A GaN HEMT power amplifier with variable gate bias for envelope and phase signals (original) (raw)
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IEEE Transactions on Microwave Theory and Techniques, 2019
Envelope tracking (ET) is a promising power amplifier (PA) architecture for current and future communications systems, that uses dynamic modulation of the supply voltage to provide high efficiency and potentially very wide bandwidth over a large dynamic range of output power. The dynamic nature of the supply voltage can lead to a problematic variation in transistor gain however, particularly in GaN HEMTs. This paper describes and analyses this behaviour and the detrimental effect it can have on ET PAs. Contributing factors and origins of gain variation are described in detail along with how, for the first time, meaningful comparisons can be made between different devices. Using these guidelines, gain variation is shown to be a widespread issue effecting most GaN HEMTs presented in literature. To allow an analysis of the intrinsic device behaviour, an extended transistor model is developed that takes the effect of gate and source field plates into account. This model is refined using measurement data and used to demonstrate the fact that the parasitic gate-drain capacitance (C GD) is the main contributor to the small-signal gain variation; a significant part of the overall gain variation. Based on this knowledge, possible strategies to reduce gain variation at the transistor technology level are proposed, allowing the optimisation of GaN HEMTs specifically for ET PAs. One identified strategy involves reducing the length of the gate field plate, and is shown to be a viable approach to reduce the gain variation in GaN HEMTs, albeit at an increased RF/dc dispersion.
Envelope Tracked Pulse Gate Modulated GaN HEMT Power Amplifier for Wireless Transmitters
IEEE Transactions on Circuits and Systems I: Regular Papers, 2015
This paper proposes a complete transmitter prototype for wireless applications using envelope tracked pulsed gate modulated power amplifier (PA). The proposed transmitter architecture is developed using two high power 10 W gate modulated PAs combined in a fashion to operate as a switched voltage source for the range of duty cycles of pulses driving the gates of power amplifiers. These PAs are designed and implemented using packaged GaN HEMT transistors from CREE to operate at the carrier frequency of 2.35 GHz. For a 5 MHz bandwidth WiMAX 802.16e down-link signal with the PAPR of 7.9 dB and the oversampling ratio of 100, the average drain efficiency of 46.2% is achieved at the average output power of 35.8 dBm. Using a 5 MHz bandwidth LTE down-link signal with 11 dB PAPR and centered at 2.35 GHz, the power amplifier delivers the average output power of 33.2 dBm with the average drain efficiency of 46%. The adjacent channel leakage ratio (ACLR) measured for this signal is less than 36.85 dBc at 10 MHz offset from the center frequency of 2.35 GHz.
IEEE Transactions on Microwave Theory and Techniques, 2011
In this paper a two-stage 2-GHz GaN HEMT amplifier with 15-W output power, 28-dB power gain, and 70% poweradded efficiency (PAE) is presented. The power stage is designed to operate under class F conditions. The driver stage operates under class F 1 conditions and feeds the power stage with both fundamental and second harmonic components. The inter stage matching is designed to target a quasi-half sine voltage shape at the intrinsic gate port of the power stage. The goal is to reduce aperture angle of the power stage and get PAE improvements over a wide frequency bandwidth. In addition to the amplifier design description, this paper reports original time-domain waveform measurements at internal nodes of the designed two-stage power amplifier using calibrated high-impedance probes and large signal network analyzer. Furthermore, waveform measurements recorded at different frequencies show that aperture angle remains reduced over large frequency bandwidth. In this study, a PAE greater than 60% is reached over 20% frequency bandwidth. Index Terms-Aperture angle, classes F and F 1 , GaN power amplifier (PA), power-added efficiency (PAE), waveform measurements.
Development of a GaN HEMT class-AB power amplifier for an envelope tracking system at 2.45 GHz
2010
A class-AB power amplifier was designed for an envelope tracking (ET) application. Class-AB amplifier is widely used in wireless communication systems due to the compromise between linearity and efficiency. As a power device, Cree Gallium Nitride High Electron Mobility Transistor (GaN HEMT) CGH4010F was chosen. The input and output matching networks were designed and simulated with Advanced Design System (ADS). After some optimization, the amplifier was fabricated using a Rogers RT/Duroid 5880 substrate. The amplifier together with a MAX2247 preamplifier as a driver was measured. A good agreement between the simulation and measurement results was observed. The maximum power added efficiency (PAE) is around 50 percents with the supply voltage Vsup= 10V and the maximum drain efficiency is around 75 percents with Vsup= 5V. An output power up to 42 dBm and good linearity of the output voltage with respect to the supply voltage in the range 0≪Vsup≪20V were achieved. Thus, the amplifier i...
2013
In this paper, implementation and testing of non- commercial GaN HEMT in a simple buck converter for envelope amplifier in ET and EER transmission techn iques has been done. Comparing to the prototypes with commercially available EPC1014 and 1015 GaN HEMTs, experimentally demonstrated power supply provided better thermal management and increased the switching frequency up to 25MHz. 64QAM signal with 1MHz of large signal bandw idth and 10.5dB of Peak to Average Power Ratio was gener ated, using the switching frequency of 20MHz. The obtaine defficiency was 38% including the driving circuit an d the total losses breakdown showed that switching power losses in the HEMT are the dominant ones. In addition to this, some basic physical modeling has been done, in order to provide an insight on the correlation between the electrical characteristics of the GaN HEMT and physical design parameters. This is the first step in the optimization of the HEMT design for this particular application.
Design of a high efficiency GaN-HEMT RF power amplifier
2015
This paper presents the design and implementation of a GaN-HEMT, c1ass-J power amplifier suitable for cognitive radio transceivers, i. e., which presents high-efficiency and wideband characteristics, being these maintained for large load variations. Simulation results are presented which show large signal measurement results of 30 dB gain with 60%-76% power added efficiency (PAE) over a band of 1.3-2.3 GHz. Adaptivity to load changes is being developed to ensure PAE above 70% for large load variations.
2010 IEEE MTT-S International Microwave Symposium, 2010
In this paper, the efficiency of a GaN HEMT transistor and its intrinsic waveforms are measured at 0.9 GHz and investigated for load-and supply-modulation applications. The results show that both techniques perform equally well for back-off levels ≤6.5 dB. At higher back-off levels, the efficiency improvements achieved by supply modulation outperform load modulation. At 10 dB back-off, supply, and load modulation provide a power-added efficiency (PAE) of 68%, and 58%, respectively. Using measured intrinsic waveforms, it is shown that PAE degradations in load modulation can be mainly attributed to parallel losses rather than series losses, which are dominant in supply modulation. The harmonic contents of the intrinsic waveforms, in both techniques, are equally strong in back-off and peak power operations. There is, therefore, a great potential for further efficiency enhancement by circuit-level optimization of harmonic terminations for back-off.
GaN HEMT power amplifier design for 2.45 GHz wireless applications
SAIEE Africa Research Journal
Electronic devices with high performances like Power Amplifiers (PA) are very important for Wireless communications. This paper proposes a design of a class AB power amplifier operating at 2.45 GHz, in the S-band frequency. The Cree's CG2H40045F GaN HEMT (High Electron Mobility Transistor) is used for this design. The Gallium Nitride (GaN) technology has been chosen in light of its advantageous properties such as high breakdown voltage, high band gap, as well as high thermal conditions. The paper investigates the different design trade-offs for finding a good balance between various key parameters of the PA (linearity, efficiency, and gain). A design approach has been proposed and the microstrip lines based on the Smith Chart tool available in ADS software have been used for the matching process. The class AB was selected to reach a good agreement between linearity and efficiency, provided by this class. After various process applications from DC characterization to simulations, the proposed design achieves a power added efficiency more than 50% at power saturation with a gain of 15 dB in schematic simulation. The layout dimensions are 55.5 x 64.45 mm 2 on PCB technology.