GaAs pHEMT class-E power amplifier design

A basic single-stage power amplifier circuit includes an active device, input matching circuit to match with source impedance, and an output matching circuit to match with load impedance. In a power apmlifier design, there are important parameters to be considered. These parameters include selection of active device, technology of active device, class of operaiton, intput and output matching network structure design, biasing, range of frequency, operation parameters such as required output power, gain, Power Added Efficiency (PAE), Input and Ouput Insertion Loss, S-parameters, etc. All these parameters shall be considered in the design and reaching design goals will end up in a successful design. Nowadays with improvements in designing wireless communiction systems with specific applications such as hand-hold wireless devices, space telecommunication subsystems, etc. it is important to have highly reliable, efficient, small-sized systems, given the limited input power source (generally battery), attaining desirable output power level and gain. The aim of this thesis is designing Class-E and Inverse-Class-E power amplifier with low voltge consumption in UHF band with application in small satellites. One of the main properties of this design is being supplied with only 5V which will result in elimintating a DC-DC down-converter in the next stage of a system. To reach this aim, class-E structure has been selected in order to have maximum possible PAE and high gain with the available input power, and other design specifications which will be discussed and mentioned in details in the text. Besides, Inverse-Class-E structure and a novel mix of Class-E and Inverse-Class-E has also been designed and tested to compare the function of each structure. Suitable transistor (available in market) and active device technology has been selected, different input and output matching networks have been designed and examined, biasing network has been designed carefully, and satisfying results for the given design goals has been achieved. Advanced Design System 2015.01 (ADS) is the software used for the design and circuits prepared and tested in RF Electronics Laboratory of Istanbul Technical University. The challenges of this project was designing Class-E and Inverse-Class-E power amplifier, while having output matching circuit, maintaining design simplicity with low voltage which resulted in very limited choices in using lumped elements. Furthermore, using lumped passive elements transformation into transmission lines is not feasible in UHF band as the lines will be very long and it makes the implementations almost impossible. Therefore, transmission lines were used only between lumped passive elements to make connections. On the other hand, using lumped passive elements resulted in having a very lossy system, that for instance, a design with PAE=59% turned to PAE=44% after implementing real passive element models and transmission lines. The main point in designing Class-E and Inverse-Class-E power amplifier is selecting the right biasing point which is almost considered as deep class-AB biasing point and the main affecting part of system is the output matching network. Thus, different output matching networks have been designed and examined and the result is, the simpler the circuit becomes, the higher efficiency can be obtained. Simplicity and using least passive elements were key factors in this design due to using lossy passive element models and the frequency domain. In this project, GaAs technology has been selected and ATF-511P8 is the active device, from Avago Technologies manufacturer. Process of input and output matching network designs has been presented in appendix .Three designes for Class-E, Inverse-Class-E and mixture of Class-E and Inverse-Class-E has been designed, fabricated and tested. Results indicated the importance of keeping simplicity of design, while satisfying design goals. On the other hand, superiority of functionality for Class-E power amplifier has been proved by having higher PAE than the other two designs. Novelty of this project is using a mixture of Class-E and Inverse-Class-E power amplifier which has been designed and tested for the first time. 1mm thickness standart RF4 substrate is preferred due to durable structure and low cost. According to our previous cube-satellite experiences, it is suitable for low-Earth-orbit (LEO) conditions. Very few references was found about Inverse-Class-E which shows how implementation of this structure is hard, and not ideally practical. Thus, part of the thesis concentrates on desiging and implementation of this structure. Furthermore, a mixture of Class-E and Inverse-Class-E including series inductance, shunt capacitance and parallel-tuned circuit in the output matching network has been designed, manufactured and tested for the first time. This will give an insight to a new structure for power amplifiers and can be further improved for future works. Simulated PAEs of Class-E, mixed strucure and Inverse-Class-E designs are 50%, 43% and 37% respectively. Measuremed gain, PAE and output power are slightly different than simulated values. In simulations, higher output power and gain but lower PAE was achieved while in measurements it was vice versa. It is impartant to mention that the mixed design was manufactured for two values of inductors 49nH and 56nH and each of them was measured separately. Measurement PAEs are 35% for Class-E, 40% for Inverse-Class-E, 57% for Mixed Design with 47nH and 37% for Mixed Design with 56nH. All results are presented in detailed at last chapter. Desinged GaAs amplifiers are suitable for cube-satellite UHF band transmitters due to small size and low voltage stable operation. In a standard cube-satellite, they can be used without an additional DC-DC convertor.