• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.115-119
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• 2017

Intermodulation distortion degrades the S/N(signal-to-noise) of the original signal and also affects the adjacent channels. Intermodulation distortion is mainly caused by the nonlinear characteristics of the power amplifier. If the power amplifier with nonlinear characteristics has a memory effect, the intermodulation distortions occurred in the power amplifier are generated in various and complex forms. The predistorter is used as a way to improve intermodulation distortions. In order to efficiently utilize the performance of the predistorter, the memory effect of the power amplifier must be reduced. In this paper, we describe the design method of bias circuit to reduce the memory effect in power amplifiers. To reduce the memory effect, the bias circuit must have a high impedance for the signal and a low impedance for the envelope(modulating signal) and the second harmonic component of the signal. To verify the performance of the bias circuit designed considering the memory effect, a power amplifier operating at 170 ~ 220MHz was designed and implemented. The designed bias circuit has a large impedance in the operating frequency band and low impedance in the envelope signal and the second harmonic of the signal. As a result of the performance measurement, it was found that the asymmetric intermodulation distortion component is improved by 3.7dB.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.492-492
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• 2012

RF biased inductively coupled plasma (ICP) has been widely used in various semiconductor etching processes and laboratory plasma researches. However, almost researches for the RF bias have been focused on the controls of dc self-bias voltages, even though the RF bias can change plasma parameters, such as electron temperature, plasma density, electron energy distribution (EED), and their spatial distributions. In this study, we report on the effect of the RF bias on the plasma parameters and the EEDs with various external parameters, such the RF bias power, the ICP power, the gas pressure, the gas mixture, and the frequency of RF bias. Our study shows the correlation between the RF bias and the plasma parameters and gives a crucial key for the understanding of collisionless electron heating mechanism in the RF biased ICP.

• Journal of Advanced Navigation Technology
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• v.13 no.3
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• pp.358-364
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• 2009

This paper shows some variable bias techniques which can improve the power added efficiency(PAE) for the designed power amplifier. Some simulations have been done to get the effect of the bias change, and variable bias is adopted to get the higher efficiency for dual mode amplifier which generates two different output power levels. With drain bias change and a fixed gate bias, the amplifier shows PAE improvement compared to the fixed bias amplifier. In addition, this paper analyzed nonlinear distortion of the power amplifier and has used the digital predistortion which can result in 10dB ACPR improvement for the dual band amplifier.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.3 s.357
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• pp.1-6
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• 2007

A drain bias switching technique is presented to enhance power added efficiency for WiBro and wireless LAN dual band and dual mode transmitter. Some simulations have been done to predict the effect of drain and gate bias change, and bias switching is proposed to get the higher efficiency for dual mode transmitter which generates different output power for different applications. With drain bias switching and simulated optimum fixed gate bias, the amplifier shows dramatic PAE improvement compared to the amplifier without bias switching. The drain and gate bias switching technique will be useful for multi mode communication system with various functions.

• Journal of the Korean Vacuum Society
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• v.21 no.3
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• pp.121-129
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• 2012

RF biased inductively coupled plasma (ICP) is widely used in semiconductor and display etch processes which are based on vacuum science. Up to now, researches on how rf-bias power affects have been focused on the controls of dc self-bias voltages. But, effect of RF bias on plasma parameters which give a crucial role in the processing result and device performance has been little studied. In this work, we studied the correlation between the RF bias and plasma parameters and the recent published results were included in this paper. Plasma density was changed with the RF bias power and this variation can be explained by simple global model. As the RF bias was applied to the ICP, increase in the electron temperature from the electron energy distribution was measured indicating electron heating. Plasma density uniformity was enhanced with the RF bias power. This study can be helpful for the control of the optimum discharge condition, as well as the basic understanding for correlation between the RF bias and plasma parameters.

• Journal of electromagnetic engineering and science
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• v.9 no.2
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• pp.78-84
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• 2009

This paper represents the effects of drain bias on the linearity and efficiency of an analog pre-distortion power amplifier(PA) for wideband code division multiple access(WCDMA) repeater applications. For verification, an analog predistorter(APD) with three-branch nonlinear paths for memory-effect compensation is implemented and a class-AB PA is fabricated using a 30-W Si LOMaS. From the measured results, at an average output power of 33 dBm(lO-dB back-off power), the PA with APD shows the adjacent channel leakage ratio(ACLR, ${\pm}$5 MHz offset) of below -45.1 dBc, with a drain efficiency of 24 % at the drain bias voltage($V_{DD}$) of 18 V. This compared an ACLR of -36.7 dEc and drain efficiency of 14.1 % at the $V_{DD}$ of 28 V for a PA without APD.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.146.2-146
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• 2003

• The Journal of the Korea Contents Association
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• v.13 no.3
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• pp.162-173
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• 2013

This study was to examine the effect of trust, stigma, optimistic bias on risk perception of nuclear power plants. For this study, we carried out a survey targeting residents, total of 383, living in Seoul. The findings showed that trust of general public on nuclear power plants influenced negatively on stigma. Second, trust of general public on nuclear power plants influenced not significantly on optimistic bias. Third, stigma of general public on nuclear power plants influenced positively on risk perception. Fourth, optimistic bias of general public on nuclear power plants influenced negatively on risk perception.

• Journal of Korean Ophthalmic Optics Society
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• v.9 no.2
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• pp.291-299
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• 2004

DLC films were deposited using the ECR-PECVD method with the fixed deposition condition, such as ECR power, methane and hydrogen gas-flow rates and deposition time, for various substrate bias voltage. We have investigated the ion bombardment effect induced by the substrate bias voltage on films during the deposition of film. The characteristic of the films were analyzed using the FTIR, Raman, and UV/Vis spectroscopy analysis shows that the amount of dehydrogenation in films was increased with the increase of substrate bias voltage and films thickness was decreased. Raman scattering analysis shows that integrated intensity ratio(ID/IG) of the D and G peak was increased as the substrate bias voltage increased and films hardness was increased. Optical transmittances of DLC film were decreased with increasing deposition time and substrate bias voltage. From these results, it can be concluded that films deposited at this experimental have the enhanced characteristics of DLC because of the ion bombardment effect on films during the deposition of film.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.2
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• pp.81-87
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• 1994

We used IR laser inteferometric technique for measuring the temperature of wafer during cryogenic ECR etching. Using this technique, the effect of RF bias power and microwave power on the wafer temperature during etching period is investigated. As the RF bias power and microwave power was increased, the temperature of the wafer considerably increased and we concluded that to prevent the increase of substrate temperature during etching period, an adequate wafer cooling is needed.