and linearity performance of RFPAs, for scenarios that require a wide instantaneous bandwidth.

A 400-W Peak Asymmetric Doherty Power Amplifier Utilizing an Integrated Baseband Termination for Extended Video Bandwidth

The signal bandwidth requirements for base station radio frequency power amplifiers (PAs) has increased with the advent of multicarrier systems employing carrier aggregation. In this letter, we discuss the design of an integrated bias network for power transistors and discuss its implementation in a high power asymmetric Doherty PA. The designed PA achieves 56 dBm of peak power from 1.805 to 1.88 GHz with 50% efficiency at 8-dB backoff and >200 MHz of video bandwidth (two-tone onset of resonance). Excellent digital pre-distortion (DPD) results are also demonstrated with a 65-MHz wide multicarrier multistandard signal.

Efficiency Degradation Analysis in Wideband Power Amplifiers

This paper addresses the mechanisms of wideband power amplifiers’ efficiency degradation in comparison with their narrowband operation. It starts by identifying some possible causes for this performance degradation, showing that the baseband terminations are dominant. A detailed explanation for the efficiency degradation is then presented, considering the scenarios where the most important baseband components fall before or after the resonance imposed by the bias and matching networks. A theoretical model that is able to describe this performance degradation is also presented. Finally, the proposed theory is validated through two implemented power amplifiers with the same fundamental and harmonic terminations, but with different baseband networks, showing that an optimized bias network design can improve the efficiency performance of a PA.

Design approach to improve linearity and power performance of microwave FETs

In this article, the minimization of asymmetry between lower and upper side band intermodulation products is discussed. Base-band and harmonics termination effects are analyzed by means of a Volterra Series approach, identifying novel conditions to minimize IMD asymmetry and IM3 power levels. The new inferred conditions do not involve base-band terminations, but harmonic load conditions. The proposed criteria are experimentally validated through harmonic load-pull measurements performed on a GaN HEMT under two-tone excitation. The resulting measurements are in agreement with the forecasted analysis results, showing an IMD asymmetry minimization, with a remarkable increase in C/I3 of 6 dBc, without affecting the output power (34 dBm) and power added efficiency (65%) levels attained at 1 dB compression point. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.

Improvement of Intermodulation Distortion Asymmetry Characteristics With Wideband Microwave Signals in High Power Amplifiers

This paper presents the improvement techniques of intermodulation-distortion asymmetries with wide carrier-spacing signals in L/S-band high power amplifiers. We proposed a novel circuit technique to directly connect LC series resonant circuits to the gate and drain electrodes of the transistor die in a package for baseband terminations with a wide frequency range. By applying this circuit technique to a 28-V operation 200-W GaAs heterojunction field-effect transistor (HJFET) amplifier, the third-order intermodulation distortion (IMD3) asymmetries were improved even if the two-tone carrier spacing (Deltaf) exceeds 100 MHz. In addition, we analyzed the IMD3 asymmetries of a Doherty amplifier through the IMD3 vector combination of the main and peak amplifiers. A newly developed 28-V operation 200-W GaAs HJFET Doherty amplifier with source and load baseband terminations also delivered flat IMD3 characteristics against the Deltaf over 50 MHz.

Bias Dependence of Intermodulation Distortion Asymmetry in Heterojunction Bipolar Transistor Using Nonlinear Large-Signal Model

The asymmetry between lower and upper intermodulation distortions (IMD) in a heterojunction bipolar transistor (HBT), which can be observed under certain baseband termination and bias conditions, is analyzed using a large-signal model. This approach enables harmonic balance analysis of IMD asymmetry in nonlinear circuits using HBTs and, therefore, overcomes the limitations of the conventional Volterra-series analysis. Closed-form expression derived from Volterra analysis is also employed to present comparisons with the large-signal model approach. Measurements indicate that the asymmetry is very sensitive to baseband termination, which varies with the envelope frequency of the input RF signal. Specifically, zero crossings of asymmetry are observed at each resonance frequency where the reactive part of baseband termination changes its sign rapidly. It is also found that the asymmetry is enhanced at a specific small bias current where the dominance of the 3rd order nonlinearity is greatly reduced by cancellation with the 2nd order nonlinearity. The bias condition for asymmetry occurrence is calculated, using a simple analytical equation, to be related to measurement data. All the measurements are verified successfully by nonlinear simulation using large-signal model. Finally, the advantage of the large-signal model approach compared to Volterra analysis for asymmetry prediction is discussed.