Yüksek dinamik aralıklı, Si-Ge tranzistorlu, 8-11GHz simetrik sürümlü B sınıfı kuvvetlendirici tasarımı

Abstract

Bu çalışmada Si-Ge HBT teknolojisi kullanılarak 8-11GHz frekans bandında işlev gösteren simetrik sürümlü B sınıfı kuvvetlendirici tasarımı yapılmıştır. Giriş ve çıkış dengeli kapıları dengesiz kapılara uyumlamak ve sisteme bant geçiren özellik kazandırmak amacıyla giriş ve çıkışlarında kullanılmak üzere Marchand Balunu tasarlanmıştır.Kablosuz haberleşme teknolojilerindeki gelişmeler sonucu, bilgiyi yüksek frekanslı işaret şeklinde gönderme ihtiyacı doğmuştur. Bunun sebebi frekans arttıkça dalga boyunun ve buna bağlı olarak da alıcı ve verici anten boyutlarının küçülmesidir.IEEE kullanılan frekans bantlarını standart hale getirmiştir. Bu bant aralıkları küçükten büyüğe HF, VHF, UHF, L, S, C, X, Ku, K, Ka, V, W ve mm bantlarıdır. Bu çalışmada kullanılan 8-11GHz bandını tam olarak karşılayan standart `X` bandıdır.Geniş bantlı yüksek frekanslı kuvvetlendirici tasarımından önce, hangi çalışma noktasında kutuplanacağına karar verilmelidir. Geniş bantlı tasarıma imkan veren A sınıfı, B sınıfı ve AB sınıfı çalışma şekilleri incelenmiştir. A sınıfının en doğrusal fakat en verimsiz, B sınıfının en az doğrusal ancak en verimli çalışma şekli olduğu görülmüş, simetrik sürümlü yapı kullanılacağından dolayı B sınıfı çalışma şekli daha uygun bulunmuştur. Yüksek dinamik aralıklı bir kuvvetlendirici tasarımında ayrıca kazanç ve doğrusallık kriterleri de oldukça önemlidir. Bu sebeple çeşitli kazanç hesaplamaları (güç kazancı, elde edilebilir kazanç, iletim kazancı) ve doğrusallık ölçütü değişkenleri (IP2, IP3 ve P1dB) incelendi.Kuvvetlendiricinin giriş ve çıkışında kullanulmak üzere tasarlanacak balun yapısı için araştırma yapılmıştır. Sık kullanılan balun yapılarından Köprü Balun, Guanella Balunu ve Marchand Balunu yapıları incelenmiştir. Köprü balunun yapısı alçak geçiren süzgeç, Gunanella balununun yapısı yüksek geçiren süzgeç karakteristiği gösterdiği için alttan ve üstten sınırlı çalışma bandı 8-11GHz bandında kullanılmaya uygun olmadığı belirlendi. Bant geçiren karakteristik gösteren Marchand Balunu tercih edildi. Balun yapısı tasarım için seçilen taban malzemesine uygun şekilde AWR-DE Microwave Office benzetim programı aracılığıyla optimize edilerek tasarlandı.Kullanılacak Si-Ge tranzistor de yine aynı benzetim programında modellenerek simetrik sürümlü yapı kuruldu. Simetrik sürümlü yapının girişinde kazancı arttırmak ve de giriş empedans uyumunu sağlamak amacıyla farksalkuvvetlendici yapısı kaskat olarak eklendi. Tasarıma balunlar da eklenerek sonuçlar alındı.

Employing Si-Ge semiconductor technology, 8 to 11GHz push-pull Class B amplifier is designed with input and output balun structures due to make two balanced port network suitable to utilize in single ended systems. Applying input and output baluns also provides impedance matching and bandpass characteristic behaving like a resonant tank filtering even harmonics produced by push-pull amplifier.This work includes literature research about amplifier design criterion, classes according to amplifier operation point, types of baluns, required calculations and finally designs of whole network with simulations done using AWR Design Environment Microwave Office. Due to increase the performance of the system, some optimization tools in simulation programmeare utilized. Developments of wireless communication technologies require using high frequency to reduce wave-lenght and related with wave-lenght receiver and transmitter antenna sizes also decrease. For common use, IEEE standardizes the frequency bands. from low frequency to high frequency these bands are; HF (3 to 30 MHz), VHF (30 to 300MHz), UHF (0.3 to 1GHz), L (1 to 2GHz), S (2 to 4GHz), C (4 to 8GHz), X (8 to 12GHz), Ka (12 to 18GHz), K (20 to 40GHz), Ku (26.5 to 40GHz), V (40 to 75 GHz), W (75 to 110GHz) and mm (110 to 300GHz). HF band is generally used in military and government communicarions, communication with the ground station in aviation applications, amateur radio applications e.t.c.. VHF band is widely used in FM radio broadcasting, sea traffic controlling applications e.t.c.. Some GSM operators utilize UHF band. Besides that some amateur satellite applications can be done in UHF band. Furthermore, UHF band is also used for GPS (Global Positioning System) which is very important technology. S and C bands are suitable for weather and sea radar applicatons and satellite communications. X band covers this work's frequency band 8 to 11GHz, and can be used for electronic warfare, military satellite communications applications. In defense technology, electronic warfare is very important and promising subject to research. The selection of the dc quiescent point for the active device is very important issue before designing an amplifier. It also means determining operation class of the amplifier. A bias network is used to acquire the appropriate quiescent point for the active device under the specified operating conditions, and it maintains a constant setting irrespective of transistor parameter variations The various classes of device operation typically employed at microwave frequencies are defined as A, B, AB, C, D, E and F. The choice of the class depends majorly on the specific application that is intended for the amplifier. For example, due to design a broadband microwave amplifier designs, class A, B, or AB should be selected. D, E and F classes are high efficient switching topologies and widely used in power electronics applications. This thesis includes a brief information about A, B and AB types of operation classes for push-pull amplifier. Due to consider and acquire high efficiency and suitability to push-pull amplifier structure, class B is preferred.Although linearity of a class B amplifier is worse than a class A amplifier, its efficiency is much better. This causes decreasing the power consumption of the system which is very important for both power cost saving and heat dissipation which effects the system performance very negatively.Another important parameter that must be especially considered is linearity. In an ideal system, the output linearly changes with respect to the input. However, transfer function of an amplifier usually not as linear as desired in real world, because of distortive effects. Intermodulation signals can be dangerous if they are in the fundamental band, and cannot be easily filtered. Linearity must be increased to achieve high dynamic range operation. Some of important and widely used linearity criterions are P1dB, IP3 and IP2 are examined before design procedure. P1dB can be physically measured using a signal generator producing an appropriate signal which has enough amplitude for the sensitivity of the amplifier under test at desired frequency chosen from the operation bandwidth It is also seen that, there are some analytical relationships between these linearity criterions. For design procedure of the input and output balun, some balunstructure types are examined to determine which is more suitable for amplifier. The most common and widely used balun types are Bridge (Lattice) Balun, GuanellaBalun and Marchand Balun. It is seen that Bridge (Lattice) balun has low-pass, and Guanella balun has high-pass characteristics so they are not suitable for the 8 to 11GHz application. Unlike Guanella or Bridge balun, Marchand balun has band-pass characteristics and is preffered for the input. Firstly, some literature research has done about Marchand balun to be sure about its functions are suitable for purpose.Marchand introduced the Marchand balun, which is designed using coaxial transmission lines, in 1944, and there are still studies done about implementation and developing this structure. Today, substrate technology is very sophisticate in comparison with 1940s. Thus, current researchs are generally based on mictostrip, coplanar, stripline transmission lines. For required calculations, previous studies about Marchand Balun are used then the results are implemented on transmission line impedance calculation tool TX LINE in AWR DE MWO. After determining the type of input balun, the next issue is indicating the output balun structure. Due to transmit higher power at the output efficiently, 1:4 balun is chosen for output balun which is also perfectly suitable to use for class B amplifiers. Only one branch of the balun transmits the signal for each half cycle of the output signal, which leads combining the two signals with 180-degree phase difference together. Another important stage is choosing transistor technology. There are many types of transistors widely used in similar applications such as silicon BJTs, silicon MOSFETs, GaAs MESFETs, InGaAs/InP HEMTs.As the active semiconductor elements, SiGe HBTs are employed in the class B push pull amplifier design due to its very high cut-off frequency. There is a differential amplifier with feedback due to adjust input impedance and besides that increase the total gain. Supply voltage of the structure is defined as 4V according to characteristics of the chosen transistor model. Class B push-pull amplifier design with additional differential amplifier and input-output baluns is completed and results are achieved with AWR-DE MWO simulation program.8 to 11GHz push-pull Class B amplifier is designed with input and output balun structures due to make two balanced port network suitable to utilize in single ended systems. Network performance is highly increased by utilizing optimization tools in simulation program after combining all stages of design. Applying input and output baluns provides impedance matching and bandpass characteristic behaving like a resonant tank filtering even harmonics produced by push-pull amplifier. Differential amplifier at the first amplification stage provides higher gain, which helps increasing dynamic range of the cascaded amplifier.After research, calculations and optimizations, very satisfactory results are acquired according to simulation graphics. Gain is over 33dB, output P1dB is 15dBm, output IP3 is 40dBm, input reflection is very good (S11<-10dBm) within desired bandwidth 8 to 11GHz. These results are very hard to achieve for X band, and promising for fabrication and implementation. After realizing the structure with lumped elements and getting good results, same network can be implemented as an integrated circuit using SiGe or some other semiconductor technology.