Yüksek verimli ve geniş bantlı güç kuvvetlendirici tasarımı
High efficient and wideband power amplifier design
Yazar: BURAK ŞAHİN
Danışman: DOÇ. DR. METİN YAZGI
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Elektronik ve Haberleşme Mühendisliği Ana Bilim Dalı / Elektronik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering
Dizin: Geniş bantlı kuvvetlendirici = Broadband amplifier ; Güç yükseltici = Power amplifier

Özet:
Kablosuz iletişim pazarındaki rekabet ve geleneksel askeri uygulamaların istikrarlı ilerleyişi ile birlikte, RF teknolojileri bu alandaki insan faaliyetlerinde birçok yönüyle kritik rolleri oynamaktadırlar. Kablosuz haberleşmede kullanılan RF sistemlerini oluşturan alt blokların en çok enerji tüketen bölümü güç kuvvetlendiricileridir. Güç kuvvetlendiricileri, verici sistemlerde sinyallerin bütünlüğünün bozulmadan antene ulaşabilmesini sağlamak amacıyla sinyal seviyesini yükselten birimler olarak özetlenebilir.
Verim kritik bir uygulama olan güç kuvvetlendirici tasarımı, çalışma bandında maksimum verimin ve çıkış gücünün sağlanması hedeflenerek yapılır.
Tezde öncelikle güç kuvvetlendiricisi temellerinden bahsedilmiş ve kullanılan teknolojiler, tasarım parametreleri ve yöntemleri hakkında bilgi verilmiştir. İzleyen bölümde bu yöntemler dikkate alınarak belirlenmiş tasarım hedefleri oluşturulmuş ve farklı çıkış güçlerine sahip yüksek verimli, geniş bantlı güç kuvvetlendiricileri bilgisayar destekli tasarım programı AWR ile tasarlanmıştır.
Çıkış katında kullanılacak eleman sayısı mümkün olduğunca az tutulmuş ve uyumlama devresini oluştururken kullanılan sistematik yaklaşım ile genişbantlı empedans uyumlama problemini basitleştirmek amaçlanmıştır. Tasarlanması planlanan güç kuvvetlendiricisi devrelerinde kullanılan transistörler doğrusal olmadığından dolayı, istenilen bantta empedans uyumlama probleminin çözümü günümüz teknikleriyle oldukça zordur. Bu sebeple devrenin elde edilebilecek optimum empedans değerlerini elde etmek amacıyla yük çekme yöntemi kullanılmış, elde edilen değerleri sağlayacak uyumlama devresi tasarlanmaya çalışılmıştır. Kullanılan yaklaşım, birden fazla güç kuvvetlendiricisi tasarımında kullanılarak geçerliliği kanıtlanmak istenmiştir.
Yapılan güç kuvvetlendiricilerden 10W çıkış gücüne sahip tasarımın bant genişliği 1.5 GHz – 5 GHz, 40 W çıkış gücüne sahip tasarımın ise bant genişliği 1 GHz – 3.5 GHz, 100W çıkış gücüne sahip tasarımın bant genişliği ise 1 GHz – 2 GHz'dir. Tasarlanan kuvvetlendiricilerin gerçeklendiği takdirdeki performansını mümkün olduğunca kestirebilmek amacıyla pasif elemanlar ideal modellerle değil, ticari modeller ile devreye dahil edilmişlerdir. Son olarak AWR'nin optimizasyon araçları kullanılarak iyileştirme çalışmaları yapılmış ve tasarımlar son halini almıştır.
Tasarım sonucunda elde edilen grafikler incelendiğinde sonuçların istenen seviyede olduğu görülmüştür.

Abstract:
With the competition in the wireless communications market and the steady progress of traditional military applications, RF technologies play many critical roles in this area. The most energy-consuming part of the sub-blocks that make up RF systems used in wireless communications are power amplifiers. Power amplifiers can be summarized as units that raise the signal level to ensure that the integrity of the signals in the transmitter systems can reach the antenna without degradation. The power amplifier design, which is a efficiency-critical application, is aimed at achieving maximum output power in the frequency band.
Developments in RF electronics require high-output broadband amplifiers to operate as efficient as possible. In the literature, many studies have been done and many methods have been proposed in order to bring these parameters to the desired level depending on the field of application. In this thesis, the efficiency, output power and gain of microwave amplifiers designed with GaN transistor, which are more advantageous than other semiconductor technologies. Therefore, in the thesis, GaN transistor broadband power amplifier design is discussed. Since the selected transistor model is nonlinear power transistors and it is very difficult to model the input and output impedance circuits with linear equation systems in a broadband design, the method for addressing these problems is presented.
In theory, there is no parameter limiting the power to be transferred to the output in linear systems. The higher the power in the source, the higher the output power. Therefore, this approach can be mentioned in the design of the output matching circuit when operated in the linear region. However, the maximum power transmission in non-linear power amplifiers should be considered under large signal condition. The aim is to go through a nonlinear load and make nonlinear matching. However, due to the absence of ideal nonlinear elements without power consumption, we can not perform nonlinear matching with today's technology.
When the impedance matching circuit of the power amplifier is intended to be designed, the optimum impedance values are first obtained by the load line method to perform power matching. This technique is based on static curves and is entirely real and linear. However, dynamic behavior in the system should be taken into account. With the introduction of the parasitic components of the element at high frequencies, the optimum impedance obtained by the load line method requires the parasitic components to be updated and added to the system. Therefore, the load line method can not be used directly at microwave frequencies. Since the power amplifier is generally driven in the large signal region, so that large signal data of the active element is needed to design. As previously mentioned, since the system is not linear, this data cannot be obtained and impedance matching circuits are designed with the data obtained by measuring the load pull contours of the transistor.
The thesis consists of four main sections. First chapter gives detail about the aim of this work and contrubiton.
In the second part of the thesis, general information about RF power amplifiers is given and a theoretical summary about the parameters and semiconductor technology used when designing a power amplifier is presented. The fundamentals of power amplifier are mentioned and information about the used technologies, design parameters and methods are given.
In the third chapter, the design phases of the broadband power amplifiers designed in the thesis, the methods used and the computer aided vehicle (CAD) which is the design of the AWR, the optimization methods were examined. In addition, impedance matching methods which can be considered as the main subject of the thesis are discussed in detail in this section.
In the fourth chapter, there are designs made within the scope of thesis. The arguments in the third section, which describe methods for broadband power amplifier design, are supported by detailed design steps and comparative results of different amplifiers made using three different transistor models in this section.
In the fifth chapter which is the conclusion part, the results and recommendations were evaluated in general.
The designed power amplifiers have a bandwidth of 1.5 GHz - 5 GHz with a 10 W output power, a bandwidth of 1 GHz – 3.5 GHz with a 40 W output power and a bandwith of 1 GHz – 2 GHz with a 100 W output power. In order to predict the performance of the designed amplifiers as much as possible, the passive elements are incorporated into the circuit with commercial models, not the ideal components. Finally, optimization work has been done using AWR's optimization tools and designs have been finalized.
When the graphics obtained from the design are examined, it is seen that the results are at the desired level.
In the first design, 10 watt output power and more than 40% power added effciency were obtained with a minimum gain of 10dB, between 1.5 GHz and 5 GHz. CREE's "CGH40010F GaN HEMT" transistor was used in this design.
The frequeny band of second design is between 1 GHz and 3.5 GHz and Cree's "CGH40045 GaN HEMT" transistor is used. In this design, the minimum output power is above 40W and the minimum PAE value is above 45%.
In the third design, "CGH40120 GaN HEMT" transistor of CREE is used. The output power over 100 W in the 1 GHz - 2 GHz frequency band was obtained with more than 50% PAE and with a gain above 10 dB.
When the results obtained from the studies in the thesis are examined, it is seen that the results mostly provide the values targeted by the studies in the band intervals. The power amplifiers designed in the thesis have been compared with similar studies in the literature and it has been seen that the designs made with the proposed method are satisfactory. When the performance results are examined, it is expected that these power amplifiers, which are simulated in the thesis study, will give performance at values close to these levels if prototype production is done in the future. In addition, it is predicted that the methods in the thesis will be useful for future studies.