3 research outputs found
Vidutinių dažnių 5G belaidžių tinklų galios stiprintuvų tyrimas
This dissertation addresses the problems of ensuring efficient radio fre-quency transmission for 5G wireless networks. Taking into account, that the next
generation 5G wireless network structure will be heterogeneous, the device
density and their mobility will increase and massive MIMO connectivity
capability will be widespread, the main investigated problem is formulated –
increasing the efficiency of portable mid-band 5G wireless network CMOS power amplifier with impedance matching networks.
The dissertation consists of four parts including the introduction, 3 chapters, conclusions, references and 3 annexes.
The investigated problem, importance and purpose of the thesis, the ob-ject of the research methodology, as well as the scientific novelty are de-fined in the
introduction. Practical significance of the obtained results, defended state-ments and the structure of the dissertation are also included.
The first chapter presents an extensive literature analysis. Latest ad-vances in the structure of the modern wireless network and the importance of the power amplifier in the radio frequency transmission chain are de-scribed in detail. The latter is followed by different power amplifier archi-tectures, parameters and their improvement techniques. Reported imped-ance matching network design methods are also discussed. Chapter 1 is concluded distinguishing the possible research vectors and defining the problems raised in this dissertation.
The second chapter is focused around improving the accuracy of de-signing lumped impedance matching network. The proposed methodology of estimating lumped inductor and capacitor parasitic parameters is dis-cussed in detail provi-ding complete mathematical expressions, including a summary and conclusions.
The third chapter presents simulation results for the designed radio fre-quency power amplifiers. Two variations of Doherty power amplifier archi-tectures are presented in the second part, covering the full step-by-step de-sign and simulation process. The latter chapter is concluded by comparing simulation and
measurement results for all designed radio frequency power amplifiers.
General conclusions are followed by an extensive list of references and a list of 5 publications by the author on the topic of the dissertation.
5 papers, focusing on the subject of the discussed dissertation, have been
published: three papers are included in the Clarivate Analytics Web of Sci-ence database with a citation index, one paper is included in Clarivate Ana-lytics Web of Science database Conference Proceedings, and one paper has been published in unreferred international conference preceedings. The au-thor has also made
9 presentations at 9 scientific conferences at a national and international level.Dissertatio
Supply modulated GaN HEMT power amplifiers - From transistor to system
Power amplifiers (PAs) for mobile communication applications are required to fulfil stringent requirements concerning linearity while keeping a high efficiency over a wide power range and bandwidth. To
achieve this, a number of advanced PA topologies have been developed, mostly based on either load modulation, such as Doherty PAs or load modulation balanced PAs, or on supply modulation such
as envelope tracking or envelope elimination and restoration. Supply modulation has an advantage
over other topologies as the power range of high efficiency can be realised over arbitrary bandwidths,
only limited by the bandwidth of the PA. This does, however, come at the cost of a significantly
more complicated voltage supply. Instead of a static supply voltage, the PA needs to be provided
with one which is rapidly changing, requiring a supply modulator capable of powering the PA while
modulating its supply voltage. This thesis investigates a number of challenges in supply modulated
power amplifiers, ranging from the transistor itself to circuit design and system level considerations
and focusses on power levels up to 10 W and frequencies between 1 GHz and 4 GHz.
Transistors, as the centre-piece of a PA, determine how well the PA reacts to a changing supply
voltage. In this work, the traits that make GaN HEMTs suitable for supply modulated PAs were
investigated, and gain variation with changing supply voltage was established as an important parameter. This gain variation is described in detail and its impacts on PA performance are discussed. By
comparing transistors in literature, gain variation has been demonstrated to be a prevalent characteristic in transistors with GaN HEMTs showing a very wide range of gain variation. Using a small-signal
model based on measurements, the voltage dependent behaviour of the feedback capacitance CGD is,
for the first time, identified as the origin of small-signal gain variation. This is traced down to the
gate field plate which is commonly used to combat surface trapping effects in GaN HEMTs. With
this in mind, two different ways of changing the transistor geometry to reduce the impact of gain
variation and thus optimise the transistor for operation in supply modulated PAs are discussed and
demonstrated using a 250 nm GaN HEMT.
As a result of the non-linearity of the feedback and gate-source capacitances, the input impedance
of GaN HEMTs changes with supply voltage and drive power. This prevents the transistor from being
matched at all supply voltages and input powers and introduces phase distortion. Using simulation and
measurement, the impact of input impedance on linearity and efficiency of supply modulated power
amplifiers is demonstrated on a 2.9 GHz 10 W PA. Careful selection of the input impedance allows
improvement of AM/PM distortion of a supply modulated PA with little cost in terms of AM/AM
and PAE.
I
Supply modulators have a significant impact on efficiency and linearity of the ET system. One
supply modulator topology with the potential to generate a supply voltage with a high modulation
bandwidth is the RF modulator in which the input DC voltage is turned into an RF signal and
rectified, resulting in an output voltage which depends on the excitation of the PA. While PAs are
well understood in every detail, there are gaps in the understanding of RF rectifiers. Using active
load-pull/source-pull measurements, intrinsic gate and drain waveforms of a GaN HEMT operated as
a rectifier are demonstrated for the first time. This allows in-detail evaluation of the impact of the
gate termination in self-synchronous rectifiers. It also allows detailed analysis of the loss mechanisms
in rectifiers and formulation of the required impedances to realise efficient self-synchronous operation,
resulting in efficiencies exceeding 90% over wide power ranges. Using waveform engineering, a new type
of RF modulator, with potentially very high bandwidths, based on even harmonic generation/injection
is proposed. The necessary operating conditions of the rectifier part of the modulator are emulated
using an active load-pull/source-pull system to successfully demonstrate that the rectifier behaves
as predicted. Using a simple demonstrator, preliminary measurements were conducted and the RF
modulator was shown to work, reaching efficiencies up to 78%.
As PA and supply modulator are combined, they present impedances to each other. These
impedances have a significant impact on the behaviour of both sub-systems. A simple way to characterise both the impedance presented to the PA by the modulator and the impedance presented to the
modulator by the PA is described. Using a state-of-the-art modulator, these impedances are measured,
the modulator impedance is demonstrated to be close to the simulated value. These measurements
also demonstrate that the impedances change significantly with the operating conditions