A CMOS active mixer based on variable load technique which can operate at 1.0V supply voltage is proposed and its operation principle is presented. The proposed mixer controls the load impedance according to the LO signal. It has only two stacked transistors at each branch, which is suitable for low-voltage applications. The mixer was designed in 0.18-µm CMOS process and measured in 2.4-GHz ISM band. With a 2.440GHz RF input signal and a 2.442GHz LO signal (4dBm), the conversion gain is 5.3dB, the input-referred third-order intercept point is 4.6dBm, the input-referred 1-dB compression point is -7.4dBm, and the single-sideband noise figure is 21.7dB. Current consumption is 3.5mA at 1.0V supply.

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The charge/discharge phenomenon of capacitance between terminals in a power MOSFET affects on its switching behavior of the device. The input capacitance is composed of the gate-source capacitance C_GS and the gate-drain capacitance C_GD, which vary with gate voltage V_GS. This paper characterizes the relationship between the input capacitance of a SiC MOSFET and the gate voltage with considering the internal device structure. The results give us a clue to understand the switching dynamics of the power MOSFET.

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For multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems working in frequency and time selective (doubly selective) fading channels, the existence of intercarrier interference (ICI) will significantly degrade system performances. In this paper, by devising a so-called optimum group filtering processing, we propose an iterative soft interference cancellation based quasi-a posteriori probability (ISIC quasi-APP) detector which has a low complexity and significantly outperforms the conventional ISIC based minimum mean square filtering (ISIC MMSE) detector.

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This paper describes an adaptive software aided technique for phase error reduction in digital carrier recovery (CR)for high-order Quadrature Amplitude Modulation (QAM). Simulations and analytical results illustrate a phase error variance improvement of at least 30dB compared to conventional CR, leading to more than 3dB processing gain enhancement for high-order QAM, using the simple 4^th power phase estimation technique. The new technique can be employed to improve the performance of any CR loop, at the cost of slight complexity overhead independent of the modulation order.

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In this paper, a new closed form expression is developed to accurately estimate the resonant frequency of an equilateral triangular patch. The proposed computation is also extended to the two-layer structure in order to define the air-gap tuning effect on the resonant frequency. The theory established in this paper is compared with the experimental and theoretical results available in the literature. The results of this study show a considerable improvement achieved over the previous theories within very small percentage errors for almost all cases.

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The conventional grid-connected photovoltaic (PV) inverter that steps up low DC voltage to high DC voltage and cascades with the high frequency inverter is complicated in control and of low efficiency due to two stages. This paper presents a novel PV inverter system formed by a hybrid DC-DC converter and a full-bridge DC-AC converter. The hybrid DC-DC converter combines the boost and flyback topologies to produce a semi-sinusoidal output current and to achieve the high step-up objective. A full-bridge DC-AC converter controlled with low-frequency switching techniques is then used to convert the current into sinusoidal form and to feed power to the grid with unity power factor. The overall efficiency of the designed system is high due to the losses of both stages are reduced. In this paper, the circuit operating theory of the proposed PV inverter is firstly addressed then an 80W prototype system is designed and built. The feasibility and effectiveness of the proposed circuit are confirmed with some simulation and experimental results.

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