• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.31A no.5
• /
• pp.68-75
• /
• 1994

A new Predistortor that is designed using Feedforward type is proposed to overcome the nonlinearity of HPA (High Power Amplifier). HPA has the nonlinearity of the gain compression and phase distorton, so digital communication system of multi-carrier TDMA needs the linear RF transmitter. Using IMD (Intermodulation Distortion) of drive amplifier, as Feedforward type, the inverse IMD is coupled to the main loop with variable attenuators, phase shifters, and sub-amplifiers well designed. At the input of main amplifier, the over-coupled IMD surpresses the main amplifier 's IMD. Adjusting the level and phase of IMD at the sub loop, C/I of HPA is better than before correction.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2000.11a
• /
• pp.146-149
• /
• 2000

SiGe HUT뜰 이용하여 Cellular 주파수 대역(824-849 MHz)에서 MMIC 상향 주파수 혼합기와 가변이득 증폭기를 설계하였다. 동작 전압은 2.7 V 이며, 이중평형 구조의 상향 주파수 혼합기는 12 dB의 변환이득, -0.6 dBm의 1dB 이득압축 출력전력, 30 dB 이상의 LO-RF 단자 격리도 특성, 1.25의 LO-VSWR. 1.34의 RF-VSWR을 가지며, 상호컨덕턴스형 가변이득 증폭기는 35 dB의 최대 선형이득, 13 dBm의 1dB 이득압축 출력전력, 42dB의 가변이득, 23dB의 3차 상호변조 교점 출력전력(OIP$_3$), 1.27의 입력 VSWR, 1.1의 출력 VSWR 특성을 보인다.

• Journal of electromagnetic engineering and science
• /
• v.13 no.3
• /
• pp.189-191
• /
• 2013

This letter presents a compact metamaterial-based tunable zeroth-order resonant antenna. It is based on the double-negative unit cell with a function of tunable inductance realized by a varactor and impedance convertor in the shunt branch. The resonant frequency of the designed antenna ranges from 2.31 to 3.08 GHz, depending on the capacitance of the used varactor. Its size is very compact ($0.05{\lambda}_0{\times}0.2{\lambda}_0$) with a relatively wide tunable range of 29.1%. The impedance bandwidth of the antenna is from 20 to 50 MHz for the resonant center frequency. The measured maximum total realized gain is from -0.68 dBi (2.43 GHz) to 1.69 dBi (2.97 GHz). The EM-simulated and measured results are in good agreement.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.10a
• /
• pp.341-344
• /
• 1997

The higher precision in manufacturing field is demanded, the more accurate servo controller is needed. To achieve the high precision, Koren proposed the cross-coupled control (CCC) method. The objective of the CCC is reducing the contour error rather than decreasing the individual axial error. The performance of CCC depends on the contour error model. In this paper we propose a new contour error model which utilizes contour error vector based on parametric curve interpolator. The experimental results show that the new CCC is more accurate than the variable-gain CCC during free-form curve motion.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2001.09a
• /
• pp.373-380
• /
• 2001

In this research, a controller design method based on optimization is proposed that can satisfy constraints on maximum responses of building structures subject to ground excitation modeled by partially stationary stochastic process. The class of controllers to be optimized is restricted to LQR. Weighting matrix on controlled outputs is used as design variable. Objective function constraint functions and their gradients are computed parameterizing control gain with Riccati matrix. Full state feedback controllers designed by Proposed optimization method satisfy various design objectives and their necessary maximum control forces are computed fur the production of actuator. Probabilities of maximum responses match statistical data from simulation results well.

• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.5
• /
• pp.173-179
• /
• 2000

While a cutting tool is machining a workpiece at various cutting depth, the feedrate is usually selected based on the maximum depth of cut. Even if this selection can avoid power saturation or tool breakage, it is very conservative compared to the capacity of the machine tools and can reduce the productivity significantly. Many adaptive control techniques that can adjust the feedrate to maintain the constant cutting force have been reported. However, these controllers are not very widely used in manufacturing industry because of the limitations in measuring the cutting force signals. In this paper, turning force control systems based on the estimated cutting force signals are proposed. A synthesized cutting force monitor is introduced to estimate the cutting force as accurately as a dynamometer does. Three control strategies of PI, adaptive and fuzzy logic controllers are applied to investigate the feasibility of utilizing the estimated cutting force fur turning force control. The experimental results demonstrate that the proposed systems can be easily realized in CNC lathe with requiring little additional hardware.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.8 no.4
• /
• pp.277-282
• /
• 2008

A fully integrated inductorless CMOS impulse radio ultra-wideband (IR-UWB) receiver is implemented using $0.18\;{\mu}m$ CMOS technology for 3-5 GHz application. The UWB receiver adopts the non-coherent architecture, which removes the complexity of RF architecture and reduces power consumption. The receiver consists of inductorless differential three stage LNA, envelope detector, variable gain amplifier (VGA), and comparator. The measured sensitivity is -70 dBm in the condition of 5 Mbps and BER of $10^{-3}$. The receiver chip size is only $1.8\;mm\;{\times}\;0.9\;mm$. The consumed current is 15 mA with 1.8 V supply.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.6
• /
• pp.1089-1094
• /
• 2016

In order to establish the robust controller design technique of series wound motor driver system. This paper proposes a method of Bang-Bang controller using a series wound motor driver system under improperly variable load. A Bang-Bang controller structure is simpler than the structure of PID plus Bang-Bang controller. This paper shows that a general 8 bits microprocessor is used efficiently implementing such an algorithm. The calculation time of software is extremely small when compared with conventional PID plus Bang-Bang controller. Both nonlinear operating characteristics of digital switching elements and describing function methods are used for the analysis and synthesis. Real time implementation of Bang-Bang controller is achieved. Concept design strategy of the control and PWM waveform generation algorithms are presented in the paper.

• Proceedings of the KIEE Conference
• /
• 2008.07a
• /
• pp.1927-1928
• /
• 2008

가변 이득 및 차단주파수 특성을 가지는 5차 CMOS Gm-C 필터를 설계하였다. 설계된 필터는 CMOS 차동 트랜스컨덕터들로 구성하였으며 트랜스컨덕터들은 각각 전압 조정에 의하여 트랜스컨덕턴스 값이 변환되도록 설계하였다. 가변 차단주파수 특성은 외부잡음으로 발생할 수 있는 필터 차단주파수의 변형을 보상할 수 있고 한 개의 필터로써 다중대역 수신 단에 적용할 수 있도록 하고자 하였다. HSPICE 시뮬레이션 결과, 1.5MHz$\sim$3.5MHz의 차단주파수의 조정이 가능하였고 이득은 -2.8dB$\sim$2.6dB으로의 조정이 가능하였다.

• Proceedings of the KIEE Conference
• /
• 2015.07a
• /
• pp.177-178
• /
• 2015

This paper proposes a power smoothing scheme of a doubly-fed induction generator. The proposed scheme aims to mitigate system frequency deviation caused by the variable wind. To achieve this, a dynamic droop loop is used and its gain changes with rate of change of frequency so that it can release a large amount of kinetic energy at the initial stage of a frequency event. The performance of the proposed scheme was investigated in a model system with high wind penetration using EMTP-RV simulator. The test results indicate that the scheme can smooth the output power by absorbing or releasing the output power under a varying wind condition.