Persons

In this work the HEMPT-transistors made of various semiconductor materials with the gate length of 0.2-0.25 µm and width of 200-300 µm have been considered and their characteristics have been compared. The current-voltage and farad-voltage characteristics and also the dependences of small signal S parameters on frequency have been measured. On the basis of the measurements the computer models of transistors: for GaAs - MATERKA, for GaN EEHEMT - have been developed. The adequacy of the developed models has been confirmed by the coincidence of the measured frequency of the parameter | S 21 | and the calculated low-signal power gain. The frequency properties of the manufactured transistors have been studied. In the schemes of linear amplifiers the limit of the oscillation frequency, on which the power amplification is lost, has been calculated. The modeling has shown the possibility of linear amplification for frequencies up to 64 GHz of GaAs transistors and 73 GHz of GaN transistors. In order to determine the maximum possible amplified oscillation frequencies the amplifier circuits with an optimized load of transistors have been designed. The maximum oscillation frequencies of the manufactured transistors a are close to ~ 82 GHz. The power parameters of the transistors have been compared. Small signal coefficients of transistors amplification power are equal and are ~15 dB at frequencies of L and S ranges. The highest drain currents for both transistors in the operation non-sparing regime were 0.34 A/mm with voltage on drain 3 V. To determine the maximum power added efficiency (PAE), the scheme of the nonlinear amplifiers, calculated for a frequency of the amplified oscillations 3 GHz has been developed. The highest PAE was 57 % for GaAs and 65 % for GaN. Taking into account that the electric field strength breakdown in GaN is several times higher that that one in GaAs, the possibility to achieve the efficiency of the transistor from GaN, exceeding 80 %, has been shown. The obtained results are useful for development of microwave monolithic integrated circuits for power amplifiers up to frequencies, including V-range.

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The conditions necessary for establishment of the stable high-frequency oscillators using the bipolar transistors have been described. The correlation between the steady-state stability conditions of the generator with the mechanism of the limiting amplitude has been analyzed. The recommendations for designing the oscillators with various schemes of connection of the stabilizing resonator have been made.

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The design method of the microwave FET mixer scheme has been proposed. These microwave mixers are intended for Monolithic Microwave Integrated Circuit. The methods have been illustrated on an example of the optimization of the mm wave FET mixer scheme. The maximum conversion gain was the criterion of this optimization.

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The possibility of reducing the phase noise of the microwave transistor oscillator by matching its resonator and transistor has been considered. The requirements to frequency characteristics of the oscillating system, allowing reducing of the generation noise, have been developed. The circuit of the oscillator with a complicated resonator, the phase noise of which is significantly lower than that one in the classical Colpitts circuits, has been proposed.

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The effect of transistor capacitance on the frequency, gain and amplifier efficiency has been studied. It is known that the maximum frequency of an amplifier on HEMT decreases with a decrease in the gate-source and gate-drain capacitance. The effect of the transistor inter-electrode capacitances on frequency, the power gain and the efficiency has been estimated. In the work the amplifiers circuits simulation based on HEMT, manufactured at MIET, has been performed. The transistor has been made on the basis of GaN with 0.25 µm gate, the EEHEMT model has been used. The amplifier maximum frequency was 59 GHz. A 20% decrease in the gate - source and gate - drain capacitances increase the maximum frequency up to 90 GHz. The transistor capacitance affects the power consumed from the input source. This is due to the direct power passage from the input source to the amplifier output. The simulations, carried out at the 4 GHz frequency, have shown a decrease in the input power, supplied to the transistor, while reducing the input and passage capacitances. With a 20% decrease in capacitance the input power has decreased by ~ 2dB, which leads to an increase amplifier Pgain and PAE. A method for reducing the capacitances of a HEMT with a T-gate has been proposed. After manufacturing the transistor the SiN dielectric layer between the gate metal and the AlGaN layer should be deleted. Removing the dielectric layer leads to a decrease in the relative permittivity of the space between the gate and the transistor channel with a corresponding decrease in capacitances. Since the capacitances of the transistor structure are an essential part of the total capacitances (up to 40%), this method leads to the decrease in the inter-electrode capacitances, which makes it possible to implement the simulation conclusions. The result of the paper can be useful for optimizing the HEMT design with T -gate.

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A comparison of the level of the phase noise of the microwave oscillations, made in the form of a single oscillator or as a chain: the low-frequency oscillator and a frequency multiplier, has been performed. It has been shown that under certain conditions the phase noise of the chain is less than that one of a single oscillator.

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