High-voltage dc/dc converters play an important role in HVDC grids. Isolated modular dc/dc converters (IMDCCs) based on modular multilevel converter (MMC) technology provide a good solution to high-voltage applications. In order to reduce the size of the system, the IMDCC is required to be operated with a high ac link frequency, but this will lead to increased switching loss and thus degraded efficiency. This paper proposes a soft-switching operation scheme for such an IMDCC. In this scheme, a quasi-square-wave (QSW) modulation method is employed, where the chain-links generate quasi-square terminal voltages with reduced dv/dt. With such chain-link terminal voltages, the arm currents which provide good condition for the soft-switching operation of the QSW-IMDCC can be obtained. Since soft-switching can be achieved for the power switches, the proposed scheme will suffer less switching loss, thus improving the efficiency of the converter. Moreover, a capacitor voltage balancing control strategy is proposed. This strategy does not need any arm current sensors, thus reducing the cost. The proposed soft-switching operation scheme and capacitor voltage balancing control strategy are verified by the simulation results.

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An integrated CMOS front-end circuit of receiver according to the IEEE 802.11a standard is presented in this paper. The front-end circuit comprises low noise amplifier (LNA), active balun, voltage control oscillator (VCO), and source pumped mixer. The proposed source pumped mixer can achieve high linearity and high gain performances. When integrated in a 0.18 μm CMOS technology, the front-end circuit exhibits an area of only 1.04 mm 2 . The proposed front-end circuit achieves measured conversion gain of 19dB, input third-order intercept point (IIP3) of -11 dBm, VCO tuning range of 780 MHz and a phase noise of -108 dBc/Hz at 1-MHz offset frequency under consuming power of 24.5 mW from 1.8V supply voltage.