Dongsoo Kim

This paper describes the analysis of an optimized envelope shaping function for the envelope tracking power amplifier (ET PA) and its implementation. The proposed shaping function, which is sweet spot tracking with crest factor reduction, improves the efficiency and output power of the power amplifier (PA), as well as its linearity. For an accurate simulation of the supply modulator, an equivalent model of the PA under the envelope shaping is suggested. To achieve high efficiency and wide bandwi

This paper proposes a method which evaluates symmetry of plate corners and extracts car license plates captured from the arbitrary directions. The generalized symmetry transform (GST) produces continuous features of symmetry between two points by combining locality constraint and reflectional symmetry. Also, we propose scan line based GST to improve time complexity of the GST significantly due to selective attention to particular distortions in case of a large searching window. The corners of a

Variable refrigerant flow (VRF) systems are known for their high energy performance and thus can improve energy efficiency both in residential and commercial buildings. The energy savings potential of this system has been demonstrated in several studies by comparing the system performance with conventional HVAC systems such as rooftop variable air volume systems (RTU-VAV) and central chiller and boiler systems. This paper evaluates the performance of VRF and RTU-VAV systems in a simulation envir

Continuously variable ferroelectric (BST on sapphire) phase shifters based on all-pass networks are presented. An all-pass network phase shifter consists of only lumped LC elements, and thus the total size of the phase shifter is kept to less than 2.2 mm /spl times/ 2.6 mm at 2.4 GHz. The tunability (C/sub max//C/sub min/) of a BST interdigital capacitor is over 2.9 with a bias voltage of 140 V. The phase shifter provides more than 121/spl deg/ phase shift with the maximum insertion loss of 1.8

The electrochemical oxidation of phenol was studied using a Ti/PbO2 electrode prepared by the electrodeposition method with PbO2 coated on Ti. The structural and morphological activity of Ti/PbO2 was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and intermediates formed after degradation of phenol were quantitatively assessed by high-pressure liquid chromatography (HPLC). Optimization of various parameters such as current density, initial phenol concentration, initi

This paper describes the implementation of a high efficiency and wideband envelope tracking power amplifier with sweet spot tracking. By modulating supply voltage of power amplifier (PA), efficiency can be increased significantly. And linearity is improved by envelope shaping and sweet spot tracking. The supply modulator has a combined structure of a switching amplifier and a linear amplifier to achieve high efficiency as well as wide bandwidth. The measurement results show efficiencies of 36.4/

Despite their potential as a naturally-available clean energy option, the renewable energy resources of the Democratic People's Republic of Korea (i.e., North Korea) have rarely been evaluated. Therefore, to estimate the availability of land surface solar irradiance necessary for solar applications and to model available energy potential, physically-based models drawing on Communication, Ocean and Meteorological Satellite (COMS) data and associated statistics for key atmospheric constituents, we

This letter describes a highly efficient dual-switch hybrid switching supply modulator for an envelope tracking power amplifier (PA). The supply modulator has a combined structure of a linear amplifier and a switching amplifier. For an improved efficiency, the switching amplifier employs two buck converters and realizes an adaptive slew rate control of the switching amplifier's current. An implemented envelope tracking PA delivers an efficiency of 39.1% at an output power of 27 dBm for long term

This paper describes an envelope tracking power amplifier for LTE application with large channel bandwidth up to 30 MHz. For the wideband operation, a supply modulator with accurate and fast envelope tracking is essential. The bandwidth of the supply modulator is increased about 2 times without stability degradation by inserting a zero in a feedback path of a linear amplifier. The supply modulator is fabricated using CMOS process and a power amplifier is fabricated using HBT process. An implemen