Yevgen   MATVIYCHUK

Abstract

INTRODUCTION

Design and development of the UHF microelectronic devices require consideration of number of factors which are caused by the small sizes of components, concentration of strong fields in small volumes, presence of circuits of parasitic communication, interaction of close located elements, difficulty of heat removal, requirements to accuracy of manufacturing and uniformity of materials.

External parameters of a communication systems in whole (the maximal distance between receiver and transmitter, the maximal transmission capacity of the channel and other) substantially depend on characteristics of final cascades of transmitters (on transmitted signal power) and front cascades of receivers (on sensitivity), i.e. on parameters of UHF amplifiers.

SCIENTIFIC INNOVATION

Scientific innovation of given master’s work consists in the following:

• research of the communication equipment of millimeter wave band;
• development of multicascade amplifiers based on Monolithic microwave integrated circuit (MMIC);
• research and development of decoupling circuits based on lines with the distributed parameters;
• the analysis of an opportunity and the offer of ways of creation of the unified UHF amplifier, capable to work in both receive and transmission paths.

Object of research is the two-stage UHF amplifier based on MMIC.

Subjects of research are parameters and characteristics of interstage matching circuits and also feed and bias decoupling circuits.

The goal of master’s work is research of special features of UHF amplifiers based on MMIC creation, a substantiation of parameters device components, and also development of a breadboard model of the amplifier and experimental acknowledgement of theoretical conclusions.

STATEMENT OF THE PROBLEM

• Following tasks are under consideration in the master’s work:
• to study principles of construction and to analyse parameters of various purpose modern radio communication devices;
• to study influence of the UHF amplifiers on characteristics of telecommunication systems;
• to analyse specified requirements to the UHF amplifiers in receive ant transmission channels, as well as modern ways of their realization;
• to study ways of matching circuits and decoupling circuits realization.

MAIN PART

Generally different requirements are put forward to the amplifiers in receive and transmission paths. Key parameters that characterize powerful transmitters’ final amplifiers are first of all amplifier gain and output power.

The greatest attention in front amplifiers design is given to the minimal noise factor (low-noise amplifiers, LNA) as to the parameter which sensitivity of the receiver in whole depends on.

The LNA’s gain should be sufficient for effective reduction of noise of next stages. The noise factor of the second cascade of amplifiers or converting devices in the modern receivers makes no more 10-l5 dB. Therefore the gain factor of front LNA should be not less than 15 dB.

Nowadays, amplifiers based on the semi-conductor integrated microcircuits received the greatest distribution. There are MMIC intended for work in a frequency range down to 70-80 GHz, providing gain factor at a level of 15 dB and above. The noise factor of the most low-noisy of them lays within the limits of 3-4 dB, that is comparable to a level of external perturbations and consequently it is a limit of expedient decrease of front stages noise. Bandwidth of such MMIC is up to 8-10 GHz. Amplifiers based on this technology are notable for compactability and low-cost.

Demands, concerning broadbandness and stability are also made for UHF amplifiers. Besides characteristics of the amplification element given parameters are affected by external circuits (matching circuits and decoupling circuits). Wrong design of these circuits can become the reason of deterioration of amplifier characteristics in whole.

Matching circuit can be presented in the form of microstrip line section which acts as the resistance transformer. As the results of modeling show, providing sufficient broadbandness, such approach allows to execute the matching of the amplifier practically with any resistance at an input and an output ends. The important criterion while developing the design of matching circuits is maintenance of stability of the amplifier.

Feed and biad decoupling circuits are applied to minimization of interrelation of various stages which is caused by use of one source and can lead to occurrence of parasitic feedback and losses of stability of the device. Influence of noise, that was brought by uncontrollable sources (both on working frequency, and on frequencies distinct from it) can become the reason of interferential and intermodulation products occurrence.

Disadvantages of decoupling circuits in UHF that based on lumped elements (relative complexity of manufacturing, an opportunity of occurrence undesirable phantoms and perturbations, etc.) can be substantially solved, using microsrostrip lines as the external decoupling circuits. Using of microstrip line in form of circle sector is proposed. Center of the sector is the point that is connected with the MMIC, and the outer side of sector is connected with the power source (fig. 1). It is necessary to note, that the size of a line (radius of sector) can exceed the length of a wave that simplifies its realization in the UHF. Modelling shows, that the transfer factor S21 of such circuit is -50 …-60 dB in a range of 30-50 GHz, that it is quite enough for realization of a qualitative decoupling. Such form lines possess sufficient broadbandness and theoretically raise stability of the amplifier.

CONCLUSION

Potential characteristics of an existing material base quite meet modern requirements. However, actually, nonideal character of external circuits (matching circuits and bias and feed decoupling circuits) can become the reason of deterioration of characteristics of the amplifier in whole. Result of the given work is definition of parameters and design features of external circuits of the microwave amplifier based on integrated microcircuits.

It is necessary to note, that the results described in the author's abstract are preliminary. Researches and experiments within the topic of given master’s work still proceed, therefore results can be specified. Abstract in Russian gives more expand description of investigated problems.