a. abrishamifar

In this paper, a new approach for improving the linearity characteristics of GaN power amplifiers is presented. The method is based on the injection of the second harmonic signal to the input of the power amplifier through a forward path. The effect of the second harmonic injection on the linearity characteristics of the power amplifier is studied using two-tone theory and simulations. An active three-port linearizing circuit with the ability to generate a second harmonic signal with adjustable amplitude and phase has been proposed to implement this method. Further, the paper method has been evaluated for improving the linearity of two 10-watt power amplifiers with different nonlinear characteristics. As a concept, the proposed circuit is also fabricated and used for linearizing the GaN power amplifier. It has been shown that by injecting the second harmonic signal and properly adjusting its amplitude and phase, in addition to improving the linearity characteristics, including third-order intermodulation (IMD3), adjacent channel power ratio (ACPR), and AM-PM characteristic, the 1-dB compression point is also increased.

Long-Range-Navigation (LORAN) transmitter is an essential part of a local positioning system (LPS) that provides high power and high precision pulses with a specific waveform. In this paper, a new method for design and implementation of the LPS transmitter, based on class I amplifiers, has been proposed. Each block of the transmitter includes MOSFET amplifier modules driven by pulse width modulation (PWM). The pulse width at each cycle has been calculated by an algorithm based on the least square method (LSM). Simulation results show that the obtained maximum zero crossing error in the 4th to 12th half-cycles is 18 ns, the generated pulse width is 4.9 kHz and the MMSE of the pulse, which is directly proportional to the ECD, is equal to 0.009, demonstrating  that with the proposed method it is possible to produce an accurate LORAN pulse with all the required parameters. High efficiency of class I amplifiers, makes this method a good candidate for light-weighted, highly accurate and flexible tactical LPS transmitters.

Multilevel inverters have great applications in medium-voltage and high-power applications and also have found successful industrial applications. Modified full bridge inverter is one of the most popular topologies among the multilevel inverters because of lower number of switches and simpler structure than others. In this paper, a seven-switch and seven-level modified full bridge topology is proposed. Compared to the practical seven-level inverters like neutral point inverters, the proposed inverter reduces three active switches and has lower conduction loss and simple control. The input voltage to the given inverter is a DC source (Vdc) which has been shared between three identical capacitors and it is capable of producing output of seven level (Vdc, 2Vdc/3, Vdc/3, 0, -Vdc, -Vdc/3, -2Vdc/3). As more steps are added to waveform, the harmonic distortion of the output waveform decreases. The proposed modulation enables the proposed inverter to operate under both active and reactive power conditions. A 1KVA single-phase sample circuit is simulated by the PSPICE software to verify the validity of the proposed topology and modulation method. The results show the proposed topology is suitable for photovoltaic (PV) applications.

In this paper a high efficiency, low cost, and low THD five-level inverter is proposed. The proposed inverter has lower number of switches than the similar structures and this feature causes that the implementation cost of the proposed inverter becomes lower than the others. Also, a passive filter is proposed to decrease the THD value, and simulation results prove this fact that THD value has been decreased dramatically. As well, high switching frequency is another important feature of the proposed converter. According to the simulation results in the PSPICE and PLECS software, the proposed converter has several advantages such as high stability, high efficiency, low cost, and proper thermal specifications. Simulation results show the effectiveness of the proposed solution.